ferpe
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Avanti Aerodynamics For Future Airliners?

Thu Jan 19, 2012 8:31 pm

Haven't found a discussion on this topic therefore:

There is one business aircraft that stand out over the others, the Piaggio P180 Avanti:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Piaggio-Aero-P-180-Avanti-II-1.jpg

At first I thought it had the looks but not the performance but ooh was I wrong. One just need to read the lyric flight test from the trade mags to realize this is really a major advancement over the classical turobprop and on many biz jets.

In short:

- it flies as fast and far as a small business jet with -40% fuel burn

- it has a larger and roomier cabin

- it is as quiet as a business jet

- it handles very well

The testers usually finishes with that the nose wheel steering is a bit sensitive, that is the only complain    , otherwise just superlatives .

All this comes from its clever aerodynamics and structural design (it is a classical al frame) paired with pusher turboprop engines. Given that we might want to use propfans in the future I would think the Avanti concept should merit follower for larger aircraft, why have we seen none?

PS
the areodynamics uses the tail as control only and balances the aircraft with the canard, thus no surface generate negative lift. Further the pusher props allows the wingflow to be undisturbed and therefore pretty laminar.

[Edited 2012-01-19 12:35:12]
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Stitch
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 19, 2012 9:03 pm

The closet concept I can think of at the moment is Boeing's "Kermit Cruiser":

Boeing Kermit Cruiser Low-Noise Concept
 
B6JFKH81
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 19, 2012 9:44 pm

Quoting ferpe (Thread starter):
All this comes from its clever aerodynamics and structural design (it is a classical al frame) paired with pusher turboprop engines.

I have a question about the props on this aircraft (don't want to steal the thread or anything, but just want to ask a quick question). Why the hell are they so loud!?! I don't get to see many pusher-prop aircraft, but there is a Piaggio that frequents FRG and when that thing takes off over my building, the prop noise is ear piercing. Other turboprops do the same departure (KingAirs and EMB120s) and I don't even hear them. But when the Piaggio goes over, I am just floored with how noisy those props are. I love engine noise from all aircraft and I'm not complaining, but I really want to know why it's so much noisier than other aircraft. Is it because it is a PUSHER-prop? Is it the blade design?

Thanks for any input!

~H81
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rfields5421
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 19, 2012 9:56 pm

This is an almost 20 year old aircraft design - first flight in 1986. The cockpit looks positively steam powered on the early build number aircraft I've seen. Haven't seen one of the Avanti II glass cockpits.

If airline designers were going to learn lessons from the Avanti - we would see those now. The big reason we don't I believe is that it is a prop - and the psychological impression of props as 'old'.

For those who don't know - the Avanti is aluminum - not composite. They use a vacuum mold to pull the thin aluminum skin into shape and weld the ribs on the inside.
 
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 19, 2012 11:28 pm

Quoting B6JFKH81 (Reply 2):
I have a question about the props on this aircraft (don't want to steal the thread or anything, but just want to ask a quick question). Why the hell are they so loud!?!

I believe it's a result of "dirty air" being fed through the props. That is, the air that is being fed into the props is turbulent from passing over the wing, and this produces more noise than a prop pulling in perfectly clean/undisturbed air.

Quoting rfields5421 (Reply 3):
They use a vacuum mold to pull the thin aluminum skin into shape and weld the ribs on the inside.

I remember hearing that there is only one exposed line of rivets on the airframe - around the nose section in front of the cockpit windows.
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Stitch
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 19, 2012 11:46 pm

Quoting rfields5421 (Reply 3):
The cockpit looks positively steam powered on the early build number aircraft I've seen. Haven't seen one of the Avanti II glass cockpits.

There are a number of pictures of both in the database. The new cockpit looks much better.  
 
ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Fri Jan 20, 2012 6:36 am

Yes the high pitched exterior sound comes from the wings downwash going into the props and creating the noise. Due to the clever design that noise is not entering the cabin.

I know it is a design that was made long ago, that is why I wonder why it has not been copied. The advantages are clear, the thing can cruise at 350 knots. I guess there are a couple of things that Piaggio had running for them:

- the had made pusher prop aircraft for a long time, they knew how to pull this of.

- they could put a long slender wing through the mid cabin as the wing could be far back with the canard balancing the craft

- they engaged some top aero people from the US to help with the aerodynamics

yet there are not the usual drawbacks from the highly efficient design like twitchy stall or flying characteristics or difficult to handle when iced. It just seems to be a very good job done and its low fuel consumption make it future proof.


Wonder when we will see copies. BTW what was the efficiency of the Starship? It seems it's cruise speed was lower about 300kts vs the Avantis 320-340 kts.
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MD-90
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RE: Avanti Aerodynamics For Future Airliners?

Fri Jan 20, 2012 11:46 am

Quoting B6JFKH81 (Reply 2):
Why the hell are they so loud!?! I don't get to see many pusher-prop aircraft, but there is a Piaggio that frequents FRG and when that thing takes off over my building, the prop noise is ear piercing.

Also the exhaust wash going through the props. It has a very distinctive buzzing sound that make it easy to aurally recognize.

Quoting ferpe (Reply 6):
BTW what was the efficiency of the Starship?

Poor compared to what Beech had hoped for. The FAA made certification of the composite airframe difficult (and consequently heavier than needed) and it turns out that having a real canard isn't all that efficient.

Personally I think the Avanti is a gorgeous airplane and Piaggio has been doing well sell Avanti II models. If the range meets your needs it's the most efficiently sized fast cabin in the sky (bigger and faster than a King Air, bigger and more fuel efficient than a light jet).
 
ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Fri Jan 20, 2012 12:50 pm

Quoting MD-90 (Reply 7):
Also the exhaust wash going through the props.

It therefore needs no prop deice, yet another little detail were Piaggio turns things into something positive.

Quoting MD-90 (Reply 7):
and it turns out that having a real canard isn't all that efficient.

Canards have the problem that you need to load the small wing (with a mostly low aspect ratio) highly to reach a statically and dynamically naturally stable vehcile. Thus the canards contributes an unproportionally large part of the lift and therefore drag of the airframe.

Piaggo seems to avoid that by having the T-tail solving part of that problem (I guess it generates a little bit of download after all to off-load the canard but certainly it is used to gain dynamic stability), yet it contributes wetted area and also about 100kg mass. Still the design seems to be more efficient than naturally stable canards.

For military aircraft FBW and relaxed stability has solved the main problem with the canard configuration (therefore so many canard designs recently), for a civil certification one needs natural stability I presume, therefore civil canards are more difficult to make work efficiently. Seems Piaggio has a solution    .
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Northwest727
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RE: Avanti Aerodynamics For Future Airliners?

Fri Jan 20, 2012 1:23 pm

Quoting B6JFKH81 (Reply 2):
Why the hell are they so loud!?! I don't get to see many pusher-prop aircraft, but there is a Piaggio that frequents FRG and when that thing takes off over my building, the prop noise is ear piercing.
Quoting 2H4 (Reply 4):
I believe it's a result of "dirty air" being fed through the props. That is, the air that is being fed into the props is turbulent from passing over the wing, and this produces more noise than a prop pulling in perfectly clean/undisturbed air.

Also due to the PT6A's exhaust. Every time a propeller blade passes by the exhaust pipes, the exhaust "hits it" versus continuing rearwards, thus giving the airplane a unique "square-note" sound, in addition to the disturbed air off the wings.
 
ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Fri Jan 20, 2012 6:30 pm

This company demo video tells it in a nice way, I think it describes a very nice cabin and flight deck:

http://www.youtube.com/watch?v=2Xxn4ahcBKk&feature=related

It is made in Genova Italy, just down the road from where I live   , one of the company investors is the hier of Ferrari, Piero Ferrari, it is their official company plane.

Wish I had the petty cash to buy one    .
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tdscanuck
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 12:17 am

Quoting ferpe (Reply 6):
I know it is a design that was made long ago, that is why I wonder why it has not been copied. The advantages are clear, the thing can cruise at 350 knots.

The design doesn't work for jets and it doesn't work for airliners...it's a great design for the particular niche it lives in but it's not that big a niche.

Tom.
 
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 8:03 am

Quoting ferpe (Reply 8):
Canards have the problem that you need to load the small wing (with a mostly low aspect ratio) highly to reach a statically and dynamically naturally stable vehcile. Thus the canards contributes an unproportionally large part of the lift and therefore drag of the airframe.

Piaggo seems to avoid that by having the T-tail solving part of that problem (I guess it generates a little bit of download after all to off-load the canard but certainly it is used to gain dynamic stability), yet it contributes wetted area and also about 100kg mass. Still the design seems to be more efficient than naturally stable canards.

While that's true of canards, it's hard to call the forward wing of the Avanti a canard. After all, it has no pitch control function. IMO, it's better to think of the Avanti as a biplane with an exceptionally large difference in wing sizes and stagger.
 
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 9:41 am

Quoting rwessel (Reply 12):
While that's true of canards, it's hard to call the forward wing of the Avanti a canard. After all, it has no pitch control function.

AFAIK nothing about a canard says it has to have a pitch control function by definition. Look at the canards on the Tu-144, for example.
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 10:09 am

Quoting ferpe (Reply 8):
Canards have the problem that you need to load the small wing (with a mostly low aspect ratio) highly to reach a statically and dynamically naturally stable vehcile. Thus the canards contributes an unproportionally large part of the lift and therefore drag of the airframe.

I know. As much as I loved the look of the Berkut kitplane, it was outperformed by 2-seat Lancairs of equal power. As a teenager a Berkut was THE airplane that I wanted to build.


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Photo © John Allan

Quoting tdscanuck (Reply 11):
The design doesn't work for jets and it doesn't work for airliners...it's a great design for the particular niche it lives in but it's not that big a niche.

Piaggio is allegedly designing an Avanti jet. It will be interesting to see what it looks like.
 
ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 3:57 pm

Quoting tdscanuck (Reply 11):
The design doesn't work for jets and it doesn't work for airliners

Tell me why...
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Lemmy
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 4:01 pm

I understand that the center of gravity is tricky with the Avanti. Since fuel is stored in the wings and the wings are located so far back, it's harder to balance different fuel loads against payload.

Gorgeous airplane, though.
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mandala499
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 5:50 pm

Quoting ferpe (Reply 15):
Tell me why...

Where should we start...
1. Wing configuration & scale & ground ops
- Expand the Avanti into an airliner sized aircraft, and that front wing is going to get in the way.
- The wings go right through the body, in an airliner sized aircraft, that would mean complications... there's a reason why airliners have wings at the bottom or on top.
- Airliners need to maximize revenue space/volume for each kg of metal (or composite) it uses. As planes get smaller, such % of "revenue space" falls. That's why Bizjets and small props have a lot of stuff to play with. Airlines, don't!

2. Wing Configuration & Laminar Flow
Much of the Avanti's amazing performance is the laminarity of the airplane. Laminarity (if I remember correctly) go al the way to 1/3 the body lenght, and about 3/4 of the wing.

The laminarity is such that if it rains, the water hitting the surface breaks the laminarity, and on the front wing, this is very noticeable. On the same power setting, hit the rain, the nose will want to go down and your speed can fall by 1 - 3kts indicated.

Have a paint chip on the front wing, and the same power setting will set you back another 1 - 2 knots indicated

Now, the custom "chic egg shape" as I describe it, is such to maximize laminarity of the fuselage and also minimize the boundary layer on the aft sections of the aircraft up to the trailing edge of the wing. That is why, there is no "straight line" on the fuselage.

Get an airbridge to hit that front wing and you're in trouble.

For airliners, the ability to "plug in or plug out" body parts to make a variant is a big factor (Just look at the 737 cross section, shortest was the 731, and can be stretched to the 739ER... Because it's a cylinder with shapes on the front and end. You can't do that on an Avanti egg shape...

3. Weight and Balance.
I'd love to see how an enlarged Avanti airliner does its weights and balances.
The Avanti has a much smaller range of gross weights in relation to the maximum gross weight than airliners.
For large gross weight (and Center of Gravity) variation on that kind of wing configuration, balance becomes a nightmare (remember how complex CG management is for the concorde), unless you want to put complex front wing with controls... Well, we saw that concept in the Sonic Cruiser, which got the axe.

One can go on and on about how good such a configuration the Avanti is (which is, AMAZING), but one can also go on and on about why such a configuration won't work for airliners.

Remember this?


That's about as close we'll get to an Avanti as an airliner...

Mandala499
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ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 22, 2012 11:03 pm

@Mandala499

Thanks for your comprehensive answer, I will comment it below. But first;

0, My post was not totally out of the blue, AFAIK Airbus had such a front wing projected on the A340 if I am not totally mistaken. It was decided not to keep it in the project for whatever reason but it would have raised the frames efficiency.

Now my comments:
In general you presume that the Avanti concept of a midslung uninteruppted main wing passing behind the cabin is the concepts main feature, it is not the part of the concept which attracts me (though it is nice), the main feature is the 3 surface lifting concept:

1. The main wing on a airliner would have to sit low or high of course so you can place it at the optimal place. Avanti takes maximum use of the aft wing for effcient and clever packaging, a 3 surface Airliner must place the main wing based on other criteria. This does not impinge on the fundamental benefit of a 3 surface lifting concept, its main purpose is to reduce your trim drag, to get lifting or close to neutral control surfaces instead of todays downward lifting tail. Piaggo claims the main wing has 30% lower area as a result. With todays FBW it is fully feasible to go for an active CG control system (which you would need for any Flying body concept as any example) so I don't buy the CG argument, you will have to invest to lower drag=increase effciency. Pumping fuel around for CG control you did on the Concorde and you do on todays airliners, such a system is run of the mill.

2. The sensitivity of the forewing is well known if not from any other then Ruthans designs. Once again FBW fixes that. More laminar flow is the next big area for efficiency improvement, B will introduce their passive system on the 789. IMO a forewing or none does not change anything re laminar flow, it is all about your shapes (to control backpressure/boundary layer build up) and any passive or active system to control a tired boundary layer. This does not change with a forewing or not.

That Avanti has a body shape to try and keep a laminar flow as long as possible is a feature for that frame, it does not have to be the same for an airliner concept, is not part of a 3 surface lifting concept.

The pusher props helps with laminar main wing flow on a prop craft, I have seen no propfan proposal with them impinging on a main wing. For turbofans slung under the wing they do not affect an overside laminar flow probIem IMO.

3. Weight and balance, see 1. There is no principle difference in the weight and balance of a 3 surface concept compared to a classical 2 surface (as long as you are free to place the main wing at the optimal place for both), on the contrary you have 2 trim surfaces and can thus optimize your trim drag better (lifting trim instead of negative lift trim).

In general with a 3 surface concept you have a much better low speed situation, as you increase camber on the mainplane you counter the nose.down moment with more camber on the foreplane, your trim action creates positive lift instead of negative. In the end you will have lower take-off and approach speeds all things being equal and you have an easier job optimizing the frame for the cruise (you trim a cruise dynamic camber systems moments with positive lift foreplane trim).

Where you have the freedom of full authority FBW you design with canards today, ref Indias MMRCA rejection of the US designs based on their lower flying performance. Civil airliner design is more conservative but we see many forewing or canard concepts being thrown around as the 2025+ concept, there is a reason other then being fancy IMO...

[Edited 2012-01-22 15:18:35]
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 23, 2012 1:10 am

The Beech Starship, as originally designed by Burt Rutan, was a 3-surface design like the Avanti. When shown to the then-President of Beech, he reputedly said "No! - Give me a big Long-EZ!" and that is what he got. The later Scaled Triumph is configured a bit like the original Starship:

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The Avanti has a canard soley to allow the wing spar to pass aft of the rear pressure bulkhead. If the canard wasn't there, the wing would have to be further forward to get things to balance out right. Its a pusher, so that the plane of rotation of the props doesn't line up the cabin. One big disadvantage of pushers is that the hot engine exhaust wreaks havoc with composite props.

People seem to think that having all of the flying surfaces producing positive lift is an advantage. If you research the issue of a lifting canard vs. a downloaded tail, you will find that this is a fallacy. For a properly optimized canard configuration, you end up with a large section of inboard wing carrying no load. This is because the sum of the canard and wing lift distributions should be elliptical for minimum drag. As the canard itself has a near-elliptical load, this results in a "hole" in the required wing lift distribution. To get the fuel near the CG for a minimum CG travel with fuel burn, the designer usually ends up with a large strake on the inboard wing to provide fuel tankage. This results in a large wetted surface that produces a lot of drag and carries no lift.

The Starship was designed to have extensive laminar flow on all flying surfaces and with the exception of the strake, this was borne out in test (AIAA paper 88-2552, "Wake Rake Studies Behind a Swept Surface, Canard Aircraft" by Neal Pfeiffer). Similarly, the Avanti was designed with extensive laminar flow (SAE paper 911003, "Development and Certification Flight Test on the Piaggio P.180 Avanti Aircraft: A General Overview" by Ing. Robertode' Pompeis, Ing. Paolo Cinquetti, and P.I. Sergio Martin).

I've heard that at one point, Piaggio looked at substituting small turbofans for the turboprops on the Avanti, but concerns about inlet airflow distortion induced by the canard wake killed this idea. The Scaled Triumph had the potential for a similar problem, but never experienced such problems during its flight test program.
 
tdscanuck
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 23, 2012 3:18 am

Quoting ferpe (Reply 15):
Quoting tdscanuck (Reply 11):
The design doesn't work for jets and it doesn't work for airliners

Tell me why...

In addition to all the stuff already listed, there are two more:
-3-surface is not very (effciently) tolerant of big CG shifts...this is OK on a biz jet, a major issue on an airliner.
-The engine placement doesn't scale well. You can't bury an airliner-sized engine in the wing (a la Comet) anymore due to rotor burst interacting with the structure. With the aft wing, you can't get much of a descent tail-mount. So you're stuck with either over the wing (a la Hondajet) which is extremely aerodynamically tricky (Hondajet is another point-design) or you go under the wing...at which point your rotation angle goes completely to hell.

There's also a major landing gear problem...where do you put it on an airliner-sized aircraft without incurring huge structural problems?

Tom.
 
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 23, 2012 6:56 pm

Quoting MD-90 (Reply 14):
Piaggio is allegedly designing an Avanti jet. It will be interesting to see what it looks like.

The 'Avanti jet' is codenamed the P1XX, and images of the concept are quite scarce, but some were leaked a few years back - the concept is a dissapointingly conventional rear engined T-tailed bizjet not unlike the Citation X.

http://www.flightglobal.com/news/art...-tight-lipped-on-jet-study-200374/

Last I heard was that the P1XX project had been shelved sadly, and Piaggio is instead focusing on the Avanti for the time being.

[Edited 2012-01-23 11:08:02]
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ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 23, 2012 7:09 pm

A

Quoting aeroweanie (Reply 19):
This is because the sum of the canard and wing lift distributions should be elliptical for minimum drag. As the canard itself has a near-elliptical load, this results in a "hole" in the required wing lift distribution.

B

Quoting tdscanuck (Reply 20):
-3-surface is not very (effciently) tolerant of big CG shifts...this is OK on a biz jet, a major issue on an airliner.

C

Quoting tdscanuck (Reply 20):
With the aft wing, you can't get much of a descent tail-mount. So you're stuck with either over the wing (a la Hondajet) which is extremely aerodynamically tricky (Hondajet is another point-design) or you go under the wing...at which point your rotation angle goes completely to hell.

There's also a major landing gear problem...where do you put it on an airliner-sized aircraft without incurring huge structural problems?

I can't agree with any of the above. You are describing the negatives of a true canard design, I talk about an airliner 3 lifting surfaces design. Like the example of the A340 this design can be identical except for one item, an additional surface on the forebody which changes the tails stabilizer function from negative lift stabilization to neutral or positive lift stabilization. Such a design has it's issues but not the ones you are describing. Now lets answer you points one by one:

A
I have never heard of this, I think you are mixing desired design and effect. A carnard due to it's downwash will disturb the lift distribution on the main wing as you describe but having a sum elliptical distribution can not be a goal IMO, each horizontal surface shall have its (near) elliptical lift distribution.

B
You would have to explain why not. If you take the A340 example you would have a foreplane and tailplane to balance the CG shifts and the wing+engines+MLG in the same position as with the 2 surface craft. Now explain why 2 trim surfaces should not be better then 1.

C
Once again you are thinking canard ie with the wing set back on the fuselage, I am not. Therefore MLG placement is as today, no problem and engines are slung as today.


I agree that the foreplanes downwash has to be carefully studied not to disturb the main wings lift distribution and engines inlets therefore you most likely need to mount it high. With careful mounting of the foreplane you would avoid its wake to disturb the other horizontal surfaces inside the flight envelope. At stall its wake would pass well over wing and horizontal tail thereby avoiding any risk of a deep stall.

[Edited 2012-01-23 11:27:59]
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ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Tue Jan 24, 2012 1:47 pm

After the last post I searched the Web for the A340 concept, here is two links:

TSA&source=bl&ots=wTI48BDvWB&sig=dlBj_AFPf9HDOjfDMTx_bKNZ0fA&hl=fr&sa=X&ei=0mUeT-j2PIH28QOAvPG8Dg&redir_esc=y#v=onepage&q=A340%20TSA&f=false" target="_blank">http://books.google.fr/books?id=toTR...c=y#v=onepage&q=A340%20TSA&f=false

Fig 2.9 on page 27 shows the A340-600 TSA and A3XX-TSA and the Avanti as TSC configs (Tree Surface Configuration). This reference gives it about 2% cruise drag advantage, it is primarly occupied with the cruise phase at M0.85:

http://www.icas-proceedings.net/ICAS2000/PAPERS/RESERVED/ICA0115.PDF

The following states the trim properties for CG compensations is superior and the trimmed drag is lower then a canard or classical config:

http://www.google.com/url?sa=t&rct=j...iWsj-Q&sig2=ELye5DpFZc1hG197UOR2cA


The following is the most comprehensive work I found with a quick scan, it concludes that a three surface desing is more effective then a conventional airliner:

http://dspace.lib.cranfield.ac.uk/handle/1826/3354

Here a short form of the concluding remarks at page 108 5.6 of this doctor thesis:
It was shown that the Direct Operating Costs and MTOW benefits are evident when switching from a conventional tail config to a three surface design. The benefits scale lineraly with the design range of the aircraft.

[Edited 2012-01-24 06:45:19]
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tdscanuck
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RE: Avanti Aerodynamics For Future Airliners?

Wed Jan 25, 2012 5:26 am

Quoting ferpe (Reply 18):
This does not impinge on the fundamental benefit of a 3 surface lifting concept, its main purpose is to reduce your trim drag, to get lifting or close to neutral control surfaces instead of todays downward lifting tail.

The issue is that it really doesn't reduce trim drag. By aerodynamic necessity, the maximum moment arm of the two trim surfaces in a three-surface aircraft is less than for the one trim surface in a two-surface aircraft. This means that the forces on the trim surfaces have to be larger on a three-surface aircraft than on a two. Given that each individual surface is smaller, at best, you have equal aspect ratio but higher force which means higher induced drag. You can see this in the PowerPoint you linked to, where they note the three-surface aircraft has higher minimum drag (Slide 11).

The whole principle of the three-surface aircraft is that this higher induced drag on the trimming surfaces is more than countered by the lower lift and lower induced drag on the main wing due to the upward, rather than downward, trim force on the forward surface. And this does, in fact, work in practice as long as you are very optimized in your lift and trim force distributions. This is exactly what you see on an Avanti and in the concept aircraft you linked to.

In practice, it's very difficult to realize those advantages across the entire operating envelope. On top of that, you're talking about adding a third airfoil to the aircraft, already the most difficult to manufacture and highly engineered item on the aircraft. It is extremely difficult for the conceptual advantage of the three-surface to translate into practically realizable benefits sufficiently large to pay for the costs.

Quoting ferpe (Reply 18):
With todays FBW it is fully feasible to go for an active CG control system (which you would need for any Flying body concept as any example) so I don't buy the CG argument

A flying body doesn't need active CG control, although it certainly helps for drag reduction. Note that nobody said a three-surface aircraft can't do CG control but that it's hard to do it efficiently. As the presentation you linked to noted, having three surfaces allows you to trim to the minimum drag configuration for any CG (within the stability band)...but doing so requires that the trim forces are equal and opposite for each surface: this means the forward surface has to be at least as large as the aft one (i.e. considerably bigger than you see on the Avanti), that both surfaces must be fully trimmable, and that when you do that you still have higher overall drag than an equivalent two-surface aircraft that's designed around that CG point. Basically, you're requiring the aircraft to have two horizontal stabilizers. That's heavy, expensive, and produces a significant placement problem for the forward surface on an airliner-sized aircraft.

Quoting ferpe (Reply 22):
If you take the A340 example you would have a foreplane and tailplane to balance the CG shifts and the wing+engines+MLG in the same position as with the 2 surface craft. Now explain why 2 trim surfaces should not be better then 1.

Because you're building two surfaces to do the job that can be done by only one. Thus the second trim surface has to provide enough drag improvement to pay for its own weight, parasitic drag, loss of fuselage volume, cost and complexity, and certification hurdles...so far, that has proven to be an extremely high entry barrier for airliners.

Quoting ferpe (Reply 22):
Once again you are thinking canard ie with the wing set back on the fuselage, I am not. Therefore MLG placement is as today, no problem and engines are slung as today.

I initially thought you were advocating for an Avanti-style design (highly aft main wing)...if we're just talking three-surface in general then I agree this issue isn't a significant one.

Quoting ferpe (Reply 23):
It was shown that the Direct Operating Costs and MTOW benefits are evident when switching from a conventional tail config to a three surface design. The benefits scale lineraly with the design range of the aircraft.

The crucial thing here is that, if this were actually true, we'd have seen it by now. Both widebody airframers have obviously done concepts where they've looked at it in a time period where they've both had advanced materials and FBW and both have chosen not to, even when it's pretty widely acknowledged they'd all sell their own grandmothers to get 1% gain on any front.

Tom.
 
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RE: Avanti Aerodynamics For Future Airliners?

Wed Jan 25, 2012 7:00 pm

Quoting tdscanuck (Reply 24):
By aerodynamic necessity, the maximum moment arm of the two trim surfaces in a three-surface aircraft is less than for the one trim surface in a two-surface aircraft. This means that the forces on the trim surfaces have to be larger on a three-surface aircraft than on a two

I don't buy this, today we have the trim surface on the tail part which most of the time is shorter then the part forward of the wing. In many of the references they split the tail volume in 2 and bolt them on the tails distance from the MAC (should be the CG to make both arms equal lenght, so change that 20% of MAC forward for the forward surface, should be no problem as said) , the drag of that config is higher of course as you add interference and form drag of another surface. When both share the nose down moment they by definition let the wing fly only the weight of the frame. Without re-optimizing the wing you will have higher drag, with a global optimization you will have lower drag, weight and therefore direct operating cost (first order concept study of course but no one has proven it moot).

Quoting tdscanuck (Reply 24):
In practice, it's very difficult to realize those advantages across the entire operating envelope. On top of that, you're talking about adding a third airfoil to the aircraft, already the most difficult to manufacture and highly engineered item on the aircraft. It is extremely difficult for the conceptual advantage of the three-surface to translate into practically realizable benefits sufficiently large to pay for the costs.

You will have aerodynamic advantages at low speed and at cruise, on top of that a lower empty weight scores in almost all parts of the envelope. Most references does not re-optimize the frame for the lower wingload, the Cranfield study does and reach substantial gains, in fact so large I did not state them here as they seemed to high (weight reductions over 5% etc). But if one look at the Avanti they seems to have gained it all, proof point IMO.

The airfoil you are adding requires an investment but then you invest to lower fuel burn today, big time (ref 787 with all it's new technology investments).

Quoting tdscanuck (Reply 24):
Basically, you're requiring the aircraft to have two horizontal stabilizers. That's heavy, expensive, and produces a significant placement problem for the forward surface on an airliner-sized aircraft.


Per the symmetrical case you state they only need to have half the surface each, globally optimized the frame is lighter. You pay a lot for the 3-5% gain in OEW on the 787 and 350. Sure it is a problem to get the forward surface there, we engineers call that a challenge  rather then a problem (bean-counters call it risk    ).

Quoting tdscanuck (Reply 24):
and that when you do that you still have higher overall drag than an equivalent two-surface aircraft that's designed around that CG point

Not correct, you forget the drag reduction from a global optimization (smaller main wing carrying less negative force).

Quoting tdscanuck (Reply 24):
Because you're building two surfaces to do the job that can be done by only one. Thus the second trim surface has to provide enough drag improvement to pay for its own weight, parasitic drag, loss of fuselage volume, cost and complexity, and certification hurdles...so far, that has proven to be an extremely high entry barrier for airliners.

I don't agree, both B and A are investing huge sums in developing the next generation with new technology to gain about 3-5% of OEW (their plastic frames   ), if the potential is in the same order I would say getting a stabilizer on the forebody will be done by someone who hasn't been burned by "unknow unknows"  recently. I don't think we expected the Avanti from Piaggio before they did it. So who will bite the bullet? B have a risk averse board by now I would say , A is threading step by step after the A380 jump. So who? The Chinese, the Russians? It might very well be Embraer, they seem to learn very fast.

Quoting tdscanuck (Reply 24):
The crucial thing here is that, if this were actually true, we'd have seen it by now. Both widebody airframers have obviously done concepts where they've looked at it in a time period where they've both had advanced materials and FBW and both have chosen not to, even when it's pretty widely acknowledged they'd all sell their own grandmothers to get 1% gain on any front.

Can't agree. Both B and A have been busy burning their risk budgets on improving the classical layout with thinks like CFRP, no bleed. Now the fuel is increasing it's part of DOC constantly, we will see framers that are prepared to risk more in the next 10-20 years. FBW, CFRP, fully linear command of all surfaces paves the way to master the difficulties of a technology like 3-surface aerodynamics, with classical mechanical control scheduling it is hard work, now the technology to master it is mature.

Normally you see new technology like canards which seems to be advantageous and then when realized it turns out it is more or less a wash. The first modern implementation of a 3 surface frame is the Avanti. I think we can agree it was no disappointment. In fact when I first saw the performance claims I though these were the typical before flight projections, not the real "Joey the pilot" flying the bird, that is why I only started to get impressed when I read the test flights from the typical GA mags.

Hat off to Piaggio    .

[Edited 2012-01-25 11:48:13]
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 26, 2012 2:58 am

Quoting ferpe (Reply 25):
Without re-optimizing the wing you will have higher drag, with a global optimization you will have lower drag, weight and therefore direct operating cost

That's not what at least two of the presentations you linked to say.

Quoting ferpe (Reply 25):
Per the symmetrical case you state they only need to have half the surface each, globally optimized the frame is lighter.

I still have a very tough time seeing how even the globally optimized frame is lighter. It's a step-change loss to add the third surface and related mounting and actuation hardware...the incremental gain on the other two surfaces has to be really amazing to make it work.

Quoting ferpe (Reply 25):
Sure it is a problem to get the forward surface there, we engineers call that a challenge  rather then a problem

It's a problem, not a challenge. Challenge implies it's hard, it's not. The problem is that you're sticking the surface through one of three things...the flight deck, the forward equipment bay, or the forward cargo hold. Going through either of the first two means relocating the stuff that was in your way, eating into the third. If you run through the third, you eat into the third. It's physically impossible with a tube fuselage to have a much revenue cargo space on a three-surface airliner as with a two-surface at equal technology.

Quoting ferpe (Reply 25):
Quoting tdscanuck (Reply 24):
and that when you do that you still have higher overall drag than an equivalent two-surface aircraft that's designed around that CG point

Not correct, you forget the drag reduction from a global optimization (smaller main wing carrying less negative force).

Again, that's not what even the stuff you linked to says. At equal optimization, the three-surface has higher minimum drag (but it can hold that minimum over a wider range). And, at equal stability, the two solutions converge to the same drag.

The downforce from a conventional tail is quite small relative to the weight, so the incremental downforce (and incremental induced drag) on the main wing is relatively small. It is almost always aerodynamically better to get your main lift from a single well-optimized surface than multiple surfaces (this is why you don't see bi-/tri-planes anymore and you "never" see multi-wing sailplanes). The main wing is usually so much better than any other surface at efficiently generating lift that it can more than "pay for" the relatively small penalty of tail downforce.

The Avanti three-surface design is a very elegant solution to the intersection of two design goals...very good fuel efficiency *and* a very spacious cabin on a biz-jet mission. The latter goal strongly favoured the highly aft main wing, which in turns drives you toward the three-surface solution to help achieve the former. All of this is supported well by a relatively point-designed aircraft. Airliner constraints just aren't the same.

Tom.
 
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 26, 2012 2:51 pm

I did have another thought this morning that would certainly impact a three-surface airliner but doesn't impact the Avanti...sufficient lift under a stab runway.

The Avanti forward surface isn't fully trimmable so you don't need to worry about it running away or getting stuck. In order to realize the full drag benefits of a three-surface, as the various links ferpe provided note, you need to be able to trim both the forward and rearward surface.

For certification reasons, that means you have to have sufficient main wing lift to support the aircraft in the event that either the forward or rear surface experiences a trim runaway and has to be locked out in the least-favourable position. That means the main wing has to be capable of supporting MTOW of the aircraft plus full tail trim...exactly the same load that it would have to support on a two-surface airliner. As a result, in a real world certification environment, I don't think you can get as much structural benefit for main wing optimum sizing as some of the linked papers may suggest.

Tom.
 
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RE: Avanti Aerodynamics For Future Airliners?

Thu Jan 26, 2012 7:46 pm

Quoting tdscanuck (Reply 26):
That's not what at least two of the presentations you linked to say.

As I pointed out many of the works on TSC you can find are on a rather shallow level, ie surfaces only (no fuselage) or with a fixed main wing, eg the ppt compares the drag of the 3 configs with the same main wing size (they reference the work of Sehlberg and Rokhsaz which is also referenced by the Cranfield thesis as a part problem study with restrictions). Only the Cranfield doc is a full airline conceptual simulation with an overall figure of merit (DOC and MTOW) which makes sense.

Quoting tdscanuck (Reply 26):
I still have a very tough time seeing how even the globally optimized frame is lighter. It's a step-change loss to add the third surface and related mounting and actuation hardware...the incremental gain on the other two surfaces has to be really amazing to make it work.

Well there is a bit to use for the extra half size, half force trim surface infrastructure, 3.45% of MTOW!

Quoting tdscanuck (Reply 26):
The problem is that you're sticking the surface through one of three things...the flight deck, the forward equipment bay, or the forward cargo hold. Going through either of the first two means relocating the stuff that was in your way, eating into the third. If you run through the third, you eat into the third.

Not really, you can relocate the forward equipment bay freely as long as it is close to the cockpit, the crown of the frames are not filled 100% and you can put it forward of a crew rest area above the cockpit using the same staircase for access. You quote " they'd all sell their own grandmothers to get 1% gain on any front" yet it seems very hard to find place for a 1/2 scale stabilizer wingbox and trim actuator in the frame (about 1,5 meter of forward underdeck space), this does not jive with me   .

Quoting tdscanuck (Reply 26):
Again, that's not what even the stuff you linked to says. At equal optimization, the three-surface has higher minimum drag (but it can hold that minimum over a wider range). And, at equal stability, the two solutions converge to the same drag.

Page 149 conclusions " All three-surface designs benefited from better cruise lift to drag ratios for increased design ranges as well as from longer cruise stage legs. "

Quoting tdscanuck (Reply 27):
That means the main wing has to be capable of supporting MTOW of the aircraft plus full tail trim...exactly the same load that it would have to support on a two-surface airliner.

Wrong, the locked out trim surface in the least favorable position has half the tail volume = authority, therefore you can still realize the benefits as described.


   I don't claim that a 3 surface airliner would be more efficient then todays configs, I am not in a position to say such a thing. I can only say that the very stimulating discussion with you Tom has not diminished my interest for such a solution. Actually I am a bit surprised we haven't found more arguments against it    (.......so far....    )
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 29, 2012 12:14 pm

To make the above discussion a bit more tangible I came to think of an application of the TSC that would be fun to analyse:

The Boeing 787-10X  Wow!  Wow!  

Here Boeing has a real dilemma as per my post 104 in this thread:

Boeing 777-8X And -9X Now In The Pipe Line (by MSN007 Jan 10 2012 in Civil Aviation)

They would need the 787-10 to be a true competitor to the A350-900 but hesitate to take on the development of a new wing, MLG and engines for such a 265t 8000nm version. Instead they look at staying with the 251t MTOW of the 789 as they then can keep wing, MLG and engines, drawback is a 6850nm spec range = the A350-900 is let alone in the 320 pax long haul market unless the 777-8X can compete there (doubtful they make that a 320 pax frame).

In the following I will show that on a conceptual level it would be possible to create a 265t 8000nm 787-10 with the existing wing (which actually stems from the 788    ) using a TSC configuration.


I will call this brilliant creature 787-10ATOPS (A.netTechOpsSpecial    )   . I am sure this will create some debate  .



787-10ATOPS DESIGN PROBLEM
The wingloading of the 788 wing at 251t MTOW is at its limits, I use to state it is 251t divided by 325m2. Actually this is wrong, it is this + the trim downforce of the tail (HTP). The HTP needs to counter the nose down moment of the wing + the moment from the distance between CG and center of lift. In stability and control there is a rule of thumb this is typcially 5% of MTOW, as I don't have the data for the 787 I will use this in the example.

The payload of the 787-10X is fine at 320 pax and 44 LD3 positions (6 pax and 8 positions more then the 359), now we need to haul that payload to 8000nm at pax+bags load. To get from 6850nm to 8000nm we need 2.4hours more flying time, at a fuel burn of 4.8t for the last part of a ULH leg this means a hike of the MTOW of 11.5t. Add 0,5t to get the fuel there and 2t for structure you are at 251 + 14 = 265t.



787-10ATOPS WINGLOAD
I wrote that the 788 wing was at it's limits at 251t, acutally this is wrong, it is at its limits at 1.05*251t = 263.6t which is the real force the wing has to counter (weight+tail downforce). As per above if we can use a well designed TSC config for trim we can balance the tail download with the canard upload, thus the wing would only carry the 265t weight, close enough to the 789 for it to leave the wing alone (also wingbending moment would be the same order  Wow! ).



787-10ATPOS CONFIG
The MLG need to be beefed up but can the 350 have a 4 wheel bogie at 268t the 787-10 can at 265t. Engines need to delivers some 80klbf for adequate start performance, this should be doable around 2018 without requiring new engines/nacelles.

Where to put the canards? As Tom says not so easy, the DLR (German NASA) A340-3XX study found that a nose mounted inverse swept canard was aerodynamically preferable (especially the transonic aero is free of supersonic flow on canard, but is also gives the same moment arm for canard and tail in our ATOPS example):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Forwardsweptcanard.jpg

The wingbox of the canard would pass in an extended forward nose forward of the NLG bay. The forces of the NLG make this area strong today thus the half scale trim forces of the canard should require reasonable reinforcements. Here a picture of the frame with half scale canards and HTP:



Not pretty    (but effective ) . (Yes, Yes I know the mustache will create problems when docking with gates and with pilot vision and ........  , lest discuss it!)




787-10ATOPS COMPETITIVE POSITION
Here its key data compare to todays 787-10X and A350-900

.................................788-10X..................787-10ATOPS.....................A359
MTOW ........................251t........................265t...................................268t
OEW...........................131t........................133t...................................136t
MZFW.........................188t........................190t...................................192t
MSP.............................57t..........................57t.....................................56t
Range nm maxPAX........6850.......................8000..................................8100


When counting home some TSC drag reduction the ATOPS should sail past the 359 on range as well!



CONCLUSION
Not bad for a 787-800 wing    .



An now the cheering or the bashing   

[Edited 2012-01-29 04:20:29]
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 29, 2012 1:47 pm

If Boeing adds back the 3m of span they originally planned for the 787-9, that would help with the wing loading at higher TOWs. They could add almost 5m more and still be within gate requirements.
 
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 29, 2012 9:37 pm

Quoting Stitch (Reply 30):
If Boeing adds back the 3m of span they originally planned for the 787-9, that would help with the wing loading at higher TOWs.

Problem is you would add 5% more span on a wing that typically weights 12.5% of MTOW = 1.7t OEW and as you now keep the download tail trim you also add an additional 13t wingload.

The increased wingload will increase induced drag which varies with the square of the load and the increased wingspan will decrease the induced drag but only with a linear relationship. Therefore:

Downforce increases from 265 to 279,5t which is 5.5% which is means induced drag increases with 11.2%.

Span increases with 5% which means final increase of induced drag is 6%. The increased wing area also increases parasitic drag, it typically constitutes 40% of parasitic drag. The parasitic drag (form or pressure drag + skin friction drag) is approx 40% of total drag at MTOW and induced is 55% and it then changes to 65% parasitic and say 30% induced as the fuel burns of. I would say you would increase total drag with something like 5+%.

The key point will be that the fuel burn will increase with 5+% and you will have to increase the MTOW to regain the your range. How much?, I would guess 270-275t.

[Edited 2012-01-29 13:44:23]
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 29, 2012 11:06 pm

Quoting ferpe (Reply 29):
I will call this brilliant creature 787-10ATOPS (A.netTechOpsSpecial ) . I am sure this will create some debate .

I move to call your creation the 787-10FABRIC ( Ferpe's A.net BRIlliant Creature ).
Thereby also laying to rest any discussions of CFRP content.

Fascinating discourse! Frightening aesthetics, though! Kind of eel-like.
 
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RE: Avanti Aerodynamics For Future Airliners?

Sun Jan 29, 2012 11:10 pm

Quoting ferpe (Reply 31):
Problem is you would add 5% more span on a wing that typically weights 12.5% of MTOW = 1.7t OEW and as you now keep the download tail trim you also add an additional 13t wingload.

For starters, you're adding span at the lightest part of the wing so scaling up by 5% is probably not appropriate (that would be appropriate for a 5% *area* increase, not tip extension).

I guarantee that a 5% span increase weighs less than an entire extra surface at the nose.

Quoting ferpe (Reply 31):
The increased wingload will increase induced drag which varies with the square of the load and the increased wingspan will decrease the induced drag but only with a linear relationship.

Induced drag *coefficient* varies with the square of the lift *coefficient*. Since you have a larger wing, lift coefficient at equal lift goes down. On top of that, the induced drag coefficient is inverse to the aspect ratio, which goes up with increasing span...those are additive effects.

Tom.
 
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 30, 2012 2:54 am

Quoting tdscanuck (Reply 33):
For starters, you're adding span at the lightest part of the wing so scaling up by 5% is probably not appropriate (that would be appropriate for a 5% *area* increase, not tip extension).

I guarantee that a 5% span increase weighs less than an entire extra surface at the nose.

You are right in terms of shear volume mass (as the 789 increase was a wingtip extension) but the weight of a a wing is also about withstanding increased wing bending moment. Here it will increase for 2 reasons, the increase of span will increase the bending moment and the increase of load will also increase the wing bending moment. I therefore made life easy (I don't know how to estimate the wingsking thickness increase, beefed up center wingbox, side of body join etc for those increased loads ) and said this all will cost 5% of weight. The true answer might be 4% or 6% but I don't think it would be something like 3%.

Quoting tdscanuck (Reply 33):
Induced drag *coefficient* varies with the square of the lift *coefficient*. Since you have a larger wing, lift coefficient at equal lift goes down.

You are right but as this is a tip extension the added area is small, about 6 m2 (the wing is about 2m wide spanwise before the swept wingtips), this is less then 2% increase of wing area, The correct term would be 279,5/331 divided by 265/325 = 3,6% increase in lift coefficient. Cl^2 would be 7.3%.

Quoting tdscanuck (Reply 33):
the induced drag coefficient is inverse to the aspect ratio, which goes up with increasing span...those are additive effects.

Yes, A is in the denominator, that is what I meant with "the increased wingspan will decrease the induced drag but only with a linear relationship" and I therefore divided my Cl^2 with A. Now A goes from 60^2/325 = 11.08 to 63^2/331 = 11.99. It means that A increases with 8% (sorry for being lazy and not calculating this properly, thought a 5% spanincrease meant a 5% A increase when planform stays the same   ).

So correctly the Induced drag coefficient has decreased 0.7%, however the reference area is now 1.9% larger so in the end induced drag increases with 1.2%  (if I have done things right this time   ).


Now induced drag is about on average 1/3 of total drag so the real discussion is what happens with parasitic drag. Area (skin friction drag) goes up with 6m2 and pressure drag has a 3m span increase to pass. Any ones guess how much this increases parasitic drag   .

Does anyone have a free copy of a CFD program and the 787 wing model lying around .

In the end I don't think 5+% drag increase is overstating how much the drag will increase, your thoughts? (Where is OldAeroguy when we need him  banghead  ).

[Edited 2012-01-29 19:16:17]
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 30, 2012 10:41 am

Quoting ferpe (Reply 18):
The sensitivity of the forewing is well known if not from any other then Ruthans designs. Once again FBW fixes that.

Well, the difference is that Rutan's design have fully controllable canards... Avanti doesn't. It's only fitted with flaps tied to the main flaps.

Quoting ferpe (Reply 18):
Where you have the freedom of full authority FBW you design with canards today, ref Indias MMRCA rejection of the US designs based on their lower flying performance. Civil airliner design is more conservative but we see many forewing or canard concepts being thrown around as the 2025 concept, there is a reason other then being fancy IMO...
Quoting ferpe (Reply 29):
I will call this brilliant creature 787-10ATOPS

WAIT!!!! We're having fun at TechOps????

I am still wondering, why the obsession with the Avanti configuration? I'm no expert in aerodynamics, but... here goes anyways...

I remembered reading an article on the Avanti a few years ago... and found it...
http://www.flyingmag.com/pilot-reports/turboprops/fuel-miser?page=0,0

Basic criteria was, "fuel efficient, mid 300kt speed range, largest cabin"

1. Why did they chose a turboprop? Simple, fuel price. In the late 80s, and with the technology at the time, the answer was turboprop.

2. Efficient Wing. High aspect ratio... span is big, but the wing area is the same size as a Cessna 172! Then, make the wing as laminar as possible. (50% of the chord, thanks to the pusher props).

3. Low drag fuselage... hence the "Avanti egg shape", the got the shape as constantly changing to maintain laminarity.

1+2+3 means, well, put the wing through the middle of the cross section. But that means, the cabin will be hindered... solution? Move it back. This then cause another problem... balance! Now a conventional configuration would mean they need a huge stabilizer at the back. This is why they have a forward wing. Note, it is a forward wing, not a canard. It has no pitch control capability. The function of the wing is purely to reduce the burden on the rear stabilizer, enabling a smaller stabilizer... and one can get away with a very small forward wing. And since it is a forward wing, it has high lift surfaces... flaps... tied to the main wing flap.

So, you got a very aerodynamic fuselage, and wing, with good stability. And oh, when you want to stall the thing, the forward wing stalls before the main wing, and the nose lowers despite full aft controls.

Flap deployment gets interesting. One needs to prevent asymmetry on the left and right side, and synchronize the front and main wing to minimize pitch changes... clean to intermediate flap (take off/approach setting) takes 15 secs.

In the case of the Avanti, the airflow from the forward wing, passes cleanly below the airflow of the mainwing, because the main wing is higher up... and that allows the wing to be simple, because the landing gear is not attached to it.

Now, why don't airliners use this kind of config?
1. They have a different set of criteria.
2. To keep weight down, you have to keep the forward wing structurally simple. No pitch controls except for flaps. FBW or no FBW, once you turn the front wing into a control surface canard, the gains can erode away very very quickly...
3. There is no need to put the wing aft if you're going to slap it below the main cabin, so therefore, a simple 2 wing configuration consisting of a mainwing and a stabilizer is likely to be the most efficient commercially feasible method. (emphasis on: COMMERCIALLY FEASIBLE). Now,if you want to extend the MD80/90 even further, then yes, you're going to need a 3 wing configuration!    Eh, hang on! THEY ALREADY GOT AN AVANTI CONFIGURATION... look...

View Large View Medium
Click here for bigger photo!

Photo © Akihiro Yamasaki


See the 3rd "wing"?   

Now, the Avanti solution could work for say... small planes... OR... want to stretch the Q400 or the CRJ further without increasing tailstrike risk?   
Although I dunno how that can work for the CRJ unless one want sto sacrifice efficiency near the wing root further thanks to the airflow from the front wing. But for high wing-ed aircraft, this looks like a possible solution...

Why not make the Dash-8-Q500    there's no need to keep the area between the front door and the wing clear of anythinganyways because it has no underfloor hold, so no ground equipment that has to come near it. I think that's the most commercially feasible solution that can be "forced" to use an Avanti kind of 3 wing config...   

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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 30, 2012 1:10 pm

Quoting mandala499 (Reply 35):
WAIT!!!! We're having fun at TechOps????
No, no heaven forbid    , we are just getting our brains some aero-bics     (pun intended ).

Quoting mandala499 (Reply 35):
but the wing area is the same size as a Cessna 172!
Exactly! And why may I ask?

Quoting mandala499 (Reply 35):
But that means, the cabin will be hindered... solution? Move it back. This then cause another problem... balance! Now a conventional configuration would mean they need a huge stabilizer at the back. This is why they have a forward wing.
A mixing of cause and effect, you can balance that wing passing behind the cabin by locating all heavy equipment aft of the wing like the Aerostar etc. But yeah, sure it is a both, that is in my mind real brilliance, killing a couple of flies with one smack    .

Quoting mandala499 (Reply 35):
once you turn the front wing into a control surface canard, the gains can erode away very very quickly...
don't think so, you can conveniently handle the half-scale forces with today's technology.

Quoting mandala499 (Reply 35):
the airflow from the forward wing, passes cleanly below the airflow of the mainwing, because the main wing is higher up...
agree this is one of the tricky bits together with the destabilizing effect the canard has...

Quoting mandala499 (Reply 35):
Now,if you want to extend the MD80/90 even further, then yes, you're going to need a 3 wing configuration! Eh, hang on! THEY ALREADY GOT AN AVANTI CONFIGURATION... look...
   and a very high aspect ratio they have   


Quoting mandala499 (Reply 35):
I think that's the most commercially feasible solution that can be "forced" to use an Avanti kind of 3 wing config...

we don't force people at A.net TechOps    , we show them the light    and they will see  
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mandala499
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RE: Avanti Aerodynamics For Future Airliners?

Mon Jan 30, 2012 5:37 pm

Quoting ferpe (Reply 36):
we don't force people at A.net TechOps    , we show them the light    and they will see

So, while I don't think this avanti config will work for widebody twins... I think for narrowbodies with sleek design has a chance... albeit slightly... like... CRJ1100/1200/1300 perhaps? (assume the C-series don't even make it on the drawing board!    ), or a Dash8 Q-500/600/700?   

Perhaps a redesigned and elongated FMA123? (well, isn't that just a prop version of the jungle jets?)

Ferpe.. more designs please !   
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
wingscrubber
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RE: Avanti Aerodynamics For Future Airliners?

Thu Feb 02, 2012 6:55 am

Does this help with imagining a three-winged airliner?  
View Large View Medium
Click here for bigger photo!

Photo © Brian Lockett



And here's another '3 winger'...


View Large View Medium
Click here for bigger photo!

Photo © Martin West

Resident TechOps Troll
 
ferpe
Topic Author
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RE: Avanti Aerodynamics For Future Airliners?

Thu Feb 02, 2012 8:36 pm

Now we are getting somewhere  .

The 757 will have slight problems in the transonic area however, but it is rightly thought    .
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tommytoyz
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RE: Avanti Aerodynamics For Future Airliners?

Thu Feb 16, 2012 11:22 pm

Quoting ferpe (Reply 8):
Canards have the problem that you need to load the small wing (with a mostly low aspect ratio) highly to reach a statically and dynamically naturally stable vehcile. Thus the canards contributes an unproportionally large part of the lift and therefore drag of the airframe.

Not only that, but the main wing must be much larger than conventional aircraft, because it must produce more lift. Why? Because, everything else being equal, the main wing must stall last and produce more lift at low speeds, the opposite of conventional aircraft. The result is, that a 2 wing canard main wing will be bigger to produce the low speed lift. Just look at the wing area of 2 winged canards. They're very large and still have high landing speeds - most of them.

Conventional designs have better performance that 2 wing canards.

Quoting ferpe (Reply 18):
In general with a 3 surface concept you have a much better low speed situation,

Yes, the 3 lift wing configuration allows for a smaller main wing compared to conventional designs and even more so against a 2 lift wing design. It produces less induced drag overall of the 3 designs an has the smallest aggregate wing area of all surfaces.

The negative "lift" produced by conventional designs must be compensated by a larger and heavier main wing, increasing induced drag, area and weight, and the 2 wing lift canard requires a large main wing with higher low speed lift capabilities that the other two main wings.

You can clearly see this in the P180, with the very small main wing and the high main wing loading, yet still has adequate low speed performance.

3 wing lift designs have better performance than either 2 wing canards or conventional designs.

I read research papers on this way back, and the take away was that the 3 wing lift design was overall the most efficient.

However, the Blended Wing concept also gets along without the negative effects of permanent "negative lift" forces being exerted. So the airliner building crowd will probably go that route instead as if offer other advantages as well. That I think is the reason we will not see a clean sheet 3 wing lift design - but who knows?
 
tommytoyz
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RE: Avanti Aerodynamics For Future Airliners?

Thu Feb 16, 2012 11:42 pm

Quoting tdscanuck (Reply 26):
It's physically impossible with a tube fuselage to have a much revenue cargo space on a three-surface airliner as with a two-surface at equal technology.

Only if you keep the tube size and shape the same. However, you can compensate for the lost inner space by making the tube slightly bigger. My hunch is that, everything else being equal, you would still see and overall net fuel savings. But I could be wrong.
 
ferpe
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RE: Avanti Aerodynamics For Future Airliners?

Fri Feb 17, 2012 7:46 pm

Quoting tommytoyz (Reply 40):
Because, everything else being equal, the main wing must stall last and produce more lift at low speeds, the opposite of conventional aircraft. The result is, that a 2 wing canard main wing will be bigger to produce the low speed lift. Just look at the wing area of 2 winged canards. They're very large and still have high landing speeds - most of them.

There is another solution to the problem of the canard stalling before the main wing and that is to make the canard more sensitive to high alfa, normally by having no droop nose or slat on the canard yet having it on the main wing. You can also reach the same effect by just making a less rounded nose shape of the forewing/canard (like the P 180) compared to the main wing.

Many civil canard designs are made as homebuilts (Rutan...) therefore they don't go to any elaborate high lift arrangements on the main wing thus average landing performance for the wing size. Further they use the trailing edge for roll control, thus they are very conservative with any droop they put on. Ideally you should use flaps + ailerons but that complicates things, therefore most designs stay with ailerons or flaperons = good enough.

The canard design per se does not mean a larger main wing, rather smaller everything else being equal.
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tommytoyz
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RE: Avanti Aerodynamics For Future Airliners?

Sat Feb 18, 2012 8:21 am

Quoting ferpe (Reply 42):
The canard design per se does not mean a larger main wing, rather smaller everything else being equal.

True. However, whatever the solution and stall speeds being equal, the main wing on a 2 wing Canard must stall at a slower speed than the main wing of a conventional design and at a lower AoA. If you have the same stall speed (of all wings) for all designs, this makes for a less efficient main wing of a 2 wing Canard at cruise speeds and for a higher overall aggregate wing area than either conventional or 3 lift wing designs.

That's why the Beech StarShip had such a large wing area/weight and low performance, despite the looks.

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