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Avanti Aerodynamics For Future Airliners?  
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Posted (2 years 8 months 5 days 18 hours ago) and read 12057 times:

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]


Non French in France
43 replies: All unread, showing first 25:
 
User currently offlineStitch From United States of America, joined Jul 2005, 31003 posts, RR: 86
Reply 1, posted (2 years 8 months 5 days 18 hours ago) and read 12050 times:
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The closet concept I can think of at the moment is Boeing's "Kermit Cruiser":

Boeing Kermit Cruiser Low-Noise Concept


User currently offlineB6JFKH81 From United States of America, joined Mar 2006, 2891 posts, RR: 7
Reply 2, posted (2 years 8 months 5 days 17 hours ago) and read 12026 times:

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



"If you do not learn from history, you are doomed to repeat it"
User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 31
Reply 3, posted (2 years 8 months 5 days 17 hours ago) and read 12020 times:

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.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 59
Reply 4, posted (2 years 8 months 5 days 15 hours ago) and read 11981 times:
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DATABASE EDITOR

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.



Intentionally Left Blank
User currently offlineStitch From United States of America, joined Jul 2005, 31003 posts, RR: 86
Reply 5, posted (2 years 8 months 5 days 15 hours ago) and read 11972 times:
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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.  


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 6, posted (2 years 8 months 5 days 8 hours ago) and read 11867 times:

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.



Non French in France
User currently offlineMD-90 From United States of America, joined Jan 2000, 8507 posts, RR: 12
Reply 7, posted (2 years 8 months 5 days 3 hours ago) and read 11785 times:

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).


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 8, posted (2 years 8 months 5 days 2 hours ago) and read 11759 times:

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    .



Non French in France
User currently offlineNorthwest727 From United States of America, joined Jul 2005, 491 posts, RR: 0
Reply 9, posted (2 years 8 months 5 days 1 hour ago) and read 11737 times:

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.


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 10, posted (2 years 8 months 4 days 20 hours ago) and read 11641 times:

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    .



Non French in France
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 11, posted (2 years 8 months 3 days 14 hours ago) and read 11404 times:

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.


User currently offlinerwessel From United States of America, joined Jan 2007, 2353 posts, RR: 2
Reply 12, posted (2 years 8 months 3 days 7 hours ago) and read 11319 times:
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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.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17041 posts, RR: 66
Reply 13, posted (2 years 8 months 3 days 5 hours ago) and read 11311 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMD-90 From United States of America, joined Jan 2000, 8507 posts, RR: 12
Reply 14, posted (2 years 8 months 3 days 5 hours ago) and read 11303 times:

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.


View Large View Medium
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Photo © John Allan
View Large View Medium
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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.


User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 15, posted (2 years 8 months 2 days 23 hours ago) and read 11234 times:

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

Tell me why...



Non French in France
User currently offlineLemmy From United States of America, joined Dec 2004, 258 posts, RR: 0
Reply 16, posted (2 years 8 months 2 days 23 hours ago) and read 11232 times:

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.



I am a patient boy ...
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6869 posts, RR: 75
Reply 17, posted (2 years 8 months 2 days 21 hours ago) and read 11195 times:

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



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 18, posted (2 years 8 months 2 days 16 hours ago) and read 11112 times:

@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]


Non French in France
User currently offlineaeroweanie From United States of America, joined Dec 2004, 1609 posts, RR: 52
Reply 19, posted (2 years 8 months 2 days 14 hours ago) and read 11082 times:
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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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 20, posted (2 years 8 months 2 days 11 hours ago) and read 11055 times:

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.


User currently offlinewingscrubber From UK - England, joined Sep 2001, 850 posts, RR: 0
Reply 21, posted (2 years 8 months 1 day 20 hours ago) and read 10909 times:

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]


Resident TechOps Troll
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 22, posted (2 years 8 months 1 day 20 hours ago) and read 10900 times:

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]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 23, posted (2 years 8 months 1 day 1 hour ago) and read 10790 times:

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]


Non French in France
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 24, posted (2 years 8 months 9 hours ago) and read 10632 times:

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.


25 Post contains images ferpe : 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
26 tdscanuck : That's not what at least two of the presentations you linked to say. I still have a very tough time seeing how even the globally optimized frame is l
27 tdscanuck : 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 s
28 Post contains images ferpe : 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 th
29 Post contains links and images ferpe : 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 Here Bo
30 Stitch : 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
31 ferpe : 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 a
32 SeJoWa : 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. Fasc
33 tdscanuck : 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%
34 Post contains images ferpe : 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 incre
35 Post contains links and images mandala499 : 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. WA
36 Post contains images ferpe : No, no heaven forbid , we are just getting our brains some aero-bics (pun intended ). Exactly! And why may I ask? A mixing of cause and effect, you c
37 Post contains images mandala499 : 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
38 Post contains links and images wingscrubber : Does this help with imagining a three-winged airliner? View Large View MediumPhoto © Brian Lockett And here's another '3 winger'... View Large View M
39 Post contains images ferpe : Now we are getting somewhere . The 757 will have slight problems in the transonic area however, but it is rightly thought .
40 tommytoyz : Not only that, but the main wing must be much larger than conventional aircraft, because it must produce more lift. Why? Because, everything else bei
41 tommytoyz : 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
42 ferpe : 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, norm
43 tommytoyz : 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 o
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