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764/CR7 Sloping Forward  
User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Posted (6 years 11 months 7 hours ago) and read 2145 times:

Why do both aircraft have this look of it sloping forward? Is there a technical reason? I got a partial answer about the RJ but didn't sound like it made much sense. Something and evacuation slide or someting.


What gets measured gets done.
33 replies: All unread, showing first 25:
 
User currently offlinePilotpip From United States of America, joined Sep 2003, 3150 posts, RR: 11
Reply 1, posted (6 years 11 months 7 hours ago) and read 2146 times:

The CRJ 700 and 900 slope down so the foward door is close enough to the ground to allow for certification without a slide.


DMI
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 2, posted (6 years 11 months 7 hours ago) and read 2146 times:
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Quoting Pilotpip (Reply 1):
The CRJ 700 and 900 slope down so the foward door is close enough to the ground to allow for certification without a slide.

Cool. For some reason, I thought it had to do with tailstrike avoidance. The Q400 seems to be sloped in a similar manner.

2H4




Intentionally Left Blank
User currently offlinePilotboi From United States of America, joined Sep 2007, 2366 posts, RR: 9
Reply 3, posted (6 years 11 months 6 hours ago) and read 2146 times:

The MD-80s series also does this. Not as much, but it is there. What's even more interesting, is that on the ground, the fuselage points downwards, but the engines point upwards. I'm sure it all has to do mostly with aerodynamics. Of course practical reasons are possible, like as said for the RJ to have a lower door.

User currently offlineHa763 From United States of America, joined Jan 2003, 3657 posts, RR: 5
Reply 4, posted (6 years 11 months 6 hours ago) and read 2146 times:
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The 767-400's main landing gear are taller than those on the -200/-300 and use the larger 777 tires to allow more tail clearance to help prevent tail strikes on takeoff.

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 5, posted (6 years 11 months 4 hours ago) and read 2146 times:

Quoting Pilotboi (Reply 3):
I'm sure it all has to do mostly with aerodynamics.

Not really a lot.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineViscount724 From Switzerland, joined Oct 2006, 25170 posts, RR: 22
Reply 6, posted (6 years 11 months 2 hours ago) and read 2146 times:

Quoting 2H4 (Reply 2):
Quoting Pilotpip (Reply 1):
The CRJ 700 and 900 slope down so the foward door is close enough to the ground to allow for certification without a slide.

Cool. For some reason, I thought it had to do with tailstrike avoidance.

I believe the starting point is a longer main gear due to the tailstrike issue, but they used the same length nosegear as the CRJ-100/200 to avoid the need for inflatable slides.

As a sidenote, the DC-8's slightly nose-down attitude on the ground made the it much easier to stretch than the 707 which has a more level attitude on the ground (compare top of fuselage with horizontal runway edges etc. in the 707 photo below).


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User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 7, posted (6 years 10 months 4 weeks 1 day 20 hours ago) and read 2145 times:

Quoting Pilotpip (Reply 1):
The CRJ 700 and 900 slope down so the foward door is close enough to the ground to allow for certification without a slide.

Oh, so my friend was right. Shame on me. He was at ASA when I was there last year on the ramp and I though he was just trying to look good because I was the new guy but I guess he knew his stuff about the RJ's. Sad though, He actually loved ASA. Been in ATL working for them like 14 years now he hd to start all over with Delta.



What gets measured gets done.
User currently offlineCanadianNorth From Canada, joined Aug 2002, 3389 posts, RR: 9
Reply 8, posted (6 years 10 months 4 weeks 1 day 20 hours ago) and read 2145 times:

I believe the 737-200 also slopes forward slightly, as I've passed stuff up into the fwd galley from the ground via the open door, but to do the same with the aft galley I either have to toss it up or find something to stand on.


CanadianNorth



What could possibly go wrong?
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 9, posted (6 years 10 months 4 weeks 1 day 19 hours ago) and read 2145 times:

Quoting CanadianNorth (Reply 8):
I believe the 737-200 also slopes forward slightly

An ideal 1 deg pitch down.
regds
MEL



Think of the brighter side!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 10, posted (6 years 10 months 4 weeks 1 day 16 hours ago) and read 2145 times:

Quoting Viscount724 (Reply 6):

As a sidenote, the DC-8's slightly nose-down attitude on the ground made the it much easier to stretch than the 707 which has a more level attitude on the ground (compare top of fuselage with horizontal runway edges etc. in the 707 photo below).

I think it's mostly the height of the main gear enabling a easier stretch. This does of course mean a forward lean unless you want to waste money also extending the nose gear. So they are related.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinePilotboi From United States of America, joined Sep 2007, 2366 posts, RR: 9
Reply 11, posted (6 years 10 months 4 weeks 1 day 11 hours ago) and read 2145 times:

Quoting Starlionblue (Reply 5):
Not really a lot.

I was talking mainly about the MD-80 having a fuselage pitch down, and engines pitch up.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 12, posted (6 years 10 months 4 weeks 1 day 10 hours ago) and read 2145 times:

Quoting Pilotboi (Reply 3):
The MD-80s series also does this. Not as much, but it is there. What's even more interesting, is that on the ground, the fuselage points downwards, but the engines point upwards. I'm sure it all has to do mostly with aerodynamics.

I think the engines are pitched to be parallel to the local airflow, which maximizes inlet efficiency. Tail-mounted engines are flying in the wing's downwash.

Tom.


User currently offlinePilotboi From United States of America, joined Sep 2007, 2366 posts, RR: 9
Reply 13, posted (6 years 10 months 4 weeks 1 day 9 hours ago) and read 2145 times:

Quoting Tdscanuck (Reply 12):
I think the engines are pitched to be parallel to the local airflow, which maximizes inlet efficiency. Tail-mounted engines are flying in the wing's downwash.

Very good observation, and it makes sense too!


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 14, posted (6 years 10 months 4 weeks 1 day 4 hours ago) and read 2145 times:

Quoting Pilotboi (Reply 13):
Quoting Tdscanuck (Reply 12):
I think the engines are pitched to be parallel to the local airflow, which maximizes inlet efficiency. Tail-mounted engines are flying in the wing's downwash.

Very good observation, and it makes sense too!

They also toe outwards, as opposed to wing mounted engines that toe inwards. This is also to align with local flow.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineChallengerDan From Canada, joined Sep 2003, 172 posts, RR: 0
Reply 15, posted (6 years 10 months 4 weeks 22 hours ago) and read 2145 times:

i remember an engineer, when i worked at Bombardier, that told me the CR7 ground attitude was in order to use the same door as on the CR2 which means lower production and certification cost.


if your flight goes MX in YUL, I might be called to fix it!
User currently offline9VSIO From United Kingdom, joined Dec 2006, 716 posts, RR: 2
Reply 16, posted (6 years 10 months 4 weeks 12 hours ago) and read 2145 times:
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Will this pitch down be picked up by the attitude indicator?


Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 17, posted (6 years 10 months 4 weeks 11 hours ago) and read 2145 times:

Quoting ChallengerDan (Reply 15):
i remember an engineer, when i worked at Bombardier, that told me the CR7 ground attitude was in order to use the same door as on the CR2 which means lower production and certification cost.

I'm no expert and someone please jump in but I know the 200 and 700 has different doors. Same design yes, but the door itself on the 70 seater is larger and has more steps.



What gets measured gets done.
User currently offlineMusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 18, posted (6 years 10 months 4 weeks 9 hours ago) and read 2145 times:

9VSIO yes the attitude is reflected in the AI.

Another advantage of a nose down attitude on the ground is that on landing, when the nosewheel reaches the ground, the wing is at less of an angle of attack, so less lift, so more effective wheel braking, so less stopping distance required.

Not sure whether this consideration ever dictated design, or was a useful by-product.

Regards - musang


User currently offlinePilotpip From United States of America, joined Sep 2003, 3150 posts, RR: 11
Reply 19, posted (6 years 10 months 4 weeks 9 hours ago) and read 2145 times:

I have a couple friends flying the 700 and this response is overwhelming regdarding the nose-down attitude: It makes it damn hard to make a nice landing. You touch down on the mains, and hold off to keep the nose from slamming down but because you're sitting two or three feet lower than level the elevator runs out of effectiveness and you slam the nose down anyway.


DMI
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 20, posted (6 years 10 months 4 weeks 7 hours ago) and read 2145 times:

The nose is down on the ground in order to keep the wings at or close to the zero lift angle of attack.

A wing generating lift will also generate drag.

Drag on the take-off roll is bad for take-off performance.

Hence it is better to keep the weight on the wheels up until you are ready to go flying. Nose down attitude means no lift is generated, less drag is generated, Vr is reached quicker and in a shorter distance. You will be able to rotate, get the nose wheel off the ground, increase the angle of attack of the wings until lift exceeds weight and be airborne sooner than you would have had the fuselage been level on the ground.

It is all about aerodynamics. Very little performance would be sacrificed in order to avoid having to redesign slides etc.



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 21, posted (6 years 10 months 4 weeks 6 hours ago) and read 2145 times:
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Quoting FredT (Reply 20):
Nose down attitude means no lift is generated, less drag is generated, Vr is reached quicker and in a shorter distance.

It seems like it's taken the industry a long time to realize this. The only aircraft type that comes to mind that has used used a nose-down attitude in the past is maybe the G-1159.

Considering the benefits you listed, Fred, why do you think it's taken so long for us to see the nose-down attitude utilized? Or have many of the benefits, in the past, been realized through adjusting angles of incidence?

2H4

[Edited 2007-10-08 15:16:51]


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User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 22, posted (6 years 10 months 4 weeks 6 hours ago) and read 2145 times:

Quoting 2H4 (Reply 21):
Considering the benefits you listed, Fred, why do you think it's taken so long for us to see the nose-down attitude utilized? Or have many of the benefits, in the past, been realized through increased angles of incidence?

I asked about the nose-down attitude before, becuse I noticed it in some models I have built and wondered whether it was because of a poor model, my shoddy workmanship, or deliberate design.

The reasons I was given were exactly as Fred says; to wit, the airfoil is usually angled higher at the front than the back, to get the correct angle of incidence in the cruise, while maintaining a reasonable deck angle. To avoid the excess drag that this would cause during the takeoff roll, the nose is lower than the tail.

It is self-evident that this did take some time to sort out, (compared to the length of our aviation history in total), but I first noticed it on a 727-100. The 73X and BAe-146 are the same.



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User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 23, posted (6 years 10 months 4 weeks 6 hours ago) and read 2145 times:
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Quoting BAe146QT (Reply 22):
I first noticed it on a 727-100

Yes, good example.

I'm also reminded of the popular nosewheel mod on many Twin Comanches. Many (most?) owners have exchanged the original nosewheel for a smaller-diameter nosewheel to achieve the aforementioned relationship between the angle of incidence and deck angle.

From what I understand, though, this mod was more of an effort to neutralize that relationship...apparently, the airplane in stock form tended to float up and start flying before reaching a safe takeoff speed.

2H4




Intentionally Left Blank
User currently offlineElpinDAB From United States of America, joined Apr 2005, 473 posts, RR: 4
Reply 24, posted (6 years 10 months 4 weeks 2 hours ago) and read 2111 times:

Quoting 2H4 (Reply 23):
I'm also reminded of the popular nosewheel mod on many Twin Comanches. Many (most?) owners have exchanged the original nosewheel for a smaller-diameter nosewheel to achieve the aforementioned relationship between the angle of incidence and deck angle.

Hmmm interesting...those said owners sound like a bunch of pansies to me  Wink On a serious note though, I've never heard of this mod, probably because the 2 Twinkies that I've flown didn't have it. It is notorious for it's tricky landing characteristics though, so I guess that's the reason. It takes a little getting used to, but once you are, you can definitely get some good greasers from her, especially after flying one a few times every day for 2 weeks.

Quoting 2H4 (Reply 23):
From what I understand, though, this mod was more of an effort to neutralize that relationship...apparently, the airplane in stock form tended to float up and start flying before reaching a safe takeoff speed.

Yes, this tendency to want to fly before reaching Vmc always kept me on close guard. Very dangerous if you were to lose an engine while floating above the ground prior to reaching Vmc. This was the case for almost every takeoff though, because no matter how hard you try to keep it on the ground, it wants to fly. You can keep it on the ground until about 5-10kts before Vmc, but even before then, she'll start doing the "twinkie dance", letting you know full well that she's ready to fly.

I think that this is mostly because the Twim Comanche's Vmc was actually raised to its current speed sometime in the 70's because there were so many training accidents attribute to Vmc rolling. Mostly, instructors were abusing Vmc to make a point to their students, and thus causing fatal training accidents that should have been prevented. But, Piper still chose to raise Vmc to improve safety. So, the Twin Comanche's reasoning for wanting to fly before Vmc is because the reasonable rotation speed is actually about what Vmc originally was, about 5-10kts slower than the current Vmc. It makes sense that they would need to modify the nose wheel after this change...it's probably better suited for the new rotation/Vmc speed. Makes me curious now, I'll probably try to search for pics of Twinkies with this smaller nose wheel.




Sorry to stray a little off topic...my Twinkie flying days are very dear to me, even though the next twin I fly will be the Diamond Twin Star hehe.

Gulfsteams also have a nose-low stance on their gear, and I heard that it was for visibility during taxi and landing. Maybe wrong though... I wonder if the Q-400's nose low stance is for flight attendant regs, forward visibility, or tail-strike concerns?


25 Post contains links and images ANITIX87 : All the Airbus widebodies have the nose-down attitude too. The MD-11 doesn't have it and I always thought that made this picture incredibly interestin
26 BAe146QT : Well now that's very interesting. I wonder - does the "gulling" and curve of the Airbus wing at the root mean that the deck angle can be more level o
27 2H4 : A casual viewer of that photo might think to themselves "Man, that tail-mounted engine must be heavy!" 2H4
28 Bond007 : deleted .... somehow got posted into wrong thread... servers are screwed! Jimbo[Edited 2007-10-09 13:19:43]
29 CRJ900 : Does this apply to the larger sisters CRJ900 and CRJ1000 as well? The CRJ900 appears to be somewhat forward-sloping too...?
30 Post contains images DeltaGuy : Not really, as visability is spectacular from the windows at most any time...the a/c doesn't slope thaaat much The engines and all of the empenage as
31 DC8FriendShip : Same for the CRJ's- in heavy check we put a 3000 lb weight on the forward jackpoint to keep the plane noseheavy Nope- basically the same door, with a
32 Starlionblue : If nothing else, the gulling allows shorter (=lighter) landing gear while still giving clearance for underwing engines. All Airbus widebodies have qu
33 FredT : I doubt it, since having the fuse level on the ground along with having the wings at the zero lift angle of attack would mean a zero angle of inciden
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