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nfield
Topic Author
Posts: 38
Joined: Fri Dec 13, 2002 9:09 pm

B52 Flight Characteristics

Wed Jan 22, 2003 11:40 pm

Is it my imagination or do Boeing B52's fly slightly nose down? Is the reason that tandem main gear prevents rotation at take-off, therefore the main wing has a lot of positive incidence compared with conventional aircraft.
 
jwenting
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RE: B52 Flight Characteristics

Thu Jan 23, 2003 5:18 pm

I've seen this as well. But then I've only seen B-52s in the flesh flying low and slow so it could be a characteristic of the low-speed part of the flight envellope only.
Takeoff is not nosedown, it's just about level. Wings start to generate lift and curve up a bit, tipwheels come loose and then the entire aircraft floats into the air.
I wish I were flying
 
TomH
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RE: B52 Flight Characteristics

Fri Jan 24, 2003 12:48 am

I believe you are exactly right, Nfield, and I think the nose down attitude may be apparent in all flight regimes of the aircraft. Further, I agree that the landing gear design resulted in positive mainplane incidence, which produces this flight characteristic.

But, this is simply personal opinion derived from my own observation, analysis, and a whole lot of speculation. Perhaps someone with an aerodynamicist background or field experience can explain it in detail.

I commented on this feature when I uploaded the photo below. It was worthy of mentioning, because the attitude you see in the photo is truly uncharacteristic of the normal Stratofortress flight regime.



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Photo © Tom Hildreth

 
FredT
Posts: 2166
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RE: B52 Flight Characteristics

Fri Jan 24, 2003 2:09 am

If it takes off level (lift equals weight with angle of attack equal to the wing mounting angle, or angle of incidence), it will have to fly nose down when going at a higher airspeed than lift-off speed. It will have to reduce angle of attack to below the angle of incidence to keep lift equal to weight. How peculiar.

I guess they could use their lift dumping devices to keep the fuselage level and less draggy. I wonder how much of a drag penalty those LDDs have?

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
bsergonomics
Posts: 458
Joined: Thu Jan 31, 2002 5:07 am

RE: B52 Flight Characteristics

Fri Jan 24, 2003 8:04 am

OK, here's a slightly educated guess:

The B-52, as we all know, is built to carry a huge payload. However, in order to get into the air from a runway shorter than the width of Canada, it needs to generate enormous amounts of lift. One method is by having a high Angle of Attack. However, this causes drag when airborne. So, some sort of trade-off is required.

Therefore, the wings are angled so that, on the runway, they provide the required high angle of attack. However, when the aircraft leaves the runway, in order to get a lower angle of attack, the nose is pointed down. Presumably, during the design and development phase, they worked out that the best in-flight trade-off between drag from the wings and drag from the nose-down fuselage was a couple of degrees nose-down.

I also wondered (although I'm sceptical) whether the weight of the engines causes the wing to rotate forwards when the aircraft is stationary. Therefore, to get the necessary ground clearance (and avoid FOD etc.) during the take off roll, and to get the optimal airflow into the engines during this phase, the entire wing was rotated backwards. This would mean that, as the airflow increases lift, the wing would rotate further backwards, resulting in the need to lower the nose to avoid excessive lift/drag.

Just a guess...
The definition of a 'Pessimist': an Optimist with experience...
 
L-188
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RE: B52 Flight Characteristics

Fri Jan 24, 2003 9:45 am

I hear an engine out landing in the thing can be a really hairy thing.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
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Spacepope
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RE: B52 Flight Characteristics

Fri Jan 24, 2003 11:40 am

Yes, the dreaded 7 engine landing!
The last of the famous international playboys
 
bsergonomics
Posts: 458
Joined: Thu Jan 31, 2002 5:07 am

RE: B52 Flight Characteristics

Fri Jan 24, 2003 5:33 pm

Just a curiosity - I deal normally with small, fast aircraft that drop nasties on the nasty people, and one of the aspects is dealing with G-Jump on weapons release. (This is basically where your aircraft suddenly 'jumps' upwards because of the instantaneous reduction in aircraft weight, but with the same amount of lift.)

As we know, the payload of the B-52 is immense. Now, although it drops its load in sticks, the effect of the rapid reduction in aircraft weight must surely cause significant G-Jump, even in an aircraft that large. Does anyone have more insight into this?

Also, it would mean that the aircraft would fly even more nose-down on the way back from a mission than on the way to the target.

===

7 engine landing ... that must really give the crew the heeby jeebies!
The definition of a 'Pessimist': an Optimist with experience...
 
galaxy5
Posts: 1952
Joined: Sat Mar 18, 2000 10:09 pm

RE: B52 Flight Characteristics

Sat Jan 25, 2003 11:27 pm

hey all hows it going , i guess i'll answer your question for you, the gear, engines and load have nothing to do with it. The B-52 was originally designed as a high altitude high speed bomber, In order for it to have the correct attitude at very high altitudes and airspeeds with large bomb loads , the incidence of the wing was placed so that at those variables the B-52 was a level, stable bombing platform. It does takeoff slighly nose down but once it gets to cruise its nice and straight and a surprisingly stable ride both low and high altitude.
"damn, I didnt know prince could Ball like that" - Charlie Murphy
 
Hamfist
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Joined: Wed Jan 30, 2002 9:40 am

RE: B52 Flight Characteristics

Sun Jan 26, 2003 1:50 am

Hmmm...

 
USAFHummer
Posts: 10261
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RE: B52 Flight Characteristics

Sun Jan 26, 2003 4:41 am

someone showed that picture to me a few weeks ago asking if it was real or fake...I thought it was fake...even though I was later informed that its completely real...it looks like that B-52 has been cut and pasted in there...

Greg

Chief A.net college football stadium self-pic guru
 
aeroguy
Posts: 66
Joined: Wed Aug 15, 2001 1:33 am

RE: B52 Flight Characteristics

Sun Jan 26, 2003 1:04 pm

The reason the B-52 wing is configured with positive incidence relative to the fuselage has to do with takeoff performance and can be traced all the way back to its bombs. For those of you who were concerned about the "G-Jump" when the bombs are dropped, I would propose that the bigger worry would be a sudden longitudinal shift in the Center of Gravity. This shift in the CG can be avoided by placing the bomb load near the CG of the airplane. (Think of the B-17, B-29 and especially the B-47). With the bombs located at the aircraft CG, when they are dropped, the aircraft CG location doesn't change. Of course, the problem this caused was that the landing gear had to be moved out of the way of the bomb bay. Boeing settled on the quad landing gear for the B-52 but this presented the problem that it cannot rotate on takeoff. (Or if it did try to rotate, it would only have a couple degrees before the aft fuselage hit the ground). So the B-52 has to keep accelerating with all wheels on the ground until it simply lifts off. Take-off without rotation obviously takes a lot more real estate, so to improve the take off performance, they placed the wing on the fuselage with positive incidence.

Consider the B-47 once again (from which the B-52 design was derived). It has a similar overall configuration. The bomb bay is at the CG and the landing gear has been pushed forward and aft to avoid it. Sitting on the ground, the landing gear is configured so that the aircraft is slightly nose up. Why? Take off without rotation once again. Both the B-52 and B-47 have the same general configuration but the approach to take off without rotation is slightly varied. They both have wings that are inclined during takeoff, the B-47 accomplishes this using the landing gear, the B-52 by the way it’s mounted on the fuselage.
 
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derekf
Posts: 888
Joined: Tue Feb 20, 2001 4:05 am

RE: B52 Flight Characteristics

Mon Jan 27, 2003 7:59 pm

Guys

Sorry about the shameless photo plug, but these pictures of a B-52H taking off at the IAT at Fairford illustrate the points made above.


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Photo © Derek Ferguson
View Large View Medium
Click here for bigger photo!

Photo © Derek Ferguson



Regards

Derek

Whatever.......
 
Eastern L1011
Posts: 124
Joined: Sat May 22, 1999 2:17 am

RE: B52 Flight Characteristics

Fri Jan 31, 2003 4:08 am

I live with a man who was a B-52 Bomb/Radar Nav for 20+ years. I brought this topic up to him and this is his response. Aeroguy is really close, he just needed to take it one step further. Yes, all the wheels are kept on the ground until the plane "lifts off". The reason the nose seem to be down is because during the lift off, the tail actually lifts off of the ground first.

Eastern L1011

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