B-29 elevator miracle

[Supercharged]

Hello,

by the way, this is my first post in this forum. I'am watching and reading here as a guest frequently for at least 10 years, so i decided to join because a lot of guys are aviation experts in here.
And now my question, it is about the design of the elevator(flight control surface) of the Boeing B-29 and its successors(B-50) which used the same design. As most of you might already know, aircraft of this size and weight need static and aerodynamic balanced flight controls, otherwise it would be impossible for the pilot to get the surfaces in the desired postion(at higher speeds). In case of the B-29 you have static(weight) balanced elevators both sides interconnected via a torque tube. At this torque tube you have two connections to the flight control cables running forward for captain and f/o side.
That's it
There is no servo tab, springloaded tab or flettner tab....nothing that would reduce the aerodynamic loads for the pilot. Except two trim tabs(one on each elevator) but this tabs have no connection to the torque tube(input) or to the horinzontal stabilizer aft spar. It is written in all manuals that this trim tabs are for elevator trim only.
I used several resources for my search:
-AAF 50-9 The B-29 - Airplane Commander Training Manual for the Superfortress Rev.1 Feb. 1945
-AAF 51-126-6 B-29 Pilot's and flight engineers training manual for the superfortress
-AN 01-20EJ-1 Pilot's Flight Operating Instructions for B-29 and B-29A Airplanes Rev.10 Feb. 1945
-T.O. 01-20EJ-2 Erection and Maintenance Instructions for Army Model B-29 Airplane Rev.20 Aug.1944
- Red Star Vol. 7 Tupolev Tu-4 (Yefim Gordon)

How is it possible for a B-29 Pilot to move the elevator at higher speeds?

Many thanks in advance

Pictures below:
- for reference a KC-97 elevator, same design as B-29 you can see the trim(only) tab
- a DC-6 elevator, just an example for an aircraft of comparable size to the B-29, you can see trim tabs and springloaded tabs

 

[Dash119]

Welcome to the forum.

 

[Wurger]

Welcome to the site.

Have you seen that thread?

Mechanism for the control surfaces of the B-29

Hello, I'm wondering how the control surfaces of the B-29 were operated. They were mechanic or hydraulic?

ww2aircraft.net

 

[Supercharged]

Welcome to the site.

Have you seen that thread?

Mechanism for the control surfaces of the B-29

Hello, I'm wondering how the control surfaces of the B-29 were operated. They were mechanic or hydraulic?

ww2aircraft.net

Thank you for your welcome and the link as well.

But the resources(manuals) "Siegfried" took for his answer are already known to me( i listed them above) and there was absolutely no word about springloaded tabs at the elevator.
Looks like i should talk to Siegfried where he got his information from......

 

[Wurger]

I see. Unfortunately the guy was banned years ago.

 

[Supercharged]

I see. Unfortunately the guy was banned years ago.

Ok bad news..... but i'am optimistic that somebody will come around with a solution for my "problem"

 

[Wurger]

Good luck !

 

[EAIAnalog]

Here are two diagrams from the B-29 engineering drawings for the elevator setup and the elevator tab setup. Bear in mind that all control surfaces on the B-29 were covered with fabric. So they would be somewhat easier to move than metal clad units.

 

[Supercharged]

Here are two diagrams from the B-29 engineering drawings for the elevator setup and the elevator tab setup. Bear in mind that all control surfaces on the B-29 were covered with fabric. So they would be somewhat easier to move than metal clad units.

Thank you for those nice drawings, but the "problem" still persist. The tab trim rod is installed inside the elevator surface, that means it can not act as an servo tab.
Down below you will see an B-29 tailplane at Guam airbase 1945( source: airliners.net)

And for comparison, FIFI's tailplane (source: airliners.net)

You note the difference at the elevator leading edges?
Guam B-29: 2 of 3 slots between the hinge points are rounded leading edge
FIFI: 1 of 3 slots between the hinge points are rounded leading edge
What does it mean? I don't know....

Additionally i'm thinking about sealed gaps for so called "balance bays" but at the moment i have no reference for this.

 

[EAIAnalog]

I suspect that the Guam B-29 is a much earlier version than FiFi. FiFi's serial number is 44-62070. So between the Guam build and FiFi's build, the elevator design was modified for some reason.

Here is a 360 degree view from the tail gun compartment in the B-29 at the Museum of Flight
MSVR.US Photo Sphere Viewer - https://vr.museumofflight.org/b29_tail

As you rotate you have a good view of the port elevator, and so-so view of the starboard elevator. Her serial number is 44-69729, which is in-between FiFi's build and Doc's (44-69972) build. Hence the elevator looks like FiFi's. Note that the elevator nose changes shape at the outboard end of the trim tab.

Maybe the simplest solution to your question would be to contact the FiFi folks or the Doc folks and see if you can talk to one of the pilots who fly the aircraft.

 

[Snautzer01]

Wasnt it Gary then has flown with FiFi? Forgot his nickname because ... wel FiFi.

 

[Supercharged]

Maybe the simplest solution to your question would be to contact the FiFi folks or the Doc folks and see if you can talk to one of the pilots who fly the aircraft.

Sounds like a plan, one of the CAF engineers should know how the elevator works.

 

[EAIAnalog]

Here's some additional info on the elevator.

The elevator hinge is about 1/3 of the way down from the its nose to its tail. So when the elevator is moved up, 2/3 is above the tailplane and 1/3 is below the tailplane. The below part should unload the pilot effort somewhat. The areas of the elevator are approximately: 2/3 - 79 sq ft (this includes the elevator tab of 10 sq ft); 1/3 - 36 sq ft. This is the total of both sides. The thickness of the tailplane will change these somewhat as far as the relative wind is concerned. The elevator limits are: 25 degrees up, 15 degrees down.

The pilot's control column is also a simple lever, and it's different arm lengths should give him a mechanical advantage when moving the elevator.

 

[Supercharged]

Here's some additional info on the elevator.

The elevator hinge is about 1/3 of the way down from the its nose to its tail. So when the elevator is moved up, 2/3 is above the tailplane and 1/3 is below the tailplane. The below part should unload the pilot effort somewhat. The areas of the elevator are approximately: 2/3 - 79 sq ft (this includes the elevator tab of 10 sq ft); 1/3 - 36 sq ft. This is the total of both sides. The thickness of the tailplane will change these somewhat as far as the relative wind is concerned. The elevator limits are: 25 degrees up, 15 degrees down.

The pilot's control column is also a simple lever, and it's different arm lengths should give him a mechanical advantage when moving the elevator.

All those measurements to balance the elevator forces (hingeline) are common practice at this era. But i still have doubts, because aircraft of compareable size and weight need to have balance tabs or springforced tabs additionally. And a lot even smaller(P-61, F4U) used this kind of "power aid" for their flight controls.

Would you say it is possible for B-29 to fly properly without such aerodynamic balance?

 

[Supercharged]

Ok, it looks like my doubts are baseless....

I was looking into B-32's manual (FSE-33-1002 Preliminary Erection and Maintenance Instructions for the Model B-32 Airplane) which for comparision is the best choice in my opinion. And it is clearly stated:
- aileron tab is for trim and servo function
- rudder tab is for trim and servo function
- elevator tab is for trim only

But anyway, it is still quite interesting for me that heavy aircraft elevator controls were build like this. It seems flight control design is like art