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View Full Version : Why no aileron trim tabs?



Alexi_Alx_Anova
02-26-2004, 01:07 PM
OK, since I'm to be snowed in and stranded at work tonight, I might as well waste some time with a question that's been bugging me for a while.

I recently visited the RAF Museum at Hendon (London) http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif I had already noted the lack of aileron trim tabs on many planes in FB so I took note of their presence/lack while at the museum. What I don't understand is that many of the planes had rudder and elevator tabs but not aileron tabs. (I did note that some of the planes there had replacment/repaired ailerons that did not have the tabs, I'm not considering those) What I particularly don't understand is why some earlier planes did have aileron tabs yet later planes didn't (I can't remember the names but there was a 1938 vintage plane immediately behind the Lancaster that had aileron tabs). If the technology was present and the need for them was recognized, why did they not get fitted to planes like the Spitfire and Hurricane? Were they viewed as not really necessary, a source of extra mechanical trouble, or just plain sissy http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif ? I also find it surprising that the Germans had the technology and engineering skills to make their props and fuel injection systems top notch but had little manually bendable trim tabs! http://ubbxforums.ubi.com/images/smiley/blink.gif

BTW, the Mustang is soooooo shiny http://ubbxforums.ubi.com/images/smiley/16x16_smiley-tongue.gif and the Lancaster is absolutely ENOURMOUS http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif (it dwarfs the B17 next to it).

Alexi

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Drug of choice....coffee

http://web.onetel.net.uk/~alx_747/coffee.jpg
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Alexi_Alx_Anova
02-26-2004, 01:07 PM
OK, since I'm to be snowed in and stranded at work tonight, I might as well waste some time with a question that's been bugging me for a while.

I recently visited the RAF Museum at Hendon (London) http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif I had already noted the lack of aileron trim tabs on many planes in FB so I took note of their presence/lack while at the museum. What I don't understand is that many of the planes had rudder and elevator tabs but not aileron tabs. (I did note that some of the planes there had replacment/repaired ailerons that did not have the tabs, I'm not considering those) What I particularly don't understand is why some earlier planes did have aileron tabs yet later planes didn't (I can't remember the names but there was a 1938 vintage plane immediately behind the Lancaster that had aileron tabs). If the technology was present and the need for them was recognized, why did they not get fitted to planes like the Spitfire and Hurricane? Were they viewed as not really necessary, a source of extra mechanical trouble, or just plain sissy http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif ? I also find it surprising that the Germans had the technology and engineering skills to make their props and fuel injection systems top notch but had little manually bendable trim tabs! http://ubbxforums.ubi.com/images/smiley/blink.gif

BTW, the Mustang is soooooo shiny http://ubbxforums.ubi.com/images/smiley/16x16_smiley-tongue.gif and the Lancaster is absolutely ENOURMOUS http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif (it dwarfs the B17 next to it).

Alexi

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Drug of choice....coffee

http://web.onetel.net.uk/~alx_747/coffee.jpg
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Taylortony
02-26-2004, 03:41 PM
ok they were trimmed, one you could set it up by rigging the system ie adjusting the length of the rod to them to make one fly higher or lower than the other to lift or drop the offending wing and to keep them in balance, but what they used to do was dope a section of dangling cord on the trailing edge of the aileron on the side that was flying low, the weight of this would assist the aileron down lifting the wing, it was adjusted by cutting a little bit off till it was right and that was used to balance it out.... remember unlike the lanc the Spit did not carry fuel in its wings as such so there was no requirement to trim the aircraft due to uneven fuel usage between sides etc and no assymetric thrust problems from losing one engine

[This message was edited by Taylortony on Thu February 26 2004 at 05:35 PM.]

Chuck_Older
02-26-2004, 04:03 PM
Very good info http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif Cut the rope and hence the term, "trimming",

I think what he was getting at though is why not just tab it? I'll use an automobile analogy. Remember when most cars didn't have overdrive transmissions? Well, 40 years ago, OD trannys were around but they just weren't common in cars. It takes time to have technology trickle down to the point where it's not only standardised but also retro-fitted.

*****************************
Did anyone prophesize these people? Only Travis. Come in Travis! ~ Clash

horseback
02-26-2004, 04:17 PM
Some aircraft had aileron trim tabs on only one side, or one ground adjusted sheet metal tabon one side and one inflight adjustable trim tab on the other. I always assumed that this was because only one side needed adjustment in flight, or the stick force required above or below cruise speed was relatively minor.

We also have to remember that every additonal control surface conferred a weight penalty, and required somebody to crawl around inside the fuselage to run those control cables (time & labor costs). As any engineer knows, every feature added is really just one more thing that can go wrong at the worst possible time.

Rudder tabs were a relatively new innovation at the time the 109 was introduced, and I imagine Willi M. deciding that it wasn't necessary because it would only add weight and complication for a relatively minor convenience for a pilot who was only going to be aloft for 90 minutes at most. As the engines became more powerful, and torque became a greater factor, you'll notice that the 'tall tail' 109s started getting adjustable rudder trim.

Pilot or crew comfort was a minor consideration for most of the war, until somebody noticed that weapons that were easy to use were generally more successful, even against weapons that were superior on paper, but so complicated that full potential was difficult to achieve on the battlefield. The democracies took the lead in this respect, not least because it was the voters' sons in those airplanes, ships and tanks.

I can just picture my maternal grandmother (a formidable woman by all accounts) giving her congressman hell because my Uncle Fred wrote that he was all beat up from invading Japanese held islands in an uncomfortable landing craft. She'd want to make sure she was getting a good value for her War Bonds, and her congressman would want to make sure that she was in a better mood the next time she saw him.

Cheers

horseback

"Here's your new Mustangs, boys. You can learn to fly'em on the way to the target. Cheers!" -LTCOL Don Blakeslee, 4th FG CO, February 27th, 1944

NimbusPlus
02-26-2004, 05:25 PM
Good info in those posts.

As has been said, aileron trim is not really useful for the pilot of a light airplane. The only scenario for their use I can think of, as previously posted, is if you end up (for not paying attention http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif ) with a wing fuel tank being almost empty while the other one in the other wing is still quite full.

Other than that, the aileron trim control would just be one more lever in the cockpit accumulating dust (ever used a carb heat in FB?).

http://ee.1asphost.com/julienag/il2_Z_SIG.jpg

Taylortony
02-26-2004, 06:19 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Chuck_Older:
Very good info http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif Cut the rope and hence the term, "trimming",

I think what he was getting at though is why not just tab it? I'll use an automobile analogy. Remember when most cars didn't have overdrive transmissions? Well, 40 years ago, OD trannys were around but they just weren't common in cars. It takes time to have technology trickle down to the point where it's not only standardised but also retro-fitted.

*****************************
Did anyone prophesize these people? Only Travis. Come in Travis! ~ Clash<HR></BLOCKQUOTE>

To answer your question, why not put 2 fins on it like a Lancaster, simple answer it didn't need it, the reason a Lanc has 2 fins is one, to increase the overall size of the vertical stabilizer and 2 and more importantly, it sits in the airflow of the inboard engines, hence on take off becomes effective earlier and is more effective due to the airflow over it... also just because there is not a tab on a planes surfaces does not say the Aircraft does not have a trim system, bringing the world upto date the PA 28 warrior series does not have a tab but has rudder trim, this consists of a screw jack in the cockpit that when wound in biases the rudder pedals over to add on a bit of rudder deflection.... also on light aircraft, the likes of the Cessna 152 has a concentric bush on the rear spar where the wing attaches, by rotating this before tightning up the wing mounting bolts can raise or lower the trailing edge of the wings to a slight degree to bias out and tendancy for it to fly wing low or drop a wing in the stall....
I would also add the secondary effect of yaw is roll, you can get an aircraft flying one wing low and the ball out because the aircraft is yawing and this is adjusted on the rudder..... let me explain, if the rudder is over to say the left slightly in flight then the aircraft will yaw to the left, as this happens the right wing advances so creates more lift than the left wing and hence lifts, to correct this you would add left rudder trim at the tab or bend the tab a bit to the left to push the rudder back over to the right and level everything back up http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

[This message was edited by Taylortony on Thu February 26 2004 at 05:27 PM.]

MandMs
02-26-2004, 06:30 PM
horseback, the 109s never got a trimable rudder. What they did get was a Flettner tab that looked like a trim tab but was there only to ease the force required when moving the rudder, or to try to hold the a/c in a certain attitude.

Chuck, forth gear is an overdrive ratio.



I eat the red ones last.

Alexi_Alx_Anova
02-27-2004, 01:23 AM
Thanks for the info. guys.

The rope (hence trimming) is very interesting, fit for party conversation! http://ubbxforums.ubi.com/images/smiley/blink.gif

Also interesting to know that some planes had an aileron trim tab on only one wing. I saw some of those at the RAF Museum but assumed that the tab-less flap was a repair and since the planes were no longer flying, they didn't bother to put a tab in.

I can see why aileron trim was needed if you had asymmetrically loaded fuel tanks, but what about torque or propwash? In FB, if it is modeled properly, there are many planes that don't have aileron trim and you definitely can't fly the planes hands-off. I'm assuming this is due to propwash. The designers/HQ must have been bonkers to think that the added mechanicals outweighed the constant struggle with the controls suffered by the pilots.

Alexi

-----------------------------
Drug of choice....coffee

http://web.onetel.net.uk/~alx_747/coffee.jpg
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Taylortony
02-27-2004, 10:14 AM
You only require a single trim tab as you only need to adjust one side, if you adjust the tab on say the left wing to "fly" aileron down to lift that wing, the opposite aileron being connected in the circuit will move in the opposite sense to the other aileron to drop that wing, so only one tab is required in the system, Torque is a major factor, but the Aircraft will normally be rigged to fly more or less hands off at its cruise settings, which it will spend most of its working life... An interesting little ditty you may be unaware of, the Spitfire has different tyre pressures on its mains to reduce the torque effect on them when taxing and take off and landings, as one of them is under more load than the other..