Elevator balancing for tube and fabric tail

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Eugene

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Looking for a good way to provide 100% counterbalancing for tube and fabric elevator construction. Nobody seems to worry about it for 100 MPH aircraft. So, I can't find good examples to follow

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I can think only about one option where elevator would be made out of aluminum tubing. Trailing edge tube can be made longer to except lead weights.

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wsimpso1

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Eugene,

Do you think that you need mass balance in a 100 mph airplane? Mass balance is usually not needed until you get quite a bit faster... There is a thread on here someplace with a pick to a document on flutter prediction. Advanced search is your friend.

Your drawings show one way balance horns are done in tube and fabric tailplanes. In steel tube elevators and rudders, lead is simply melted and poured into the end tube from the aft end up to get the lead as far forward as you can. That method will draw the heat treat of a built up aluminum tail, so you will probably have to use shot and resin or cast a weight and glue it in. Another way is to attach a plate to the end of the last chordwise tube and then bolt more plates at the forward end of the first plate.

With the weight fully exposed to free stream flow, it will offer more drag and may have too much aero balance effect - make the elevators too light. If that turns out to be the case, you may want to build a little extension (fairing) on the stabilzer that the balance horn will be behind most of the time. See this on Cessna's.

Oh, grammar gripe alert - "except" when you mean "accept" - greatly different meaning. Throws me every time I hit it.

Bill
 

Pops

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Some where I read that with a well built elevator control system balancing is not an issue under 150 mph. My Falconar F-12 cruised at 150 mph and the VNE was 189 mph and didn't have any balanced control surfaces. But, I know know much on the subject. I did balance the elevators on the JMR and the rudder is aerodynamic balanced but I like light control surfaces. Also have large area ailerons for the same reason.
The rudder on the SSSC is aerodyamic balanced and was light and very responsive. Made for good slipping for bush flying over trees on short fields.

I have painted a lot of Cessnas and the maintenance manual has plans for building the tools for balancing the control surfaces after painting. I made the tools and I always checked the balance of the surfaces after painting. The allowed range for balance is very broad. With no paint, the surface will balance in specs. in one direction and you would have to put on a huge amount of paint to be out of the allowed specs in the other direction. Far more than a normal paint job.

Bill -- Hope there is no grammar or spelling experts on this site. If so, I'm sure I keep them busy.
 

Eugene

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Eugene,
Do you think that you need mass balance in a 100 mph airplane?
Bill
This is what I know. Airplane on picture below has exactly same tail boom and tail planes like on Skyboy. Was designed by same team of engineers. Removable composite fuselage rear part was made much shorter for original prototype. During test flight they develop some sort of elevator vibrations. Tuft test was showing that tufts was pointing opposite direction to the flow. On final version afterbody was made longer and problem went away to the point that Skyboy original designer flying this airplane at tiger speed 120 MPH with elevator weights removed completely. You can see on some pictures only brackets and no weights at all. Or we dealing with very sensitive tail to airflow quality. Or boom is flexible. Don't know.

What we do know that this aircraft doesn't have any issues with the 50 hp engine. After they start installing 912 engines, they start experiencing same problems again. For a few years they were installing small weights on short brackets and after that they change them to much larger weights installing on much longer brackets to get to 100% balancing. My attempt to fly with weights removed completely, turned into very short and very exciting event. Not something I want to repeat again.
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Eugene

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All airplanes of this type of configuration with tail pipe as boom using surprisingly short tail arm. About 2.1-2.2 X MAC. For tandem seating and low engine position apparently works OK. For side-by-side arrangement longer tail arm will allow airflow to relax maybe . So, maybe my airplane will benefit from new composite tail boom in many ways. That's my hope anyways. Have no better explanation of why this airplane have "dancing" stick at only 90 miles an hour.


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Eugene

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Everything on my airplane was made out of 2024T3 aluminum. Wondering how much heavier my elevator will get if I use steel tubing and create something similar to what we see on picture below. I think this approach will give me a little bit more flexibility, to be able to weld.

Or different question. Why couldn't I use aluminum tubing but instead of riveting use welding technique? I'm sure there's a very obvious reasons why we don't do that (weld on aluminum), but I don't know what it is.

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Mcmark

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Eugene the parts shown in your #9 are for the Wolf Pitts aerobatic airplane (with carbon) and for a retrofit for the Pitts (all steel) to have the same look and most of the benefit.
Very different airplane and type of flying and have been researched and demo'd by some of the biggest names in the aerobatic industry.
I was in that shop over the weekend.
 
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Eugene

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Very different airplane and type of flying
I am simply trying to find good way to build new larger elevator with counter weight incorporated into the structure. Trying to find answers and good reasons to stay with aluminum tubes versus steel tubes and welding versus riveting. Covering will be for sure fabric to be as light as possible. Obviously I don't know anything about it and any information is welcome.
 

Mcmark

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Eugene,
I ferried Skip Stewart's Promethius 2 to OSH several years ago. The airplane is one of the most sensitive and THE MOST authoritative in any axis at any speed I have flown. Even with less than stall speed during rollout, you had the ability to pull the mains off the ground with elevator.
10% more elevator area makes you a test pilot. Be prepared! Not being ready can mean a bad outcome to the flight and nobody wants to see that.
I have seen a counter weight added in the control system with nothing in the breeze to counteract the "weight" of the stick. You might look into that to avoid the additional drag of the external counter balance. Building in aluminum it shouldn't take much weight.
 

wsimpso1

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Everything on my airplane was made out of 2024T3 aluminum. Wondering how much heavier my elevator will get if I use steel tubing and create something similar to what we see on picture below. I think this approach will give me a little bit more flexibility, to be able to weld.

Or different question. Why couldn't I use aluminum tubing but instead of riveting use welding technique? I'm sure there's a very obvious reasons why we don't do that (weld on aluminum), but I don't know what it Is.
Ok, the way to choose method of construction is you design your structure to mIn weight that makes strength and stiffness in each material, then you can pick. This size and speed of ship is usually riveted aluminum. Pitts Specials with with high speed mods need much more strength and stiffness than you do. Bet is good that mIn weight welded 4130 is substantially heavier.

Reason we do not see welded aluminum is when you weld aluminum alloys, they go to condition O, annealed. 2024-O is 11-15 kpsi yield when it used to be 48 kpsi. So we do rivets and gussets and keep strength.

You talk like you have weight to give, but we keep telling you that you do not want to do that back at the tail. It will do more than shift CG aft, it will add significantly to your mass moment of inertia, which complicates a bunch of control and stability issues, including slowed pitch and yaw response and increased difficulty recovering from spins. You want to protect from adding weight at tips and tail.

Design in aluminum and be happy.

Billski
 

wsimpso1

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But do you have just as simple explanation of why that is? Why do you need it at only 90 miles an hour? Was my conclusions correct? Or we don't know?
No explanation. You had nasty behaviour without the mass balance, I believe you. It needs the mass balance.
 

Eugene

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10% more elevator area makes you a test pilot. Be prepared!
I am simply trying to return to original elevator size and I have OK from original designer to do so. Problem I have that original elevator was used only on 50 HP models and no balancing. For models with 912 engine smaller elevator was used and real need for balancing showed up immediately. So, shouldn't be any surprises at all. I hope

Just need to find good way to add ballast to this elevator

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Eugene

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You talk like you have weight to give, but we keep telling you that you do not want to do that back at the tail. It will do more than shift CG aft, it will add significantly to your mass moment of inertia, which complicates a bunch of control and stability issues, including slowed pitch and yaw response and increased difficulty recovering from spins. You want to protect from adding weight at tips and tail.

Design in aluminum and be happy.

Billski
No! No! No! That was last week! I am not talking that way anymore! I am much smarter already! I did get same explanation a few days ago in the Russian. So, I do listen. Can't say that I always understand, but I do listen.

Yes, will stay with aluminum, rivets and fabric.

Thank you!!!
 

Lendo

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Eugene,
Simple answer welding aluminium weakens (makes brittle) the area next to the weld and that's were it will fail first, so no way around it, it's the nature of the material and the heat affected area around/ near/ next to the weld.
George
 
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