Horizontal tail construction

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Eugene

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Screen Shot 2020-04-11 at 21.53.28.png

Turns out that original tail on Skyboy was designed with much larger elevator. For US market they reduced wing from 168 to 138 sq. ft., airfoil was changed from P3 to 4412 and elevator area was reduced.
Looking at this pictures I see that original elevator was much bigger. This is good news to me! If I can find original blueprint with dimensions, then I can build new larger elevator without worrying of over stressing the tail pipe. Horizontal tail volume will go up and this is maybe all I need!

Is my thinking correct?

Pictures below is what I have now:

Screen Shot 2020-04-11 at 22.24.01.pngIMG_5600 2.jpeg
 

Dana

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Increasing the elevator size without increasing the fixed stabilizer size will increase your elevator authority and "stick fixed" static stability, but won't increase the "stick free" stability. But if the increased authority is all you need, that might be the answer.
 

wsimpso1

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+1 on Dana's comments.

The rest of our concern has been with the tail boom on your airplane. We were assuming that the tube selected and mountings for it were minimum size to carry moments arising from the current tail:
  • If that assumption is true, you may still have an inadequate tube size and mountings once the tail is enlarged;
  • If the assumption is false, and they just carried over the prior boom tube and mounts, then you will simply be returning to the original design.
It is essential that you not only find out what the original tail surface design was, but also what the original tail boom size (OD, ID, length) and mountings were. Remember that the designers made the wing and tail smaller for our market - that is a fair chunk of work. Maybe they also revisited the tail boom design and reduced its section and/or length too. Better make sure you return to the original design tail boom and mounts too.

Billski
 

poormansairforce

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then I can build new larger elevator without worrying of over stressing the tail pipe.
See my earlier post about elevator vs stab sizing. With a larger engine/higher speeds it requires less elevator to keep manuvering loads within limits. The engine in the picture is obviously smaller. I would be careful about increasing elevator size.
 

Eugene

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+1 on Dana's comments.


  • If the assumption is false, and they just carried over the prior boom tube and mounts, then you will simply be returning to the original design.

Billski
I did send same question to Skyboy designer

Screen Shot 2020-04-12 at 09.09.52.png

And this is how he responded

Screen Shot 2020-04-12 at 09.06.09.png

Screen Shot 2020-04-11 at 22.51.13.png

There was no counter weights on original elevator with 50 HP engine. I will need for sure to install them for 100% balancing with 100 HP engine
 

Eugene

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See my earlier post about elevator vs stab sizing. With a larger engine/higher speeds it requires less elevator to keep manuvering loads within limits. The engine in the picture is obviously smaller. I would be careful about increasing elevator size.
Yes, I will need to think about best way to do it. Only talking at this point. (only thing we can do right now). Good news to me is that airplane (tail pipe) was designed with larger tail. How big it was? We will find out when he finds blueprints for me.
 

Eugene

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The boom was not designed for a larger tail AND more power blast and speed.
That's why the boom is deflecting under load. Raymer warns of boom deflection in his book.

Yes, if you made decision to install more power from 50 HP to 100 HP and increased MTOW from 992 LB to 1320 LB. Maybe some changes needed for your tail as well.

IMG_2738.jpeg
 

Eugene

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The boom was not designed for a larger tail AND more power blast and speed.
That's why the boom is deflecting under load. Raymer warns of boom deflection in his book.
I was told by russians that my "good news" not really big deal at all. If your speed with big engine is going up by 10%, then your tail load will be increasing by 20%.

So, new carbon tail, aerodynamically shaped to avoid flow separation and calculated for new load with 100 HP engine is my best theoretical solution. But in real life I will need to get much smarter to make this happened.
 

Eugene

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The boom was not designed for a larger tail AND more power blast and speed.
That's why the boom is deflecting under load. Raymer warns of boom deflection in his book.
Found from original designer tail pipe dimension. It was something that was already available on German market and was made for another ultralight

120 X 2 mm 2024T3
 

Dana

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Pretty close to the 5" OD x .050 irrigation pipe used on the lighter Kolbs, though that's 6063 alloy. I believe they went to 6" for the later (larger) models.
 

Eugene

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Pretty close to the 5" OD x .050 irrigation pipe used on the lighter Kolbs, though that's 6063 alloy. I believe they went to 6" for the later (larger) models.
Thank you! Without any calculation we can make statement that to upgrade 50 HP ultralight to 100 HP LSA bigger pipe should be used.

IMG_2738.jpeg
 

Eugene

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Yes, Kolb did change from 5" to 6" for bigger models. But not sure wall thickness on 6 inch pipe. Here is some numbers to compare:

I have 120 mm pipe 2024T3 with 2 mm wall = 4.72 inch with 0.08" wall

5 inch pipe 6063 with 0.05 wall = 127 mm with 1.27 mm wall

6 inch pipe = 152 mm
 

wktaylor

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Ever thought about Composite tubes made specifically for structures?

Here are a few examples of companies making 'stock' and 'specialty' composite tubes [various shapes/sizes]...
 
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