Horizontal tail construction

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Eugene

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If you have weights already on a surface, you are a brave soul to remove them.
My attempt to fly without counter weights was recommendation from Skyboy designer. He was telling me that his personal aircraft has exactly the same tail and boom and he removed them long time ago. What you see on picture below is only brackets without weights. That was bad idea. I see 3 things different on his aircraft vs Skyboy:

- tail load on Skyboy is higher
- stabilizer incidence 5.7° vs 1 or 2°
- Tail on Skyboy is working in very turbulent environment

2366087.jpegthree-view_drawing_of_p27_poc_20110623_1883608201.jpeg
 

Eugene

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This is what I got out of your long message. I will twist things a little bit like want them to be, like I always do.

I am looking at my Skyboy and thinking that really nothing wrong with first half of this aircraft, but second half definitely needs some work:
- tail boom is flexing under load
- tail boom is too short
- rear removable cowling is shrinking too abruptly and that's creating turbulent environment for horizontal tail
- flow separation generated drag
- vertical tail is too small as well

So, my original plan was to create non structural composite removable cowling to improve airflow to the tail and drag. This situation is sort of like pick-up truck with body-on-frame construction. So, tail boom is frame and body will be my new composite afterbody.

Wondering if I can take saw and cut my tail pipe somewhere 16 inches from fuel tank and create attachment point for all new composite tail. This will be unibody construction were we can catch 2 birds with one stone. Maybe my whole empennage can be like on this white aircraft (picture below)?
View attachment 94587View attachment 94588View attachment 94589

This is of coarse only idea and I am not going to cut my tail boom tomorrow morning.

View attachment 94590
View attachment 94591View attachment 94592View attachment 94593View attachment 94594View attachment 94595
I received answer to this question from my Russian composite expert. He thinks that to cut old tail boom off and build all new composite tail not crazy idea at all. This will be most time consuming and expansive way, but for sure will have best outcome. He doesn't see any problem to connect new composite empennage to the frame and left over tail boom. He recommended to find local expert who will be able to help with this. There is no way I can do it only by reading some books and watching some videos.
So, any ideas were can I find experts like that?

IMG_1881.jpegIMG_1882.jpeg
 

TFF

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If you do build one, mock up the rear of the plane and build from it. Go fly your plane while building
 

Eugene

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Here is another question.
Some day when I am all done with my test flights and I know what shape my future composite tail boom should be. If I decided to build one, then I was told better way is to find used horizontal and vertical tails. This will make this project little easier and more predictable.
So, where do i go to find used tail, or in kit version, or unfinished or so on?
 

Eugene

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73CC3E74-06CF-4139-9626-84C6E5B9569C_1_201_a.jpeg
Interesting to see on this picture that to get 20 MPH faster with same engine and same wing they needed to change the tail boom. So, it is important. Also wheel pans and all moving horizontal tail.
Aeroprakt A22 vs A32
 

Pops

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Let me guess which one is the fastest. I always liked a red airplane , but I will guess the yellow airplane.
Cessna made the same mistake when they went to the back window in the C-150, 172, 182. The swept tail gave pitch change with the rudder.
Then they widened the fuselage. Then went with the bigger engine to make the difference up on speed decrease with all the drag they added, that required larger fuel tanks , all with a weight increase. Just like snow ball rolling down the hill.
 
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Eugene

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I went back to read some replies and found another question inside of my head.

Anything I will do with my tail will for sure add some weight and will shift CG aft. In my mind this fact was never really very big deal. I made many times statements, that I will get my CG back to where I need by changing positive wing swept.

But didn't find any support for this approach. Why not? This is not very good way to move CG on your aircraft?

We have local rental Sundowner with 100 lb sand bag strapped permanently behind rear seat. I understand how easy is to miscalculate CG during design. But why don't they fix it by simply change wing swept? Why keep making it like that?
 

Lendo

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Yep! CG can be difficult to identify exactly at initial design stages. My philosophy is everything in an Aircraft should be adjustable :) however that could be a nightmare to achieve, and then there's the extra weight to consider.
However to answer your question, adjusting sweep involves all sorts of interactions with the wing as well as the wing itself with forward sweep - it's just easier to move some weight around. Having said that - 100 lbs is a lot.
George
 

Eugene

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However to answer your question, adjusting sweep involves all sorts of interactions with the wing as well as the wing itself with forward sweep - it's just easier to move some weight around.
George
I agree, that simple ballast is very easy way to solve CG problem, if you have one. I am not suggesting that average experimental aircraft owner should move the wings instead of using ballast to move CG on your aircraft.

Question was about crazy people like me, who is doing a lot of work and changes on experimental aircraft. When you're all done with your changes CG most likely will move and you will need to get it back. Changing your wing sweat sounds like a very good option to me. I did it one time and I can do it again and it was not really very big deal at all. No comparison of course to a simple ballast. 1° swept on my Skyboy resulted in CG movement of 2.5% or 1.3 inches MAC.

On another hand why do they keep making airplanes year after year with CG problem and letting end-user to fix it with ballast. Didn't they see this problems during test flights? Changing wing swept in factory environment should be relatively easy process.
 

Pops

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Even the big boys puts out a bad airplane once in a while. We all can name a few.
 

Eugene

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Even the big boys puts out a bad airplane once in a while. We all can name a few.
I understand that it takes a lot to design successful airplane. But to nail CG exactly where you want it should be very easy to do ( in comparison with many another things on aircraft) by changing wing swept 1-2°.
 

TFF

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100 lbs is probably there with stipulation that no one rides in the back. Keep low time people from landing on the nose wheel. Those things will prop strike if you slam it. Why they did not put 5 lb in the tail is a little silly except for the possibility of flying back seat passengers with a accessible ballast to remove. The thing will fly with it out just fine. Just stay off the nose gear with that trailing arm.
 

Dana

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I understand that it takes a lot to design successful airplane. But to nail CG exactly where you want it should be very easy to do ( in comparison with many another things on aircraft) by changing wing swept 1-2°.
Yes, but changing the wing sweep itself is not such a simple thing, it's not just a matter of changing the attach points, each rib needs to be angled parallel to the airflow (not as important with a metal skinned wing), now things aren't at 90°, so things are harder to jig and build, etc.
 

Lendo

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Probably one of the hardest things to predict, is the HT Incidence. I'm speaking in terms of designing here (as production aircraft should be well and truly tested and adjusted), so adjusting those is IMHO needs some sort of adjustment mechanism (for prototypes) - some aircraft actually have that on their production models.

As for C of G , I came up with the bright idea of having a tube running front to rear with a weight attached, with in-flight adjustment (somehow) - but it seems someone has already thought of that for prototypes. It would still be a good idea for a Tandem fine-tuning for specific mission.

You might see why I think everything should be adjustable.
George
 

wsimpso1

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Anything I will do with my tail will for sure add some weight and will shift CG aft. In my mind this fact was never really very big deal. I made many times statements, that I will get my CG back to where I need by changing positive wing swept.

But didn't find any support for this approach. Why not? This is not very good way to move CG on your aircraft
I disagree with your premise.

If you extend the tail arm, you may not have to enlarge the horizontal tail at all. Your current boom is big enough at the supports, but way oversize as it goes aft. A new tailored tailboom will be right-sized everywhere and is thus likely to save some weight aft;

If you enlarge the tail but hold the tail length, the W&B result will be similar to the above. Your current boom is big enough at the supports, but way oversize as it goes aft. A new tailored tailboom will be right-sized everywhere and is thus likely to save some weight aft;

In between we have smaller changes in boom length and tail size, with similar effects;

In total, a well designed new tail boom, tailored appropriately will likely have little effect on Weight and Balance.

Remember that any increase in tail volume also moves your neutral point aft, giving you more margin on aft CG. Now as to adjusting wing sweep, it both moves your CG and moves your neutral point. It can change the stall behaviour too. This makes you the test pilot for finding your new aft CG limit while exploring your stall behaviour.

Billski
 

BBerson

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Beam stress tapers toward the tail but the torsion stress doesn't taper. That big engine puts a bunch of cycling air shock loads on that tail. Flutter is always a concern.
Might want to save up for a parachute for the dive testing.
 
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