Horizontal tail construction

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Eugene

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The tail with that much incidence is working hard even if in trail. If you had 200 hp, the plane would be looping with those incidences.
Yes!!! But reason for this aggressive 5.7° angle is only one thing and one thing only = is low horizontal tail volume! Yes or no?

In level flight if I remove power abruptly without moving trim lever forward = nose will zoom straight up and aircraft will stall. With correctly sized tail with small 1-2° angle we would have much friendlier aircraft.
 

Eugene

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IMG_3766.jpg

This is what In have right now after changing wing from 4.5° to 2° and stabilizer from 5.7° to 3.5°. At one time I tried to tilt engine by 3° down to get self- trimming effect and really, really didn't like it. So I changed that back to original setting. It was giving me very uncomfortable vibration on control handle in flight.

https://drive.google.com/file/d/0B9ZeEB_79LEPUFZNbmdoOWNVVDA/view?usp=sharing

This problem was fixed after I found loose airframe connection, that was supporting tail pipe.

https://drive.google.com/file/d/1u4-VeiMaF0l3x3xXeqi8O7ldjpzuZ2Vu/view?usp=sharing

Changing stabilizer incidence didn't do me any good. Simply needed more nose-up trim for level flight. Make perfect cense now.
 
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BBerson

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This is what In have right now after changing wing from 4.5° to 2° and stabilizer from 5.7° to 3.5°. At one time I tried to tilt engine by 3° down to get self- trimming effect and really, really didn't like it. So I changed that back to original setting. It was giving me very uncomfortable vibration on control handle in flight.
The pink Skyboy in post 30 has the engine tilted down.
 

Eugene

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The pink Skyboy in post 30 has the engine tilted down.
IMG_5600 2.jpeg

Yes, I found this picture online sometime ago. And yes, looks like engine is tilted 3° down on this Skyboy. This was recommendation from factory test pilots after testing aircraft with 80 HP engine. This is only Skyboy I know with engine installed this way. On all that I have seen engine was tilted up by 3°right from factory. They tried to solve problem of "flutter" or "buffering" and result was larger and heavier elevator counter ballast with engine tilted up. They made that aircraft for about 10 years and nobody made conclusion that tail simply too small.

IMG_5635.jpeg
 

BBerson

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A higher aspect ratio tail is more effective. But higher aspect ratio stalls at a lesser angle. Tail stall must be avoided.
So be careful increasing aspect ratio.
Of course your tail boom tube is already flexible. So a larger, stiffer tube is needed. And heavier. There is no easy answer.
 

poormansairforce

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So a larger, stiffer tube is needed.
This has been mentioned several times. My question is, does it need to be stronger? By how much?

If there is enough down force currently to fly safely and he doesn't increase the elevator area itself then nothing really changes but the incidence needed to trim the plane out with less drag.

If the elevator is made slightly bigger then maybe some beef up is needed but that extra area would be used at takeoff/landing speeds. Just a thought and its probably wrong.
 

fly2kads

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This has been mentioned several times. My question is, does it need to be stronger? By how much?
It will need to be stronger if the current factor of safety is to be maintained. The current small tail can provide X lbs. of down force. The proposed larger tail could provide Y lbs. of down force. The difference in strength required would be: (Y x moment arm) - (X x moment arm). The values of X and Y are unknown, and Eugene would have to figure that out. The difference won't be huge, but it's not zero.

If the elevator is made slightly bigger then maybe some beef up is needed but that extra area would be used at takeoff/landing speeds. Just a thought and its probably wrong.
Here's a visual, as a refresher:
RV9_VN_Diagram.jpg
The load factors can be exceeded anywhere in the shaded areas around the perimeter of the flight envelope. Who knows, maybe our "crazy Russian" friend is yanking and banking that Skyboy around! :pilot:
 

Pops

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There is a Genesis homebuilt on our field. Very similar to the Skyboy. All the same problems. Has had 6 owners and repaired 7 times. Last owner tore the nose gear and one main gear out 2 times. Parked it in the back of the hanger and bought another airplane. With 2 people it runs out of elevator when landing among other problems. Bad design. As you know the stab is fighting the download from the high thrust line plus the normal download from the CG being in front of the Neutral point , and not having the varying weight of the people very near the CG.
These airplanes shows what happens when you don't have all of the varying loads, ( people, fuel ) close to the CG and a high thrust line. Huge trim changes with different weight and power.
You are whipping a dead horse, it will never be without problems.

https://www.pilotmix.com/genesis
 

poormansairforce

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The proposed larger tail could provide Y lbs. of down force.
I'm aware of all the customary thinking. If you read what I wrote its obvious it doesn't need to be that way. But I do understand what your saying.

Who knows, maybe our "crazy Russian" friend is yanking and banking that Skyboy around!
He made it clear earlier that he not a yank and banker.
 

poormansairforce

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There is a Genesis homebuilt on our field. Very similar to the Skyboy. All the same problems. Has had 6 owners and repaired 7 times. Last owner tore the nose gear and one main gear out 2 times. Parked it in the back of the hanger and bought another airplane. With 2 people it runs out of elevator when landing among other problems. Bad design. As you know the stab is fighting the download from the high thrust line plus the normal download from the CG being in front of the Neutral point , and not having the varying weight of the people very near the CG.
These airplanes shows what happens when you don't have all of the varying loads, ( people, fuel ) close to the CG and a high thrust line. Huge trim changes with different weight and power.
You are whipping a dead horse, it will never be without problems.

https://www.pilotmix.com/genesis
No one is disagreeing and has been discussed repeatedly. But sometimes people get stuck with a dead horse. So it is either fly it, fix it, or sell it. And, yes ,people's lives are valuable! I think experimental aviation has been dead for awhile....
 

fly2kads

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I'm aware of all the customary thinking. If you read what I wrote its obvious it doesn't need to be that way. But I do understand what your saying.
Please elaborate, because I don't think I understood your point. You seem to be implying that the balancing moment is coming from the elevator only, vs. the horizontal tail as a whole.
 

poormansairforce

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Please elaborate, because I don't think I understood your point. You seem to be implying that the balancing moment is coming from the elevator only, vs. the horizontal tail as a whole.
If he increases the HS area he'll need less incidence to get the down force needed. The current HS is working hard to get there. If he doesn't go crazy with increasing the elevator itself then where is the extra stress? Yes, I'm aware that there would be some increase due to the camber change over the entire tail. But there would be increased load with gap seals, VGs, etc as well.

If the larger HS allows a more rearward CG then there is even less load on the HS.

At one point he angled the engine down 3° like other SBs and it buffeted a lot which tells me there was a bit of stress there as well. All I am asking is, are we over reacting a smidge? Its an honest question. My biggest concern is gusts.
 

Eugene

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I am very happy to see that much smarter people, than this crazy Russian, wondering what to do with this airplane. I also have something -

- I was told by original designer, that airframe is plenty strong enough to handle 100 HP engine.

- To stay in level flight Skyboy need tail down pressure. More power = more pressure needed. Flying with passenger = more pressure needed.

- To generate same balancing pressure we have only 2 options:
#1- small hard working tail at 6-8°AOA
#2- large easy going tail with only 1-2° AOA.

- Tail boom will have exactly same deflection with any tail, but abrupt gust changes will generate bigger moment with large tail. I was told that by Russians and that is reason for only 20-25% tail size increase limitation.

- About bad design. There is good flying airplanes and not so good. I am convinced that if you have something not performing very good = there is for sure reason and explanation for it. And if you not smart enough or patient enough to find it = you can call it "bad design" and walk away. I see at work every day not very good performing systems. Yes, sometimes not easy to find this problem, but its always there. So, let's say on your first flight you find out that you have not very good flying machine. What is your next step? Turn around and sell it to next guy? Is this how we see experimental aviation today?

"You are whipping a dead horse, it will never be without problems." No I disagree. If you know what you doing you can fix anything. "Time and pressure, time and pressure" - Shawshank redemption.
 
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BBerson

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If there is enough down force currently to fly safely and he doesn't increase the elevator area itself then nothing really changes but the incidence needed to trim the plane out with less drag.
Right, but as Eugene said above, abrupt gusts will react more bending/torsion force with more tail area.
I would say the same for any abrupt pilot stick pulls.
The Basic Glider Criteria and old FAR23 give simplified tail load calculations based on tail area. So more area equal more bending load.
My concern is stiffness more than strength ( beam and torsion). I would be making a rectangle truss of same weight, but stiffer and several inches larger diameter than his 5" or 6" tube. So that the down thrust could then be used without shaking the tail too much. Might not need any more tail area with down thrust.
 
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