Horizontal tail construction

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Eugene

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Someday I will be converting my flat horizontal tail to symmetrical NACA 0009 airfoil. Something like what we see on this picture, but little different. I would like to use foam ribs vs wood and I would like to install hard leading edge about first 20% or so like we do on our wings. Wondering if someone did this already on his homebuilt airplane. Trying to learn more about correct materials to use and so on. Thank you.
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lr27

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Is there any reason you wouldn't use the same materials as the wing uses, whatever those might be?

What's the purpose of the change, and what kind of aircraft is it? If there are many struts and wires, you might not notice much drag reduction.

If you're going to sheet only the first 20 percent or so, it might look better with a section with the thickest point further forward and the surfaces behind that rather flat. Like an ellipse with two tangent lines. I don't know if it would work better, though. If I'm not mistaken, some acrobatic airplanes use airfoils like this, and we use thinner versions on some model airplane tails.
 

don january

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My HZ on the Taylor-mono is symmetrical and made all of wood. You will need spars at certain location and drag anti drag supports. The 20 percent hard leading edge will be a issue in my opinion but doable if you build up the foam ribs with balsa to get the same height as the covering material used to cover leading edge. I would also recommend to add in vertical wood stiffeners next to spars and 50 percent of the cord length along with ply gussets on each side of the vertical stiffeners to help support the foam. Another area to keep in mind is how the HZ will be mounted and will the weight of the HZ throw the CG way out of specs and is there a trim tab on elevator? May be more trouble then its worth. IMO
 
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Dana

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As lr27 asked, what are you trying to achieve? Aerodynamically, there won't be much difference, as at the low Cl a tail sees a thin airfoil doesn't have much advantage over a flat plate. Structurally, a thicker airfoil can have an advantage over a thin flat section, but if you're just fairing out an existing structure that doesn't apply.
 

Eugene

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Is there any reason you wouldn't use the same materials as the wing uses, whatever those might be?

What's the purpose of the change, and what kind of aircraft is it? If there are many struts and wires, you might not notice much drag reduction.
Yes, 100% agree! Same approach should be used as we building small wing. I have friend who is up to speed on carbon fiber construction and he trying to convince me to built ribs and leading edges that way. It will be interesting blend of 19th and 21st century construction when it's done.

Drag is not my problem and if I will get any reduction at all, it will be very small.

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Skyboy was designed as 50 HP ultralight with original stabilizer incidence of 3° and horizontal tail volume of only Vh=0.34. During German certification angle on stabilizer was increased to 5.7°. Center of drag was lower in real life and forward piching moment was greater than was predicted. Result of open engine and abrupt ending of rear fuselage. For American market 100HP engines was used = larger moment, but nothing was done on horizontal tail!!! In normal 75% power cruise tail is up and working very hard at 8° angle with all kinds of buffering on control handle. Aircraft can not be trimmed for level flight and hunting up and down by 300-500 ft apart. And aircraft with passenger feels like filled with lead.

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So, I found that symmetrical airfoil can be up to 30% more effective vs flat tail. And area will be increased by 20% or so to get get Vh to 0.42-0.44 or so.
https://backcountrypilot.org/forum/horizontal-stabilizer-shape-air-foil-vs-flat-pros-cons-18170

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Dana

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Sounds like it's a tail volume problem more than anything else. High mounter pusher configurations need more tail volume than a typical configuration, changing that will have far more effect than changing the airfoil. Remember that dCl/dα is independent of airfoil shape for thin sections, approximately 2π/radian. Of course Clmax will be better, with later/softer separation with a "real" airfoil, bIut it's clear you understand that from your sketch.
 

Eugene

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Sounds like it's a tail volume problem more than anything else changing that will have far more effect than changing the airfoil.
Yes, I agree, but how much change is OK to do. Originally I was told not to increase horizontal tail area by more then 20-25%. Main concern was tail boom loading in gusting high speed conditions.

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Working right now on changing rear part of my fuselage and should be able to install some additional bracing.

To do it right, my tail should get 2 times larger! That is 100% increase !
 

lr27

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Your approach seems reasonable to me, though I'm no expert. If the tail is stalling, a real airfoil ought to make a large difference. You could even use some camber. BBerson's idea may require less work than a whole new stab. How's the handling in a climb at full power? At low power? Obviously an enlarged horizontal stab with a real airfoil can put a larger load on the fuselage, but I imagine you know this and have already looked at the strength of the attachment points, etc.

If the tail isn't actually stalling, then an airfoil won't help with pitch stability.

Your fuselage modifications appear to be much larger than would be required for structural reasons. Do they have an aerodynamic purpose? I wouldn't guess how they would affect static stability, handling or stall behavior, but I'd guess there are effects.

Your chart only includes aircraft with flaps, which may require a larger horizontal stab than is required strictly for stability, just to deal with any possible nose down pitching moment from the flaps. I suppose you're also dealing with a nose down pitching moment too. Plus, if the horizontal stab is larger, you can probably put the c.g. a little further back, which ought to help with the pitching. I suppose a larger vertical stab would be a good idea if you're going to move the cg back. Perhaps in the form of a larger sub-fin, which won't be blanked by the larger horizontal stab in a stall. Assuming you can do it without scraping it on the runway during takeoffs or landings.

So many complications! I think I'll go back to designing a table or a doorstop, or something like that. ;-)
 

Dana

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Yes, I agree, but how much change is OK to do. Originally I was told not to increase horizontal tail area by more then 20-25%. Main concern was tail boom loading in gusting high speed conditions.

Working right now on changing rear part of my fuselage and should be able to install some additional bracing.

To do it right, my tail should get 2 times larger! That is 100% increase !
If the required increase in tail volume due to the larger powerplant causes structural issues, then that's a whole 'nother problem. If the tail stalls just when you really need to get the nose up, that's a problem too...
 

lr27

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You need to go back a ways and catch up.
I know the aerodynamic purpose of the enlarged tail with a real airfoil. I don't know the purpose of fuselage modifications much larger than required for structural purposes. What did I miss after going over the thread anotber time?
 

Eugene

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If the required increase in tail volume due to the larger powerplant causes structural issues, then that's a whole 'nother problem. If the tail stalls just when you really need to get the nose up, that's a problem too...
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No tail stall, but more engine power = will need higher tail balancing load = stronger tail pipe needed. I found that under 100lb load on stabilizer boom is flexing and decalage increasing by 1.5°.
 

poormansairforce

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I don't know the purpose of fuselage modifications much larger than required for structural purposes.
The foam is not for structural issues, it is to streamline the airflow around and underneath the fuse. The tail enlargement is a separate idea that is the basis of this particular thread. I should have posted a link to his other thread. My apologies!:(
 

Eugene

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The foam is not for structural issues, it is to streamline the airflow around and underneath the fuse. The tail enlargement is a separate idea that is the basis of this particular thread. I should have posted a link to his other thread. My apologies!:(
Yes, foam is flying Experimental plug to find perfect shape for streamlining the airflow. Final rear cowling will almost cover tail boom completely and will be made out of fiberglass or carbon fiber.

Side benefit from this cowling, is that I can hide some kind of reinforcement for tail boom. No idea what that will be. Just brainstorming at this point.

Or maybe this fiberglass shroud can be reinforced to serve as structural support for tail pipe, to prevent it from flexing under load in flight??? Just asking, never did this before.

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Riggerrob

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If you are making structural changes to the tail boom, it might be simpler to extend the boom up to a metre. That will improve stability and control while still using stock tail feathers. Stock tail feathers will be easier to build and get approval.
 

Eugene

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If you are making structural changes to the tail boom, it might be simpler to extend the boom up to a metre. That will improve stability and control while still using stock tail feathers. Stock tail feathers will be easier to build and get approval.
No need really to get approval from anybody. It is experimental LSA and I have repairman certificate.

Well, will need to be approved by my wife of coarse, but somehow I will find my way to convince her. After reading my books for 3 years I can talk so......ooo smart. She will never know the difference.

Work on tail feathers is 100 times easier than making tail pipe longer. I can remove all 4 pieces in 40 min and have them on my table. Usually takes about 2 hr to install everything back to normal. I did it many times.
 
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