Weights of Fabric/Dope Tails vs. Alum Skin

[Brian Jackson]

Hi All.

Hoping to pick the brains of some experienced builders with respect to approx. sq. ft. weights of various empennage constructions. In the preliminary design of a tail section skinned with .020" alum with generous surface areas, I'm calculating it would put the assembly well over the 20 lb. mark, with 12 lbs. just in the 020 skin alone. It's airfoil shaped with cross-bar spar tubes.

I'm entertaining the idea of using the 020 skin just from the leading edges to the spars and covering the rest with fabric. However, I don't know if this path yields any significant weight savings. Is there a "rule of thumb" for sq. ft. weight of cloth & dope coverings? And any practical knowledge from those who have experience in this area?

Originally a composite tail seemed attractive but I don't see how it would be lighter than aluminum. Any guidance would be appreciated. Thank you.

Respectfully,
Brian Jackson

 

[AirScooter]

I have weighed one of ernies tails and if i remember correctly it was about 12 pounds complete. That gives you a reference point.

 

[phantom]

Aluminum frame and fabric is the lightest, I have built Bensen sized tail that were around three pounds covered with superflite system. If you use thinner skin and frame you can get a dominator type tail just over ten pounds but I'm not sure how many years it will hold up, I built one much like it some years back and after just over four hundred hours it had several cracks showing up so there is a reason that it uses the thickness that it has.
Norm.

 

[Brian Jackson]

Thank you Scott and Norm. Interested to learn more about tube and fabric construction. Strength will be a concern on the vertical axis since I'd like to diagonal-brace the tail assembly from the HS and let the tall VS above the HS cantilever. Would like to eliminate the need for bracing the top of the tail to the mast over the prop. Will share some images once it's better fleshed out.

Brian

 

[JPAnderson]

I need to skin that cat in few months on my build. To build a lightweight tail we need to know the various loads involved. Full deflection, max G load etc. Otherwise it's just a W.A.G. and will probably be overweight or worse, be too light and fail in fight. I notice that in the Gyro world build it stout wins out over detailed design work.

I've built a VariEze so composites are an obvious choice for me but I'm leaning to a all aluminum T tail as I think it would be the lightest and easiest to build. I've been looking over the T tail in the Cri Cri plans as it a very well engineered structure. I like the T Tail as it get the Horizontal Stab up and out of the weeds.

I've also been thinking about the V tail configuration as it would reduce overall height allowing a long moment arm and would be very light. I don't have any plans that utilize a V tail such as a Davis. Has anyone tried a V Tail?

John

 

[Brian Jackson]

...in the Gyro world build it stout wins out over detailed design work.

Hello John. Agree with the simple and stout. Have scaled back the design a bit in favor of those attributes. Not heard much good about the V-tail configurations you mentioned. I remember reading about one RF member here that built and test-flew one and ended up ditching it in favor of a more effective tail.

You mentioned the Cri-Cri (Cricket). I've had a long-time crush on that design but have never had a chance to see the plans. Anything on the web regarding its tail construction and/or details?

Thanks for the reply, and looking forward to seeing your build.

Brian

 

[JPAnderson]

Brian,

I was given a bootleg copy of the CriCri plans once upon a time. It's incredibly complicated for it's size. I'm pretty sure a RV-8 would take less time to build.

John

 

[Brian Jackson]

Brian,

I was given a bootleg copy of the CriCri plans once upon a time. It's incredibly complicated for it's size. I'm pretty sure a RV-8 would take less time to build.

John

That's what I was told as well during my initial inquiries many years ago. Lots of bonded metal, not for a novice. Still love the tail on that thing. Going with a taller tail on the Bee though to help combat the need for left rudder. From all reports it's a good choice for a gyro. I'd like the HS to be fixed (not all-flying) around 6" below prop center at -3 deg. Not going quite as tall as a Dom tail but close. There will be a folding mast so that's one of the reasons I'm hoping to eliminate the top brace arms to the mast in favor of a strong enough design to allow diagonal bracing to the HS instead of being braced at the top pivot.

Brian

 

[JPAnderson]

The all-flying horizontal stabilizer like on the CriCri would be easy to set as a fixed horizontal. It pivots about it's rear mount that attaches to the spar on the vertical stabilizer. Where the forward control rod attaches could be converted to a fixed mount. Setup properly it would be easy to adjust during flight testing. The finished product would need to be static loaded tested. Balancing would still be important.

I'd steal the construction method from some Luscombe tail feathers I have hanging out. No Bonding.

The need to hold rudder isn't torque. It's the rotating air mass from the prop smacking into the vertical stab and rudder. A VariEze or Long-EZ with no tail has no P factor. They track straight and true.

John

 

[Doug Riley]

Er, JP, all props exhibit P-factor. P-factor arises when the prop disk is not meeting the oncoming air at a 90-degree angle. A steep mush or a slip are examples of this state of affairs. The result is that each prop blade assumes a greater angle of attack as it passes through one half of the disk than the other. The result can be either a yawing or a pitching tendency.

Sailboats with inboard engines have the same problem, since their prop shafts typically sick down through the bottom of the boat at an angle to the water's surface. The resulting yaw effect is known as "prop walk." It's particularly noticeable in a sailboat motoring in reverse.

A gyro with a tall tail, like a Dominator, needs very little attention to the rudder, compared to one with a "shorty" tail. P-factor will still turn up in mushing or slipping flight, though.

 

[JPAnderson]

Er, JP, all props exhibit P-factor. P-factor arises when the prop disk is not meeting the oncoming air at a 90-degree angle. A steep mush or a slip are examples of this state of affairs. The result is that each prop blade assumes a greater angle of attack as it passes through one half of the disk than the other. The result can be either a yawing or a pitching tendency.

Okay, you don't do much mushing in an Eze. If your under power and you have a tail in the propeller slip stream I'm betting the tail is a larger percentage of what your feeling than P factor which is considered pretty negligible compared to the rotational air hitting flat stuff.

I have some high time Kasperwing friends that could help answer the debate. I'll run it by them. I have had my Eze in ever attitude you should or shouldn't and you feel zero P factor. Have you ever flown anything without a tail?

John

 

[Alan_Cheatham]

A couple of threads on V-Tail gyros:

https://www.rotaryforum.com/forum/showthread.php?t=16463

https://www.rotaryforum.com/forum/showthread.php?t=10065

.

 

[JPAnderson]

It sounds from the top thread the T tail twists badly. Dominator tail.... duh.

 

[JPAnderson]

I do wish detailed plans like the CriCri were more readily available for Gyros.