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PA-10
10-07-2004, 07:42 AM
I'm building a Light Miniature Aircraft kit, full-size Cub, in spruce (www.lightminiatureaircraft.com). The elevators are aerodynamically balanced like a PA-18, but the designer says not to bother with counterweights since flutter won't be an issue below 100 mph.

I'm not totally satisfied with that approach, so I'm wondering if other Cubs (Piper's and experimentals) counterweight the elevators and ailerons? Any input from other builders? This will be an 80-100 mph airplane.

John
Jacksonville, Fla.

Bill Rusk
10-07-2004, 08:58 AM
John

This will be a tough nut to crack. I have tried to research this subject regarding a biplane that I am building. Not much info on the subject of low performance/low speed aircraft. It seems that all the research and Phd thesis concentrate on transonic or supersonic regions of flight. Dr Paul MacReady would probably be able to help as he has spent a considerable amount of time working with flight in the slower speed regimes. (The Gossamer series of human powered flight). I don't know how you would contact him or if he would be receptive or not. It might be worth a shot. Sometimes these folks are really nice when they are not too busy. I had a very nice conversation with John Roncz (possibly the premier airfoil designer in the world) regarding the Supercub airfoil, but that is a whole different thread.
Flutter is a function of True airspeed, and in general does not often occur below 100 MPH; however, it can occur at just about any speed. If you will be flying below 3000 MSL I don't think it will be a problem as your TAS and IAS will always be fairly close. If you will be flying out of Leadville Co and routinely be above 10000 MSL then it would be a factor as your TAS might be well over 100. I am not an Aero Engineer so take this for what it is, just an uneducated opinion.
Best of luck.

Bill

Fortysix12
10-07-2004, 09:14 AM
I'm building a Light Miniature Aircraft kit, full-size Cub, in spruce (www.lightminiatureaircraft.com). The elevators are aerodynamically balanced like a PA-18, but the designer says not to bother with counterweights since flutter won't be an issue below 100 mph.

I'm not totally satisfied with that approach, so I'm wondering if other Cubs (Piper's and experimentals) counterweight the elevators and ailerons? Any input from other builders? This will be an 80-100 mph airplane.

John
Jacksonville, Fla.

I agree with the designer. 200 knots I would give it some consideration.

I am unaware of conterbalancing except for bungee springs to conteract different speed loads on the elevator and horizontal stab.