Re: Ceiling Bumps was Re: Word.

If you are flying Cat 1 with a full motor it needs plenty of thickness! I suspect that prop pitch is too low, allowing model to accelerate quickly and cause something to tuck in. Tailboom shouldn't deflect appreciably under its own weight plus that of tailplane. If you haven't done so,, boron up the boom and extension to the stick with one filament top and bottom. The extension has the maximum bending moment and needs eg 4thou boron or 2 of 3 thou to minimise angular deflection of the whole.

I recommend minimal pitch reduction and beefing up the motor as necessary for Cat 1.

Bob

On Dec 23 2012, joshuawfinn_at_gmail.com wrote:


Bob Bailey wrote:
>Sounds to me like longitudinal stability being marginal which allows
>tucking in due to speed build up in the dive. Much depends on
>component stiffnesses; the stiffer the model the less the stability
>required for quick enough recovery.
>
>Bob

Bob, I fly a pretty forward CG; Standard stab sizes, static CG is about 70% chord, more forward of that with the motor aboard. 3-4 degrees incidence. Still won't pull out when the prop is at a low enough pitch to use most of the available winds in a Cat I site.

Do you have any deflection data for tailbooms? I've thought that might be part of it, but I don't have the slightest idea what the stiffness should be on an F1D tailboom since no one publishes that data.

-Joshua Finn