Re: Re: F1M Design

Tapio

You need to move the CG forward about 5% of wing chord since the model hasn't enough stability - that will get rid of the bad stall you describe.

Bob

On Apr 22 2013, Tapio Linkosalo wrote:

On Mon, Apr 22, 2013 at 12:50 AM, aldershine wrote:

> **
>
>
> I'm catching on that getting the CG rearward enough is important with F1M.
> I may plan to go with a built-up prop to help reduce nose weight and I
> guess I can plan on a rather large stab.
>
> To assist with design planning I guess my next step is to calculate moment
> weights for the models various components so that I will not have to put a
> stinger behind the tail to get the CG right.
>
>

I suppose it is. Then again, I have only flown short-fuselage F1M's more
than 10 years ago, and without VP, so I cannot really tell what would there
performance be.

For the reference, the component weights for my latest model are:

- front fuselage 820mg (plus some added boron later on)
- rear fuselage 400mg
- prop 475mg
- wing (200mm wide) 760mg
- tailplane (140mm wide at root, 430mm span flat) 400mg

- total 2850, but the added boron brought the weight to quite close to 3
grams.

The nose of the model is about 20-25mm long, and my CG lies at 120% of wing
chord. Incidence is about 2 degrees (but this is really hard to measure
accurately... :-) I started with a tail that was a bit larger in span (same
size as my F1D tails), but as my decalage seemed to be too large, I built
a new, slightly shorter tail. The stability is now quite on the edge, in
heavier turbulence the model may stall both wing and tail and fall (flat)
down a meter or more before acquiring forward momentum again. But in
steadier conditions it seems to fly OK.




-Tapio-