stunthanger.com

Speed,Combat,Scale,Racing => Carrier => Topic started by: Bob Reeves on August 04, 2011, 11:42:38 AM

Title: Flat bottom or symmetrical
Post by: Bob Reeves on August 04, 2011, 11:42:38 AM
Thinking about the next version of my FJ-4 and wondering about a semi flat bottom airfoil. From what little I remember it won't hurt the high speed and may help on low speed..

So the question is...... symmetrical or (not really a true clark Y) flat bottom airfoil?
Title: Re: Flat bottom or symmetrical
Post by: BillLee on August 04, 2011, 12:28:25 PM
Many (MANY!) years ago when I built my last carrier model I used a Clark-Y airfoil, essentially a flat-bottom section. It worked TOO well! It created so much lift that I could not get the model to stall/land, it had to be driven(!) into the deck.

I suggest a symmetrical airfoil is the better choice.

Bill
Title: Re: Flat bottom or symmetrical
Post by: Tim Wescott on August 04, 2011, 12:43:43 PM
Many (MANY!) years ago when I built my last carrier model I used a Clark-Y airfoil, essentially a flat-bottom section. It worked TOO well! It created so much lift that I could not get the model to stall/land, it had to be driven(!) into the deck.
In the full-scale and RC would not stalling is a sign of not enough elevator authority -- there the prescription would be either for more elevator or a more forward CG.

But I don't fly carrier, so take the above with a big grain of salt.
Title: Re: Flat bottom or symmetrical
Post by: bill bischoff on August 04, 2011, 02:03:08 PM
If the model is meant to hang, use a symmetrical airfoil. It makes a smooth transition into and out of the hang.
I use 12-13% at the root and 15% at the tip. Phil Cartier recently told me that the thickness didn't make much difference in high speed, and I can't dispute him, but I've been using the thinner airfoils with good results. If the model isn't meant to hang, you could probably use something flat bottom"ish", but I would mount it a few degrees negative (leading edge low) To keep it from climbing as Bill Lee described.
Title: Re: Flat bottom or symmetrical
Post by: Bob Reeves on August 04, 2011, 02:54:50 PM
Sounds like symmetrical is the right answer..

Thanks guys..
Title: Re: Flat bottom or symmetrical
Post by: john vlna on August 04, 2011, 03:07:26 PM
I have normally used symmetrical airfoils, but My seafire with a flat bottom has no problem hanging. It is not a Clark Y however but a KFm 2