Re: Catapult glider question
Hi Gary,
The correct flap flexibility/weakness is really determined by the site or how high you need to get the model. You want the flap just weak enough to get it to the top of the ceiling. The flap should be strong enough so it doesn't flutter on launch. The weaker the flap the more incidence you need for launch. So if you had weak flaps you would have needed a lot of positive incidence so the model would go up straight or not bunt sharpely. It is very hard to set the incidence of a flapper by measurements, because the flap flexibility determines the amount of incidence needed. My suggestions for the next one you build are:
1) Make the wing on a pylon and tape it on with masking tape. Make sure the wing is positive. Remove the wing and sand pylon to set incidence. I set all my flappers "incidence" by the " trail and error "way. Once you got the incidence right, then glue it to the fuse.
2) Make the flaps stronger than you think they need to be. If after you gotten the model to launch correctly and no flutter is heard, you can then lighten the flaps and better your times. Note if you lighten the flaps you will need to set the incidence over so don't glue the pylon on until after you done this step.
3) Put a nice radius about at least a 1/16" rad. in your "V" launch hook.
I think you will be sucessful if you follow these suggestions, these small indoor gliders are a lot of fun.
Good luck,
Kurt
-- On Fri, 8/26/11, Warthodson_at_aol.com <Warthodson_at_aol.com> wrote:
From: Warthodson_at_aol.com <Warthodson_at_aol.com>
Subject: Re: [Indoor_Construction] Catapult glider question
To: Indoor_Construction_at_yahoogroups.com
Date: Friday, August 26, 2011, 11:39 PM
Kurt,
First, I apologize for misspelling your last name. I knew I had it wrong immediately after hitting the send button.
Thanks for the detailed instructions. I'll bet I had more that one problem. My hook was a sharp "V". I doubt that the rubber was pulled perpendicular to the stick. And I have no idea what the incidence was at launch, but my flappers were weak. I though that would be a good thing. Gliders are trickier that they look! I never destroyed a Peanut Scale plane this quickly.
Gary
-----Original Message-----
From: Kurt Krempetz <krempetz_at_yahoo.com>
To: Indoor_Construction <Indoor_Construction_at_yahoogroups.com>
Sent: Fri, Aug 26, 2011 7:50 am
Subject: Re: [Indoor_Construction] Catapult glider question
Hi Gary,
Sorry to hear your glider had problems. What you are describing can be causes by many things. Launching technique is one. The rubber needs to be stretch perpendicular to the stick, the model needs to be held with the stab/wing parallel to the stretch of the rubber. The hand that is holding the stick must stay still, no motion. Once you hit your hand or stick the tendency is to pull the stick down and away from the model, ....this motion just makes things worse.
Another issue is the hook and whether the rubber can catch or stick on it. The sideways "V" the rubber sits in should have radius, more like a sideways "U" or an upside-down "L", Also I found that metal wire hooks and hooks with little mass to no mass in front of the hook tend to hang up on the rubber.
The typically issue is incidence/flapper. Either incidence was too negative or flappers are too flexible and weak.
I have also seen this happen when the fuse is too weak.
Now moving the hook and hold point to under the wing and at the stab in a model that has these issues will probably make the model not hit the stick but it will also not be a good launch. You will need to adjust/change the other things I mentioned to get a good launch. Once those adjustments are made then the hook and hold point can be forward. A forward hook and hold point allows you to build a lighter model and to get more stretch of the rubber.
I hope this helps. Let's hope the next one flies great.
Kurt
--- On Thu, 8/25/11, Warthodson_at_aol.com <Warthodson_at_aol.com> wrote:
From: Warthodson_at_aol.com <Warthodson_at_aol.com>
Subject: [Indoor_Construction] Catapult glider question
To: Indoor_Construction_at_yahoogroups.com, freeflightml_at_yahoogroups.com
Date: Thursday, August 25, 2011, 8:13 PM
Last year I built my first indoor catapult launched glider. It was sort of based on Kurt Krempet's plans on his web site. It was intended for use in a Cat. 1 or 2 site. After a few horizontal test flights & adjustments I determined it was time to launch it vertically. The first launch it hit the "launching stick" (does that stick have a better name?) & almost destroyed it. After repairs, I tried again. This time it hit the stick again & was completely destroyed. I located the rubber hook near the nose & the grip was located under the wing. I am thinking of building another one this year. I was told I should locate the hook under the wing & the grip behind the stabilizer. What do you think was my problem? Now there is an opening!
Gary Hodson
Received on Sat Aug 27 2011 - 04:15:49 CEST
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