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Jun 17, 2021, 02:34 PM
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F3-RES - Is this legal?


Hi Guys,

I have a v-tail F3-RES glider and the tail is very flutter prone. I put some fiberglass packing tape on the bottom of the ruddervators to stiffen them up and it's worked pretty well.

My question: for competition is it legal to use fiberglass tape on an F3-RES airplane? In the rules I see that fiberglass is allowed on the fuselage but I couldn't find any reference to fiberglass and control surfaces.

Thanks for the help,

Eric
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Jun 17, 2021, 02:45 PM
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Eric:

I am a CD here in the States, and I would allow it. The rule is intended to discourage molded surfaces, and thus discourage an arms race, where the winning airplane is only available to the person with the bucks to afford it. Your use of the tape is as a fix to what is a build problem. In your case, the heavy tape is a fix has altered the mass properties of the tail enough to shift the flutter margin, and allow good flight.

If you were to attend a contest in Europe, you might get a different response, but also, maybe not. Those guys are not interested in fiberglass as an issue, but in getting newbies into the game at a reasonable cost.

I know from my own experience that at least one CD in Europe would look at your setup, think to himself that you have other, bigger problems, and allow you to fly just like I would. His argument would be that getting you to fly is a good thing, and that your fix probably penalizes the performance of your airplane, and does not therefore constitute an unfair advantage.

Finally, F3RES is still not yet an FAI class. So, any issue like yours is up to an individual CD to think about and decide. There is no International cabal of FAI-designated cops fanning out across the landscape, looking for miscreants. Again, my own goal is to get more flyers in the game, not to enforce rules in minutia. Any other CD in any other State other than New Mexico might take a different stance, and more power to them.

See you in Muncie?

Yours, Greg
Jun 17, 2021, 08:21 PM
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Originally Posted by glidermang

I know from my own experience that at least one CD in Europe would look at your setup, think to himself that you have other, bigger problems.
Well you've hit the nail in the head there. Adding the packing tape on the tail necessitated a corresponding larger weight gain in the nose. So now the plane is overweght and flys like it's overweight. But at least I can launch it without having it come apart on the hi start. So many choices... .

So Greg, thanks for your help. Now I can sleep easy knowing I will be allowed to fly, assuming I ever go to a contest.

Thanks and take care,

Eric
Jun 17, 2021, 11:22 PM
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Eric: You should come to the F3res contest Greg and his buddies hold in Albuquerque - you will have a great time, have the opportunity to learn a few things from friendly contestants, perhaps have the opportunity to teach one or two old know it alls a thing or two (we all have something to share), and did I mention it will be fun.
Jun 18, 2021, 10:10 AM
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Originally Posted by sllimakram
Eric: You should come to the F3res contest Greg and his buddies hold in Albuquerque - you will have a great time.
Thanks for the invite and I'm sure I would have a great time. But I can't even motivate myself to go to contests that are two hours from my house much less in New Mexico.

I'm basically lazy.

Eric
Jun 20, 2021, 03:11 PM
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Pilot A's Avatar

Missed you today


Eric,
You could have flown it with us today.
Anatol
Jun 20, 2021, 04:28 PM
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Originally Posted by Pilot A
Eric,
You could have flown it with us today.
Anatol
Yeah, but since it was Father's Day I was forced to spend time with my... err, at home.
Jun 20, 2021, 07:14 PM
Registered User
Eric,
I agree with Greg and the others that it is unlikely anyone will consider your tape to be a violation of the rules. However, I would come at it from a slightly different angle.
The reference in the rules to "fiberglass" was not intended to refer to glass fiber reinforced packing tape, but rather to the common meaning of "fiberglass", a glass fiber-reinforced thermoplastic matrix. You know, like boat hulls and kit car bodies, and molded glider fuselages; glass fibers encased in resin. Hard on the outside, and hard on the other side. I think you win on the definition and don't have to rely on the kindness of strangers, as nice as it to have.
As a possible alternative to the tape, you might look into document laminating film, AKA "new stuff." Possibly lighter and stiffer. Definitely not prohibited by the rules.
As to the contest that Greg and his buddies hold in Albuquerque, I have been wanting to attend for years; all I have to do is complete an F3RES glider and drive to the Land of Enchantment. Maybe this Fall. Or next.

Gary
Jun 21, 2021, 09:08 AM
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Hi Gary,

Thanks for the clarification. I didn't know how closely F3-RES CDs followed the "no fiberglass except on the fuselage" rule. Since F3-RES isn't an FAI class yet seems like there is some latitude. I can see a day when that changes, at least for competitions that award points.

Eric
Jun 21, 2021, 01:18 PM
Registered User
I hate the discussing rules, they should be clear to everyone

Well, I like V-tails, and recently built a replacement tail for my 100" e-glider, and reinforced the "angled joint" with a carbon roving epoxied from top and bottom - effectualy creating I-beams. It seems to work, 12 grams and no flutter experienced so far.

I am wondering - is this legal for the RES class? I am contemplating to design and build my own E-RES model to complement my Slite V2.

Thanks, Jan
Jun 24, 2021, 07:16 PM
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Eric,

Is the boom perhaps the issue and not the tail group? I know others flying a certain design who have done a simple wrap on the boom and solved the issue.

Dave R.
Jun 24, 2021, 08:47 PM
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My Monarch has fiberglass on the wing joints and holds the tail on.
Jun 24, 2021, 09:32 PM
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Originally Posted by dreisinger
Eric,

Is the boom perhaps the issue and not the tail group? I know others flying a certain design who have done a simple wrap on the boom and solved the issue.

Dave R.
Hi Dave,

On the suggestion of Robert T I glued .8mm carbon rod at the 12, 3, 6 and 9 positions on the length of the boom and it had no effect. In fact when the boom flexed the rods just popped off.

I also X-ed some packing tape on the bottom of the wings. That stiffened things up somewhat but not enough to keep the plane from shaking itself apart.

A shame too because if you can get these planes in the air they fly great.

Eric
Last edited by eteet; Jun 25, 2021 at 03:50 AM.
Jun 25, 2021, 01:27 AM
Registered User
Something tells me that if the rods were properly glued on, they would have helped quite a bit. At least with the boom's bending stiffness. They wouldn't help in torsion very much. I'm assuming the rods were the usual unidirectional type.
Jun 25, 2021, 03:52 AM
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Originally Posted by lincoln
Something tells me that if the rods were properly glued on, they would have helped quite a bit. At least with the boom's bending stiffness. They wouldn't help in torsion very much. I'm assuming the rods were the usual unidirectional type.
They were the typical CF rods that are used for push rods. I used thin CA and in my experience CF to CF using CA is pretty darn strong.


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