Grim Reaper

[Bigander]

I've been playing around in rsim, i'm in an engineering club hosted by my local air products for teens. We do different competitions and one of the final ones will be some sort of rocket challenge. I figured i have the upper hand since i'm the only one at the club that's really into rockets! Decided to make a max altitude min diameter rocket. 667.5 mph max velocity, 5044 feet altitude. 29mm heavy walled motor mount, 1/4" ply fins. Will have to play w/ nose weight to get maximum altitude.

 

[jj94]

For more altitude, I'd extend the body a bit more, decrease the nose weight, maybe change the fins around and see which shape gives the most stability with the least weight/drag, and make the fins 1/8 CA'd basswood.

 

[Bigander]

part of the fin shape is i don't want anything sweeping back past the bt so i can bring the whole thing down faster.

 

[Bigander]

Just extended the bt and dropped nose weight, lessened performance, i think the best route is the shorter bt and nose weight, because there's less surface area so that means less drag, and there's more weight which also means less drag.

 

[SpartaChris]

Check out the Loc Weasel's fins. That design has been a favorite among the go high/fast crowd.

 

[Rocketjunkie]

Also use one of the new G80's. Lots more power

 

[loopy]

Elliptical fins work well too. They wouldn't extend past the BT, but would have less drag, I believe...

 

[Pantherjon]

Wouldn't also a forward swept trailing edge on the fins create less drag?

 

[loopy]

Wouldn't also a forward swept trailing edge on the fins create less drag?

Could you really call it a trailing edge then???

 

[Stuck Fingers]

Buy an Apogee Aspire and launch it on an F10.

 

[Bigander]

Buy an Apogee Aspire and launch it on an F10.

I just opened up the rsim file, right now the current version of the grim reaper can get 6000 feet, about 500 feet more than an aspire.

 

[Bigander]

Ok quick question, will 1/8" g10 fiberglass fins hold up to mach speeds? I'm simmed just a few feet over the sound barrier.

 

[jj94]

G10 fins will easily hold up to Mach forces. I'd use 1/16" G10 too, 1/8" is way overkill.

 

[Bigander]

G10 fins will easily hold up to Mach forces. I'd use 1/16" G10 too, 1/8" is way overkill.

Thanks for the help jj, it may not even break mach only 3.92 ft/s past it in rsim, so it may just tickle it but i trust the g10 alot more than the basswood too.

 

[jj94]

Try to resim the rocket with the thinner G10, the velocity may be higher because of the loss of weight. If you want to try to loose more weight, use 3/32" balsa for the fins and airfoil them too. Then glass them, tip to tip, with light to moderate glass. That may be lighter than the G10. I haven't glassed anything in my life, but I'm almost certain that balsa with a bit of glass can withstand Mach.

 

[Stuck Fingers]

I built an Apogee Aspire. I have launched it on a G79. Apogee claims it will break Mach1 on that motor.

I papered the balsa fins with Avery label stock. No shread, no problems.

 

[jj94]

I built an Apogee Aspire. I have launched it on a G79. Apogee claims it will break Mach1 on that motor.

I papered the balsa fins with Avery label stock. No shread, no problems.

Wasn't the motor a G80?

 

[Bigander]

The aspire sims past mach on a g80 but only makes it to about 4k. The grim reaper can make it to 6k and 3 f/s past mach.

 

[Stuck Fingers]

I'm sorry, the engine was a G77-10 R/L

My point was, that papered balsa wood fins and standard cardboard tubes are adequate materials for a G powered rocket.

Tip to tip glassing is overkill, puts weight at the wrong end of the rocket too.

 

[Bigander]

I take it aerotech doesn't make the g25 anymore, sims to 9000 ft too!