Foamboard sr-71 build question

Tyson York

New member
I built a foamboard sr-71 with 2 50mm edf's. It had a 24" wingspan and a length of 43". Anyone have a ballpark figure on where i would need to be weight wise?
 

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quorneng

Master member
With those substantial fuselage chines I would worry more about the CofG.
You may find it flies 'nose heavy' at normal speed (normal depending on wing loading) but as the angle of attack rises it will move towards tail heavy and at the extreme it could go into a 'super stall' which equals recovery only if you have the height.
 

L Edge

Master member
Yeah, glad someone else used EDF's to get it to fly.

Weight is not a main issue. Provide the necessary battery and find the CG that will make it fly.
Just make it a little nose heavy and 2 big factors to remember are 1) make wide turns 2) do not point the nose at any steep angle(up or down) for it will trash your 71. Use throttle management in changing elevation
Check my thread on my SR-71 by doing a search.

How are you launching it? Chuck it or use landing gear? How are you handling yaw?

Any questions, fire away.
 

Tyson York

New member
Yeah, glad someone else used EDF's to get it to fly.

Weight is not a main issue. Provide the necessary battery and find the CG that will make it fly.
Just make it a little nose heavy and 2 big factors to remember are 1) make wide turns 2) do not point the nose at any steep angle(up or down) for it will trash your 71. Use throttle management in changing elevation
Check my thread on my SR-71 by doing a search.

How are you launching it? Chuck it or use landing gear? How are you handling yaw?

Any questions, fire away.
Hand launch, differential thrust for yaw. My cg is a bit nose heavy.
looks amazing any chance there will be a set of plans?????
looks amazing any chance there will be a set of plans?????
If it flies well i will draw up a set of plans.
 

PsyBorg

Wake up! Time to fly!
Hand launch, differential thrust for yaw. My cg is a bit nose heavy.


If it flies well i will draw up a set of plans.

If your anything like I was.. do a few unpowered glide tests as what I thought was a "little" nose heavy was actually a lot on more then one aircraft. That will give the best indication of flight worthiness.
 

Tyson York

New member
If your anything like I was.. do a few unpowered glide tests as what I thought was a "little" nose heavy was actually a lot on more then one aircraft. That will give the best indication of flight worthiness.
Yes, I'm actually planning the glide test for today after work. I'll update and let ya know how it goes.
 

L Edge

Master member
Be sure you take some video of what your doing. Then you can figure out what was going on.

If you chuck it without power, pick a day with 5 to 10 mph wind. That way, make the first throw (have a little up elevon) about a foot off the ground into the wind. If it nose down immediately, move aft. If it rides high and tends to go nose up, CG needs to be forward.

That way , 3 or 4 ft high chuck will not cause damage.
Also, roll is going to be quick, so be prepared.
 

PsyBorg

Wake up! Time to fly!
Be sure you take some video of what your doing. Then you can figure out what was going on.

If you chuck it without power, pick a day with 5 to 10 mph wind. That way, make the first throw (have a little up elevon) about a foot off the ground into the wind. If it nose down immediately, move aft. If it rides high and tends to go nose up, CG needs to be forward.

That way , 3 or 4 ft high chuck will not cause damage.
Also, roll is going to be quick, so be prepared.


I do my first tosses in the bedroom over the bed before anything I try to fly now sees the sun light hehe. If it clears the bed n hits the wall its allowed to go outside to play.
 

Tyson York

New member
I built a foamboard sr-71 with 2 50mm edf's. It had a 24" wingspan and a length of 43". Anyone have a ballpark figure on where i would need to be weight wise?
I did the glide test yesterday, it was a success on the first launch, i believe the cg is about perfect. I didn't take any video, but apparently i didn't need to. Still super nervous about maiden. Any thoughts on hand launch or catapult? It does have an aura 5 lite in it with launch assist. Also, the weight came in at 1129 grams, so i suppose i could fit landing gear on it. Any feedback is appreciated. Thanks guys.
 

L Edge

Master member
I did the glide test yesterday, it was a success on the first launch, i believe the cg is about perfect. I didn't take any video, but apparently i didn't need to. Still super nervous about maiden. Any thoughts on hand launch or catapult? It does have an aura 5 lite in it with launch assist. Also, the weight came in at 1129 grams, so i suppose i could fit landing gear on it. Any feedback is appreciated. Thanks guys.

Anything going on?
 

quorneng

Master member
1129 g for a 24" span, even a delta, sounds on the heavy side to me.
My Depron SR-71 is bigger at 40" and lighter at 650 g. One 70 mm EDF exhausting through 6 nozzles.
Newcmplt1.JPG

It hand launches easily which is just a well as it has no undercarriage.
Incidentally I changed the wing tips from 5 degrees up (the take off position on the original) to 5 degrees down which upset its gentle handling characteristics. I will have to change it back. North American were quite right.