Great idea (?)

[kuririn]

In a comment to one of Chris Michielsson's posts on the "Model Rocket Building" blog N Kimura says:

Naoto KimuraFebruary 24, 2020 at 10:49 AM
"I wonder how many people had toyed with the idea of making a Lockheed D-21 model (perhaps as a parasite glider) to sit atop their SR-71 model?"

Maybe a parasite glider atop the Estes SR-71 or the Apogee SR-72 Darkbird?


I thought about the plastic drone that comes with the Revell 1/72 SR-71 static kit but I doubt that it would glide. More probably fall like a brick.
Has anyone done a D-21 drone parasite glider? If not I think it would be a cool project.

Unfortunately I have too much on my plate at the moment.
Laters.

 

[Cape Byron]

C'mon, kuririn. You haven't built anything since... like... lunchtime.

 

[Funkworks]

That's a ramjet so yeah, unless it's already beyond Mach something, pretty sure it drops.

But on calm day, I wonder how that shape would glide if it carried a helium balloon instead on an engine. And made of balsa or polystyrene.

 

[kuririn]

With fixed "up" elevons and trimmed for neutral glide with nose ballast, almost anything light enough with wings can be made to glide. As I said, too much on my plate right now. Anybody want to take up the challenge?
The big question is would the piggy back configuration throw off the stability of the carrier rocket?

 

[BABAR]

The big question is would the piggy back configuration throw off the stability of the carrier rocket?

Interestingly if I understand the plans correctly the Centuri Space Shuttle actually had the motor on the Parasite glider

https://www.semroc.com/Documents/pdf/Space Shuttle.pdf

So you can get away with some pretty off center thrust vectors if you have enough fin area

https://www.rocketryforum.com/threa...20-rocket-nuther-asymmetric-fin-design.65399/

https://www.rocketryforum.com/threa...fin-design-think-c-141-kevlar-failure.124493/

https://www.rocketryforum.com/threads/audacious-another-asymmetric-fin-design.136258/

 

[hermanjc]

With fixed "up" elevons and trimmed for neutral glide with nose ballast, almost anything light enough with wings can be made to glide. As I said, too much on my plate right now. Anybody want to take up the challenge?
The big question is would the piggy back configuration throw off the stability of the carrier rocket?

Challenge Accepted
https://www.rocketryforum.com/threads/1-4x-upscaled-estes-sr-71.161818/

 

[Mugs914]

About fifteen years ago (maybe more) I built a D-21 glider based on a BT-50 tube. It was accurately dimensioned based on the Revell kit and scaled up to match the BT-50. It sure wasn't a lightweight, but it had a decent, if somewhat wobbly glide. It was a boilerplate for what was intended to be a true scale D-21B with booster, which was the B-52 launched version:







The booster would have been the "pop pod" on the model and would be recovered by parachute while the D-21 wobbled its way back down. After I got the glider flying I got involved with other projects and never flew it on rocket power.

I thought the glider had been lost in the last move, but I found it in a box just the other day while looking for something else! I'll get it out and take some pics in a bit...

It is pretty rough (being a proof of concept it never was meant to be pretty!), but still in serviceable shape. Maybe it's time to get another booster built (It was actually lost) and see what she'll do...

 

[Cape Byron]

Maybe it's time to get that booster built and see what she'll do...

Yes. It's that time.

 

[Mugs914]

Here are a few pics of the ol' bird... (One inch squares on the board, for size reference)

 

[hermanjc]

Very nice! How did you trim the glider? Just adding nose weight? I'm thinking I may need to add trim tabs. Are your wings on the tube with an angle of attack or is that just an optical illusion?

 

[Mugs914]

Very nice! How did you trim the glider? Just adding nose weight? I'm thinking I may need to add trim tabs. Are your wings on the tube with an angle of attack or is that just an optical illusion?

Thanks Herman!

Yep, I just trimmed it by careful adjustment of weight. The finished version was (is) going to have the scale control surfaces hinged with copper wire or something so they can be used to adjust trim.

As for the angle of the wings, the wing root is parallel to the centerline of the tube (just like a fin would be), but they do have a bit of droop (anhedral) when viewed from the front. This angle is scale for the D-21. The shape of the wings, the anhedral and the massive fillets really mess with the perspective and make it pretty hard to see what is really going on!