SR-71 anyone? - RC Groups
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Nov 14, 2000, 12:13 AM
steve neill
steve neill

SR-71 anyone?

Well I can't stand it anymore. As soon as the X-1 is finished I'm going to give the SR a shot. I have more than seen them fly as ducted fan wet jobs so why not EDF?
I still remember all the tricks to this tricky plane from my old friend Lowel Wexler who built two SR's with Dynamax setups.
So I'm thinking of two SP 480 fan setups, 36 inch span and a 60 inch lenght. Made out of foam my early numbers estimate over 700 inches of wing area and 48 to 58 ounches ( I hope! ).
With those numbers it should fly on a variety of setups. This one will have retracts, taking off the runway is the only way to ensure a fighting chance on the maiden flight and who wants to belly land the Blackbird!
If this works out it will be a kit for sure, although the main reason is, it's always been that dream plane. I think the technology is up to it now, so here I go.
Would anyone be interested in this bird? Or I'm I the only one? Let me know your thoughts, oh and if anyone out there knows the CG on this beast please let me know. I'm using the scale numbers to build from.
Steve Neill
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Nov 14, 2000, 12:41 AM
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Kevin Murray's Avatar
Steve if it goes to kit as you mention, put my on the top of your list.
Even if not kitted, I'd be very interisted in your progress and design.
As for ROG with two SP 480's - I have never heard of that. The retracts are a definate must for a Blackbird. But ROG & Retracts in that size may need two AstroFlight 05 brushless motors, like the EJF Rafale. But then $70 dollars in motors quickly passes the 400 mark.

Keep up posted and I'll check my SR-71 book about the CG.
Nov 14, 2000, 02:18 AM
steve neill
steve neill
Thanks Kevin for your reply. The size of the fans would be 480 sized but I think 480 race motors would have it on the edge for ROG, your right there.
Two astro's would be great but the cost doesn't make the kit very attractive however AP-29 BB's were another consideration but in looking at the data sheets on these motors the 480 race produces more trust on 8 cells.
If I can keep the weight down the low wing loading might make ROG possible, we'll see. If this is the case then 480 race motors or AP's could be used with mini fan or Kyosho which are available everywhere. Now it's more attractive.
Buildng the plane isn't the hard part, it's getting it to fly and them behave well enough so you don't have to be Chuck Yager to fly it.
Yes if you can locate the CG that would be great. I haven't heard from my friend Lowell in a long time and don't know how to get hold of him. It would save me the step of making a CG throw glider and that method can be off sometimes too and you don't find out until you rotate!
Nov 14, 2000, 04:05 AM
Registered User
Daren's Avatar
Originally posted by steve neill:
oh and if anyone out there knows the CG on this beast please let me know.
I have a set of plans drawn by R. M. Green which is approx. the same size as you indicate. His was designed for 2 channel slope soaring. The exact measurements are as follows:
Length: 57"
Wing Span: 35-1/2"
C.G. Range: 36 - 36.5 inches back from the nose.

I can't vouch for the C.G. as I have not yet built this model. It's been in the 'someday' pile for several years now.

Hope this helps,
Nov 14, 2000, 04:13 AM
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Sluf7's Avatar
Yes please I'll have one. The C of G shouldn't be a problem with a moment arm that long but would be interesting to see what yacome up with.

Nov 14, 2000, 07:05 AM
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Andy W's Avatar
Count me in!
Nov 14, 2000, 07:49 AM
H301 Libelle Pilot
Dr. Jet's Avatar
We are working on the plug for the "small" B-58 (4xSpeed400, with props, belly flopper) as a precurser to the "big" one (4x brushless EDF and retracts). The "smal" one may actually wind up as Diversity Model Aircraft's first "jet" kit. Wanna trade an SR71 for a B-58?
Nov 15, 2000, 02:27 AM
steve neill
steve neill
Daren thanks for the imfo you have. That gives me something to start with. I will make a hand glider after all just to make sure.
Doc a B-58 sure sounds good to me. And I think a pusher prop version would be a good way to test the airframe and I will do the same. Twin 480's to 600's should do the job. I'll use three bladed pusher props which should pretty well hide them.I'll stay with the retracts, I've got the wing area.
Got a big block of foam tonight and I'll start pretty soon.
Thanks to all you guys for the help. I'll post everything here and on my site. Here we go!
Steve Neill
Nov 15, 2000, 09:33 AM
Registered User
Alan W's Avatar
Steve....I've been on the sidelines waiting for the right EDF kit to swing my interests away from props and you've found my WeakSpot !!! I've even got one MF480 i one at a raffle so im half way there (yea right !!)

Certainly count me in - only thing i think compares to an SR-71 is a B70 Valkyrie (pant Pant Pant)
Nov 15, 2000, 01:05 PM
Electric Coolhunter
Thomas B's Avatar
I'm a big SR-71 fan from way back. Sounds like you are on just the right track.

Back in the early '90s I designed the HobbyLab SR-71 rocket powered model for FF and R/C. It used hollow foam construction and was about 20" in span and 33" or so long. The planform was exact scale, except that we cut off the rear of the fuse a little. We took some liberties with the airfoil and chine thickness, for manufacturing purposes.

I must have 300-400 flights on the R/C version, both rocket boosted and .049 pusher powered. Have GOT to put a speed 480 in the back of one soon!

Flew amazingly well even at this size, but rather needed a roll gyro to help out with some dutch roll in normal flight.

A good place to start out with the CG is to look at the inboard edge of the engine nacelle. Try the CG at a point about half way between the inlet lip and where the wing intersects the nacelle.

Good luck and keep us posted!

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Nov 15, 2000, 01:27 PM
Registered User
Steve McBride's Avatar
Yes, I too am a big fan of the SR-71. Please keep us updated on the progress!

As for the Hobby Lab SR-71 - would anyone know where one could be had? Seems they are out of production and I really would love to find one.

Nov 15, 2000, 01:49 PM
steve neill
steve neill
Thanks you guys! Your giving me hope. All I've ever seen fly is the Yellow Aircraft version. Didn't know the rocket version had been flown RC powered, it's good to hear.
So far everyone's report on the CG is consistant, thanks for that. We'll run the numbers past everyone first before that scary maiden flight. I think the larger size will cure the dutch roll problem. The Yellow version didn't need it.
Keep em coming you guys! This is something we all need in the hanger and I'm on it!
Steve Neill
Nov 15, 2000, 01:58 PM
Registered User
Alan W's Avatar
I remember when Yellow first came out with the was a complete kit i believe with fans and motors for just over a grand ??

I must have stared at it for hours at the WRAM show....walked by over and over and over....

How did the one you saw perform ?? Never heard or saw of one being would be nice to hear a small flight report after so many years of that model tumbling around in my head

Nov 15, 2000, 10:07 PM
Electric Coolhunter
Thomas B's Avatar
I saw Dennis Crooks demo the Yellow SR-71 at the Southwest Fan Fly here years ago. Flew well and had great presence. (Also saw the even bigger YF-12A (2 X 6" Byron fans)that Byron had at one the the big fly ins in Ida Grove)

Late in the flight Dennis lost an engine. Made a decent single engine approach but got a little slow after he throttled back on final. The model landed a little hard, lost even MORE speed, rebounded into the air, DEEP stalled and pitched up almost vertically and then belly flopped back to the ground, flat. Other than some retract mount damage, it was in pretty good shape.

I have seen the smaller HobbyLab SR-71s do that when the CG is a little marginally aft. It is ok until you get to a certain AOA, but then it wants to keep pitching up.

The entire forward chine acts like a big canard surface and it has a good bit of moment arm...
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Nov 15, 2000, 11:05 PM
steve neill
steve neill
Tomas your right on the button. You have to consider the long movement of the forward fuse. An engine out on that bird has always been a problem, not anymore with electric.
The one I'm building will be a little nose heavy for the first flight. Thanks for the details!