Hobbey labs SR-71

[Bowhunter]

Has any one flown one of these yet? I have one and I was wondering if a D11-P would push this bird alright

 

[Silverleaf]

EMRR has a review and one fairly successful flight with your motor of choice...

https://www.rocketreviews.com/reviews/kits/hl_sr71.html

Would love to have one of the HL Blackbirds..mmm

 

[JStarStar]

I've got one, just the free-flight version.

I haven't made the plunge into R/C as yet - my LPR activities are devouring my bank account fast enough as it is!! I did buy a $19.95 styrofoam B-2 on e-bay thinking I would learn to fly it, but I havent' kept the **** thing in the air more than 10 seconds yet. If I get to the point where I actually am able to fly the B-2, maybe I'll look into getting the SR-71 converted over to R/C.

I haven't had a chance to build and fly the HL SR-71 yet - the actual construction looks pretty simple, if perhaps not quite as durable as we'd probably like. The decal application is probably a little problematic as the EMRR review says, probably needs a lot of clear coat to get it to stick.

WARNING: do NOT click on the "Jim's Hobbies On-Line" link in the EMRR review, it takes you to one of those GD-MF page-jacking search engines. DO NOT CLICK THIS LINK.

The other question, is whether D11-P engines are still available. The EMRR piece states Estes has quit production, but they still seem to be available on-line.

Is it considered an unacceptable "user modification" to simply epoxy a balsa disc over the end of a normal D12-3 to in effect, create a plugged engine?

Another solution would be to simply epoxy in a balsa bulkhead in front of the engine mount (probably a good idea to epoxy a thin sheet aluminum (pie-pan thickness) shield over it as well, since it's going to be catching the ejection charge.

The obvious question: "wouldn't the ejection charge blow out the sealed tube?"

I don't think so - you still have the open end of the combustion chamber back at the other end of the motor, your ejection charge would escape back there, giving you a very instantaneous final "kick" of thrust when the ejection charge went off.

 

[Silverleaf]

Perhaps the best method would be simply to place a blast plate in front, and rear eject the motor mount with perhaps streamer recovery.

One method is to pour a thick wax seal into the top of the motor and let it set up. Although as I understand it, altering an engine does indeed void its warranty and is against NAR and Safety guidelines.

 

[JStarStar]

Hmm, then you'd have issues with glide profile - when you kick out the motor mount, the CG shifts way forward, so the model in effect becomes nose-heavy and if you had had a reasonably straight boost, you'd go into a dive.

Of course, if you're generating much lift WITHOUT kicking out the motor mount, the bird would have been pitching up throughout powered flight and probably come close to doing a loop.

The old original R/Gs from the Sixties, the Astron Space Plane, etc., used to kick out the engine, and then they usually had elevons that would be pulled up by elastic, etc, to turn the bird into a lift-generating glider. That might be the way to go with this one.

EDIT: Now that we're talking about it, I took my model out of its carrying case - I hadn't had it out in quite some time. (Too many other irons in the fire!! ) It does have spring-loaded elevons which apparently are activated during flight.

Probably attach a streamer to the engine pod for recovery and use a little dowel or something to keep the elevons straight while the engine pod is in place. When the pod ejects, the elevons spring up and you (hopefully) start gliding.

I'll also second the big thumbs-up in the EMRR review for the enclosed launch pad and ignition system included with the SR-71. The pad is a nice PVC tripod a couple feet off the ground, a big thick blast plate, and a heavy-duty 2-piece 1/4" rod which should be fine to launch MPRs. The pad can pretty easily be modified to acommodate 3/16ths and also 1/8th rods (you'd have to drill two holes would be the extent of the necessary mods), so it's pretty adaptable for whatever you want to use it for.

The wiring system looks nice too, feels solid to the touch, etc. Definitely a nice bonus, because I didn't really have a MPR launch pad, (well actually i have 2 now - dang gift-givers!!!) So who knows.... may be the time to take that leap into F's and above...

 

[Jase]

Bowhunter,

Talk to KenParker. He has one and flies it fairly often. He uses AT motors for it. I don't remember the impulse though.

 

[KenParker]

Bowhunter - a D11-P will work, but it will be a pretty low and short flight.

If you have an AT 24mm RMS, there are a number of loads available for it that will work: E11-J, F12-J, E-18-W. The only thing you do differently in prepping the engine is do NOT put any black powder in the ejection charge holder. No black powder, no ejection charge. Simple.

The way that the free flight SR-71s work is that the thrust of the motor pushes forward on the motor mount, which is tied into the elevons. The forward motor thrust keeps the elevons at neutral (level) position doing the thrust phase. When the motor burns out and the thrust drops to zero, the spring loaded motor mount can then shift slightly rearward which also pulls the elevons into up-trim for the glide.

I have seen two "gotchas" on the free-flight SR-71s:

#1 - the motor mount / elevon control system must be working smoothly. Any binding of this system will result in bad things. If it binds under thrust and the elevons stay in up-trim flight mode, you get the dreaded loop into the ground under power death flight. If the system binds when the motor burns out and the elevons stay in neutral position, then you get a dive into the ground from altitude, which is also a fairly certain way to end the life of the bird.

#2 - even if your motor mount / elevon control system is working smoothly in both thrust and non-thrust modes, you can still experience a crash if you don't have the CG of this bird set properly.

If you are unfortunate enough to have both the #1 and #2 gotchas at the same time.... kiss your SR-71 good-bye for sure.

 

[Missileman]

I have a Hobby Labs SR71.
The elevons on the free flight one are moved to launch position by the thrust of the motor. The motor MUST stay in for recovery.
There is not enough throw in the elevons to overcome a nose heavy descent.
D11-p, Commonwealth has them in stock.
There was an SR71 launched today at our launch.
It flew on a D11-p, went about 75 to 100 ft. imediatly nosed over and went into a fantastic circular glide. very impressive.
I would like to try mine on a RMS load

 

[Silverleaf]

Is there a diagram of the SR-71 motor mount-thrust plate that shows how its tied to the elevrons ?

I ask because the Estes #1284 Space Shuttle relies on that central string running through the shuttle to flip the elevrons up to glide position and I'm looking for an alternative - this "might" work.

As well, this could be useed for the giant 1/77th scale Guillows Space Shuttle with ET and SRBs project I'll be doing this winter and might be the answer I need for its flight profile.

Cheers,

 

[Stymye]

Is this the kit ?looks like they are scarce!I logged this site a while back but they never removed the "discontinued" part

https://www.galaxyrpv.com/featured_sr71.html

 

[Silverleaf]

It looks like it, BUT if you check online at Rocketry online auctions, you'll normally see one - or through Ebay.

https://www.rocketryonline.com/cgi-bin/auctions/auction.cgi?all_rockets&1095014816

 

[airwolfe1]

I recently purchased (i.e. got hosed) this kit on eBay. Was advertised as new, but I received no instructions with it and the right elevon was cracked. Seller won't respond...surprise, surprise.

My question to the forum...Does anyone have a set of insructions they would scan for me? and If I epoxy the styrofoam elevon how critical will the weight imbalance be to the flight characteristics?

 

[hokkyokusei]

Originally posted by JStarStar

Is it considered an unacceptable "user modification" to simply epoxy a balsa disc over the end of a normal D12-3 to in effect, create a plugged engine?

...

The obvious question: "wouldn't the ejection charge blow out the sealed tube?"

Actually I've seen this done (albeit with a solid epoxy plug rather than a balsa plug epoxied in) and it didn't work. The ejection charge DID blow out the front, and the blew that particular glider to pieces!

The technique works fine with a -0 motor though.

 

[mikeyd]

Originally posted by airwolfe1
I recently purchased (i.e. got hosed) this kit on eBay. Was advertised as new, but I received no instructions with it and the right elevon was cracked. Seller won't respond...surprise, surprise.

My question to the forum...Does anyone have a set of insructions they would scan for me? and If I epoxy the styrofoam elevon how critical will the weight imbalance be to the flight characteristics?

Here is a link to the instructions!
https://members.cox.net/shortckt4/main.htm
Just clik on
"Hobby Labs SR-71 Instructions" I also have other links on my site to pictures of mine, and my sons, and a video of one of the flights. Hope this helps!

 

[airwolfe1]

Thank you soo much for the instructions. This will be a great help.

Nice website too!!

 

[JStarStar]

Originally posted by missileman
I have a Hobby Labs SR71.
The elevons on the free flight one are moved to launch position by the thrust of the motor. The motor MUST stay in for recovery.
There is not enough throw in the elevons to overcome a nose heavy descent.
D11-p, Commonwealth has them in stock.
There was an SR71 launched today at our launch.
It flew on a D11-p, went about 75 to 100 ft. imediatly nosed over and went into a fantastic circular glide. very impressive.
I would like to try mine on a RMS load

Hey Missileman, have you ever flown yours on an E9-P? Those sound like they would work pretty well.

I have one that I think is finally ready to fly. I just have to apply decals and a coat of clear coat and it's ready to go. And hopefully find a place with some nice soft grass...

 

[Missileman]

I haven't flown mine yet.
I still need to trim it out yet.
Like I said I did see one fly on an D11-P
When I am ready I want to try it on an RMS motor.

 

[JStarStar]

OK, now that I have actually done some work on the SR-71, read all the instructions, seen how the moving parts work, etc., I think I can straighten out all my misconceptions (that is, I get how the spring-loaded elevons work ).

Checking the new-improved Estes website, which does allow you to check engine availablility, the D11-P and E9-P are still listed in their current lineup, plus I picked up some E9-Ps at my local shop. (So the idea of gluing plugs in engines is now a moot point.)

If the SR-71 gets adequate height (100-150) feet on a D for at least a decent gliding flight, an E ought to take it up almost twice as high. Now if you really wanted to get some sky, obviously you'd be talking an F.