Estes SR-71 Blackbird: Results and Questions

[Denis]

Greetings!
My first post here. Recently completed the build of an Estes SR-71 blackbird (our 2nd rocket; first we ever built). It came out beautiful. We launched it today under near perfect weather conditions, mid 70s, low humidity (we are in the greater Boston area). First two launches were with a B6-4. Probably got to about 150 feet altitude but I'm not yet a good judge of height.

Launch 1, the rocket nosed down a little into a very slight but graceful arc near the tail end of its thrust, no twisting or spinning, just a gentle droop. Looked great from the ground actually. Landed maybe 50 feet from the launch pad.

Launch 2, the rocket got to about the same altitude, but this time nosed over more steeply onto its back. Landed maybe 100 feet from the launch pad.

We were feeling minimal if any wind at ground level, so I decided to test and see if wind was happening up higher. To do that, I loaded a C6-5 into our first rocket, an Estes 1827 Ready-to-Fly NSA 18" rocket, good for 700 feet. Thing went up straight as an arrow, and landed even closer to the pad than the Blackbird on its first launch. Hmm..these Blackbirds have a stability problem?

Feeling lucky, I popped a C6-5 into the Blackbird. My son lights it off, it shoots up, this time maybe 200 feet before it noses down, and is now STREAKING across the park near horizontal. Looked AWESOME, beautifully level, but we aren't exactly in no mans land up here. Finally the engine cuts, it starts heading earthward, the nose cone pops and it lands in a vacant lot unscathed.

So, now that you know the story, my questions are:

a) whats the story with this rocket? Its obvious that without a laser alignment system, I could never get the fins or wings to be dead nuts straight, but since it nosed over in two opposite directions without any twisting, I'm wondering if this rocket is inherently unstable..any comments?

Would love to hear others experience. Even if we never fly it again, its a beautiful rocket to look at if I do say so myself.

Regards,

Denis

 

[Rocket Guy 1317]

First I want to say Welcome to TRF.

My SR-71 Black Bird on its first flight went up about 20 feet land sharked and then lawn darted under full power into a bunch rocks on a B6-4 and the rocket was completely destroied. What I think I would next time if I build another one is add more nose cone weight to help keep it stable. They Estes SR-71 kind of flys like the Estes Spaceship except spaceship one does and bunch of loop de loops before smashing into the ground. They are both unstable rockets they probably just need more nose cone weight.

 

[JStarStar]

I built a Blackbird about 10 years ago, that I customized to use dual motors in the engine nacelles and dual 8" chutes for recovery.

I can't find the rocket - I think it's in a crate of stuff in my attic - but as I recall, I did have to add a good amount of clay to the nose to get it stable before launching it.

It did fly a few times, reasonably OK -- no death dives or power prangs -- but as I recall, it usually did roll a couple times during boost. Given the tricky construction of the embossed body skins, the canted rudders, etc. etc. plus the dual motor mounts separated by several inches, that hardly surprised me.

Plus, one factor I think when you have cluster motors laterally separated by any significant distance, may be non-synchronous ignition. If one motor ignites, say, .02 second before the other one does, that would throw their thrust curves significantly out of synch, and give you periods during boost when your thrust from one motor would be greater than the other - thus the rocket would tend to diverge from a straight flight path, accordingly.

None of which, of course, would have anything to do with your SR-71 if you built it according to the stock plans, with one motor mount in the main fuselage body.

My guess more than likely that minor misalignments in the body skins, rudder fins, and other aerodynamic surfaces destabilize the flight path.

 

[cls]

our SR-71 never really went straight up, especially on C6-5s. it always arced one way or another. it finally died when we launched it in a moderate breeze, it weathercocked and took off screaming, didn't land so much as shredded itself on the dry lake bed.

for the truly brave, try a C6-7 - sometimes it will glide a little, just barely.

one of the funniest launches I've seen was a Blackbird on A8-3. dunno why the RSO let it go but he did. the rocket barely made it off the end of the launch rod, and promptly stuck the nose in the grass and then ejected.

 

[shreadvector]

!) What kind of clay was used in the motors you were using? By this I mean was it the powdery white "Poopy Clay" or the mottled looking "Strong Like Ox Clay"?

Poopy Clay erodes and produces assymetric thrust.

If it was Poopy Clay, then that was your problem.

If it was not Poppy Clay, then:

CONTACT ESTES!!!

They need to b e told - repeatedly - about each and every unstable incident with each rocket.

Otherwise they assume everything is fine.

When notified of problems they usually implement a fix right away. Like the Space Ship One where they doubled the nose weight.

Originally posted by Denis
Greetings!
My first post here. Recently completed the build of an Estes SR-71 blackbird (our 2nd rocket; first we ever built). It came out beautiful. We launched it today under near perfect weather conditions, mid 70s, low humidity (we are in the greater Boston area). First two launches were with a B6-4. Probably got to about 150 feet altitude but I'm not yet a good judge of height.

Launch 1, the rocket nosed down a little into a very slight but graceful arc near the tail end of its thrust, no twisting or spinning, just a gentle droop. Looked great from the ground actually. Landed maybe 50 feet from the launch pad.

Launch 2, the rocket got to about the same altitude, but this time nosed over more steeply onto its back. Landed maybe 100 feet from the launch pad.

We were feeling minimal if any wind at ground level, so I decided to test and see if wind was happening up higher. To do that, I loaded a C6-5 into our first rocket, an Estes 1827 Ready-to-Fly NSA 18" rocket, good for 700 feet. Thing went up straight as an arrow, and landed even closer to the pad than the Blackbird on its first launch. Hmm..these Blackbirds have a stability problem?

Feeling lucky, I popped a C6-5 into the Blackbird. My son lights it off, it shoots up, this time maybe 200 feet before it noses down, and is now STREAKING across the park near horizontal. Looked AWESOME, beautifully level, but we aren't exactly in no mans land up here. Finally the engine cuts, it starts heading earthward, the nose cone pops and it lands in a vacant lot unscathed.

So, now that you know the story, my questions are:

a) whats the story with this rocket? Its obvious that without a laser alignment system, I could never get the fins or wings to be dead nuts straight, but since it nosed over in two opposite directions without any twisting, I'm wondering if this rocket is inherently unstable..any comments?

Would love to hear others experience. Even if we never fly it again, its a beautiful rocket to look at if I do say so myself.

Regards,

Denis

 

[Micromeister]

I've beem building and flying SR-71's in various configurations for a very long time. From then to now I've never had an SR do anythiing but fly straight up on B6-4 and C6-3 and 5's. 3 motor clustered B6-0/B6-6 or C6-3 or C6-0/C6-5 or 7's they go like a bat out of ... well you known.

Wing alignment is very easy if you use the gluing jigs provided and the canted tail/ dorsal fins can be held in alignment by duplicating the alignment pattern and adding a back plate to hold two in place while glueing up the sets. I used two of each so I didn't have to wait for one tail or dorsal to dry while setting the other, a couple small strips of masking tape are the only ofther tools needed to make these fins prefectly line up.

You should check the nozzle of your motors some of the newer motors seem to be having an out of round burn problem. We've also seen a few C6 motors with the nozzle hole set slightly off-center. Roll the motor on a flat surface and watch the nozzle end, if the nozzle isn't centered you'll pick it up very easily as it rolls. If you find either of these conditions fill out a mess report and send it to NAR standards and testing, as well as notifying Estes.

Here's a BEAUTIFUL flight but a Lousy Landing clustered SR-71 flight. The two C6-0'd lite in the pods but the core C6-5 didn't...no deploy, gerogous spiral into the ground. All SR-71 clusters after that had the pods ducted into the main body as will, I don't like to repeat mistakes

 

[vjp]

Hey John-

Just curious - did you vent, or plug, the C6-0 outboards?

Reason I'm asking is that I've been RockSim'ing my next planned Vostok, with 4 C6-3's in the core and A10-PT's in the strap-ons. But it's so draggy that it would really benefit from C6-0's in the outboards.

However, venting the blow-through is going to prove difficult, so I'm looking for reliable, tested methods of retaining C6-0's so they neither eject, nor cause any damage to the motor mount.

(sorry about the threadjack!)

 

[Fred]

Hi Micro,
That was a great photo of the Sr71. Do you have one where all three candles lit?

 

[Micromeister]

Hi Vince:
The model in my "death of a cluster" pic were set-up with nose plugs and eject the casings at burnout. I've used this same set-up on the Deep Space Transport and Geo-Sat HLV models they all are very exciting launches After that Photo and necessary new SR-71 build I vented the outboards into the main by soldering up sections of 1/8" x 3/16" rectangular brass tubeing which was made a part of the 1/8" balsa interwing between motor pod and main body. I think I have a pic of this somewhere.

Fred22:
Yes I have a bunch of photos of 3 motor liftoffs unfortunately the SR is so fast off the pad they are all so burry i've never scanned them. Here's a DST 3 motor in-line cluster lift-off that's a lot less of a black streak on the film you get with the SR-71...it's SOOOOOO fast! I'm sure you can see how blurry this heavier model is off the line, so you can imagine what you see with the SR

PS: Vince; apparently I've never scanned the SR vent construction pics. I'll have to look them up and scam for later posting. Maybe I'll do a SR-71 cluster converstion thread sometime soon

 

[Fred]

Nice pictures Micro and a very nice rocket. I can't see myself building a blackbird because I am more of a scifi, actual spacecraft kind of guy. Having said that I can still admire the skill.
Cheers
Fred

 

[Denis]

Figured I'd throw in a pic of the rocket. This has been a great thread. Thanks for all your feedback!

 

[Micromeister]

Now that's a Great lookin Bird Denis! Hope your funny flight prob. was one of those poopyclay nozzle problems, Can't see any drastic misalignments on the fins from your photo

 

[vjp]

Beautiful workmanship and a great photo, too!

I agree with the others that a little nose weight will probably add much to its stability. Estes, being penny-wise and pound-foolish, seems to skimp on the clay.

p.s. Estes also makes a B6-2 which would probably be safer for the SR-71 than the B6-4.

 

[Fred]

that is a great looking rocket

 

[cudacharger]

I've just completed my second SR71 Estes rocket (Ready for fill, sand and paint). My first one has over 8 successful launches...all on C-6-5.

I had a question on the decals and finish coat....best method of applying decals after several coat's of gloss black (Coat decals?).....Then I shot a few coats of clear...but was not really pleased with the results....I would like to get the second one right....any suggestions are much appreciated!

Thanks in advance.

 

[cjl]

Hello, cudacharger. Good to see you again. Nice fleet you've got there (i like the X-15's). I also had issues (i'm sorry, problems) with the decals on my Estes Blackbird. They were eventually solved by a stuck chute, but I never managed toget hem to look good.

Chris

 

[Denis]

Great looking fleet Cuda!

The instructions say to paint the rockets with gloss black, apply decals, then clear coat.

It would seem logical that a gloss black surface would provide a nice smooth surface for decals to adhere to.

However, in reality these planes are not glossy-black, more satin or flat. In mid-May of this year we had the opportunity to look at a real Blackbird up close in New York City. There is an A-12 Blackbird (virtually identical to SR-71) sitting on the deck of the USS Intrepid aircraft carrier (now a floating air-power museum), harbored around 40th Ave on the Hudson River. I highly recommend visiting!

Based on the above, we painted the 'bird flat black. Then we applied decals. Some of the decals, particularly the curved ones on the engines had a hard time staying there. With pressure you could get them to stick. Then we clearcoated the plane, resulting in a neat, grainy black finish that looks and feels more like hard plastic than paper and cardboard. This is also supposed to protect the decals.

So there you have it.

Question Cuda' - where did you get the large blackbird and x-15s?

 

[Stymye]

some nice models!
to get the best results paint the model gloss black , apply the decals than spray a flat or satin clear coat.

 

[cjl]

Yes, as styme said, paint it gloss black, and apply a flat clearcoat.

 

[cudacharger]

Originally posted by Denis
Great looking fleet Cuda!

The instructions say to paint the rockets with gloss black, apply decals, then clear coat.

It would seem logical that a gloss black surface would provide a nice smooth surface for decals to adhere to.

However, in reality these planes are not glossy-black, more satin or flat. In mid-May of this year we had the opportunity to look at a real Blackbird up close in New York City. There is an A-12 Blackbird (virtually identical to SR-71) sitting on the deck of the USS Intrepid aircraft carrier (now a floating air-power museum), harbored around 40th Ave on the Hudson River. I highly recommend visiting!

Based on the above, we painted the 'bird flat black. Then we applied decals. Some of the decals, particularly the curved ones on the engines had a hard time staying there. With pressure you could get them to stick. Then we clearcoated the plane, resulting in a neat, grainy black finish that looks and feels more like hard plastic than paper and cardboard. This is also supposed to protect the decals.

So there you have it.

Question Cuda' - where did you get the large blackbird and x-15s?

Denis-

You are correct about the color of the SR 71 blackbird...I've also witness one up close and the bird has a flat black stealth finish...so I painted my first SR 71 flat black with a clear finish....came out okay....this time I'm going gloss black with a matt clear coat finish. I'm in the process of primer and sanding...I will post a pic once completed. Your SR71 bird looks great!

The larger SR-71 is a freeflight discontinued HobbyLabs bird and the X-15's are a Quest kit and the new RTF Estes model. I'm going to start the 1/20 scale Paul Clark X-15-A-2 kit next month.

 

[Fred]

That is a great photo of some great rockets.
Cheers
fred

 

[cudacharger]

Just finished 4th coat of Matt clear....pic as promised.

 

[Denis]

Very nice!!

Hey now I have a question about the shock cord.

The shock cord on this bird is very long. Can it be shortened? is there a minimum length?

 

[BobH48]

Originally posted by Denis
Very nice!!

Hey now I have a question about the shock cord.

The shock cord on this bird is very long. Can it be shortened? is there a minimum length?

Don't do it!!

Most kit shock cords are too short as it is and usually need to be replaced with longer ones.

By the way, welcome to the forum. The member here are very friendly and helpful.

I see you're from Boston. CMASS has regular launches in Amesbury and Tewksbury.

 

[cudacharger]

You can make the cord shorter if you prefer...I like the longer shock cords on this application because the ejection charge is more dramatic to watch...and looks as if the rocket is breaking up in free flight because of the longer cord....you do have to take a little more time packing the cord and recovery shoot...but I don't mind.

Furthermore, the recovery looks cool with a longer cord...and the rocket seems to have less of a spiral effect..which happens with shorter cords winding up in the recovery shoots....I guess it's all personal preference.

The Fleet:

 

[gpoehlein]

Originally posted by Denis
Greetings!

<snip>

Feeling lucky, I popped a C6-5 into the Blackbird. My son lights it off, it shoots up, this time maybe 200 feet before it noses down, and is now STREAKING across the park near horizontal. Looked AWESOME, beautifully level, but we aren't exactly in no mans land up here. Finally the engine cuts, it starts heading earthward, the nose cone pops and it lands in a vacant lot unscathed.

So, now that you know the story, my questions are:

a) whats the story with this rocket? Its obvious that without a laser alignment system, I could never get the fins or wings to be dead nuts straight, but since it nosed over in two opposite directions without any twisting, I'm wondering if this rocket is inherently unstable..any comments?

Would love to hear others experience. Even if we never fly it again, its a beautiful rocket to look at if I do say so myself.

Regards,

Denis

My stepdad (In his 70s, but I got him interested and he's build about 10 birds so far!) built one of these. He got frustrated with the paper shroud, so he just left it off.

On his first flight, it did just fine (B6-4 I think). But on the second flight, again with a B6-4, it went horizontal as soon as it left the pad and augered in under power. The crash ripped the engine hook out and crumpled the front of the BT. Adding a thrust ring and replacing the front two inches restored her to flight status. But the real question is why she went unstable in the first place.

My theory is that he didn't get the wadding and chute in far enough, and as the plastic expanded a bit it pushed the nose cone out some. On thrust, I figure that flat nose cone tilted, acting like a forward fin and deflected the flight path. Mind you, this is just a theory, but I think it likely given the perfect first flight.

Greg

 

[AlexM]

Keep your shock cord long. The shorter the cord, the more likely your rocket is to sustain damage upon ejection.