SR-71 Blackbird build thread - FINISHED

I built an SR-71 from the Estes kit about 15 years ago in which I converted it into a 2-motor flyer (like the actual plane).

It wasn't real tough -- I just installed motor tubes in the two nacelles (along with small 8" parachutes) and put a tail cone on the main fuselage (where the motor mount is in the stock kit). Finished it up nice with all the decals and it looked awesome.

Flew it a half-dozen times and it always flew OK although it did exhibit a slow corkscrew roll under power. My bet is that while installing the motor tubes inside the plastic skins, I got one of them misaligned by a couple degrees, or maybe one of the fins was a bit off. It LOOKED fine -- nothing obviously crooked -- but under power it always went into this slow roll.

It was lost along with a carton of other rocket stuff when I moved in about 1998. Dang that p$$$$$ed me off. :bang: :bang:

Since the Blackbird is getting harder to find I suppose I ought to track down a kit and build another one.

Not sure if you can find the kits. I think/not sure but they might be on the OOP list of kits from ESTES?

I think Estes took it out of the lineup this year, but you can still find kits around in the stores.

The last time I checked AC Supply still had some.

they are all over ebay!!!

I just picked up a SR-71 today. I'm on the road a lot for work going from job to job so I like to check out the small town hobby shops when I roll through! I opted for the SR-71 but I will be back for what looked to be a full line of the X-Prize models

I'm bummed to hear it has stickers rather than waterslides- I guessed waterslides for a level 3 model. Oh well, I'll have to order a set.

Thanks for all the details and tips, I'm sure this thread will come in handy!

pick1e said:

I just picked up a SR-71 today. I'm on the road a lot for work going from job to job so I like to check out the small town hobby shops when I roll through! I opted for the SR-71 but I will be back for what looked to be a full line of the X-Prize models

I'm bummed to hear it has stickers rather than waterslides- I guessed waterslides for a level 3 model. Oh well, I'll have to order a set.

Thanks for all the details and tips, I'm sure this thread will come in handy!

Click to expand...

I hope it helps! I'd love to see you do a build thread too. But if not, definitely post pictures so we can see when you're done.

Apparently the early versions of this model had decals and they were replaced with stickers later. Ordering decals from Excelsior is the way to go! And whatever you do, glue the engine mount in place BEFORE you put the paper on the wings, and have the nose cone in place when you're gluing the paper on!

I've flown mine about 10 times and it's flown great every time. Straight up like it was on rails. The first time I flew it at a club launch I had about 3 people tell me that these were problem kits and they've always seen them cock sideways quickly and fly screwy - and were very surprised to hear me say that I'd already flown it and it did fine. They were pleased to see that I was correct and at the club launch if flew straight up too. No problems.

On one launch I did have a bit of zippering, so I reinforced the upper body papers with some thicker cardstock inside surface and it hasn't been a problem since.

Mushtang said:

Apparently the early versions of this model had decals and they were replaced with stickers later.

Click to expand...

I opened mine up this morning and I have stickers

I'm considering building it with a 24mm mount so I have the option later for C11 and D motors. Does it seem to leave the pad quickly enough with a C6 or could it use a C11? Could its velocity off the pad be why people say it doesn't fly straight?

I've flown mine about half the time on B and half on C. Depending on the size of the field I'm in.

My guess about why some don't fly straight is that the fins and wings aren't put on correctly. I think if the fins are twisted so that the root edge doesn't line up with the body tube lines it would tend to fly wonky. I'm not talking about the fins leaning of course, they're supposed to do that.

The SR-71 is a very complex model aerodynamically, with a LOT of wing/fin/rudder/body wrap surfaces which are not hard to get misaligned by a degree or two, which would result in slow rolls. The model I built in the 1990s used to roll gradually, almost lazily.

Now, if you get a really violent corkscrew spin or some kind of dive/loop problem, something's got to be seriously wrong.

My thought is that the SR-71 has so much wing it's over stable.

As soon as it leaves the launch rod, if there is any wind at all, the wind hits the fins, it just turns into it and goes horizontal.

Actually makes for a great show...unless it's going in the wrong direction.

sandman said:

My thought is that the SR-71 has so much wing it's over stable.

As soon as it leaves the launch rod, if there is any wind at all, the wind hits the fins, it just turns into it and goes horizontal.

Actually makes for a great show...unless it's going in the wrong direction.

Click to expand...

I've launched in wind before, nothing super heavy, and it still flew fairly straight. I've never seen it go horizontal under power.

Mine probably flies so well mainly because of the excellent decals on it!

Mushtang said:

I've launched in wind before, nothing super heavy, and it still flew fairly straight. I've never seen it go horizontal under power.

Mine probably flies so well mainly because of the excellent decals on it!

Click to expand...

Actually I have seen them fly straight on one flight then go horizontal on the next flight.

Perhaps it depends on which way the wings/fins are facing when it leaves the launch rod.

This thread makes me want to start mine.

SCIGS30 said:

This thread makes me want to start mine.

Click to expand...

This thread makes me want to build another one!

pick1e said:

I opened mine up this morning and I have stickers

I'm considering building it with a 24mm mount so I have the option later for C11 and D motors. Does it seem to leave the pad quickly enough with a C6 or could it use a C11? Could its velocity off the pad be why people say it doesn't fly straight?

Click to expand...

Be careful doing that... if you go up to 24 mm motors, you need to add extra noseweight to keep the CG in the same place to account for the heavier rocket motor... Otherwise it would easily go unstable...

Later! OL JR

luke strawwalker said:

Be careful doing that... if you go up to 24 mm motors, you need to add extra noseweight to keep the CG in the same place to account for the heavier rocket motor... Otherwise it would easily go unstable...

Later! OL JR

Click to expand...

Yes, I wonder how much... Can anybody measure and tell me about where the CG of their Blackbird is? Loaded or unloaded? Knowing the location of the design CG and the weight difference between an 18mm and 24mm motor it should be a simple algebra equation to figure how much additional weight I'd need in the nose.

pick1e said:

It should be a simple algebra equation to figure how much additional weight I'd need in the nose.

Click to expand...

Or you could just use OpenRocket and add a mass object in the nose and adjust to taste after modifying the MMT....

mdoering said:

Or you could just use OpenRocket and add a mass object in the nose and adjust to taste after modifying the MMT....

Click to expand...

I just didn't think OR would be anywhere near accurate with this model because of the odd shapes, cardstock overlay, etc. I figured if Estes has it balanced I should just try to achieve that same balance. Same idea anyway, just need to know where the CG is on the original.

I meant to measure mine yesterday when I had it out to take some launch pictures of it. I'll get back to you on this, hopefully tonight, and let you know what I find out.

pick1e said:

I just didn't think OR would be anywhere near accurate with this model because of the odd shapes, cardstock overlay, etc. I figured if Estes has it balanced I should just try to achieve that same balance. Same idea anyway, just need to know where the CG is on the original.

Click to expand...

Sorry it's taken so long to get around to measuring mine. I was fixing another rocket tonight and just measured it. Without an engine, or wadding, the
Blackbird balances nearly exactly at 11.5" from the tip of the nose. That's just behind the front of the nacelle tubes.

Mushtang said:

Sorry it's taken so long to get around to measuring mine. I was fixing another rocket tonight and just measured it. Without an engine, or wadding, the
Blackbird balances nearly exactly at 11.5" from the tip of the nose. That's just behind the front of the nacelle tubes.

Click to expand...

Thanks for that. According to my calculation then, it would need an additional 6g in the nose for a C11, or an additional 12g for a D12 for the CG to end up in the same place as with a C6.

Bumping thread to add a picture. My step daughter took some pictures of the SR-71 launching and sent me this picture, so I had to share it.

That's cool! If you have details of how the "multiple exposure" shot was done / processed I would be interested!

what a cool picture!!!

pick1e said:

I opened mine up this morning and I have stickers

I'm considering building it with a 24mm mount so I have the option later for C11 and D motors. Does it seem to leave the pad quickly enough with a C6 or could it use a C11? Could its velocity off the pad be why people say it doesn't fly straight?

Click to expand...

Did you ever build it 24mm? I'm wondering how much nose weight you used?