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1.4X upscaled Estes SR-71

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hermanjc

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Well that escalated quickly.... Inspired by markg's thread on the Estes SR-71, and remembering it being my favorite kit as a kid (flew it once.... Into power lines) I decided to put one together myself. Given that I have a pile of body tubes and balsa kicking around, I decided to scratch build it and base it around BT-55 tubes (1.4X scale of the Estes kits which use BT-50). Also went with a 24mm motor mount.

The most challenging part was the 8+ inch nose cone, which I shaped out of a glued up block of balsa. Right now bare without parachute, motor and any needed nose weight it sits at 156g.

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markg

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Looks great! Carving the nose cone was a good idea, I was thinking of 3D printing for my upscale.

I'm still waiting on delivery for my decals that I ordered to finish mine. Last seen in Chicago a month ago - USPS. I hate to file a claim with paypal when it's obviously the fault of the postal service, so I'm waiting for a bit longer.

cheers - mark
 

hermanjc

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Looks great! Carving the nose cone was a good idea, I was thinking of 3D printing for my upscale.

I'm still waiting on delivery for my decals that I ordered to finish mine. Last seen in Chicago a month ago - USPS. I hate to file a claim with paypal when it's obviously the fault of the postal service, so I'm waiting for a bit longer.

cheers - mark
I will have to do some woodfiller/bondo smoothing, but overall definitely happy with the shape of the nose cone. Granted it make more wood shavings and sanding dust than I care for :)

Have you thought of trying to print your own decals? I am by no means an expert, but after reading a few threads here on TRF I had success with some inkjet waterslide paper from Amazon when making my Falcon Heavy. I made sure to add multiple thin coats of clear spray paint before soaking in water, and they came out crisp and rich in color.

I just ordered more waterslide paper, this time with white base paper (previously I bought clear) for the decals to be applied to the black paint of the SR-71. I will probably paint up a couple scrap pieces to test them on before applying to the rocket itself.

Just a thought. Can't wait to see your finished product!
 

afadeev

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Estes SR-71 [...] decided to put one together myself [...] 8+ inch nose cone, which I shaped out of a glued up block of balsa. Right now bare without parachute, motor and any needed nose weight it sits at 156g.
Nice job on the nose cone!
What are your plans for sealing it, and making it less likely to chip, ding, and crack?

I've always had rotten luck with balsa nose cones, and vacillated between sealing them with Elmer's wood filler, CA, primer, and combination of thereof.
Still not entirely happy with the rigidity of the end product (all of them get dimples from transportation mishaps), but it's getting better with each iteration.

IIRC, Estes SR71 kit included a few rectangles (forgot how many) of clay ballast that goes into the nose cone, to improve stability.
How much ballast are you planning to include in your nose?

FWIW, my Estes SR71 is ~19" in length, and CG is at 12" from the nose tip.
 

mbeels

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Very nice! Did you use cardstock to shape the fuselage? If so, what weight?
 

hermanjc

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Nice job on the nose cone!
What are your plans for sealing it, and making it less likely to chip, ding, and crack?

I've always had rotten luck with balsa nose cones, and vacillated between sealing them with Elmer's wood filler, CA, primer, and combination of thereof.
Still not entirely happy with the rigidity of the end product (all of them get dimples from transportation mishaps), but it's getting better with each iteration.

IIRC, Estes SR71 kit included a few rectangles (forgot how many) of clay ballast that goes into the nose cone, to improve stability.
How much ballast are you planning to include in your nose?

FWIW, my Estes SR71 is ~19" in length, and CG is at 12" from the nose tip.
I might try a few coats of this CA to harden the nose a bit. For added weight I plan to use a long eye bolt that I'll thread into the nose thru the tube coupler. I'll just have to find the right length one. Is that CG on yours flight ready or without motor?

Very nice! Did you use cardstock to shape the fuselage? If so, what weight?
I did use cardstock. Not sure on the weight, don't have the package anymore. it's from a pack bought at Walmart or Target years ago.
 

afadeev

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Is that CG on yours flight ready or without motor?
Without the motor, since different motors have varying weights.
Since building an accurate sim model for this kit will be a massive challenge (OR wont do it, RS may, or may not), it's hard to simulate CP vs. CG. Preserving the relative CG placement is an imperfect proxy.
 

markg

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Have you thought of trying to print your own decals? I am by no means an expert, but after reading a few threads here on TRF I had success with some inkjet waterslide paper from Amazon when making my Falcon Heavy. I made sure to add multiple thin coats of clear spray paint before soaking in water, and they came out crisp and rich in color.
I just ordered more waterslide paper, this time with white base paper (previously I bought clear) for the decals to be applied to the black paint of the SR-71. I will probably paint up a couple scrap pieces to test them on before applying to the rocket itself.
Yes, I've printed some inkjet on my own as well, on clear. They are okay on light coloured rockets, but for a black rocket you would definitely need to do white-backed for them to look okay. That of course means you'll have to cut right to the edge of the decal which will be pretty finicky.

The full set of decals I ordered are meant for plastic models so it has a whole whack of tiny little red decals that would not really be practical to print out with white backing.

In reality, we probably just need a couple of decals and some red pinstriping to get the look we want for this rocket. After all, we're going to stick a rocket motor (or two) into this thing and blast it into the air!

cheers - mark
 

neil_w

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That really looks great. The cardstock job is really clean, is that just white-glued on?
 

hermanjc

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That really looks great. The cardstock job is really clean, is that just white-glued on?
Thank you. I actually used titebond ii, made sure to apply it very thin to prevent wrinkling. It did come out very smooth.
 

hermanjc

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I was able to finish the parasite drone and release hooks last night. Just need to do some final filling/smoothing on the nose cone and will start paint. Once paint is done I can work on adding nose weight as necessary to shift CG forward for the main rocket, and nose weight in the drone to trim it out for best possible glide results.

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hermanjc

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Without the motor, since different motors have varying weights.
Since building an accurate sim model for this kit will be a massive challenge (OR wont do it, RS may, or may not), it's hard to simulate CP vs. CG. Preserving the relative CG placement is an imperfect proxy.
Agreed that my best strategy would be maintaining the CG relative point based on the Estes kit. Lucky for me someone else alerady made a Rocksim design file and it is available on RocketReviews (https://www.rocketreviews.com/rocksim-estes-sr-71-blackbird.html). When opened the file closely agrees with your measured CG, showing 11.2" from the nose. I upscaled it in Rocksim to match my model and it shows the CP is about 18.5" from the tip of the nose. I'll aim to keep my CG at least 2.5-3 inches ahead of that when loaded with a motor.
 

kuririn

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Yes, I've printed some inkjet on my own as well, on clear. They are okay on light coloured rockets, but for a black rocket you would definitely need to do white-backed for them to look okay. That of course means you'll have to cut right to the edge of the decal which will be pretty finicky.
Or print the decal with a black background on white decal paper.
 

BABAR

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That is an interesting idea, never thought of that one. I might have to try it if my decals don't show up...
You can touch up the edges of a white decal with a black sharpie so they don’t show up.
 

neil_w

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That is an interesting idea, never thought of that one. I might have to try it if my decals don't show up...
I've had mixed results with this.

Works OK with laser decals, and I don't see white edges. Does not work as well for me with inkjet decals, at least not with the clear coat I've been using (Krylon UV-resistant gloss).

My new strategy, which will be tested on my current build, is this:
1) Put down a piece of unprinted white decal paper, cut just large enough to cover all the white (or light) areas in the finished decal.
2) Print the final design on clear decal paper, with enough black border (a few mm) to safely cover the edges of the white decal paper. Then I will add another few mm of clear edge to the decals, to give a buffer area to the black ink when water-soaking.

Yeah it's a pain but it seems necessary for me at least. Double-layering decals like this is not an original idea from me; this has been a recommended approach from others as well. Your mileage may vary.
 

stantonjtroy

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I've had mixed results with this.

Works OK with laser decals, and I don't see white edges. Does not work as well for me with inkjet decals, at least not with the clear coat I've been using (Krylon UV-resistant gloss).

My new strategy, which will be tested on my current build, is this:
1) Put down a piece of unprinted white decal paper, cut just large enough to cover all the white (or light) areas in the finished decal.
2) Print the final design on clear decal paper, with enough black border (a few mm) to safely cover the edges of the white decal paper. Then I will add another few mm of clear edge to the decals, to give a buffer area to the black ink when water-soaking.

Yeah it's a pain but it seems necessary for me at least. Double-layering decals like this is not an original idea from me; this has been a recommended approach from others as well. Your mileage may vary.
I like this! Where room allows, I like it! Have to give it a shot.
 

hermanjc

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I printed up some decals on white waterslide paper with black background where necessary for white to show up. Need to get a few coats of clear on them first. I also painted a piece of scrap wood and printed a couple extra decals to test, and will report back the results. I did get the black paint on last night, so could be applying decals (at least on the test piece) as soon as this evening.

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hermanjc

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Decal application went well. Only real issue is the black doesn't exactly match, oh and I have no patience to make sure the decals are perfectly symmetric 😁

I also weighed the parts before and after paint, and I added about 15g to the SR-71 and 3g to the D-21, so not terrible. The SR-71 alone (no chute or added nose weight) sits at 181g and the D-21 is 21g. Not too bad considering I was targeting 175g. Goal is to maiden on a C5-3 which has a max recommended takeoff weight of 227g.
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hermanjc

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Added nose weight using furniture insert nuts into the bottom of the nose cone, so I can thread in 1/4-20 screws. Of course I way underestimated how much weight the parachute and nose weight would need to be, so fully loaded with a C5-3 puts me at a flight ready weight of 259g (a little over the recommended 227g). Good news is I'm well within the weight for a D12. Anyone have suggestions for my maiden?
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hermanjc

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Successful maiden if the SR-71 today (without the drone). Then followed it up with a second beautiful flight. Both flew on D12-3s.
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mo2872

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Always loved launching my Estes SR71....beautiful flights. Absolutely hated packing the chute. Well done!
 

hermanjc

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Always loved launching my Estes SR71....beautiful flights. Absolutely hated packing the chute. Well done!
Thank you. Wasn't too bad packing the chute (20" scratch made from ripstop nylon) since I upscaled it to BT-55, but I made sure to wrap it pretty tight in the shroud lines to ensure it ejected cleanly.

Also got a good slomo video from the launcher. *EDIT* fixed the quality, new video upload
 
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hermanjc

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Since she landed way down the field, do you want a smaller chute, or spill hole or tie the lines?
Yeah, the Altimeter2 I had in there measured a descent rate of 9mph, which is nice and slow. I think the wide flat body contributes to the descent drag quite a bit. Next flight I might reduce the parachute size. I will also likely avoid flying this one in breezy conditions, especially for smaller fields, which will help reduce concerns with descent drifting.

The Altimeter2 also showed that I was ejecting before Apogee (which was 301ft and 329ft for the 2 flights). I might get motors with longer delays going forward to maximize altitude and allow some descent before ejection.
 
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