Old Rocket Specs - Flip-Flap

Kruegon · Jan 21, 2015

So I'm working on several old Estes rockets. Came across a Flip-Flap from an old MRN contest that I want to build. Seems pretty straight forward. One thing I'm missing. Length of body tube. Based on the simple plans, it's a BT-20. The balsa fin thickness isn't stated either. Guessing it's 1/8th. And the nosecone appears to be a BNC20J. So any suggestions on how to find the BT length?

K'Tesh · Jan 21, 2015

A quick google search turned up a link from rocketreviews to JimZ's site.

JimZ's got the plans.

If the drawings are close to scale, it looks like the bodytube would be about 3.5"-3.75" long (calibrated eyeball measurement)

jadebox · Jan 21, 2015

Based on the diagram and the position of the engine block, I'd guess that the tube is 4 to 5" long.

-- Roger

K'Tesh · Jan 21, 2015

I'd be willing to bet that the fins are cut from 3/32" stock

One thing you could do is make it with a longer body tube, then cut it down until it looks right. You waste some material, but it's a small sacrifice, and this isn't going to be heavy anyways.

Woody's Workshop · Jan 21, 2015

Be careful where you put the engine block. The engines for this to use are no longer made.
No BT part #. Do more research or just wing it off the scale of the nose cone.
Good Luck with your build.

BobH48 · Jan 21, 2015

BFS-20 fin stock. If I remember correctly, that was 1/16

Rex R · Jan 21, 2015

the plans call for both 1/16" and 3/32" balsa(bfs20 & bfs30 respectively).
Rex

Micromeister · Jan 21, 2015

Rex is correct 1/16" and 3/32" for the fins.
Body tube looks like 3.90" so I'd go with 4" body tube.

Kruegon · Jan 21, 2015

Thanks guys. After I get it figured out, I'm planning to try up scaling it. Figure I'll work it through maybe 24mm then definitely 29mm. Might even try a composite engine build if I can find the tubing I want. Not sure if phenolic tubing is available in the right diameter.

bradycros · Jan 21, 2015

Kruegon said:
So I'm working on several old Estes rockets. Came across a Flip-Flap from an old MRN contest that I want to build. Seems pretty straight forward. One thing I'm missing. Length of body tube. Based on the simple plans, it's a BT-20. The balsa fin thickness isn't stated either. Guessing it's 1/8th. And the nosecone appears to be a BNC20J. So any suggestions on how to find the BT length?

4 inches.

Here's how that number was arrived at:

The page was printed out and measurements were taken.
The diameter of the nose cone in the picture measures13.5 mm
The length of the body tube in the picture is 74.5 mm

Divide the length of the body tube by the diameter of the nose cone and you get a ratio of 5.5:1

You stated the nose cone was a BNC-20
The outside diameter of a BT-20 is .736 inches.
.736 inches times 5.5 = 4.048 inches.

Kruegon · Jan 21, 2015

I like the math. Awesome help. Never crossed my mind to compare the image as scale.

bradycros · Jan 21, 2015

Kruegon said:
Thanks guys. After I get it figured out, I'm planning to try up scaling it. Figure I'll work it through maybe 24mm then definitely 29mm. Might even try a composite engine build if I can find the tubing I want. Not sure if phenolic tubing is available in the right diameter.

Do you know how to get the scaling factor you will need to upscale to 24 mm?

I can help if you need it.

BEC · Jan 21, 2015

Looks like a BNC-20B to me (I don't think there was a BNC-20J). I had thought that if I found the whole issue of MRN that this was in that the missing details would be on an adjacent page (as they are with many other MRN plans) but not this time. That said, here's the whole issue: https://www.oldrocketplans.com/mrn/mrn_V6_n2/MRN_V6_N2.pdf

I think if I were to do this one I'd put a 13mm motor mount in it rather than fly on full length 18mm motors. But that's just me.....

Kruegon · Jan 21, 2015

Bradycros, haven't started considering the upscale yet. I want a successful launch first so I can adjust as needed. If all goes well, I may skip the 24mm and jump to 29mm. Depends on my confidence after the first few flights.

BEC, the only thing I'm looking at is that it appears the engine ejects at the same time it blows the nosecone. There is no engine hook or retainer of any kind just wondering if the mini could do both with the volume of the BT-20 vs the BT-5. Not sure how much fill gas a mini would have.

That being said, anyone think this design could be adapted for high power? I worry about altitude vs drift on a flap recovery. Not to mention gross weight vs decent speed when flaps are the recovery method.

BobH48 · Jan 21, 2015

BEC said:
I had thought that if I found the whole issue of MRN that this was in that the missing details would be on an adjacent page (as they are with many other MRN plans) but not this time. That said, here's the whole issue: https://www.oldrocketplans.com/mrn/mrn_V6_n2/MRN_V6_N2.pdf

I still have that issue. I built the "Bat" from that issue and it flew exceptionally well. Good enough to glide into the swamp in Amesbury. :sad:

BEC · Jan 22, 2015

Kruegon said:
Bradycros, haven't started considering the upscale yet. I want a successful launch first so I can adjust as needed. If all goes well, I may skip the 24mm and jump to 29mm. Depends on my confidence after the first few flights.

BEC, the only thing I'm looking at is that it appears the engine ejects at the same time it blows the nosecone. There is no engine hook or retainer of any kind just wondering if the mini could do both with the volume of the BT-20 vs the BT-5. Not sure how much fill gas a mini would have.

That being said, anyone think this design could be adapted for high power? I worry about altitude vs drift on a flap recovery. Not to mention gross weight vs decent speed when flaps are the recovery method.

I'm sure the intent was to friction fit a Series III engine rather than eject it and hope the recovery system would deploy as well. Estes mini engines generally have really strong ejection charges. I would have no concerns that there was enough on this fairly tiny model.

As for scaling up.....it would be a good idea to do it in stages to get some idea of how slowly it recovers as designed and maybe done with BT-50 and flown on, say, a C11 before getting much bigger. Clearly there is not as much drag producing area as even a fairly small parachute, so one would want to stay with lightweight building materials as you go bigger. None of the flying furniture style of building for HPR.....

Kruegon · Jan 22, 2015

So BEC, you think phenolic tubing and g-10 fins might still be too heavy for even low end HPR?

BEC · Jan 22, 2015

That is my opinion, yes....but I come from an aircraft background and don't really like adding weight. I also know from experience that paper and plywood stands up perfectly well to fairly energetic motors from CTI.

My main concern is that the drag-producting area will go up as the square of the scale factor but the weight will go up as the cube and before long it will just be coming down too fast to be safe. The "wing loading" of the drag flaps will just be too high (and will need something rather stronger/stiffer than elastic thread to hold them open as the model descends).

Kruegon · Jan 22, 2015

That's something I didn't consider. I knew the drag would increase exponentially with the increase in surface area, but never considered that the mass would increase as much as you say.

So drop some knowledge on me. Assuming I stick with standard "Estes style" tubing and balsa or thin birch, what do you think the largest scale I could do is? I'd love to be able to hit an H engine with this design. I feel extremely confident that I could stabilize it to an F just not sure about G or H.

Old Rocket Specs - Flip-Flap

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