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What is this and need ideas on how to build.

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Senior Space Cadet

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I'm no expert on fighter jets. What is this. A Raptor?
Whatever it is, I think I might take a stab at building a facsimile. I don't have the skill or patience to build an exact scale model. I just want something that has the flavor.
I have a nose cone with cockpit that fits a 24mm tube and I'm thinking two 18mm tubes for the engines.
I'm not sure how to transition from the cockpit/nosecone to two tubes.
Sand down balsa transition maybe?
I wonder if two 13mm tubes would fit inside a squished 24mm tube?
 

Antares JS

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Yes, that's an F-22 Raptor.

I'm not entirely sure what you're going for, but be very cautious building a rocket with big wings in the middle. It will shift your CP way forward and you will probably need significant nose weight to compensate. Transitions can easily be made out of paper, but transitioning to a cluster of tubes is a bit trickier.
 

lakeroadster

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Anteres JS speaketh the truth. Here's the nose weight I added to my F-79 to make it stable. That's a 5/8" diameter steel threaded stud in a custom turned ash nosecone... it's heavy.

The F-35 was what inspired me to scratch build my F-79. Basically pushing the wings back as far as possible.

I've done a swing test, it appears stable, but I have yet to launch it.

Lakeroadster's F-79 Lone Wolf

001.JPG002.JPG003.JPGF-79 004 Avatar.JPGF-35-Thunderbird 002.png
 

jqavins

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I wonder if two 13mm tubes would fit inside a squished 24mm tube?
13 + 13 = 26, so no. But 2 BT-5s will fit into a BT-52 and easily into a BT-55. Two BT-20s will fit easily into a BT-60.

What I would do is go from the BT-50 front end to a BT-55 or -60 then mount the two motors in that. The alternative, which might well look better, is to make a special adapter from the one forward tube to the two smaller ones. That comes with two issues: 1) making it out of balsa requires a better hand at carving (Including hollowing it for the ejection charges) than I've got, and 2) 3D printing it (which is probably more practical) requires better CAD chops than I have as well as access to a 3D printer. If it were me, and I really wanted to do this, I'd go with 3D printing, as I suspect the CAD would be easier to learn enough of to get the job done (trial and error can be done in silico) and I can find a printer to use, somewhere.
 

Nytrunner

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13 + 13 = 26, so no. But 2 BT-5s will fit into a BT-52 and easily into a BT-55. Two BT-20s will fit easily into a BT-60.
Squished 24mm, an ellipse or rounded slot. Could work, only way is to find out
 

jqavins

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Hmm. Here's a picture of a squished BT-50 wrapped around two BT-5s. The red lines are the OD of the BT-5s and the black line is an ellipse of the same circumference as the inner surface of the BT-50. (The circumference of an ellipse is impossible to find analytically, but using a quite good approximation and Excel's goal seeking function, I found the height needed to match BT-50 ID when it's stretched the required amount in width.)
1611337127071.png

Zooming in on one end, we can see that it's a very tight fit; if the inside tubes were any wider in X, and the outside tube thus had to be any shorter in Y, then the red and black lines would cross.
1611337773202.png
So it would just barely be an ellipse. Which is good. Of course, they could be forced in anyway, but the distortion of the BT-50 would be irregular and that would make designing an adapter piece taking the cluster to a round tube a lot harder. As it is, that design would be (relatively) easy to design and print.

It will be so tight that one should keep motors in those MMTs at all times to keep the outer tube from springing back and pushing a little bit of its squish into the them.

(Am I the king of overthinking, or am I? I have to at least be overthinking royalty.)
 

lakeroadster

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Hmm. Here's a picture of a squished BT-50 wrapped around two BT-5s. The red lines are the OD of the BT-5s and the black line is an ellipse of the same circumference as the inner surface of the BT-50. (The circumference of an ellipse is impossible to find analytically, but using a quite good approximation and Excel's goal seeking function, I found the height needed to match BT-50 ID when it's stretched the required amount in width.)
View attachment 447455

Zooming in on one end, we can see that it's a very tight fit; if the inside tubes were any wider in X, and the outside tube thus had to be any shorter in Y, then the red and black lines would cross.
View attachment 447457
So it would just barely be an ellipse. Which is good. Of course, they could be forced in anyway, but the distortion of the BT-50 would be irregular and that would make designing an adapter piece taking the cluster to a round tube a lot harder. As it is, that design would be (relatively) easy to design and print.

It will be so tight that one should keep motors in those MMTs at all times to keep the outer tube from springing back and pushing a little bit of its squish into the them.

(Am I the king of overthinking, or am I? I have to at least be overthinking royalty.)
One man's "Overthinking" is another man's "Attention To Detail". Well Done Joseph.
 
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