kicking around doing a 4 inch with 75mm 2 stage?

ColumbiaNX01 said:

I am kicking around the idea of doing a 4 inch with 75mm 2 stage. 75mm in both stages. Not going for max performance hence not doing booster min diameter.

Any thoughts?

Doing it because I want to do it.

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JimJarvis50 said:

I would suggest making the booster minimum diameter to retain the flexibility to fly 98 mm motors if you want to later on (assuming the rocket is built such that it could fly on 98mm motors). You can use a removable motor adaptor for 75mm and then pull everything tight with forward motor retention. Yes, you have to surface mount the fins. An important part of the strength of surface mounted fins is to keep the tube round and not let it deform. With 98mm motors, the motor tube performs that function. With 75 mm motors, you might want to construct a removable motor mount that includes a 4" coupler tube to essentially double the wall thickness of the 98mm tube.

Jim

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RGClark said:

If you stage at 100,000+ feet, then a small off-the-shelf APCP motor used as the upper stage could cross the 100 km Karman line for space.

But you have to be able to stage and fly stably in near vacuum conditions, something no amateur has done before. Would your spin can approach supply the stability from the gyroscope effect only, where fins have no effect?

Bob Clark

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markkoelsch said:

Bob, why is every post about this idea of yours versus the subject of the OP?


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RGClark said:

Every amateur rocketeer is interested in maximizing altitude.

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RGClark said:

Every amateur rocketeer is interested in maximizing altitude. So far only one amateur team has passed the 100 km Karman line for suborbital space.

But several amateurs have passed 100,000+ feet altitude. But the point of the matter is any of the small APCP motors sold to amateurs could reach 100 km when launched at the 100,000 foot altitude.

Fins could not not start the spin stabilization when staging at the high altitude because of the low air density. Either sufficient spin would have to be induced low in the atmosphere with fins or some other method would have to induce the spin at staging such as cold gas jets.

In any case staging at high altitude, in near vacuum conditions has never been done before by amateurs and would be an even more important advance than reaching the Karman line.

This is because it would mean amateurs could do multiple stagings in near vacuum so they could ultimately reach orbital velocity and altitudes for stable orbits.

Bob Clark

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ColumbiaNX01 said:

Thanks Jim for your thoughts. I would like to do 98mm. I was thinking of 75mm b/c to keep it light enough to fly on large 54mm. Thats the only reason. I wanted to keep it at 75mm b/c I could fly it at my local field.

I have my 2 stage 75mm min to 54mm I plan on doing at black rock next year that I plan for max altitude. This one would not be built for max altitude.

You opinion matters thanks.

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