Dual 29mm Super Bertha?

I was thinking about making it a dual 29 and making a plug for 1 side so I can launch single or dual If I have the room. Thoughts?

If you have both motors loaded (so mass of both motors on board) and only one lights, will it still be a safe stable flight? If so, sounds like a great idea. Not sure if you’ll need to paper or otherwise strengthen the fins.

BABAR said:

If you have both motors loaded (so mass of both motors on board) and only one lights, will it still be a safe stable flight? If so, sounds like a great idea. Not sure if you’ll need to paper or otherwise strengthen the fins.

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Excellent points.

eRockets has some replacement ply fins I believe.

-Bob

Just wondering how you are configuring the cluster so that you get thrust in line with the vertical axis for both single and dual configurations?
I had a 2 motor cluster power prang when only one motor ignited. Second flight both motors ignited and it was a perfect flight.

kuririn said:

Just wondering how you are configuring the cluster so that you get thrust in line with the vertical axis for both single and dual configurations?
I had a 2 motor cluster power prang when only one motor ignited.

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that surprises me, assuming one motor was enough to get it to adequate rod speed. That's why I don't like clusters that DEPEND on all motors lighting to get adequate thrust off the rod/rail.

I've done a number of "off axis" designs and found them very forgiving (lots of corkscrew flights, but net trajectory was always straight.) Sims for dual motor configs with one motor lighting need to include the mass of the second "inert" (for simulation) motor.

Now, motor pods at the far end of fins (waaaaay off axis) is another matter entirely.

Design an interchangeable motor mount system.

(1) Single 24mm
(2) Single 29mm
(3) 18mm / 24mm / 29mm Cluster ( different number and/or combination of motors )

It would be very versatile ! The PDF's below should be helpful !

Dave F.

Oooooooooh I always wanted an interchangeable rocket. Lot of work though, might save that for a nicer kit.

FlyingMonkey said:

Oooooooooh I always wanted an interchangeable rocket. Lot of work though, might save that for a nicer kit.

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Doing it on this one would be "less pressure" and give you the ability to "hone your skills" . . .

Plus, it's not like you don't have enough "spare time", right now - LOL !

When you do the mount, please post lots of pics !

Dave F.

I'm still working full time and taking online courses but let's see...

I have bt70, 24mm and 29mm motor tubes.
I could make a bt70 motor mount with estes hooks and then use bt70 couplers to create the interchangeable drop in mounts.

Looks like that would allow 1 29mm, 3 24mm, or an unknown amount of 18mm as I don't have any bt20 to test fit. Dual 29mm interchangeable only works if I use a bt80 coupler and maybe an external hook, rivets, or similar.

FlyingMonkey said:

I have bt70, 24mm and 29mm motor tubes.
I could make a bt70 motor mount with estes hooks and then use bt70 couplers to create the interchangeable drop in mounts.

Looks like that would allow 1 29mm, 3 24mm, or an unknown amount of 18mm as I don't have any bt20 to test fit. Dual 29mm interchangeable only works if I use a bt80 coupler and maybe an external hook, rivets, or similar.

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I am envisioning your "external hooks" to be "nested" in the Fin Root Fillets, both for strength and overall appearance . . . My two cents !

Building all of the motor mount variants, inside BT-80 couplers, could greatly simplify things.

FWIW - 7 BT-20's will fit in a BT-70 . . . Of course, a BT-70 Coupler is smaller in diameter.

Dave F.

Here is a sketch of my thought process . . . They DO fit - LOL !

Hey the root filled idea is good! Dang it, we may have just talked me into this lol.