Motor mount question and my Estes Saturn V so far

I have started working on my old kit by changing the motor mount to a 29 mm and making all of the rings and bulkheads out of 1/16 aircraft plywood and attaching them with CA and slow cure epoxy. The only exception is the center (gusseted) mount which I cut out of a 1/16 corrugated plywood box and soaked with very thinned down epoxy to stiffen it. The middle mount was not necessary I think but it helps keep the BT stiffer in between the others. I plan to fly it on Es and Fs because of the added weight due to the Sirius Rocketry's molded components. I have not attached the motor mount to the body tube and am concerned about installing it so far foreward. It seems like it could be a problem with the exhaust burning the tail of the rocket. Especially with larger motors.
Mike

How far forward were you thinking of installing it? Be aware of the "Krushnic Effect" when positioning the motor mount. You don't want it too far forward. If you're trying to keep the CG as far forward as possible use nose ballast instead of repositioning the motor mount.

kuririn said:

How far forward were you thinking of installing it? Be aware of the "Krushnic Effect" when positioning the motor mount. You don't want it too far forward. If you're trying to keep the CG as far forward as possible use nose ballast instead of re positioning the motor mount.

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I was talking about the Estes instructions which have the rear mounting ring at 3 3/8" from the bottom of the tube. I am assuming that people who build it lat the instructions say and use the recommended D12 motor do not have a problem with the Kushnic Effect but I might be wrong about that. My other concern is the larger motor exhaust burning the tube. I know that I will probably have to add some nose weight for stability.

Thanks Mike

I just checked my model and instructions to be sure: The 3 5/8" inset is to accomodate the engine cluster nozzle display piece. Since you already have it glued together, you can shorten the display spacer ring and bring your mount further back and still use the display piece. Of course, this will have an effect on stability, take appropriate measures.

qquake2k said:

1/16" plywood for the centering rings seems pretty thin to me. What motors are you planning on flying it with?

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Agreed... 1/8" ply makes a lot more sense to me.

qquake2k said:

1/16" plywood for the centering rings seems pretty thin to me. What motors are you planning on flying it with?

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With the plywood and the middle centering ring which is reinforced with gussets and very stiff because it is completely impregnated with epoxy I think that an E motor will be OK. All of the mounting rings have slow cure epoxy fillets also. It all feels very stong.

Anything above an E, and you should think of adding more surface area contact (let's call those "stiffeners") with the body tube and the motor mount.

The last thing you'd want to see is your motor mount blowing its way through the center of your hard work and leaving the damage behind.

To achieve the body tube/"stiffeners" internal fillets, you could use small well placed holes that can be hidden by fairings and wraps.

K'Tesh said:

Anything above an E, and you should think of adding more surface area contact (let's call those "stiffeners") with the body tube and the motor mount.

The last thing you'd want to see is your motor mount blowing its way through the center of your hard work and leaving the damage behind.

To achieve the body tube/"stiffeners" internal fillets, you could use small well placed holes that can be hidden by fairings and wraps.

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I've found that you can make a pretty sturdy MMT with stock cardboard CRs if you do it right. You need to somehow get a good amount of glue on both CRs- with standard motor mounts, you can-
Put a ring of glue in the tube even w/ the top CR
Put the MMT in halfway
Add another ring at the bottom CR
Slide it in flush

That makes a MMT that's pretty solid, at least for using thin CRs. 1/8" ply would be fine for up to G's or baby H's with no stiffening though- that might be easier.

It's sounding like this Sat5 is getting a bit heavy.

Make sure your motor can get it off the rod fast enough.

Having done a lot of high power rocketry in the past I am always in the habit of impregnating the centering rings with thinned down slow cure epoxy and making pretty good epoxy fillets where ever there will be stress applied.

I'm also in the process of building the Estes Saturn V and have decided to go the cluster route.

In the picture a 3D printed adapter that, in my case, holds up to four 18mm D engines.

The adapter will be glued to the shortened kits BT-50 motor tube.

Cool - a four-into-one device similar to the three-into-one (well, actually one-into-three) version in the Estes MIRV.

It looks like getting the spent motors out of that is going to be "fun".....

BEC said:

Cool - a four-into-one device similar to the three-into-one (well, actually one-into-three) version in the Estes MIRV.

It looks like getting the spent motors out of that is going to be "fun".....

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I believe there are 4 engine hooks down the centerline gap. Well thought out. You could also use the wingnut/bolt/washer/epoxy method of cluster engine retention.- What I don't understand from the picture is if you are only launching with the central (24mm) motor, how do the engine hooks clear the exhaust? Are they removable?
EDIT: Never mind, after looking more closely I see that the four engines will be ducting the ejection into the bt-50 tube: no central engine, cluster only.
Leo, will you be making an interchangeable 24mm mount as well? Will increase your rocket's versatility.

@Bec: The four hook design was done because I have a Saturn 1B with the same setup, kinda for nostalgic reasons. The motors can actually be removed quite easily, if you have small fingers I also have a design that uses screw, nut and washer which is the far better solution.

@kuririn: Interchangeability could easily be incorporated but I have yet to finalize a design.