Could I use Liquid Nails and not epoxy

[AdrianParticipant]

As I usually fly minimum diameter, I always orient the core between fins and I like to use carbon airframes on moonburner shots, as I know carbon is a better insulator than glass.

Thoughts?

Actually, carbon fiber is a great heat conductor in the direction of the fibers. I think that carbon fiber makes good fin material for high-speed flights for that reason, so it can conduct the heat away from the leading edge. The pictures I have seen with the worst leading-edge damage have had fiberglass there.

Fiberglass is considered a pretty good thermal insulator. On spacecraft, when we run thruster fuel lines around the sides of the spacecraft, we use FG standoffs to keep them thermally insulated.

[edwardModerator]

The reading is taken near the nozzle. I know that is where the thermocouple was on my hybrid tests. It should be the hottest part of the burn because of all the mass that passes through.

I’d really like to see what it takes to loose a fin. I barbequed Pokey when the moonburner lit in the middle, yet the fins near the nozzle are rock solid. The top of the tube is a slinky now.

One note that I’ve thought about moonburners is that you have all this mass (propellant) traveling down the side of the motor NOT in the center of your rocket. This creates a moment arm – a lever on your rocket. Now, if you line up the core between two fins, then directly opposite the core is only a single fin, in plane with the core. The moment arm of the two fins adjacent to the offset core is very small – because they are very close. This means that if the rocket needs to correct itself it is using those two fins and it may wobble a bit to try and correct.

Now if you line up the offset core directly on the fins then opposite you have two fins that have a bigger moment arm and are more able to dampen any oscillations induced by the motor. From a thermodynamic standpoint the heating along one root of the fin isn’t optimal. I think it would take a couple of flights before it becomes a problem that you would have to address.

Just my thoughts. 🙂

Edward

[MLionbergerParticipant]

Edward,

I have also had some thoughts about the offset mass on the moonburner motors. While there is no doubt that the unburned propellant mass and gas flow down the offset core produce some type of moment arm as you describe it, this appears to be negated by the flow of gas out the centrally located nozzle. The flow or thrust produced by the axially aligned nozzle is probably way more significant than the offset mass inside the motor.

I think on minimum diameter birds, a high-temp epoxy is a real good idea for fin fillets and any glassing/lamination.

[MikeSModerator]

Just a note. My ‘Mad Dog’ fell from about 6000′. Seven feet of it
was in the ground, had to be dug out.

What was left….And what was held togeather, was held
with PL Premium.

Most all points of glue were broke. EB portions were still
togeather even in many parts. Couplers were intact in
airframe.

Very impressive stuff.

Thanks for the advise. Sorry it was tested this way. But a good
test it was.

[Steve JensenParticipant]

In my PML QT kits for everything except the external fin fillets with very good results. I also have used foam in concert with it as urethane foam should adhere to it rather well.

Sort of feel foaming a fin can may be overkill, but I’ve been wary of the QT.

[Steve JensenParticipant]

I used PL Premium Polyurethane in my PML Sudden Rush, which I built with an extended motor tube to accept 4 grain CTI 54mm motors.

PML Sort of warns against using a K load in this kit. It’s their Quantum Tube without fiberglassing.

I shot up my Sudden Habanero Rush to slightly over 10K using only PL Premium on the internal fillets. I did use epoxy (Aeropoxy) on the external fillets and in the assembly of the couplers and e-bay.

The K-445 worked nicely, as did all the other J impulse motors. I’ve flown this rocket 4 times on CTI 54’s with great results.

The PL Premium Polyurethane seems to work fine successfully binding quantum tube, G10 fins, and a PML phenolic MT together well.

Think I’ll use it some more. Thanks for the suggestion Edward!

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