Statement removed due to foot in mouth condition, or is it brain fell out before hands typed.... DOOOOOH

I've had some success using PL Premium polyurethane glue. I built a rocket fin can as described by Edward: See the Forum "Construction Help" Thread titled "Fin Options".

The construction technique described by Edward seems to work, but I've only tried it through I Motors.

I've a rocket ready to launch with some big J motors that I built using his technique. My variation is that I foamed the fin can with a urethane foam, which should readily bond to the polyurethane glue.

Th PL Premium polyurethane glue (I got mine at Home Despot) is really easy to use when setting up a fin can.

Now let's see if the fins come off my new build (a PML Tethys). Hopefully the weather for December will let me after the November incident...

Interesting. You learn something new every day. Is the PL the same poly base as LN?

Here is the MSDS on PL Premium.

http://www.stickwithpl.com/pdf/PL%20Premium%20msds.pdf

All the temperature ratings seem to be before curing..??
They are pretty low. Flash point is 250 Deg.

I have two tubes that are going to be used on my next
8" rocket.

I used it on a bulkhead and coupler of My Mad Dog. Sets
real hard. Nice working with something a little less runny.

Ed has used it on some pretty heat intensive projects. I
am sure it is what You could call 'Ed Tested'

I love PL Premium for fincans. Makes construction a snap. I had constructed Bunny Thumper that way (5.5" rocket, 1/16" G10 fins). It worked great until I spacked it at Hartsel. The fins pulled off from the paper tube, but the PL is still firmly bonded to the G10. I found the weak component. My other rocket I used PL Premium for the fillets, then went over it with 2" strips of glass that I then used epoxy on. Those have not come off yet.

Remembering from my materials science classes we used Liquid Nails and PL Premium as well as a few other subfloor adhesives and did pull tests. The PL Premium was 4x as strong as the next competitor. The 3/4" OSB would always delaminate in the middle of the sheet with the glue staying firmly attached to the floor joist. When the floor joists were TJI's either the 3/4 OSB would delaminate or the top flange of the TJI would delaminate.

I was also very impressed when I used PL Premium to glue 2L soda bottles (PET plastic) together for water rockets. The bottles would delaminate before the glue gave up the ghost.

For bulkheads, centering rings and couplers it works very well. Doesn't run, easy to apply and sets up nicely. I don't think you'll get better adhesion being that it is paper to wood.

Motors are required not to exceed 200C (392F) during and after the burn. I know my hybrids go to 81C (178F). Some get warmer, some are cooler. I'm not worried about it giving up during boost - the motor temps generally haven't transmitted through the motor mount yet. I'll have to go back and ask my professor if I can do some tests of adhesives at elevated temps.

Edward

I wanted to know if liquid nails could be used in level one and two rocket construction. Liquid nails in very very stong and is great for bonding wood. It is flammable though. Or is epoxy still the best way to go.

Just try it so we will all know! 😉

Thanks for the useful info, Ed.

-Adrian

I second that.
My apologies for jumping the gun a bit. 😳

Edward, I had once heard the 200F limit on motor temps. I assume that is the surface temp (duh) and it is taken several places around the circumference of business end?

I ask because I've always worried about moonburners getting so hot nearest the area along the offset core. The way I see it, if a motor burns for 8-10 seconds and the core is close to one edge, then the area nearest that offset core will be subject to astoundingly high temps -- while the opposite side will stay very cool. I can't see the surface temp on the side nearest the core staying that low. If one AVERAGED the temps around the circumference, maybe -- but not near the core.

Am I missing something? does the liner soak up that much heat energy?

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?

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.

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

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.

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.

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.