Fiberglass tubes as motor mounts

[brianwh]

I have purchased a 3" Madcow fiberglass tube and a 3" Rocketry Warehouse fiberglass tube to use as motor mounts on two different projects. I couldn't find maximum temperature specs on either website, but I see lots of build threads where fiberglass tubes are used as motor mounts. Should I worry about the temperature from the motor degrading the strength of the tube over time, or do the manufacturers use an epoxy capable of this heat?

Thanks!
Brian

 

[McKailas Dad]

I had wondered about that as well in building LPR, as far as epoxying the outside of a cardboard MMT.

What I found (obviously) is it is the ejection charge that does the most damage. I had well over 100 launches on an Estes Patriot, anything ahead of the front CR was gone, but rest of the motor tube was fine. In my opinion, I don't think the heat of the motor is a concern with cardboard.

 

[llickteig1]

It isn't a issue.

 

[rharshberger]

iirc one of the NFPA documents specifies the maximum external temperature of commercial motor casings, even cardboards ignition temperature is not exceeded by a certified motor.

See the NAR S&T document page 19 for a reference.

Motor casings during or after firing may not exceed 200C (392F), the autoignition temperature of paper is 424F to 475F. A FG motor mount will indeed outlast a cardboard one however, if the rocket is cardboard/phenolic then I can't personally see putting a FG mmt into it.


View attachment ST-MotorTestingManual.pdf

 

[McKailas Dad]

Fahrenheit 454 if I remember correctly....

Edit... Oops! I did NOT remember correctly. Sorry Mr.Bradbury, thanks Google.

I stand corrected, Fahrenheit 451

 

[rharshberger]

Fahrenheit 454 if I remember correctly....

Or the movie version Farenheit 451....

 

[jimzcatz]

I personally don't get the practice of using expensive glass components as mmts. Granted they are kitted that way but I believe paper or phenolic will do just fine.

 

[brianwh]

Just to clarify, the rockets are all fiberglass, I just wasn't sure if it was necessary to be careful in selecting heat-tolerant fiberglass tubes for motor mounts or if all of the Madcow/Rocketry Warehouse tubing is sufficiently heat tolerant. My tubes didn't specify motor mount use and I don't know what resin they use. Seems like others haven't had issues though.

 

[watermelonman]

All my fiberglass rockets have fiberglass mounts. I have never thought twice about it.

 

[Bat-mite]

All my fiberglass rockets have fiberglass mounts. I have never thought twice about it.

Ditto. Use JB Weld to put the retainer on, and you're good to go. My MAC Performance Radial Flyer is going to have an M motor in it with an XX phenolic MMT. No worries.

 

[patelldp]

All of the tubing provided in the hobby is sufficient for motor tube applications except for Quantum Tube from PML.

Remember that your motor tube does provide strength when a through the wall design is used. The strength of the tube, its acceptance of the epoxy you used, and its resistance to delamination may come into play on higher powered rockets (i.e. 4" rockets with 76mm motor mounts on large M's). While it's unlikely to matter, it could matter in extreme applications.

 

[Bat-mite]

Every FG kit Rocketry Warehouse sells uses an FG MMT. Lots of people happily flying them.