Friction fit "the correct way?"

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Buckeye

Buckeye

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I searched the forum several times over about friction fitting 38 and 54mm motors. The are many responses like, "If done correctly, friction fitting works just fine." There is very little elaboration on the "correct" method, however. I get the idea about wrapping tape around the end closure and motor tube. I am not so sure about the tape that gets jammed into the motor tube. Anyone care to explain in more detail and with pics?

Thanks!
 
The tape that gets jammed into the motor tube is your friction fit, the tape around the tube and rear closure is not. You want to wrap the tape thinner around the top end of the motor, and progressively thicker towards the back to ease installation. It sometimes takes a bit of futzing around to get it just right, be patient.
 
Thin to thick - good info. Spiral pattern or constant wrap? (Reminds me of re-gripping golf clubs.) Twist in or push straight it? What determines when it is "just right?" Should I be able to pull it back out by hand or should a hammer and stick be required? I know these are all personal preferences/experiences, but some guidelines would be helpful.

My next build will be fiberglass min diameter where I will be comfortable with hardcore friction fit. Cardboard MMTs are more susceptible to damage, so I never seriously tried it.
 
The LOC Precision MMA-1 Adapter has a pretty good visual explanation of friction fit.

1167754839719825731376.jpeg
 
After the flight pull the motor as soon as you pick it up and it is still hot. Usually the glue on the tape is soft and comes out easier.
I am old school and friction fit most of the time.

Mark
 
It should be somewhere between almost impossible and impossible to remove by hand. When I friction fit, a hammer, stick, and access to the front end of the motor mount is required to remove it.
 
The last time I did a launch with a friction fit 29mm SU motor, when I recovered the rocket the motor was sticking halfway out of the motor tube. Disaster narrowly avoided.
 
grouch said:
It only has to be tighter than the fit of the nosecone.
Click to expand...

Not necessarily. I've seen rockets with a fairly tight (certainly tighter than the nosecone) friction fit kick the casing and deploy the chutes. Certainly better than not deploying at all, but I like to get my casings back, personally.
 
Hopefully this won't offend any die hard friction fitters, but with so many options to retain the motor, why use such a dicey method to hold in that expensive motor casing??

In Bunnell last year I saw a group of 12 guys going for their L1 certs. They each had build a rocket (LOC graduators I think), and were sharing three motor casings. And they were friction fitting their motors. By about the 6th launch, all three casings had been lost. So easy to have been avoided.

I realize that Aeropack's aren't cheap, but some screws and metal S clips from the hardware store can be made to work for pennies...... and it sure keeps the motor from being covered in sticky tape goo after each launch.
 
For minimum diameter rockets you can use these:

https://aeropack.net/min_dia_retainers.asp

or if you want to use motor ejection ( NOT RECOMMENDED!!!!!!!!!!!!!!) use a half inch aircraft plywood bulk head and a length of all thread the right diameter into a threaded forward closure, just drill several holes through the bulkhead, so the gases can pass through as if you are making a baffle.
 
gldknght said:
or if you want to use motor ejection ( NOT RECOMMENDED!!!!!!!!!!!!!!) use a half inch aircraft plywood bulk head and a length of all thread the right diameter into a threaded forward closure, just drill several holes through the bulkhead, so the gases can pass through as if you are making a baffle.
Click to expand...

How do you do motor ejection with a tapped forward closure? LOL!

I perfer using a bit of blue masking tape around the motor. But tape is not always the best idea. It can melt and leave you with a sticky gooey mess.

A way that had been taught to me before was that you can paint on some thin coats of SUPERGLUE to the inside of your motor mount tube. let dry. add another coat. let dry. add another coat. let dry. Keep adding coats of superglue untill the motor is tough to insert and remove.
Just be cautious of how big of a charge you're blowing, and you should be fine.
 
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I've done enough friction fitting over the years. It is tough to do with a fiberglass motor mount since it has not give and usually just pushed the tape off.

With cardboard, I use tape in the last few inches closest to the nozzle. Usually as tight as I can get it without damaging hte rocket. Pliers may be needed to remove it. Adding a trust ring of tape to the casing may geive you more of the motor sticking out to grab to extract the casing after - also protect the case if pliers are used.

That said, I usually use one of the many other retaining methods - clips or circular retainers that bolt centering ring with T-nut imbedded is my choice. Got a couple Aeropacks to try as well for rockets that do not have room on the centering rings (near min diameter).
 
+1
grouch said:
It only has to be tighter than the fit of the nosecone.
Click to expand...

I friction fit my LOC IV all the time. I spiral wrap blue tape from the top down on the motor casing. It is tight enough that I have to spin it in but can still get it out using my aft closure wrench to spin it and pull. Just make sure it is tight enough to stay in when the shock cord hits.
 
gldknght said:
I'm fairly certain I've seen tapped forward closures that had cut outs for the ejection gases to pass through.
Click to expand...

Really? Ive never seen that. Not saying your wrong. Infact, I want you to be right. Show me where I can get that because I want one! lol. But I dont think anybody commercially produces that. It would be custom. and a strange custom at that. Generally speaking, from what ive seen, tapped forward closures are plugged. Ive never seen a forward closure that you can screw an eyebolt into that you can also fill with black powder and do motor eject with.
Also dont see any on the web.

I presume youre confusing this with Giant Leap Rocketry's hard point anchor system. This allows for SHOCK CORD ATTACHMENT with an eyebolt and it has holes for ejection charge gasses to pass through. Though this has nothing to do with motor retention.

Although, now youve got me thinking! Just use a metal hose clamp to attach the shock cord to the forward closure itself, around the neck, below the "bowl" if you will. That way, even if it does blow out of the back, it will all still be leashed together by that cord.

OR... you could use the superglue method to create the friction inside the motor mount tube.
 
Last edited:
Frozenferrari said:
Really? Ive never seen that. Not saying your wrong. Infact, I want you to be right. Show me where I can get that because I want one! lol. But I dont think anybody commercially produces that. It would be custom. and a strange custom at that. Generally speaking, from what ive seen, tapped forward closures are plugged. Ive never seen a forward closure that you can screw an eyebolt into that you can also fill with black powder and do motor eject with.
Also dont see any on the web.

I presume youre confusing this with Giant Leap Rocketry's hard point anchor system. This allows for SHOCK CORD ATTACHMENT with an eyebolt and it has holes for ejection charge gasses to pass through. Though this has nothing to do with motor retention.

Although, now youve got me thinking! Just use a metal hose clamp to attach the shock cord to the forward closure itself, around the neck, below the "bowl" if you will. That way, even if it does blow out of the back, it will all still be leashed together by that cord.

OR... you could use the superglue method to create the friction inside the motor mount tube.
Click to expand...

Ok, now I have to go figure out where I saw what I think I saw, and what I'm remembering if it's not what I think I saw. Puty Tat, maybe.
 
Spiral wrap right at the aft end of the motor. Twist the motor in and you should not be able to pull it out. After flight use a wood dowel to push it out from the top. If you have a bulkhead and cant use the dowel method, take a piece of steel plate maybe 1/4" thick 4" x 10" or so, put a hole in the center, insert about a foot of 3/8" allthread with a nut under the plate. Remove aft closure. Put allthread through closure and then put a piece of wood dowel a couple inches long with a 3/8 hole drilled doen the ceter over the allthread. Screw the closure back on and stand with one foot on each side of the plate. Start pulling up on the rocket body until the casing comes out. Hope that makes sense cause it works great.
 
Buckeye said:
Thin to thick - good info. Spiral pattern or constant wrap? (Reminds me of re-gripping golf clubs.) Twist in or push straight it? What determines when it is "just right?" Should I be able to pull it back out by hand or should a hammer and stick be required? I know these are all personal preferences/experiences, but some guidelines would be helpful.

My next build will be fiberglass min diameter where I will be comfortable with hardcore friction fit. Cardboard MMTs are more susceptible to damage, so I never seriously tried it.
Click to expand...

I use a spiral with the tape..Canted on the motor so that when you insert it in the tube you then twist it clockwise as in tightening a screw(righty-tighty)..Then when removing you pull and twist to the left(lefty-loosey)..In essence you make 'threads' with the tape and then you 'screw' the motor in, and un-screw it out...If done properly it should be near impossible to pull the motor straight out..

Yeah, in a f/g tube you go real hardcore on friction fitting..
 
cjl said:
It should be somewhere between almost impossible and impossible to remove by hand. When I friction fit, a hammer, stick, and access to the front end of the motor mount is required to remove it.
Click to expand...

Thats WAY overboard dude. It doesn't have to be that tight!!
 
I’ve flown with one club where the RSOs are very leery of allowing friction fit motors.

At least with mid/high power rockets.

They are a bit more willing to allow FFM flights if the rocket is not using motor deployment.
 
Wait a minute, you are supposed to RE-USE the casings? Dang, I have just been tossing them in the dumpster after each flight.

cjl said:
... but I like to get my casings back, personally.
Click to expand...
 
Seriously though, with few exceptions (small BP motors in small models), I am not a FF'er. I have lost enough cases without them falling out of the motor mount tube. I figure out some way of providing positive retention on anything 29mm and above.
 
Frozenferrari said:
A way that had been taught to me before was that you can paint on some thin coats of SUPERGLUE to the inside of your motor mount tube. let dry. add another coat. let dry. add another coat. let dry. Keep adding coats of superglue untill the motor is tough to insert and remove.
Just be cautious of how big of a charge you're blowing, and you should be fine.
Click to expand...
This is not reliable. I tried it with a 24mm casing on a boattailed rocket. I had the motor tube so tight that I literally had to grab the grab the rocket by the boattail and push it down on the table to push the motor in. It was so tight that I was worried I might not even get it out. Lost the casing on it's first flight. The nose and chute were fairly loose so that wasnt it. I figure that heat expansion had something to do with it. You really want the little bit of squish and grippyness that masking tape has.
 
for small BP and SU motors you can use the lariat loop method.

Ive had someone's 29 motor kick out, whizzed past me, hit 1 car on the side behind me, ricocheted across and hit the other car next to it.
It was a 3 cluster setup where the one motor lagged behind coming up to pressure. All were friction fit.
 
Last edited:
For minimum diameter (granted I haven't done anything bigger than 29mm) but I just imbed an allthread into one of the fin fillets. Then I just use a nut and washer to keep the motor safe. With a 29mm a 6-32 works great. for 38mm I would use an 8-32 or 10-32.
 
gldknght said:
Ok, now I have to go figure out where I saw what I think I saw, and what I'm remembering if it's not what I think I saw. Puty Tat, maybe.
Click to expand...

For Aerotech 38mm, when you use the spacer system, they have an anchor retaining ring threaded for retention that replaces the forward ring in the spacer system It has 3 holes that allow gas to pass through which permits motor ejection to be used. However, to use it, you must use at least one spacer. Aeropack has a matching 38 mm min dia retainer with holes in it to allow the gas to pass through as well, so you can do true minimum diameter with motor eject and threaded retention in 38 mm.

David
 

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