AT Sumo Piston

I've read several reviews of this kit. It seems that most reviewers who have built this kit have had problems getting the piston to fit properly. Mine is pretty tight, even after rough-sanding the piston and the inside of the body tube (I found the piston was hanging up on the launch lug). Besides sanding, is there anything else that can be done to get the piston to move freely? Maybe a lubricant? I've found the same problem with AT couplers on the G-Force and Astrobee-D.

I've also heard that the ejection charge on a G motor may not be powerful enough to eject the piston and extra BP should be added. Any truth to this rumor?

I have heard the same thing about both kits as you mentioned. I was going buy either of the kits for my Level 1. Not sure if this will work, but anyone want to correct me feel free, but what about adding baby powder to the piston? I wonder if that would make it slide easier?

My brother has built many PML kits and always omits the pistons and uses Nomex plankets instead.He dose not trust them after one got jammed in the BT. I remember how tight it was ,and how much he had to sand it....seemed like a PITA.
I also wonder how high humidity days would effect the fit ?Could cause some swelling of the cardboard.
In a Quantum tube,you could spray the inside with high temp. graphite spray to help it slide.Might work as well with the Aerotech tube .


Paul T

I left the piston out of my Sumo.

I did put some cooling mesh in the motor mount tube just like other AeroTech kits.

Works fine.

I worked on this kit when it was developed. There were two reasons we used the piston-

1) We found that the .7 gram ejection charge on the "hobby" motors was not adequate.

2) The N/C is a tight fit in high temps and would bind even with the larger 1.4 gram charges found in the bigger motors.

The piston addresses both issues, and it is suggested to use the .7 gram charge in any application

I would peel a little paper off of the outside of the piston, then sand it with 400 grit and then finish with 600 grit.

Well, there you have it.

Doesn't get more authoritative than having Initiator001 and J Blatz weighing in on the "issue". :clap:

Ah shucks:blush:.

Actually, there is a story.

When we started work on Sumo, there was a CG/CP issue using the normal weight cone. We tinkered with the idea of filling it with foam, clay nose weight, gluing in lead shot, etc. There were problems with all of them - the foam either wouldn't cure properly or would get hot and melt the cone. The clay nose weight was hard to get into play and we worried that with either it or the lead in the tip that either 1) customers who didn't read instructions would leave it out, resulting in a dangerous flight or 2) the clay or epoxy/lead could come off the inside of the cone. Truth be known, I think issue one was the really sticky point. Gary had seen a lot of "user-error" issues over the years and didn't want to see Sumos chasing people....

So we came up with the gray heavy-weight nosecone, which is made with same mold but double the material. Is is a very nice N/C.

Here comes the good part of the story - we got the new prototype cone in and built a Sumo quickly. We used the usual AeroTech "labyrinth" cooling system with NO piston. Bobby Rosenfield did an awesome paintjob on it and we got it ready to fly at the NRSHA trade show held in Vegas that year. Loaded it up with the also new 29/180 RedLine reload.

So there's maybe 100 people there watching. Estes was there, they had the Dude and the then new E9. And of course, we're like, "wimpy, wimpy, wimpy" you know, check out the Sumo. H motor in this bad boy!

We lit that candle and it was great on the way up. It turned over, blew the ejection charge out of the nozzle due to the cone being a tight fit in the 100+ degree weather, and pranged way hard.

Lesson learned - test before bringing to trade show/launch .

Me and Bobby spent the next couple days working on possible solutions,and when we started to work with piston we could see that it would be the way to go. We ground tested the piston setup in back of the shop with e-matches and charge stuck thorugh the forward closure of an empty 29/40-120 reload case. I think we did 20+ tests until we were well satisfied that we wouldn't have any more issues. I can still remember the nose conme going like 50 ft in the air when were using the bigger charges. Positive ejection!!!

Those were some good times.

Of course YMMV but the theme does seem to hold. I beg of you,please never, never use a piston!! It might work from the start, but you will inevitably always have some kind of troubles. I agree with the theory,but it just dont work in practice.

jimzcatz said:

Of course YMMV but the theme does seem to hold. I beg of you,please never, never use a piston!! It might work from the start, but you will inevitably always have some kind of troubles. I agree with the theory,but it just dont work in practice.

Click to expand...

Leaving the piston out shouldn't cause a problem...it would be just like any other rocket. Use the steel mesh and it's all good

leave it the motor tube naked, no mesh or baffle, put an eye bolt in the top centering ring, nomex flame protector, fly it on an I200. Well, that's what I'd do :tongue: I still have to get a Sumo some day, or maybe and upscaled one?



Braden

For me, it's too late to use the mesh. I could leave out the piston, but tearing off the outer layer pf paper seems to have solved the problem. It slides very smoothly now. I'll find out for sure next weekend, but I think it's good to go.

I would still leave it out...and the mesh too. Never did like that stuff

If you use the mesh, but not the piston, please use a heavier charge. Even then, the NC may bind depending on temp/humidity.

Mesh does dampen the burning of the BP ejection charge. I know this. I would be very interested to see a frame by frame of the charge hitting the mesh. I would say that it lowers effective volume of the BP's "exhausT' gas by 50% or so

The Sumo, as sold, with a properly fitted piston, will eject the NC.

Myself and Bobby Rosenfield tested this hard. It worked 20+ times that I can confirm.

One thing I've found that helps pistons in cardboard tubes is to spray paint the inside. I've done this on mine and then run some 320 sand paper down it to take off the fuzzies. A coat or two of paint on the inside again an you get a smooth surface for the piston to slide along. It also seals the tube and makes it much less vulnerable to humidity. The piston doesn't need to be tight, just not wobbly in the tube.

I never had a problem of a plastic nosecone getting stuck due to temp/humidity (Balsa cones this happens all the time).

I find that in general, pistons are more trouble than they are worth. I would take the piston tube couple and use it to reinforce the aft end of body tube next time I build a sumo. I can always use more BP if I decide to fly it with a hobby load.

I think ( if you take a layer of paper off the piston tube off) I would coat it in super thin CA ,let cure then sand with 320/400. This will harden and set the fibers and make the outer piston tube very smooth ,slick and very durable.


Paul T

UPscaler said:

leave it the motor tube naked, no mesh or baffle, put an eye bolt in the top centering ring, nomex flame protector, fly it on an I200. Well, that's what I'd do :tongue: I still have to get a Sumo some day, or maybe and upscaled one?



Braden

Click to expand...

I just bought all the parts to do an upscale based off all LOC 5.38" stuff, want to have a central 38mm motor and two 29mm motors for airstarts

The problem with nomex pads is that gases can blow around the pad and the parachute can hang up inside the airframe without ever coming out. I had this happen on one flight model and two back yard ejection tests that had plenty of BP. I converted the models to pistons. I've always sanded the piston so that it slides easily. If you don't sand enough, you run the risk of trouble. Obviously, there are two camps on this subject.

Tronman said:

For me, it's too late to use the mesh. I could leave out the piston, but tearing off the outer layer pf paper seems to have solved the problem. It slides very smoothly now. I'll find out for sure next weekend, but I think it's good to go.

Click to expand...

I tore off a layer at the bottom of the piston. Doesn't look good, but slides in and out real easy.

I had two flights on my Sumo. First maiden flight was my L1 on an H250. Flight was perfect. I opted out of the piston and decided to go without the ejection mesh. Second flight same motor. Came in ballistic! Ejected the motor out the aft end of the motor tube. My friend Mat said I should have used an Aeropack retainer. Seems the motor ejected out the aft end and the nose cone remained stuck as it came in ballistic. So the next one I'm building I plan on using the piston. So yes it does happen.