Greywolves. I friction fit all of my motors in min dia rockets. Here is a link to a 5" P that was friction fitted.

Bingo. You have relatively few options for motor retention in a min dia rocket. Tape is a good thing... I haven't done a 5" motor with friction fit, but I would if I was flying one in a 5" rocket.

Two things can make friction fitting easier: Thrust rings and bulkheads.

If your motor doesn't have a thrust ring (like some CTI loads designed to minimize drag), then you'll want to have something up front for the motor to push against to take the motor thrust. If it's a bulkhead, then it will withstand the deployment charge pressure too, and then all the friction fitting needs to do is keep the motor from falling out the back when the main comes out. But if there is nothing keeping the motor from moving forward other than the friction, the friction would need to withstand most of the motor thrust and all of the deployment charge pressure. Nobody does that for motors with thousands of lbs of thrust, do they?

I'm a firm believer in zipperless booster designs with a threaded rod going through the zipperless bulkhead to an eye-nut on MD projects. Problem comes when you're talking about single-use motors.

OK, next question, do they make a forward motor closure that fits CTI casings with an eye bolt? certain sizes? 38mm, 54mm.....250mm 😯

Warren, how would the rod be attached to the motor case?

Adrian, yeah no thrust, if anyone could figure out a way to avoid that, it would be you. Poor piece of tape rolled up into a little miniature cigarette, as the motor shot threw my nosecone, hehe.

Threaded forward closure in all cases. Alternative for motor cases without a threaded hole would be a bulkhead on a T-nut plus tape to prevent rear-ward loss of the motor case.

CTI doesn't have that on 38mm cases, but those I wouldn't think twice about friction fitting with masking tape

Warren

I was able to get some work done on my KestreL last week. One thing I wanted to say was that, there is nothing wrong with the stock KestreL. I'm doing some stream lining, which the average person can do to squeak out a few more feet.
After playing with the fins in Rocsim. I went with cutting .375 off the root edge of the fins. This reduced the fin span to 2.375. I roughed up the fins and body tube with 60 gritt and tacked the fins in place. The fin jig made this very easy to do. The slotted body tube will add lots of strength to the fins and is a great idea for min dia rockets.

I also got most of the electronics bay done. I cut the coupler/electronics bay down to 4.25" long. For the board I used some .063 G-10 and sandwiched some balsa wood between them leaving space for the threaded rod to pass through. I was able to get an ARTS 2, 9 volt battery and a Bee Line TX in there. For a switch I'm just going with twisted wires,

In the next couple of days I hope to get to glassing the fins on.

Tony

I got the fins attached and glassed. I made a video of the process I use.

http://www.youtube.com/watch?v=7Aqj3xcCWjU

Tony

Nice video Tony. Now if you only vacuum-bagged, you could get 6oz fabric to lay down that tight and have a much stronger layup.

Edit:
- I'm curious about the epoxy too - what brand? Post-cure?

Thanks for sharing that, Tony - I always learn something when I look over your shoulder. Some questions:

- is your "wet cat hairball" fillet the only fillet you apply? earlier on it looked like you had a small fillet, and the carbon-laced one looked like the 2nd set of fillets (but I couldn't tell for sure)

- what is that brand of epoxy again? I couldn't make it out in the video and I didn't recognize the name on the bottle

- how much sanding do you do? And I'm assuming you do wet sanding?

For my part, I tend to use more glass - but I know I also sand a tremendous amount of it away. I also forego paint, so I must save a few microns there 8)

Tony, it is awesome you are sharing all this with us, when are you going to fly it? and are you going to go with your Swamp Gas formulation when you do?

Thanks for posting that! I watched it a couple of times last night. Always cool to see how other people do it. I'll probably start on my KestreL next so that was a welcome bit of motivation.

What a great video!
question: when do you remove the tape?

you also mentioned that thinning epoxy was "controversial". What are some of the pros and cons to that?

If you chemically thin pretty much any epoxy more than 10%, you significantly reduce the cross-linking in the polymer during cure and thereby reduce the strength of the epoxy. Some manufacturers will even tell you that it reduces strength more than 75%! If I need my epoxy thinner, I warm up the two parts SEPARATELY before mixing in a hot water bath. Be careful with this as it will accelerate the cure rate and shorten pot life.

I use the PRO-SET epoxies because in addition to different hardeners, they also offer resins of different thicknesses. I prefer their 125 Resin Low Viscosity for everything and always add fillers to thicken it up to desired consistency. By using different hardeners dictates my working and set up time.

Doug

Warren. My modifications are meant for the average builder. The epoxy I use is called Raka. Greg Fannin turned me on to it years ago. In 2004 Greg went 33K at mach 2.4 with this epoxy. His fins held up fine. The paint did not.

John, Yes that cat hair ball is the only filet that I use. It is kind of hard to contain all those little carbon fiber hairs. The filets are smaller then they look in the video. A little hair ball smearing does take place..making things look bigger then they are.

Raka 900 epoxy and 631 hardner I'm not sure there are any specs on it. I just know I've had good luck with it It's a 5 - 1 ratio
[/url] http://www.raka.com/

Tony

John, was that you calling him? 😉 That is one of the best instructional videos I've ever seen. Traditionally, the elliptical fin is the most drag "free" fin, and the clipped delta just 1 % below that, the thing I really love about this hobby is that we all try different things. That was really impressive and eye-opening. So nicely done! Bret, this was really great for you, dude… as well as the rest of us! Tony does what Warren does, unlike me going full-bore on multi-layers, Tony feathers it out. Hmmm…

Warren. My modifications are meant for the average builder........ Again This has all been working for me. I don't have fins raining down on me and I feel I push my rockets pretty hard. Until I have issues I'll keep doing it this way. Tony

We can all learn from Tony. It is no exaggeration to say that he has gone higher than any 3 of us put together (I'm serious) and if it is good enough for T... it is good enough for me!

Those fins on Greg's rocket look vaguely familiar! Greg is another exceptional flyer.

Thanks for the insight, Tony - I can't wait to see what you get for altitude. I just hope it doesn't burn up during re-entry 8)