Oh, I probably didn't make myself clear: The removable cluster mount is a BT-60 size tube
that has three BT-20 size engine tubes with an engine clip for each. It's the BT-60 size tube
that has to be friction fitted inside the Saturn's engine tube for flight. Maybe later this evening I'll try to scan the prep page from the Centuri Saturn - V's instructions so you can
get a clearer picture.

As for the two flights flown already, I made sure the cluster mount was very snug, but not
too tight. It held perfectly each time. Removing the cluster mount is a breeze (just use a
needle nose pliers and pull the sucker out). If you think using the friction fitting is going out
on a limb for this model, check out my You Tube video of the second flight; I flew this bird
without the clear slipons on that flight. Link below:

http://www.youtube.com/watch?v=0uTm-rbvQJk

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Dave, NAR # 21853 SR.

All you guys getting wussy here about friction fitting need to man up It requires making some effort and learning new skills to get good at it, but it ain't that hard. It's part of the sport, so step up to the plate and master it instead of joining this pity party.

In the pic you see three taped-together motor pairs friction fit into the sustainer. They're in so tight you can't get them out without inserting a dowel and hammering them out from the top. The motor tubes are 0.013" walled BT-20's. And they're holdin up just fine. Furthermore, when I twisted the motors in, I had to avoid breaking the cellophane tape joining them. It requires the right touch, but it's not brain surgery.

You learn how to wrap the tape to avoid it curling on the edges. You learn how to hold the rocket without breaking it. If you want to fly more than single engined 3FNCs all the time, you will work your way thru this and master it. Doug



.

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YORF member #11

I have successfully used FF in motors from 6mm to 38mm, and probably so has everyone who has responded to this thread. Yes, it can be done without drama or trauma. It's just not one of my preferred methods of motor retention. Fortunately, I usually don't need it, because I don't build that many minimum diameter models. Almost all of my clusters use positive motor retention, and so do almost all of my multi-stagers (gap-staging makes that possible). Your clustered two stager looks interesting, but I haven't had any occasion to build anything like that yet.

Everyone knows how to friction-fit a motor into its mount. It's one of the first things you learn in model rocketry. That doesn't mean it's popular.

Mark \\.

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SAM # 0011

Doug is right; using the friction fitting is really a skill and an art. Some of my favorite scale
models use friction fitting engine mountings for flight (Centuri Saturn - V & 1/45 scale Apollo
Little Joe - II [3 engine cluster], PDRocketry Gemini Titan - III [2 engine cluster] and my
Estes Gauchito [4 engine cluster] and my clone of Estes Thor Agena - B [single engine]).

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Dave, NAR # 21853 SR.

LOL! I guess you told us Doug! I'll have to give it a try sometime.

With my luck I'll try it at a club launch, the engine will spit out, the rocket will sit on the pad, and everyone will get a good laugh!

Hey that's an awful nice looking bird in the pic!

If you mean that we are all any good at doing it and can reliably do it without burping motors and losing rockets to ballistic recovery, then no, I don't know how to do it.




Again, no. the price of learning this particular trick without benefit of having someone knowledgeable to show me "hands-on" style simply by trial and error (and crash and burn) is just too high. I don't have money to throw at this particular problem, so I'm happy sticking to what works for me. You want call me a wuss, I suppose I can live with that.

I meant that we have all learned about it and have seen diagrams of how to do it, and all (or maybe most) of us have been able to successfully retain a motor in its tube with this method at least once. (I forgot to add: almost all of my cardstock rockets also retain the motor with friction.) When I use this method, it usually goes without a hitch. But I've also torqued enough airframes while trying to get the motor in or out to lead me to the conclusion that I really don't like this method all that much.

I've never had a friction-fit motor get kicked out at ejection, John. Usually, it's the opposite problem - I can't get the thing out after the flight! In one occasion, on a competition model, no less, I had to take my hobby knife and "carve" out the 13mm motor case, bit by bit, from the inside out. And every last bit of it, even the last quarter of an inch, had to be carved out; even after 90% of it was out, I still couldn't pull the remaining bit out. It was hardly worth the effort, too - by the time I was done, the rocket was thoroughly tweaked. I just salvaged the nose cone, the fins and the Kevlar, and will eventually use them on another rocket.

Mark \\.

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SAM # 0011

Friction fitting is absolutely necessary on scale models where the motor clip has no business being there. I have added clips on non scale models where it doesn't matter for convenience sake.

I have never had a friction fit motor pop out. In the old days, while trying to pull out a motor after a flight, I did tweak my share of body tubes. No more. I use a dowel and push the engine back out from the front of the rocket. Since doing this, I have NEVER damaged the rocket while removing the engine.

The advice to tape the inboard end of the engine is also great. I love the idea of taping without having the tape go over itself, and when necessary to layer it, do it in concentric rings.

It is very important on friction fitted models to make sure the nose cone is not too tight and the chute or streamer is packed small enough to slide out easily.

Most of the stuff I built as a kid had engine hooks. When I got back into the hobby a few years ago, one of the first kits I built was an Arapahoe-E, which has a boat tail with no hook. While mods can be made to boat-tail designs to provide positive motor retention, I decided to build it stock to keep the clean lines, and to force myself to learn friction fit. I was pretty proud of the build, and thus a bit leery about friction fit, but decided I would just read up on it a bit and figure it out. It has been launched on C11, D9, D12, and E9 motors, all friction fit. I've since built a number of birds using friction fit, and have learned how to make it work well. While once I really wasn't keen on the idea, I'm now completely comfortable with it. For certain model types, I prefer it (could you imagine a Hydra VII with 7 engine hooks?). It has been a challenge to learn, and now I feel I've expanded my design repertoire, no longer limiting myself to designs that can use a hook (or some other form of PMR). Some kits that come with a hook I build without, and some that don't, I add a hook; it all depends on what I'm trying to achieve with that build, and what types of motors I plan to use.

I tend to tape the aft end of the motor, so that I'm not fighting the friction all the way in; if it gets too tight, I just leave it hang out a bit. The downside is that the forward tape edge can rollover. I'll have to try it the other way next time. Another learning opportunity

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Paul
If we weren't all crazy, we would go insane - Jimmy Buffett
NAR #87246 www.wooshrocketry.org

I don't know that there is really all that much to learn for it; just put tape on, and push the motor in. If it is too tight, pull the motor out and peel off a little bit of the tape. If it is too loose, add a little more tape. Repeat until you are satisfied with the fit. As I said, I haven't built much that absolutely required it, but when I did, it usually worked out fine. In designs that would allow other options, I have always chosen to install some form of PMR instead, though. I have never gone with friction-fitting when other options were available.

BTW, I don't know about the Hydra VII, but I have a 7 motor cluster mount that retains all of the motors with PMR via just three thin pieces of all-thread, three hex nuts, and three washers.

I don't think anyone should, or even could, totally eliminate friction retention of the motor as a technique from their repertoire, since, as you point out, there are many designs where it is pretty much mandatory. Implementing it is not, pardon the pun, rocket science, though. If I were to ever have a motor that needed several layers of tape to achieve a good, firm fit into the mount, I would construct an adapter for it first. I never seem to need to put any more than a single layer of tape onto the motor to give it a good solid fit into the mount; more often, all I need is a half-wrap or a 2/3rds wrap at most. Nothing more elaborate than that. The only extra thing that you need to do is to burnish the tape down with your thumb to give it good adhesion and insure that it doesn't roll when you insert it into the mount. If you still get some rolling, it usually means that you put on too much tape.

Who builds rockets with motor mounts that are so oversized for the intended motors that they have to use multiple layers of tape to give the motor a good solid fit? That just sounds like poor construction to me.

Mark \\.

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SAM # 0011