On Topic.... Motor block question

If you are using the engine hook for retention then you really *should* use the engine *block* as well. If you were to use *epoxy* to secure the hook, this may not be necessary, but not tite bond.

*however*, if you choose to use "friction fit", then you can eliminate the engine block AND hook all together. Most of my models use friction fit as I never seem to have hooks laying around when I need them...

jim

a.hornsbyiii wrote:

Thank you very much, Mr. Flis. And also keep up excellent work on those very cool kits. I can't wait till pay day as I'm most definitely going to place an order. :o)

John Hornsby

the engine block functions like a thrust ring, transferring the power to the airframe. To omit it in favor of friction fit means the friction is needed to not only prevent backward ejection of the motor (either falling out from garvity or in reaction to the ejection charge), but also to prevent the motor from flying through the inside of the airframe and coming out the top.

just something to bear in mind when considering exactly how much friction you will actually need.

if you omit the enine block, I would wrap several turns of a thin masking tape (you can get 1/8 and 1/4" at arts and crafts store, or a good stationery store), around the base of the motor, then a few turns of normal 1/2 or 3/4" tape to provide the friction.

like so:

+----------------------------- ===| ===|------------------------- MMT ===XXXXXX friction tape +----------------------+ | motor | +----------------------+ ===XXXXXX friction tape ===|------------------------- MMT ===| +-----------------------------

where the === is the 1/4" wide buildup beyond the motor tube diameter to function as a "thrust ring", and the XXXXX is the 3/4" wide (less) buildup for a tight fit in the motor tube

this way you would have both power transfer with less risk of the motor moving forward in the MT than what the friction fit would provide, and the friction fit to prevent the motor from falling out or being forced out by the ejection charge

- iz

jflis (FlisKits) wrote:

On Estes kits? Are you kidding?... No thrust ring required. A little practice on friction fit, and you'll never use any kind of thrust ring

*inside* the MMT again.... now a little extra wrap of 1/4 or 1/8 inch masking at the aft end is about the nearest I would come to a thrust ring.

If an internal MMT thrust ring is used, you limit your motor options.

I friction fit everything I have through G range... not yet had a single frictionfit-related failure.

~ Duane Phillips.

I didn't think you would need it with the way the motor hook is on the Estes kits. Now, the Custom motor hooks, those things need take rubber bands and almost need to be glued in to hold somewhat ok.

John

You don't need the hook either.

1) They don't last. 2) Replacement is a pain (extreme understatement). 3) It adds weight to the aft end, where you don't need it. 4) The forward end of the hook limits motor options. 5) Try using an AT RMS casing in a rocket with an Estes hook... the forward end scratches and gouges the delay forward closure. Yes, it can be remedied... but why bother with the hook at all? 6) Having a hook in the thust stream can ruin otherwise perfectly vertical flight. 7) The hooks do not always retain the engine.... hot hook... ejecting engine...

Need I go on?

I find that a good friction fit with masking tape works perfectly for average G and smaller motors.

~ Duane Phillips.

Duane, your post reminds me of one I saw about fin fastening

the group was going into the finer points of fin fastening, including filleting with fiberglass strips and carbon fibers mixed in the epoxy, fillets both outside the body tube and where the fin joins the motor tube, etc. etc.

someone (I think an EX flyer from an Arizona club) popped in and said he never bothers with fillets at all. He just puts a few holes in the fins in the area that is between the body tube and motor tube, and uses two-part expanding foam, saying the foam has enough adhesion, stiffness and strength to hold the fins just fine, and never had a fin come off a rocket (and he flew pretty big motors)

there was a dead silence in the thread after that

- iz :)

Duane Phillips wrote:

With the cost of the 18mm hardware and reloads have me off of the idea of that. Three reloads for 15 bucks versas 5 bucks at Wally World. Not to mention that I have this very bad habit of feeding the tree gods on a regular basis. I've already lost too many 24mm cases to them for comfort. At least I should say, to live a comfortable life with the wife. Yes that many. :o)

John

This raises the obvious question. AeroTech designed the 18mm RMS specifically to retrofit the Estes products. So why doesn't it fit?

And why do they get called errortech so often?

And why do they keep filing bankruptcy?

Inquiring minds want to know.

Jerry

"> This raises the obvious question. AeroTech designed the 18mm RMS

Absolutely!

John

Doh. Because you have to take the "Estes" motor out first. ;)

What does this have to do with motor blocks?

What does this have to do with motor blocks?

What does this have to do with motor blocks?

Inquiring minds want to know.

Cheetah

ours fit, without modifying the hook

because end users never want to blame themselves?

They've done so more than once?

I tried Jerry, anything else minds want to know?

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