Estes Phoenix mmt

[madmax]

Quick question here. Why is the mmt in the Estes Phoenix mounted so far inside the tube? Does it have something to do with the cg or is it purely for looks? If I can, I would like to mount it a little farther back. Any help would be appreciated.
Thanks

Oh yeah... FIRST ACTUAL POST! WOOHOO!

 

[loopy]

It's to help stability. Keeps the CG farther forward.

 

[madmax]

Would it matter if I moved it back a little bit so I dont fry the inside of the body tube with the exhaust. I did it on rocksim and it still says that it is stable.

 

[Fore Check]

If you prefer to mount it further to the rear, here's what I'd do:

Assemble the motor mount, and then insert it into the airframe tube *without glue* as if you were building it according to the instructions in the kit. You know, dry fit it. Then, when the model is complete (other than gluing in your motor mount), insert an engine and the chute and some wadding as if you were getting ready to launch it.

Then lay the rocket on it's side, and find the balance point (or the CG.) Make a small, erasable mark at that point.

Now, pull your dry fit motor mount backwards into the position you prefer. Then add some modelling clay or some other ballast to the nose cone to put the CG back in its original place.



I will note, though, that keeping the motor mount in the location that is given in the instructions does make for an interesting sound when the rocket is launched - noticably different than a standard "D" engine sound. Pretty cool! If you don't care about that as much as having your engine further back, it shouldn't be too hard to accomplish.

Good luck!

 

[BlueNinja]

Or you could get a length of coupler tube and replace it when it gets too cruddy.

 

[Habu]

Blue,
Now that's a great idea!
I'm just working on a Phoenix with some modifications
and was thinking of how to protect that 1½" of BT
that will be exposed to the exhaust.

Fore Check,
Having never seen one launched I don't know about the
sound but I'm looking forward to it.
I also have a package of the AT F21's just for this model

 

[firemanup]

Another option similar to Blue's that I used was just painting the inside of the body tube there at the rear with epoxy, added strength and has held up fine.. i just wipe it out with a papertowel after each flight.

 

[jetra2]

I have, on some rockets, taken a piece of coupler tubing or normal tubing cut to fit, smeared epoxy on the inside of the MMT aft of the lower centering ring, and pushed that piece of tubing so it is touching the CR. This is really really helpful when you are flying composite motors, especially White Lighning, in a MMT up inside the tube.

If you ever feel like replacing the "shield," just sand away the black crud and cut another piece of tubing to fit inside the original shield and epoxy it right in there!

Jason

 

[wyldbill]

TT has some Nomex paper that could be used in this application as well...

 

[Steward]

Having built and flown several stock Phoenix models... I've never had one burn or damaged at the rear...

 

[madmax]

Steward, have you ever flown your phoenix with composite motors? That is my plan and is the pretty much the basis of my earlier question.

Thanks to all who answered.

 

[hokkyokusei]

Flown mine on composites lots of times, more so than BP. I can recomend the inserted coupler method, IMHO it is needed, and certainly works.

Though, if doing it today I think I would try wyldbill's nomex paper idea.

 

[Stymye]

the coupler insert is also important to help keep those rear fins intact during landings

 

[hokkyokusei]

Mine still come off from time to time. But it's usually the tube rather than the fin that gives first. Consequently the fins now have huge filleted "tabs" that make gluing back on a snap.

Actually it's been a while since I lost a fin. I guess the entire rear end is now a CA and paper laminate!

Really, this is a cool kit. I can't stress enough how much fun it is on composites!

 

[wwattles]

Foil tape is also available at your local hardware warehouse store. Put a full coating of it around the inside of the exhaust area, and replace it as necessary. Very effective, and fairly cheap.

Wipes clean with a baby wipe after each flight.

WW

 

[madmax]

wwattles: does that foil tape add a lot of rear weight or is it lighter than the coupler method.

Another question for ya, during the build process should I beef anything up to withstand the higher force of composites, perhaps the centering rings?

thanks

 

[wwattles]

The foil doesn't add as much weight as the coupler, but it doesn't provide the strength, either. The number 1 complaint of Phoenix owners is the tendency to mess up those rear fins, and strengthening would be advantageous, since the stock tubing is rather soft.

As for strengthening the rest of the bird, it's up to you. You've got 2.6 inches to play with, and it's really a fairly forgiving model. I laminated my fins with card stock and used thick epoxy fillets, as well as installing a full-length coupler for higher power engines (got a 29mm mount in there now). The stock cardboard centering rings work well if you just want to fly on the recommended D motors, but if you want to go to more power you might consider going with some light plywood rings.

WW

 

[Donaldsrockets]

I built mine stock and I've never had a fin come off. I did have one peel away from the body tube slightly but some CA took care of that rather quickly.

My last flight ended with a parachute failure. Guess what???
NO DAMAGE!!!

I haven't flown a composite motor in mine but I think that if I built another one, I would make a few changes so that I would be able to do so such as trimming the end of the motor clip back to allow proper fitting of a 24mm RMS casing.

I'm sure it'd be a killer on E18W and F24W reloads

 

[loopy]

I replaced the stock balsa fins with basswood, coated the stock centering rings with epoxy, 24mm LOC motor tube, and built with CA and 30 minutes epoxy fillets. Planning on an E-18 for the first flight, but haven't had a chance to do that yet. I need to check stability before hand - might need to add a little more weight to the nose. I also painted the inside of the body tube aft of the motor mount with epoxy to help resist the heat. I replace the stock recovery system with kevlar epoxied around the motor tube behind the upper CR, then fed through the CR and up out the top of the tube, then attaching a 4 foot piece of elastic and a nylon 'chute. It will also have a nomex heat shield to protect the nylon chute.

Loopy

 

[JeromeK]

I use 1/4oz to 1/2oz fiberglass cloth and finishing resin inside the tube. this strengthens the lower fin can quite a bit! I also drill a few small holes on the tube where the fins mount and use epoxy. Shove some epoxy in the hole then glue the fin base to the tube all with epoxy. This anchors the fins in and makes it fairly bulletproof on impact.

I launch in a harsh environment at a clay dry lakebed in Southern California. The lakebed eats fins!! This seems to help.


Good Luck!


Jerome