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-   -   Help with removing and matching motors on a Cessna 337 (https://www.wattflyer.com/forums/showthread.php?t=74018)

Porcia83 07-03-2014 09:24 PM

Help with removing and matching motors on a Cessna 337
Looking for some possible help, and of course some suggestions.

Picked up a Cessna 337 recently and maidened it a few weeks ago. Was super nervous as usual, and did all of my pre-flight/range checks, got my 3 rate settings down on my DX8, and finally said to hell with it, letís go. Off it went and took most of the runway to get off the ground. Once it did I eased the throttle back a touch as well as the elevator. Big mistake. It took a dive immediately, which resulted in me yanking completely back and up it went. After confirming no leakage in the pants, gulpÖI got up a couple hundred feet to level off and trim it out. As I came across the field I felt a sudden loss of power, but still heard a prop going. Turns out I lost the rear motor. Its heavy overall, and no way this can go with one motor. It was harrowing trying to land what felt like a rock, and with the wind too! It came down hard, bounced a few times, and finally came to a rest. Overall plane was o/k, cracked a piece of plastic from the front landing gear, and easy fix. Got a constant studder from the rear motor, checked all connections, they were fine. Tried another two motors, they worked fine, so itís the motor, even though it doesnít look or smell like it fried.

I had two Turnigy aerodrive xp, 3536 -1100 kv motor on both the front and back. Wasnít able to buy new ones, so I went with the closest possible, D3536/9 910KV. I replaced the rear motor fine, then went to the front one, and now Iím stumped. See pic:

How the heck do I get this motor off of the stand-off bolts? They go behind the bulkhead and are attached not with blind nuts (that would have made sense), but with bolts. They are impossible to get to, so they just turn. The builder must have put this one, then glued the box. I canít get a screwdriver in to get the motor off. Any suggestions?

Second question. As a backup plan, I was thinking of leaving this motor on. Would that work? The front motor would have about 200kv less than the rear, but I still run the same props, or I guess change it up if I had too. Otherwise, I would guess my solution is to cut the bolts off and put a new motor mount on.
Your thoughts are appreciated!

Porcia83 07-03-2014 09:30 PM

2 Attachment(s)

fhhuber 07-03-2014 10:33 PM

Use pliers to loosen the nuts directly behind the X mounts and then you can turn the screws with the appropriate screwdriver.
A "nut driver (screwdriver that has a socket for a nut on the end) would let you hold the nuts inside the fuselage.

A properly set up model C337 SHOULD fly on one motor...
Might have a CG issue. One of many possible reasons it doesn't hold altitude (and should be able to climb) on just one working motor.

Close to 80 inch span? Looks a lot like the Nitroplanes big C337. If so the motors are too small.

Porcia83 07-04-2014 02:34 AM

I'll give that a shot, thanks.

I wish is was an 80 incher! Don't know who the maker of this one was, it's about 50 inches. And ya, I need to work on the CG. This was made for two small nitro engines, so it's hard to get CG right, actually had to use weights in the front.

Thanks for the help!

hayofstacks 07-04-2014 03:39 AM

Throw a huge motor up front and get rid of the weights. might as well have it work for ya.

Porcia83 07-04-2014 12:08 PM

That is probably the best thing to do. I brought it in to a LHS and we gave it the once over. No way to loosen those bolts without taking them completely out, and once they are out, that's it. whoever built this did it in such a way that it's a once shot deal. I can always put a different motor mount on there. And more power is always good! :)

fhhuber 07-04-2014 04:04 PM

I went a 3rd route for CG when I had the big 80 inch C337. Snce it wanted to turn out tailheavy with the servo for elevator (rudders were not functional) way back in a vertical stab.... I moved the servo and used Pull-pull. It was a bit "interresting" to set up but added almost no weight and fixed the CG.

Similarly the rudder servos for the plane in my avatar were supposed to be back almost under the horizontal stab. I moved them to just forward of the wing TE.

Needing nose weight would give different issues with the airplane's performance than what was described... The description sounded nose-heavy. The plane should balance like a classic ".40 trainer" and should just about fly like one too. Wing design and general proportions are the same.

Porcia83 07-04-2014 04:21 PM

80" would be sweet!

It was nose heavy for sure, and it didn't help that I didn't center the elevator and it was down way to much. Classic error of not checking everything at least twice, and then again once at the field ready to fly.

hayofstacks 07-04-2014 11:54 PM

Going to a lower kv motor up front will get you the exact same effect as pitching down the front motor. the rear motor will spin faster, and the front motor will spin slower. i still really recommend pitching.the rear motor up a size or two. you wouldn't beleive the performance differance when i did it on my bipe, but the motors were only.about 12" apart and i had no fuse to.get in the way.

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