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FMS P-39 Hells Bells

Old 07-22-2016, 04:58 PM
  #1  
cmdl
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Default FMS P-39 Hells Bells

The P-39 is a legendary plane. While it wasn't appreciated by American pilots, it was of much use to Soviet pilots, during WWII. Five of the 10 highest scoring Soviets aces logged the majority of their kills in P-39s . My own interest in this plane is that it has the clean lines of sleek European fighters rather than the brutish looks of American fighters. Thanks to Gearbest, I have the opportunity to experience this marvelous plane.

Arrival
The plane arrived from Gearbest with plenty of packing tape I appreciated this since it kept the package secure and only involves minimal extra effort or cost.

Unboxing
https://www.youtube.com/watch?v=UbG70MnKHNw
The plane's paint seems to sit better compared to some other companies more prevalent in the US. It gives it a more scale look rather than having it feel like a hastily painted toy.

Assembly
The assembly is where the FMS attention-to-detail really shines. First, the hardware is clearly superior to both Horizon or Hobbico. The screws used by FMS are sturdy in the heads and not "butter-headed" where the slightest touch of a phillips-head screwdriver would ruin them.
The use of pictures, rather than diagrams, in the FMS manual, is also a superior mode of instruction. Moving on, among other pros, I was thankful for the consolidated connector interface for the landing gear, flaps, and ailerons. Having the wing servo connectors not only accessible but properly identified and aligned precludes headaches for the assembler.
And it gets better. The pushrods are strong and firm, not thin and bendy as some may have experience with in the American manufacturer market. Having rudder and elevator servos aft, rather than fore in the battery compartment, is a great idea, in my opinion. This minimizes the dependability on long bendy pushrods and allows for much better control of elevator and rudder.
Perhaps the one issue I may have with the plane is the foam cowl. While a cowl integrated with the fuselage certainly has better looks, my concern is the heat dissipation. Foam, being an insulation material, would likely trap more heat around the motor and convey it back. Then again, this may not be an issue. But it is something that caught my eye and worth noting.
Among other components, I do appreciate the extra capacitance added to the speed controller to account for the lengthened battery<->ESC wire. It is good to know that FMS pays attention to electronics. More so, since I measured amp draw at full throttle to be 47A. On a 60A ESC, that is wise headroom.
I now come to my favorite part. While I was hooking-up the electronics, I noticed that the ESC and motor were not connected. I determined that the cleanest way to connect them would be by taking off the motor mount. It is then when I discovered that the motor mount firewall is actually a cylindrical ring that runs the inner perimeter of the cowl fuselage. An elegant design vastly superior to the typical cover mounting firewall with unnecessary mesh blocking central axial access. The FMS firewall allowed easy passing through of ESC and drop-in of the motor and remounting. Further, the motor has a metal motor mount, not the plastic jobs you see on Horizon and Hobbico models. Superior for heat dissipation and torqueing.
The wing mounting and horizontal-stabilizer mounting were effortless and optimal. They both used metal screws rather than unreliable plastic pins and saddles.
If there is one con I noted in this model, it is that FMS did not account for the differences in screw-pillar lengths for the flap control horns. Each flap control horn should have had at least one long screw so as to accommodate for the pillar farther from the trailing edge (where the foam is thicker).
As the assembly wrapped up, I checked CG. At recommended 65mm, the plane was very slightly nose heavy with gear retracted and quite a bit nose heavy with gear deployed. This was using a GForce 2200 mah battery.

Flight
This part of the review is best described as "not boring".

Maiden: Plane looks pristine and pretty. After reading every single page of the sage advice posted at: http://www.rcgroups.com/forums/showthread.php?t=2265815, I settle for 60% Travel Adjust on aileron and elevator and 80% on rudder this equates to reduced throw linear rates. The choice of rates is personal and subjective.
Plane set on runway, takes off beautifully, and I lose control seconds later. No response on any of the controls and she plummets down. At the crash site, I notice that the nosegear retract is completely retracted but the maingear/wing retracts did not fully retract.
Went home, tested all electronics, they functioned fine. I got the maingear retracts to completely retract but they wouldn't cease their movement seemed they registered as not having fully retracted. So they hummed endlessly while retracted. My approach was to leave all landing gear deployed and not push my luck. She's fixed up with JB Weld, and since at this point she won't look any worse, I go with my beloved packing tape. The spinner is damaged but I can use the backplate. The prop is busted so I go with a 9x9x2. This has higher pitch than the stock 6" pitch. While I'm not looking for a speed demon, it should be noted that due to higher pitch, this prop will result in higher speed than the stock prop. Full throttle pull is 31A.

Second maiden: Takeoff, she stalls just as she lifts off and cartwheels. She has a minor crack in the fuselage, and more importantly, the ESC is not working. There isn't a scratch on the ESC but it just quit.

Third maiden: I replaced the ESC with an E-flite 60A. This time, I get to finish what I started. This airframe handles wonderfully in the air. She has a high stall speed when inverted (inverted flight begins 2:10 into the video), as I found out at the end I'd say more Spitfire than P-47.

https://www.youtube.com/watch?v=ZbnfRtC1VtQ

Because she's been battered, the fuselage is a bit warped and I have a lot of right trim added just to get her to fly straight. But she flies "on rails" once trimmed. And, of course, that last part in the flight video was my fault, nothing to do with the plane.

Conclusion
An awesome plane. She'll be back up in the air, next week. Love the airframe, and I'm glad I got the chance to figure out that the ESC was causing the mishaps. Sometimes, we aren't so lucky to determine what went wrong. Finally, many thanks to my cameraman, Ben Cheung.
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Old 07-22-2016, 07:07 PM
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dahawk
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Glad you got her sorted out. Many might have thrown in the towel.

Looks like FMS is on the move again. Introducing a nice looking 1100mn WS PC-21.

I look at FMS and Freewing as being on par with quality and value.

Cheers,

Hawk
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Old 07-22-2016, 11:38 PM
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Mogg2112
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Thank you for the detailed write up and sharing photos of this beautiful plane. Sorry you had to break out the glue and tape on her so soon. A guy in my club has the exact same bird and he flies his on 4S most of the time. The thing is like a missile. When he first maidened it, he was having trouble with one of the flaps deploying consistently; sometimes it would deploy, sometimes it wouldn't. The first time it happened he nearly lost control, but he got her back down without using flaps. I can't remember what he did to fix it, but I believe he was able to sort it out.

The quality and finish on this P-39 is absolutely amazing. The panel lines are superb, the paint job is fantastic, and the plane just looks sinister and badass. I don't own any FMS birds yet myself, but they seem to be extremely good quality, probably better than most of Horizon's brands (E-flite, Parkzone, etc.) in my opinion. I don't trust retracts on an RC plane personally. Our flying field is a large parking lot covered in small gravel, and if your retracts fail to deploy, you're going to be belly landing on tiny sharp rocks and shredding a foamy to pieces. Even though flying with fixed gear looks funny on a war bird, at least I know they're not going to fail me when I need to land.
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Old 07-23-2016, 09:54 AM
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JetPlaneFlyer
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Very nice looking plane... So did you figure out what the cause of the first crash/loss of control was?

Sadly this plane is a non starter for me. I know for sure that the long retractable landing gear wouldn't last an outing on the grass field i fly from.
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Old 07-24-2016, 01:44 AM
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cmdl
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Thanks, dahawk, Mogg, JPF.

@Mogg - I share your opinion. I prefer fixed LG for the same failure reason. I realize retracts are statistically quite reliable but my observations have been skewed. The one other plane of mine that has retracts is the PZ P-47. Retracts functioned fine but one day she came down with a strut ready to fall off even though I check screws weekly. I took the retracts off and slapped the fixed LG back on.

@JPF - My best guess is a bad BEC. The dead ESC seems to be an indication of it since the BEC eventually failing would lead to a dead ESC overall. I still have the FMS ESC but I'm not sure how to diagnose it further. Visually looks fine but the most experience I have with ESCs is soldering caps under Ron van Sommeren's guidance. Given how unreliable it was, I'm not sure I'd trust it in another plane even if I did figure out exactly why it is dead.
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