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Apr 22, 2012, 09:07 AM
Vertical Unlimited
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Top Flite Mustang 60 ARF


A few months ago I was lucky enough to pick-up first place in the ElectroFlightRC.com prize draw, and scored a $500 voucher from Tower Hobbies. One of Tower's planes caught my eye: the Top Flite P-51D Mustang 60 ARF. I've never owned a warbird, and this would be a serious step into that camp! This one is definitely not a park flyer!

Despite being an ARF, the build was not straightforward, and took more than the standard "week of evenings". The plane was intended for glow power, and built in the traditional way - i.e. servos and gear all in the mid section of the plane. If I had followed the intended layout it would have needed half a pound of lead in the tail to hit the recommended CG! So some re-engineering was required, focusing on getting all gear as far aft as possible. Hobby King came through with the power system:
  • Motor: Turnigy Aerodrive SK3 - 5065-320kv
  • ESC: Turnigy dlux 120A HV Brushless Speed Control
  • Batteries: Rhino 8S (4S x2) 3700mAh 30C
  • Prop: Turnigy Ultra-light wood propeller 15x10

The specified weight was 9 -10lb (4.0 - 4.5kg) and I was shooting for a power loading of ~500W/kg (230W/lb) - that nuclear power loading I'm so fond of ("F3A Pattern" setting in EAS) that enables my planes to fly in any direction I choose at my nominated speed, including plumb vertical. This translated into a target power of 2000W. It would be grossly overpowered, but only at full throttle. Therefore it should cruise very comfortably at 1/3 - 1/2 throttle.

The plane required 8 servos, and unusually for me I didn't select a single digital. All servos were basic analog - this is not a pattern plane and was not intended to fly fast, despite all the power, so I couldn't justify digitals. I had all but the elevator servos in my spares bin, and selected a pair of Hitec HS-485BB for the elevators. Twin switching voltage regulators (with anti-backfeed diodes, of course) would supply the radio power from one of the flight packs. A cheap "Orange" FASST receiver from Hobby King completed the radio package. The spare retracts from the expired Hawk were mounted in the wings, and a comprehensive air servicing station (air feed, air pressure gauge + retract speed regulating needle valve) was mounted in the battery bay - great for access.

Final weight was a staggering 5kg (11lb). However, I wasn't concerned with power given I'd high-balled the power system. True to form, 2000W was achieved, albeit with a 16x10 prop (actual Kv turned out to be 295 rather than 320 - within the precision of the measurement). Final power loading was reduced to 400W/kg (180W/lb) - still likely to achieve unlimited vertical. When it flew, I wasn't disappointed. My buddy Kristian was there to help me out with telemetry readings and any major trim adjustments, but it flew straight and true. Those Quanum telemetry systems are simply awesome for large installations! The user is kept informed of individual cell voltages, instantaneous current draw, temperature (of a nominated heat load) and charge consumed. If I'd had this on-board my Hawk I wouldn't have lost it on maiden.
https://www.hobbyking.com/hobbyking/s...mp_mAh_V2.html

The first few take-off attempts failed, with the massive torque dragging the nose away from the runway centreline and overpowering the rudder. However, a runway change at Kristian's suggestion to put the wind on the other side of the fin made all the difference. I set 15 flaps for take-off and advanced the throttle slowly to minimize the risk of nose-over and also avoid torque pirouettes. As the throttle passed 50% she was airborne and climbing away swiftly! I immediately retracted the gear and cleaned up the wing. She flew very solidly. Not fast, but very scale-like, except for the unlimited vertical climbs with minimal speed loss. Trim was good, and she flew in smooth arcs all over the sky.

As the consumed charge passed 2500mAh I selected "gear down" and began a landing circuit. The gear failed to drop! What the!?!?!? During the build I identified that the massive air scoop would be at severe risk in the vent of a belly landing. I worked hard on the retracts to ensure they would be reliable. Heck, they were ultimately spring-airs, so any loss of air pressure would lower the gear. Why the heck was the gear hung up in the plane!?!? Figuring it was stuck, we tried pulling high Gs to knock it loose. That failed, so we tried "pilot induced turbulence", to no avail. With charge being rapidly consumed it was realised that a belly landing was inevitable. Bye bye scoop! She came in smooth and straight, with me desperately scanning the runway for a soft patch. I spotted the sand fill I deposited in a depression a week before and dropped her in. Damage was very minor and easily repaired the following week, but I was really angry to have scarred the bird on its first flight. Kristian's young son learned a few new words that day - not good . Inspection back in the pits revealed I'd neglected to Locktite ONE nut - the nut that secures the retract valve to its mount. Instead of the barrel sliding in/out of the valve, the whole valve body was moving! My bad - I suck. The nut has since been lock-tited in place.

I've since flown it and managed to get the undercarriage working perfectly. The flaps are very effective and really steepen the glide slope plus keep the landing speed manageable. The stall is slow to come on, but it is NASTY! Just like the full-size. The left wing plunges and it takes a bit of height to recover. This is only a problem during landing flare - don't get too slow! I consider myself a capable pilot, but I'm yet to grease this one onto the deck. I better get it right soon!

Anyhow, what an awesome plane! Nice work Top Flite and Hobby King - 5kg electric plane with unlimited vertical but cheaper than glow - who knew? My sincerest thanks to the generosity of Electro Flight RC (http://www.electroflightrc.com). Thanks also to Kristian for putting up with my maiden flight jitters and consequent outburst, and both Kristian and my other buddy Terry Sears for helping me to ship the plane at reasonable cost.
Last edited by Straight Up; Apr 22, 2012 at 09:35 AM.
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Apr 22, 2012, 10:37 AM
You can't take the sky from me
copperbricks's Avatar
Looks very nice. Can't say I'd use an Orangerx though :P
Apr 22, 2012, 08:55 PM
Registered User
Well done mate, I will see it soon.
Apr 22, 2012, 09:50 PM
Got the Slickness
gabrielisrael's Avatar
Did this plane come with a battery hatch?
Apr 23, 2012, 01:06 AM
Vertical Unlimited
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Quote:
Originally Posted by gabrielisrael
Did this plane come with a battery hatch?
Strangely YES! The hatch is not mentioned in the instructions, but it is installed. Inspection from inside (via the wing saddle) revealed it - I could see the structure. It took some very careful work to locate it and cut it free. The top sheeting must be carefully cut through at the right points.
Apr 23, 2012, 01:07 AM
Vertical Unlimited
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Quote:
Originally Posted by copperbricks
Looks very nice. Can't say I'd use an Orangerx though :P
Yeah, I've had concerns about crashing a $500 plane due to a cheap receiver, but I've got 6 Orange receivers and they've all worked perfectly. Let's hope they stay good!
Apr 25, 2012, 01:43 AM
Registered User
Looks great man! I built mine up from the kit armed with a .75 glow (took more than a week of evenings!). I'm strongly considering making it electric before I maiden though. I've never flown glow, but have 8 other electrics. Just much more familiar, ya know?
Apr 25, 2012, 01:50 AM
Registered User
Is it possible that you could show some pics of how the motor is mounted in there? That would be awesome.

I think I want to make the swap using your parts list (maybe a smaller ESC. That motor's stats says it draws 70A tops. Why did you get such a huge ESC?)
Apr 25, 2012, 01:52 AM
Registered User
One more question. What did you use for UBEC?
Apr 25, 2012, 09:00 AM
Got the Slickness
gabrielisrael's Avatar
Quote:
Originally Posted by zakkhoyt
Looks great man! I built mine up from the kit armed with a .75 glow (took more than a week of evenings!). I'm strongly considering making it electric before I maiden though. I've never flown glow, but have 8 other electrics. Just much more familiar, ya know?
Go electric! Yours came with the battery hatch as well I take it?
Apr 25, 2012, 01:31 PM
Registered User
No it didnt' but I can make one easily enough. I haven't covered mine yet, but am about to.
Apr 26, 2012, 06:09 PM
Vertical Unlimited
Straight Up's Avatar
Thread OP
Quote:
Originally Posted by zakkhoyt
Is it possible that you could show some pics of how the motor is mounted in there? That would be awesome.

I think I want to make the swap using your parts list (maybe a smaller ESC. That motor's stats says it draws 70A tops. Why did you get such a huge ESC?)
Thanks for your interest! I'll pop the cowl off and show how I mounted the motor this weekend. It was quite simple - just a ply box to set the motor the correct distance from the firewall. I opted for a relatively large 5mm clearance between the spinner and nosering to ensure plenty of room for cooling air to find the motor.

As for the ESC, good question! I like to "highball" my ESCs to ensure the current is not near the rated limit. Running a motor beyond its spec is OK (within reason), but push an ESC beyond its spec and the FETs let the magic smoke out quite quickly. Depends on cooling, of course (same for motors) but ESCs are much more sensitive. Also, I needed an HV ESC (rated beyond 6S), and I really like the new Turnigy DLUX ESCs with their heatsink cases. The only smaller DLUX HV ESC is the 80A, and costs almost as much as the 120A ESC. Weight was no major concern, so I ordered the big one.
Last edited by Straight Up; Jun 10, 2012 at 06:03 PM.
Apr 26, 2012, 06:13 PM
Vertical Unlimited
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Quote:
Originally Posted by zakkhoyt
One more question. What did you use for UBEC?
I used TWO of these:
https://www.hobbyking.com/hobbyking/s...Reduction.html
The 2 x 4S batteries require a Y-lead to achieve 8S. I tapped ONE of the packs to supply power to the two UBECs. They access different ports on the receiver, to reduce the risk if a receiver plug should lose contact. This arrangement requires a diode on each BEC output to prevent the BECs backfeeding each other. No biggie - diodes are cheap and very easy to install.
Apr 30, 2012, 09:52 AM
Vertical Unlimited
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Videos of the maiden flight. Thanks Kristian!
Take-off:
Top Flite Mustang 60 electrified - take-off.avi (0 min 19 sec)


Belly landing:
Top Flite Mustang 60 electrified - belly landing.avi (0 min 14 sec)

The beeping is my telemetry system warning me the flight battery is low on charge.
May 09, 2012, 06:05 PM
Vertical Unlimited
Straight Up's Avatar
Thread OP

Another flight, and another emergency landing!


I've managed to get the retracts working as planned, but my next few landings were poor - too much elevator throw, leading to poor flaring, followed by pancaking. For this next flight I'd reduced the elevator throw considerably, but it seems an earlier knock to the port main retract resulted in it jamming in the up position. What a dilemma! Another belly landing and more damage to the radiator scoop, or a tricky one wheel landing? I went the latter, and did my best landing ever with this bird. Take-off was pretty solid, demonstrating the mega power system I've got on board. Movies from a friend's iPhone...

Mustang take-off 2.MOV (0 min 19 sec)


Mustang lands on one mains wheel.MOV (0 min 37 sec)
Last edited by Straight Up; May 10, 2012 at 05:58 AM. Reason: Videos finally uploaded!


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