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Old Dec 25, 2010, 01:00 PM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
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FlyFly P51D mods

I'm usually into edf jets, but I could not resist getting the Flyfly P51D because it just looks so good. The P51 is my favourite propellered plane, having flown the um P51 for a while now I wanted something just slightly bigger and more scale looking with a clear canopy. I dont know if this is really a micro rtf, at 200g stock its about 1/2 way between micro and park flyer I guess, I hope its ok to post this in the micro forum.

The stats are:
wingspan: 555mm
length: 478mm
weight: 200g (originally advertised as 170g, now revised)
wing area: 5.5dm2 (as calcualted by me, Flyfly's figure is wrong)
battery: 450mah 2s lipo
motor: 17g outrunner 2450kv from Flyfly
esc: 12A 10g Flyfly with 1 amp Bec
The foam is EPO

When I opened the box I was pleased to see the P51 looks just as good as the photos suggest. Unfortunately the tail was broken off. This is because it was only held on by the thin section of foam above the horizontal stab (circled in picture). In a way this is a good thing because now I can glue the elevator to the rear fuse properly, after removing paint between both parts. I was also thinking about hollowing out that solid tail section to reduce weight a bit more. The main aim of my mods will be to reduce weight from the stock 200g, I am quite happy with the power system so I will leave that alone for now.

The next thing I noticed was that the prop and motor where terrifyingly out of balance. I went no further than 1/2 throttle, but even at idling speed the whole plane shook violently. I have never seen a motor/prop so out of balance. I took the prop off - very tricky as the plastic cowl (nice design feature by the way) was glued onto the foam a little bit. I found the motor itself was out of balance and vibrating badly (although much worse with the prop). I tried to balance the motor by drilling a little from the casing opposite from the side where it needed weight added to run smooth. However, too much weight needed to be added/taken off so I gave up on the drilling and put the prop back on and dynamically balanced it by sticking duck tape on and moving it until I found the spot where it needed to be added. A huge amount of duck tape was added to finally achieve smooth running, about 10 8mmx8mm squares of duck tape stacked on top of each other (sorry about the dark picture I had to take it at night - couldnt wait to re-assemble).

The ailerons go out all the way to the edge of the wing. I dont like this aesthetically anyway, but there was a mechanical issue that caused me to decide to cut them shorter. The servos could not bend down the edge of aileron, therefore the last few cm of aileron where pretty much pointless. Hopefully now less stress on the servos. The aileron servos where already linked together. I immediately changed this to have separate plugs so I could activate the flapperon function.

The elevators have a plastic rod connecting them, and the groove for this was not deep enough causing the plastic rod to pull the inside of the elevators down, I fixed this straight away - elevator picture is after this fix.

I fried the navigation leds by plugging them into the receiver. Didnt bother to read the instructions to plug them into the ESC (very odd arangement). I have since removed their wiring (about 1g) and will replace the leds with a nice tinybritelights kit which is much lighter anyway. This has allowed me to remove the LED plug & wiring form the ESC. This wiring alone weighed 1.7g!

Next observation. The landing gear, whilst very nice, is very heavy. Each main gear sits in a plastic cube, which must weight at least 2g, but each gear itself weighs a further 8g! much of this weight is due to heavy rubber used for the tyres. My next mod will be to fabricate a new set of landing gear using light weight wheels from somewhere? Also I'm thinking about making them retractable with 2 x 1.5g linear servos.
The tail wheel weighs 2.2g. I have since removed the side doors, and drilled holes in the very thick base for the tail wheel, reducing it to 1.5g. I think there is still more weight to be saved here.

The supplied battery is 450mah 25C 2s, and when I tried to install it into the fuselage it was immediately obvious why people where having cog problems with this plane. The battery is 30mm wide and will only fit right above the centre of the main wing, probably behind where the cog would be. However, there is a nice slot 25mm wide which goes right to the nose of the plane, unfortunately this battery wont fit in there even diagonally, unless some foam is cut. I believe this plane will balance nicely even with a small 325mah thunderpower battery of only 21g, because this can be pushed all the way forward to where it should be, not above the wing.

I have swapped the badly thought out rx power plugs to 2mm bullets on both battery and esc. The motor wires are soldered directly onto the esc so I left those alone. This allowed me to do a static power test. At half throttle this motor draws only 3amps, however at full throttle it draws 11.3amps!!!
This is a bit insane considering the ESC is only 12amps and battery only 450mah. I will do a thrust test next, hopefully full throttle will never be needed and there is enough power to fly around at 1/2 throttle so that a 325mah battery can be used (0.325x60/3 = 6.5minutes should be plenty).

The prop is very brittle as the other thread already reported. I ordered 3 spares and one was already broken during transport! very dissapointing.
Another mod that will need to be done soon is to buy 2 graupner 5x2 props (only ones I could find that look similar to the stock prop) and try to fit them into the nose cone. An interesting fact is that the stock prop is the same size as the ultra micro P51 prop, they are both 5".

Ah, one more observation. Flyfly chopped down the servo horns for the elevator and rudder servo to fit into the fuse. Unfortunately the chopped the elevator servo's horn too much and now there isnt much material to hold the rod in. I will have to swap this for a new horn before flying just to be on the safe side.

I dont want to put anyone off this plane with all these little issues, it looks fantastic and the overall build quality seems excellent. I always expect to have to sort out some quirks with every new model so these are just routine checks before flying.

Hopefully I will have a flight report & video soon, as soon as the weather over here warms up a bit.
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Old Dec 25, 2010, 01:12 PM
Doing it in the Lateral Axis
modfly's Avatar
USA, OH, Akron
Joined Dec 2006
15,360 Posts
Nice little plane. It reminds me of the GWS Free Flight Mustang thats about the same size. I modded one to r\c and it is a super flyer. I like planes this size as they are big enough to fly in some wind but can be easily stored when not being flown.
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Old Dec 25, 2010, 01:22 PM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
870 Posts
I'm a big fan of your threads Modfly, I read your thread about the Cox F4U Corsair, I think you got it down to only 4oz. I wish this P51 was a bit lighter. I'll be watching out for any mods you do on these planes if you do get one.
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Old Dec 26, 2010, 12:01 AM
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United States, CA
Joined Jul 2010
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The FlyFly mustang looks like its a scale airplane rather than an RC airplane.
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Old Dec 26, 2010, 06:41 AM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
870 Posts
apologies, I was wrong about the battery not being able to fit. Last night I discovered there is a wedge cut out at the top of the fuselage compartment that does allow it to go quite far forwards. Hopefully this will be enough to achieve a good c.o.g.
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Old Dec 26, 2010, 11:36 AM
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Toronto, Canada
Joined Jan 2005
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where do you get these flyfly planes?
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Old Dec 26, 2010, 01:47 PM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
870 Posts
I bought mine from RC Castle. They thoughtfully wrote 'toy plane gift' on the box so I didnt pay any import charges.

http://rc-castle.com/shop/index.php?...sort=2a&page=3

In the main thread I think a shop in the US was mentioned that was selling them.

http://www.rcgroups.com/forums/showthread.php?t=1335599
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Old Dec 27, 2010, 11:50 AM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
870 Posts
I did a static thrust test today, with the stock 450mah 2s 25c battery (freshly charged).

FlyFly P51 static thrust (1 min 58 sec)


The low-to-3/4 throttle numbers look promising.
At half throttle around 90g thrust for 3.3amps, hopefully enough to fly around.
At 3/4 throttle around 130g for 5.3 amps.
At full throttle around 200g for 10.7amps dropping to 190 for 10amps.

Full throttle amps seem a bit high, I'd be worried to hit full throttle for the second half of the flight in case it hit low voltage cut-off? I dont know much about propeller planes but does it seem that this motor 2450kv is a bit high for this 4-blade prop? Perhaps a lower kv motor would do better (lower amps) at full throttle.
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Old Dec 27, 2010, 02:20 PM
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modfly's Avatar
USA, OH, Akron
Joined Dec 2006
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Yea, those numbers are not very good. I would say that prop is not a good match for that motor. You need a 1000KV motor for that is my guess. Try a GWS 5030 or 5043. This just goes to show why I don't like Direct drive motors. Too much current draw for the thrust they produce. If I had this plane I would convert it to a BL gearbox. With a gearbox, you can tune the ratio to any prop and thrust and current draw that you want. I mentioned that I have a plane very similar to this one which I think may be about the same size and I use a gearbox in that one. I will post a few pix of that setup but Its looking like your plane needs this mod.
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Old Dec 27, 2010, 02:41 PM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
870 Posts
Thanks Modfly, I'm going to look for a lower kv motor of similar weight as direct drive. I would like the gearbox mod but it looks like it could be quite complex with the amount of room available in this model. I'll try the easy route first. As it is this motor draws way too much current. I just realised I have a small 50mm edf which draws 11 amps for 260g thrust, a prop should not be less efficient than an edf!

do you think a 10g outrunner would be ok, I saw your F4U corsair uses a 10g outrunner?

I really like the look of the 4 blade prop and will try to keep it. I'm going to have a go at making a new 4 blade form a grapuner 5x2, hopefully thats not too low a pitch.

How much thrust did you get out of the set up on your mustang at how many amps?

Thanks!
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Old Dec 27, 2010, 02:54 PM
Doing it in the Lateral Axis
modfly's Avatar
USA, OH, Akron
Joined Dec 2006
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Ok, I found the specs and the plane I posted is 622mm and yours is 515mm winspan so your plane is smaller, quite a bit smaller actually. No I don't think the 10mm outrunner is the ticket for you as your plane is too heavy for that motor. As a matter of fact it is hevier than the one I posted. The 10g outrunner works in a plane that 5 oz or less. It might pull a 7 oz plane but I'm sure its would be sluggish at best. Try one of the props I suggested. That should get the current draw down but ultimatly it needs a gearbox of of some kind.

The Mustang I posted makes 10oz thrust @ 4 amps draw.
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Old Dec 27, 2010, 03:14 PM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
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you're right, I need to let go of the looks for now. I dont want to fly this mustang as it is right now, drawing 11 amps. I'll get a 5030 and put it into the spare nose cone.

Thanks
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Old Jan 08, 2011, 08:23 AM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
870 Posts
I finally got a GWS 5030 prop to test. Results are pretty good, just over 200g thrust for 5amps. Thrust is almost the same as the stock 4-blade, but for 1/2 the amps.

FlyFly P51D GWS5030 (0 min 40 sec)


The pitch of the stock prop is too large, its more than double the pitch of the 5030, its probably around 7, making it a 5 x 7 prop. Sorry about the fuzzy picture, my camera is rubbish.

Next, I want to try making a slimmer 4 blade from 2x GWS 5030.
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Old Jan 08, 2011, 01:44 PM
Doing it in the Lateral Axis
modfly's Avatar
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You really like those 4 blade props eh?
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Old Jan 08, 2011, 02:12 PM
we can take off without that
green_flyer's Avatar
London, UK
Joined Nov 2008
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I cant help it. When I think Mustang, I think 4-blade prop. Hopefully with slimmer blades and a portion of blade hidden inside that big nose, it wont increase the amp draw too much.

I got the Graupner 5x2 as well, however its shorter than 5" and it weighs too much, more than 5g!
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