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Apr 15, 2018, 03:05 PM
Scratch building addict
rotagen's Avatar
Discussion

Big ass p51


Just thought I'd throw this out - Well I made this a few mos ago and haven't really found proper weather/time to fly out to a big field.

Found a good deal on Rochobby strega wings and since the epp cores place seems to tack the minimum 20 bucks onto their orders, well..

And since I much prefer the fatter p51 fuselage with scoops below, I made a sandwich styro fuse with thin center piece including the vert stab, hot wire and sanding to general shape.

Made the fuse at same proportions rel to wing as my little near-micro p51 which flies great.

I wanted it to be pretty fast, but the rochobby has an insane motor over 200gms which makes for difficult hand toss perhaps? And I had a hard time cg balancing a 150gm motor - So I went with this motor at 100gms.

Those of you who fly these big things might have some feedback on this motor? Biggest battery I have is 1800mah 3S.

https://hobbyking.com/en_us/turnigy-...ner-motor.html

43 inch wingspan
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Apr 15, 2018, 03:21 PM
treefinder
springer's Avatar
So how big is it? Span and weight. That motor is gonna need an awfully big prop to load it up enough. My 7foot span wing flys with a dys 2830 1300kv 52 gm motor and 9x6 prop. I use a 2200mah 3s pack for 8-10 minute flights. Half the motor on a 2lb plane with 7' wingspan.

Oops, just noticed the span at 43". I think your motor will be loafing all the time.
Apr 15, 2018, 09:46 PM
Scratch building addict
rotagen's Avatar
Quote:
Originally Posted by springer
Oops, just noticed the span at 43". I think your motor will be loafing all the time.
Amazing you can fly such a big plane with that weight motor. Sorry don't know what you mean by loafing? too slow?

Darn I need to weigh this thing I should have posted that.

I forgot, I think I've got a 10 inch slow fly prop on there.

thx.
Apr 16, 2018, 07:49 AM
treefinder
springer's Avatar
I was surprised at how well the wing flew as well. The motor gets warm, so i may be right at the high limit for loading it up. Heres the thread: https://www.rcgroups.com/forums/show...g-MPF-and-wood . Generally one wants to get the most performance from electric motors as one can. The way to do that is to increase the load on the motor to the sweet spot where it works most efficiently. The way to load it up is to increase prop diameter and pitch. My experience has been diameter loads up the motor faster. I.e. an additional inch in diameter will add more load than an inch of pitch.

I am no expert, mostly empirical fumbler, but my guess is that to get the most out of that motor you will need a big prop, with high pitch. I guess there isn't too much of a down side if you don't work it much, you just don't get what it is capable of, (it will be loafing - running at low load and speed) and still have to carry it's weight around. On the other hand, if you prop it right, you will have an exceedingly fast and powerful plane! Not a bad thing if ya want it. . .
Last edited by springer; Apr 16, 2018 at 07:55 AM.
Apr 16, 2018, 09:26 AM
Scratch building addict
rotagen's Avatar
Oh cool, I was hoping this would at least be hand-tossable, thanks for the info, I also do everything empirical and just hope my old-fart mind can remember what worked.

When I finally get out to my larger field and try it I will post video, my little 23 inch p-51 is so stable I'm hoping it is a property of the airframe.
Apr 16, 2018, 10:20 AM
Registered User
Extreme Sports's Avatar
Mmm. 43" is still pretty 'small ass', so a 200g motor will be way too much. I've got a bunch of corro-scale warbirds with spans between 45" and 48" weighing in the 700-900g range and all fly plenty fast on circa 50g - 80g motors - for example the 2826 range of the turnigy motor you linked to. The most versatile is the 1450KV one, but for speed you might use the 2200KV version that is the standard for park jets, with a 6x4 prop (or 7x6 if you push it).

I do in fact have the exact motor you linked to on a 1100mm (~44") corro Edge. It weighs about 1100g IIRC, but I've set it up for power rather than speed so as to fly like an Edge should. I can't believe your foamie would weigh anything close to this, so I'd suggest trying the smaller range. 1800mAh Lipo or high C 1300mAh is a perfect match. The 2200mAh just adds weight.

Also, for a Mustang, the thinner diameter (28mm vs 35mm) motors might be a better fit. The ones I suggested above have a 12mm long stator - where the stator is longer, the motors tend to be lower KV, so not really what you want.

Keda, however, do make a range of larger high KV 28mm motors - see this link: http://www.kedamodel.com/product/tr28.html. IIRC, the 2830 range corresponds to the Turnigy 2826 size, so anything above that will give you more power. Try the TR3837/08 or /04.

If HK is your store of choice, try the Propdrive series - e.g. this one: https://hobbyking.com/en_us/propdriv...ner-motor.html
Apr 16, 2018, 11:08 AM
Scratch building addict
rotagen's Avatar
thanks, Fantastic info. I saved those links.

I was thinking since I have a 50gm motor on my little Hacker EPP warbird, at something like 22-inch wingspan and it flies pretty good, I would need at least a 100gm motor on this thing....apparently NOT. Reason I did ...That little thing was gonna be my "windy day" flier and it does handle around 12mph winds, but still flying upwind takes forever... I wanted to put a gyro on that thing for windy days on small local fields.

Those 2830s look good, I have been unimpressed with the Propdrive series, I did some testing on one and it pulled less amps, far less watts than another motor I had at half its size.... crazy. Others noted the same problems but I might have got a lemon.
Apr 16, 2018, 11:53 AM
Registered User
Extreme Sports's Avatar
Yup, I've only got one of the Propdrive motors (the 2200KV) and it does not seem to do much more than the same KV 2826 XP motor despite being a lot heavier. So I never bought any more of them.

The Keda Thumrum are a little unusual - they are quite light and the magnetic field is not well contained in the bell ring. So probably not that efficient or likely to last forever, but they do give you a nice choice of higher KV motors in this size range. If you get one, suggest you check your amps before flying and temps afterwards...I suspect the current ratings are optimistic.

I find that a KV of between 1400 (8x6 prop) and 1800 (7x6 prop) is a really nice match for warbirds in this size range. 2200 with a 6x4 is a little too fast and lacking in low speed thrust for scale like flying.


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