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Which motor + propeller to use on 120% scaled FT Racer?

#1
Hey all,

New here on the forum, but not new to building Flite Test models and watching these great videos. Learned I lot this way!
Models build so far (in this order):
  • FT F-22 Raptor
  • FT Racer
  • FT Mini Mustang
  • FT Arrow
  • FT Tiny Trainer, for teaching my son to fly :)
  • FT Super Bee
  • 120% FT (not so) Tiny Trainer, as a replacement for the other FT Tiny Trainer

I started of building with foamboard (F-22 and Racer). But the Dutch foamboard is rather heavy. The F-22 Raptor managed, but the Racer turned out to be too heavy.
Since then I’ve been using Depron (like) foam (3mm and 6mm thick) laminated with wing tape. In the beginning I first laminated a whole sheet of foam before cutting (like Experimental Airlines), but often this would curve the foam. So now I first cut out a piece of the airplane before laminating it. This works fine for me. I use both hot glue and Clear Foam Glue (Hobbyking) building the plane.

As a new project I would like to rebuild the FT Racer (love the looks of that plane), but scaled to 120% size. Since I am building with 6mm foam, I only need to print at 120% and that is it.
For the motor and propeller combo to use I would like your advice. The other FT Racer flew of a Park480 (1320kV) and 8x6 prop. But I presume this will be too small a motor and prop for the 120% Racer.

What kind of motor and prop size would you recommend? I prefer to use 3S 2200mAh batteries. I also have a couple of 6S 3300mAh batteries (from my T-rex500) which I could use. I do not own 4S batteries (yet…).

Open to your suggestions!

Best regards, Martijn
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#2
Welcome to the forums!

I reside in Australia and the Foamboard we get here is definitely heavier than that used by FliteTest, so it would cause the same weight and balance issues as you have mentioned with your previous builds.

Should you want to build in FB there is a way as our FB is actually stronger than most others. I undertook some build lightening experiments a while ago by building a couple of FT Spitfires and checking balances and build weights. I ended up wit ha Spitfire weighing around 20% less than one built in the local FB following the original FT plans. Also the resultant plane balanced perfectly whereas the version built to the original plans required a large amount of nose weight to fly properly. For information on what the changes to the build process and materials I used you should read; http://forum.flitetest.com/showthread.php?32734-Balsa-Foamboard-test-build-FT-Spitfire.

As for what motor I would spec as a replacement for the originally specified motor, I recommend that you do not bother as your original setup used a 8x6 and the motor can swing a 9x5.

From the HK website: Test Data @ 11.1v:
8x4.3 - 18.2A - 1000g Thrust
9x5 - 25.2A - 1310g Thrust

So just fit a 9x5 and see how it goes! Should you require a little more just get a motor around 320 to 350 watt with a 9 inch prop and you should be fine.

Just my thoughts!

Have fun!