Help! Power pack for scratch build

[Mark408]

Story (not important):
A few months ago, I gave my brother a Flite test plane (I built it and spent a while painting it). This would be his first plane but I was reluctant to let him fly it, that's because the plane was a FT FW 190 mighty mini. And since he has little experience at flying, he would probably end up crashing it within a minute. So instead, I decided to make him a scratch built DTFB 4 channel "trainer". I ended up making a large A1 skyraider with a similar technique as the master series (just crappier). And I made the wings longer than scale to make it floatier and possibly stall better (undercambered wingtips).


Specs (Airframe):


Wingspan: 60" (1524 mm)

Length: 33" (838 mm)

Airframe weight: 150 grams (0.33 pound)

Wing chord at root: 9.5" (241 mm)

Wing chord at tip: 5.5" (140 mm)

Airfoil: Clark Y, undercambered wingtips (last 7 inches of wing)


Concern (Important part):

My main concern is what power pack to use. I was thinking of using a power pack A or power pack B. The point of this plane is to be a trainer that flies slow and won't do many aerobatic maneuvers. (The spar I used for the wing was a 1/4", 10 inch wooden dowel and a few pieces of depron stacked on top of each other. The strength on the rest of the wing comes from mostly the paper on the bottom surface and the fact the wing has 2 sheets of foam for it's airfoil.) The max weight I would want to go is 300 grams (150 grams airframe, 20 grams from servos, 20 grams from motor, 60 grams from the battery, ~20 grams miscellaneous). Would a mini power pack like this be enough or should I get a power pack B?


Minor Concern:

The horizontal stab and vertical stab are currently single sheet depron pieces with an airfoil sanded into them. The horizontal stab has a piece of 2 mm (iirc) carbon fiber in the middle. Would this be enough or should I keep the paper from the DTFB on the stabilizer? My idea was making the stabilizers from depron and the actual control surface from foamboard for rigidity.


Pics:

The ugly bird herself. The elevator is tilted and not glued it for the reason mentioned above. The rudder is also not fully complete + other cosmetic issues. (please excuse the dirty concrete, had to take pics somewhere with good lighting)

Thanks for reading!

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[Byrdman]

IMO, that plane is too big for an A or F power pack. It may get it in the air, but you are going to probably be full throttle to make it happen. You should use a C. It may still not fly like a trainer, but at least you will be able to fly around at half throttle with the C.

There is a reason most people start out on a trainer style plane, tutor, scout, etc. Slow, predictable, flying characteristics. Good luck!

 

[skymaster]

Use the power pack B with a slow fly prop 10x7

 

[Mark408]

IMO, that plane is too big for an A or F power pack. It may get it in the air, but you are going to probably be full throttle to make it happen. You should use a C. It may still not fly like a trainer, but at least you will be able to fly around at half throttle with the C.

There is a reason most people start out on a trainer style plane, tutor, scout, etc. Slow, predictable, flying characteristics. Good luck!

I was originally going to use a slow fly prop with a slow KV motor but those 2212/2218 motors are heavy for how light I'm making this (Power pack A motor is 18 grams, Power pack B motor is 60 Grams) Is there a motor that can use a larger diameter prop that weighs closer to 30 grams or less? (Thanks for the help!)

 

[HVB79]

Don't worry about the motor weight so much. You are talking about adding 42 grams on a plane that has a 60" x 7.5" wing or about 450 sq. inches of wing area.
Wing loading:
300g / 450 sq. inch = .66g/sq. inch with light motor
342g / 450 sq. inch = .76g/sq. inch with the "heavy" motor
Change = 0.1g per sq. inch

Your wing loading is already very light and adding 42 grams to a plane this size is not going to make a noticeable difference.

 

[Mark408]

Don't worry about the motor weight so much. You are talking about adding 42 grams on a plane that has a 60" x 7.5" wing or about 450 sq. inches of wing area.
Wing loading:
300g / 450 sq. inch = .66g/sq. inch with light motor
342g / 450 sq. inch = .76g/sq. inch with the "heavy" motor
Change = 0.1g per sq. inch

Your wing loading is already very light and adding 42 grams to a plane this size is not going to make a noticeable difference.

The battery I was planning to use is a 850 mah Tattu 3S that weighs around 75 grams.

 

[HVB79]

You could save a little bit of weight with a smaller battery but the amount of weight you could remove by making the battery smaller is limited because you are already using a small battery. Your plane is already so light for the wing size I would not worry about trying to squeeze a few more grams out of it with a special motor.