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Old Mar 02, 2014, 08:14 PM
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United States, NV, Carson City
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in need of a motor size

Hi, I need some help with choosing a motor. I just finish a poster foam board trainer plane. On the maiden flight the plane took off but started sinking right of way until I had lo land it. Do I need a bigger motor? and if I do, what size should I use?

Plane specs: Trainer 40" wing span,71/4" chord with ailerons - 30" long with motor included

Power Plant:

Motor2212-1000KV-thrust 650-680- Max current:13.8A- Max 150W
ESC:30A
Batt:11.1v 1000mah 30C

The plane is a 4 channel it is balanced as it should and total weight is 20 oz.
Any ideas?
I'm 72 and new to the hobby and this is the second plane that I build from scratch, the first was a little 16" wing span trainer type that flies beautifully. I have read a lot and learned a lot but this one is bigger than I can muster.
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Old Mar 02, 2014, 08:21 PM
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I forgot to mention, the prop I used is a 9x5 I also have some 10x6 that I have not try.
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Old Mar 02, 2014, 08:23 PM
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Welcome. What prop are you running ? Should fly with that setup. Do you have any pics? Are you getting full throttle ? With the prop removed turn on your radio and move throttle stick to full on ( to the top). Plug battery into plane and listen for the normal beeps ( usually hear 3 for 3 cell battery). Once beeps have sounded move the throttle stick down to minimum you should hear a beep when it gets there. Now try cycling the stick a few times to confirm throttle works. Remount prop and see if it has more. Oomph then before
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Old Mar 02, 2014, 08:29 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
Joined Feb 2010
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150W should fly a 40" 20 oz plane.
Was the battery fully charged?
Is the correct prop fitted? Is the prop mounted the right way? (curved side to front, flat side to back)
Did you allow the plane to accelerate to a reasonable airspeed before trying to climb? A low-powered plane can get stuck in a high-drag configuration and not be able to gain flying speed.
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Old Mar 02, 2014, 08:34 PM
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I'm running a 9x5 I also have some 10x6, wish one should I use? It seams to run full throttle, I have a tachometer I will read the rpm and see if it is giving all the rpm. It should turn at about 11000 rpm at full throttle, is that correct?
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Old Mar 02, 2014, 08:45 PM
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Yes to prop right side and acceleration. I also launch it by hand with same result, straight flight unable to climb an sinking. battery was 90%, I check for beeps from ESC to make sure that everything is correct.
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Old Mar 02, 2014, 08:48 PM
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I will post some pics tomorrow, I have to learn how to post pictures in here.
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Old Mar 02, 2014, 10:13 PM
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These are the pictures of the plane before finish.
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Old Mar 03, 2014, 06:47 AM
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Assuming your CG is between 25 and 30 percent chord, then here's my guess:
From the pics, I would guess that the horizontal stabilizer and elevator may be undersized. In order to get away with so small an elevator it would need to be placed further back from the CG (like on a Bixler).
One way to find out for sure: Launch the thing from a high place (like third floor window or garage roof), let it dive a bit and then try up elevator. If you get really anemic nose up rotation then you know your elevator is too small.
Another thing to try: If your CG is at 25 percent chord, try 30 percent chord. That will give the elevator more authority, but be advised that it will also make the plane more "twitchy".
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Old Mar 03, 2014, 08:59 AM
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The horizontal stab is too small for your type of high winged trainer design. A good 'rule of thumb' is that the total area, including the elevator, should be 25% of the wing's area.
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Old Mar 03, 2014, 09:25 AM
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i agree with nuteman : The size of horizontal stabiliser seems very small but it also might be an optical effect because of the camera lens.
Anyway, I would say : Built another horizontal stabiliser twice bigger than this one and give it a try.
The moving part on the horizontal stab should be at least around 20 to 25% of the total surface.
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Old Mar 03, 2014, 09:41 AM
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Ermavi some excellent advice here . Heres a nice link for trainer design http://adamone.rchomepage.com/design.htm

lets see how it goes with a bigger tail
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Old Mar 03, 2014, 04:40 PM
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The horizontal stab and elevator are WAYYYYY too small.
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Old Mar 03, 2014, 07:01 PM
flyin' fool
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Also, be careful of your prop choices, it will effect the amp draw. Do you have a wattmeter? It's the next most important thing to your transmitter if doing electric power.
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Old Mar 03, 2014, 10:09 PM
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motor angle

I have a Watts meter coming if it ever gets here. Thank you all for your advise, I thought the elevator and rudder was kind of small. I will build one bigger. Now, should I use a 10x6 prop or keep the 9x5? The other thing that kind of bothers me is the angle of the motor facing down in relation to the horizontal line of the planes fuselage, ( see pictures) I welcome your comments on that.
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