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Mentor won't take off.

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Old 11-06-2010, 12:08 PM
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garyji
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Default Mentor won't take off.

I have a stock eFlite T-34 Mentor 25. I tried flying it for the first time the other night off of a "damp" low cut grass field. It won't take off. Anyone have this issue? Do I need to be flying it off of pavement? I am new to this and am using the droops and "beginner" flaps. The grass is cut very low, and my nexstar mini handles it fine. It wasdamp though. I tried two different batteries (3S 3200mh eflite lipos). No luck.

Ideas??
Gary
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Old 11-06-2010, 08:51 PM
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Dr Kiwi
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Default RE: Mentor won't take off.

If your pack is up to it you should be getting 4lb of thrust for a 5lb aircraft... surely plenty for take-off... but how well is your pack coping... are you getting 40A static draw?


Motor: E-Flite Power 25 Outrunner 870KV; 870rpm/V; 2.4A no-load; 0.03 Ohms.
Battery: Thunder Power TP2250 (G4 ProPower 30C) (30C); 3 series x 2 parallel cells; 2250mAh @ 3.7V; 0.008 Ohms/cell.
Speed Control: Castle Creations Phoenix 45; 0.0026 Ohms; High rate.
Drive System: Direct; 12x8 (Pconst=1.16; Tconst=1) direct drive.
Airframe: Anything you want.
Motor Amps = 40.2
Motor Volts = 10.5
Input (W) = 423.1
Prop RPM = 7656
Thrust (oz) = 64.4
PSpd (mph) = 58.0
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Old 11-07-2010, 07:51 AM
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Default RE: Mentor won't take off.

Check that you don't have the elevator reversed (ie, you think you are giving up elevator, but you are actually giving down). This is real obvious on a tail dragger but not as obvious with a nose gear.

I did this on one plane I had... simple fix.
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Old 11-07-2010, 09:44 AM
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Leisure_Shoot
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Default RE: Mentor won't take off.

Do you have a small scale you can test thrust with? What about a battery voltage tester?
It would be great to establish that there is a problem with the actual powerplant, or something else.

You should be getting about 75% throttle to weight on the Mentor. (off the top of my head, I think that was my reading on mine)
The mentor weighs about 81 oz (per the specs) I think I was getting about 70 oz thrust when I measured it a few weeks ago.
If you are extremely cautious, and perhaps have a friend to work the throttle, you could always hold it vertical and run the throttle up to see if it producing enough thrust.
this particular aircraft could be held securely by the nose gear while the throttle is run up gently. It should feel like it is very light, almost strong enough to lift itself, but not quite.

Have you made any changes at all?
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Old 11-07-2010, 05:43 PM
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garyji
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Default RE: Mentor won't take off.

Thanks guys as always. I have a meter on order and will check the power plant. All the control surfaces are correct and I calibrated the throttle end points on the ESC. The only change I made was the prop. I replaced the stock 12x8 with an APC 12x8E. Iwasn't sure what to expect from a static runup but will follow your guidance. I'm out flying the real things this week but have some checking to do when I get back.

Thanks,

G.
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