Nitroplanes F86 49" Wingspan Thrust Help - RCCanada - Canada Radio Controlled Hobby Forum
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Old 09-24-2010, 12:20 PM   #1
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Nitroplanes F86 49" Wingspan Thrust Help

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I received the following ARF today and weighed everything.

With an 8S 4000battery pack and 45mmx77mm motor, it looks like it will weigh close to 7.7lbs (3400g) unless I made a spreadsheet error. The cover on the 6! page manual says 5.29lbs. I have to fly it off somewhat uneven somewhat bumpy grass field. I am using the 7 blade Haoye fan.This is my first ducted fan but I have done a lot of electric planes. It appears to be identical or a clone of the Easy Tiger F86 which there is a video of it flying off grass using 6S and 6.5 lbs but it was a somewhat weak take-off and almost runs out of run(err grass)way. The planes wheels are foam 60mm (2.1") main and 50mm (1.8") front.


Any idea how much thrust would I like to have to fly it off grass with a 7.7 lb plane ?

Is there any general conservative rule of thumb of watts into motor versus thrust out (based on Chinese motor and fan efficiencies) ?

I had originally hoped to use 8S but in light of the weight I am concerned. Though the plane documentation talks of a 85A speed controller and 6S, I am concerned it won't produce enough thrust to get off our somewhat uneven grass field. My best guess is a 5000 25C 6S battery (100a max speed controller) might produce 2000W. Any guess if thats enough to take off grass ?

The manual vaguely hints that metal geared servos should be used. Anyone confirm metal gears are highly recommended for DF (maybe due to vibration or speed) ?

This plane came with a sheet of thin plastic to make an air exhaust tube but I don't believe there is an air tube in front of the fan which is mid mounted. Is that normal or should I be trying to add a tube in the front ? There is no curved lip to the front edge of the fan, just a wood bulkhead

Last edited by DEdwards; 09-24-2010 at 02:54 PM.
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Old 09-24-2010, 09:10 PM   #2
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Smile Re: Nitroplanes F86 49" Wingspan Thrust Help

My largest EDF is only 90mm. It only produces a little over 2Kg thrust on 6S at around 1500watts. Your 8S fan will need some serious power to lift 7.5 pound F86 into the air (off grass). I only fly on pavement and doubt there are many scale EDF's that can handle grass regularly. The rolling resistance with small wheels is the problem. Not to mention most landing gear mounts are not strong enough to take the bumps grass will dish out.
As for flight control servos, I'm only using cheap plastic gear servos with good results (but my aircraft don't fly super fast). Metal geared are not that expensive and are probably a good idea (for the few extra dollars). If you have servo driven retracts, metal gear is the only option.
Many (if not most) EDF's don't have a separate duct tube on the intake as they are difficult to secure. Should it come adrift and go into to the fan it's deadstick time! A sharp edge on the intake is not good. A proper curved lip helps fan efficiency and most shrouds have a lip supplied or available.

Second post on this page has some good info.
Good luck!
Zen thinking * It's rebuildable till it fits back in the box. **

Last edited by 4stripes; 09-24-2010 at 09:28 PM.
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Old 09-25-2010, 01:37 PM   #3
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Re: Nitroplanes F86 49" Wingspan Thrust Help

Thanks. You have confirmed what I suspected all along. Its not going to be easy!

I'm hoping to have up to 90 amps at 8S available with batteries that are good at holding their voltage. So that means I might have 2500-2800W and using your 2kg from 1.5kw thrust ratio yields 3.3kg->3.7kg so I might be close to 1/1.

Prob 1: Keeping the fan from exploding at that power level
Prob 2: Keeping the motor from self destructing at that power level.
My strategy is to use "emergency full power" only for the # of seconds required to take off to a safe height and limit power after that (I hope my throttle finger cooperates . The motor will be drilled for cooling and I will try to add a finned heatsink.
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Old 10-05-2010, 03:17 PM   #4
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Re: Nitroplanes F86 49" Wingspan Thrust Help

I looked at the Nitro website and it looks like there is no intake ducting, is that correct and if the there is no thrust tube as well, then you are loosing a lot of performance. Also they indicate that the EDF unit is a 101 mm, not the 90 mm that you intend on using. If so, making the ducting to smooth out the airflow is most recommended. The ducting for the Sabre is really not that hard to fabricate out of fiberglass for the intake and thin mylar for the thrust tube. You can fashion the mould for the intake out of styrofoam and cover it in heat shrink covering ( Ultra Cote works good as it bonds at low heat). Then wax it and if you have some release agent like PVA apply it after waxing. Make the intake out of a lamination of 2.3 oz and 4 oz cloth. Once you have the duct off the mould, spiral wrap it with some carbon string so it will hold its shape when under suction pressure. You can secure the front of the intake ducting using Goop adhesive, that is if you do not wish to mould it into the front lip of the fuselage. The best way is to mould it in and then round over the intake lip so the airflow in the ducting stays smooth. I have never had a intake duct dislodge itself from the fuselage, I have seen them collapse though.
I've generated nearly 2000 watts of power from the Hoaye 90 EDF and it seems to hold together really well.
Hoaye does make a 100 mm EDF unit, I have 4 of them that I'm going to do some testing on, once I get the 5 mm adaptors delivered as they are enroute from Hong Kong. The fans came with 6 mm adaptors.
Also, if you can shorter those strip ailerons and fashion a set of flaps, the flaps would help get you off the ground as well. The extra lift always helps.
Good luck
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