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Old Jul 18, 2002, 08:45 AM
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Kerberos's Avatar
Datteln, Germany
Joined Jun 2001
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my new Aerobatic Plane

please let me show you my new aerobatic plane ......... from ebay .... for only 150€ around 150$
with retracs





technical data

lengh : 136 cm
wingspann : 164 cm
wingarea : 42 dm˛
weight : 1700 g ( with retracs and radioinstallation)

will try a Mega 22/30/3 with Velkom 2.5:1 gear and 14x8 prop on 16 cells

what do you think ?

Erik
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Old Jul 18, 2002, 10:16 AM
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Colfax, WA
Joined Oct 2001
622 Posts
Nice looking design. Who makes it? What is the span ect?

Rob
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Old Jul 18, 2002, 11:46 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,761 Posts
I'd up the power some

Erik

I'm concerned that you're a little undergunned in terms of power and prop. You're looking at maybe 675 watts from 16 cells and a pretty slick airframe. Don't know your wing area, but I'm guessing that this airplane is going to fly faster rather than slower. Shaving weight with CP 1700s instead of larger cells may make sense. I'm flying something similar but a bit smaller (140 cm) on 500 watts (hot off the charger (12 cell CP 1700 pack), direct drive using the Jeti 30/3. Flights aren't all that long but they are fun. However, my pitch speed (9.5 x 7 prop) is about 140 kph, and I think you need to be at a minimum of 130 kph for your plane. Also, my all up weight is about 2.0 kg- that's ready to fly, so this plane may be a bit heavier. I don't think you'll be close with that prop. See what happens on something like a 12 x 10 prop with that amount of watts.

Sam
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Old Jul 18, 2002, 10:47 PM
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Rutherfordton, North Carolina, United States
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Erik,
Nice looking airplane ! Let's see, 1700g with radio, 980g for a 16 pack of RC-2400's, and about 300 g for motor+gearbox+controller = approximately 3000g auw (6.6 lbs and 105 oz ). Clean design, area = 650 sq in, but that likely includes about 100 sq in for the tail surfaces, so lets say the wing area only is about 550 sq in.
Here's a Mega option, and the following post is a Hacker option. My choice would be the Hacker.
Ed
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Old Jul 18, 2002, 10:48 PM
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Here's the Hacker option.
Ed
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Old Jul 18, 2002, 11:27 PM
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Ontario, Canada
Joined Jul 2001
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A Saphire?

Erik, that looks like a Saphire by a small British Firm if I am not wrong, it has a foam wing and built-up fuz. I built one back in the wet days. BTW, nice finishing.

Good F3A pattern plane, designed for a 61 and larger engine; to go fast. I think Ed has provided you with some very good information as a baseline. Good luck in converting it, and keep us posted.
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Old Jul 19, 2002, 12:10 AM
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San Jose, California, United States
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Erik
Congratulations on your new plane - it looks great!

I agree with the comments about the Mega being too small. The "30" in 22/30/3 is roughly a 30 sized gas plane.

What you have is bigger than a 40 sized pattern plane. Most 40 pattern planes are roughly:

Wing Span: 54 in. / 1370 mm
Wing Area: 564 sq. in. / 36.4 sq. dm
Flying Weight: 6 lb. / 2650 g
Fuselage: 54 in. / 1370 mm

These are the specs for my Zen 50.

Your plane is larger but seems to be light. I would take advantage of this and use more batteries to keep to amps down, the powerup and the duration longer.

To have a pattern plane fly well you want to have the static thrust be greater than the weight and the static pitch speed greater than 31m/s(70mph). My Zen is config'ed this way and flies very well.


You can accomplish this with a Hacker B50-13L, 5.2 gearbox, 14x10 prop, 21 cells 3000 Nimh HV accumulators.

This will provide - 3400g (123oz) of thrust, 32.8m/s(73mph) pitch speed @37amps. You want to keep you amps under 40 to not damage your Nimh batteries. Your AUW is roughly 3200g.

If you need more thrust, use a 15x10. You will need to experiment.

I think your Lehner motor might work in this config with the right gear box.

Good Luck!
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Old Jul 19, 2002, 08:34 AM
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Well Kyle .....you may be right, but what you are suggesting adds another pound to the airplane ( 7.5 lbs vrs. 6.5 lbs ) and this takes the wingloading from 27.6 to 31.5 oz/ft3
The overall thrust to weight ratio is a little better than the 13S version I recommended, and I do see advantages in top speed ( 70 vrs. 60 ) and in runtime. I just hate the idea of the powertrain having to carry that extra pound of batteries around.
The Venus that Jason flew for Aero-Model at SEFF was about the same weight (had the same powertrain) and flew great. I say keep the weight down with 16 cells and work the batteries harder.
Ed
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Old Jul 19, 2002, 10:30 AM
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San Jose, California, United States
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Ed
I agree with what you are saying. I think the difference between our calcs is the wing area -- I believe it should be 651 sq ins. Which makes the plane 7 lbs and the wing loading 25oz. This is a very reasonable wing loading.
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Old Jul 19, 2002, 10:33 AM
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Datteln, Germany
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Hi to all :-)
the Wingarea (without Tail surface) is 42 dm˛
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Old Jul 19, 2002, 11:09 AM
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Kyle,
OK, with 651 sq in wing ....I believe your proposed power setup is closer than what I suggested. The reason I reduced the wing area from what Erik said is that it is common practice for european designs to include the stab area in their advertised wing area. This confused me more than once until I learned to compensate.
Now that Erik has stated that the 42 dm2 (650 sq in) is wing area only ...... the picture changes.
I still think a B50 S motor might do the job ...... with less cells. I'll play with that a bit more and offer another suggestion or two later.
Ed
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Old Jul 19, 2002, 12:18 PM
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Good info Ed. I didn't know that about the wing area.

I will be testing my Artist with 24cells on a B50-13L, 6.7 gearbox. See if I can push through the dragginess with some thrust and speed. I am also going to test the Zen with some higher cell counts for longer duration. Stay tuned.
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Old Jul 19, 2002, 11:21 PM
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Hi Folks
I finished my Artist test - see thread at:

http://www.rcgroups.com/forums/showt...965#post412965

It's running 24 cells and is heavy but I think a similar system with 21 cells would work very well for your plane. Your wings look much thinner than the Artist and there is less area -- should be less draggy.
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Old Jul 21, 2002, 02:01 PM
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Erik & Kyle,
OK.....adjusted the wing to 650 sq in. Looks like it needs a couple more cells....so I upped the count to 18. I think this B50 13S setup has some merit. A 15x10 prop would also be an option ...just lowers top speed a bit.
Ed
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Old Jul 22, 2002, 01:03 PM
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Datteln, Germany
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thanks for all your help,
now i know that the Mega setup is not the right choice.
I will try my Lehner 1930/11 with 5:1 gearbox, 20 Cells and 14x10 prop, looks like the Hacker B50 12L is very similar to the Lehner :-).
All the Data i have will not suit the Motocalc needs to design this motor for use in Motocalc

Erik
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