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Old Jan 09, 2013, 04:25 AM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
Joined Apr 2012
2,920 Posts
Woke up thinking about this. I hooked up a 3S 30C battery and got 90W at 8A out of the system.

Looked at the ESC documentation and saw that the default timing for the motor is "Low" (3.75 degrees) with Medium (15) and High (26.25) available.

I think that, tonight, I will play with the ESC programming and retest.
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Old Jan 09, 2013, 08:49 PM
The "pro" in procrastination
Steve85's Avatar
Canada, ON, Kingston
Joined Mar 2004
2,662 Posts
Hey David,

I have few thoughts on your power issues for your consideration. As lightly loaded as your Skua is, 100w/lb ought to provide fighter-like performance, assuming the pitch speed of your prop is in the right range. Your Rufe may have suffered from a combination of low pitch speed and the high drag of its floatplane configuration. I've flown a Guillows Spitfire with around 50-60 w/lb, and it was fully aerobatic.

If your batteries are oldish, 12A can be a lot to expect from a 800 mAh pack, even one that is nominally 25 or 30C. Check the voltage under WOT and see if it sags noticeably; that'll be a sign that your packs are getting tired.


Steve
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Old Jan 09, 2013, 10:25 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
Joined Apr 2012
2,920 Posts
I conducted further power system tests this evening. Changing the timing of the ESC did improve the overall performance in Watts, but only about 3-4 percent.

I'm using a GWS EP 8040 (I wish it wasn't orange), as recommended by the seller. I did a vertical-orientation, WOT, "hold it gently in your hand" thrust test and find that it's just at 1:1. So I can be happy with that. I might replace the 18A ESC for something smaller... but I might change props.

I installed the ESC and Receiver, hooking up the servos and checking the correct direction of deflection. I set up dual rates and throws, expecting it to be sensitive in roll, there not being much dihedral. Everything is tested and put together. To achieve CG, I had to move the ESC, receiver and battery forward of the crew compartment, into the area behind the motor.

All that is lacking is finishing and installing the sub-fin and tailwheel, the hatch, and the crew compartment transparencies...

Saturday and Sunday are supposed to be unseasonably warm and essentially wind free. If I flat-pattern and fold a prototype forward canopy transparency, and temporarily forgo detailed pilots, I may be able to try first flight this weekend.

Current weight of the airframe (no hatch, no pilots, no transparencies, no hook fastener [for battery], no battery) is 283.7 g. I may still come in under the 300 g target weight if I can keep the hatch weight down.

My 3S 800 mAh batteries run between 60 and 72 g... so, flying weight should be around 370 g.

Yay!
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Old Jan 10, 2013, 08:45 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,600 Posts
Quote:
Originally Posted by davidterrell80 View Post
Working my spreadsheet... I see that 80 watts works out to be 100 W/lb... about trainer performance.
Funny how things move on. 50 watts/lb used to be touted as an acceptable ratio for a trainer, 75 watts/lb for a scale job and 100 watts/lb for more aerobatic flight!

As one gets more experienced and power trains get more powerful and lighter, the availability of extra power "just in case" is more and more tempting.

I like it!
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Old Jan 10, 2013, 08:18 PM
Heads up...
RMCCOR7737's Avatar
United States, VA, Stafford
Joined Jun 2009
744 Posts
I generally try to strictly adhere to these rules:


> Less than 50W/lb - very lightweight / low wing loading slow flyer.
> 50 to 80 W/lb - powered gliders, basic park flyers and trainers, classic biplanes and vintage ('Old Timer') type planes.
> 80 to 120 W/lb - general sport flying and basic/intermediate aerobatics. Many scale (eg warbirds) subjects suit this power band.
> 120 to 180W/lb - more serious aerobatics, pattern flying, 3D and scale EDF jets
> 180 to 200+W/lb - faster jets and anything that requires Arnie-amounts of muscle!
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Old Jan 11, 2013, 12:03 PM
MPP
In Unusual Attitude Recovery
MPP's Avatar
Danbury CT (DXR)
Joined Oct 2005
2,152 Posts
Looks great.
Quote:
GWS EP 8040 (I wish it wasn't orange)
You can clean it with Denatured alcohol or lacquer thinner then wipe with white vinegar and it will take spray paint really well. Doesn't hurt to rebalance it either. Or a black sharpie will do if you just want to do it quick.
Quote:
temporarily forgo detailed pilots
I always like to have a PIC, forget the detail, put a driver in . Best of luck on the maiden!
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Old Jan 11, 2013, 01:05 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
Joined Apr 2012
2,920 Posts
I had some long days this week and got my hours in before lunch, today. So home for the final stretch.

I built a flat-patterned and fabricated a forward canopy, completed the hatch, and finished preparations for first flight.

All systems are tested and things seem to be ready; leaving only the pilot and orange propeller for later in the flight test program.

If the weather behaves as forecast, I should fly her tomorrow morning.

Cue "Shine on Crazy Diamond"
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Old Jan 11, 2013, 03:56 PM
Registerd Beaver
Smokin' Beaver's Avatar
Australia, WA, Warwick
Joined Jul 2003
3,572 Posts
Good luck Dave.
Looking forward to hearing the flight report.

- Phil
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Old Jan 11, 2013, 06:24 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
Joined Apr 2012
2,920 Posts
Engineering math...
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Old Jan 11, 2013, 07:25 PM
Heads up...
RMCCOR7737's Avatar
United States, VA, Stafford
Joined Jun 2009
744 Posts
Quote:
Originally Posted by davidterrell80 View Post
I had some long days this week and got my hours in before lunch, today. So home for the final stretch.

I built a flat-patterned and fabricated a forward canopy, completed the hatch, and finished preparations for first flight.

All systems are tested and things seem to be ready; leaving only the pilot and orange propeller for later in the flight test program.

If the weather behaves as forecast, I should fly her tomorrow morning.

Cue "Shine on Crazy Diamond"
I'll be out there too David, maidening the Camel. I wish you all the luck on yours.
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Old Jan 11, 2013, 07:33 PM
Registered User
Nederland, Noord-Holland, Krommenie
Joined Nov 2010
421 Posts
Thanks for introducing me to the Skua (and to Outerzone)
Good luck with the maiden!
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Old Jan 12, 2013, 09:50 AM
Balsa Lover
gupi's Avatar
Vienna, Austria
Joined Jul 2010
811 Posts
Good luck!
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Old Jan 12, 2013, 03:35 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
Joined Apr 2012
2,920 Posts
Good News and bad news.

Good news: the first flight was a success. She was a little twitchy in roll but I expected that, after eliminating most of the dihedral. She also needs more down thrust, being prone to climb under power more than I'd like but... I expected that, too; as a result of using the flat-bottom airfoil. I had to put my camera on a tripod and fly in front of it. I'll try to have some video up tonight. It's transferring from the camera to the other computer now. I won't spend time on it until later as I need to finish preparing the Sunday School lesson I have to teach in the morning.

Bad news: the second flight was not a success. About 20 seconds after hand-launching, during a full-power climb out, the motor separated from the motor mount. Looking at the interface, the little hex screws were not quite tightened enough. When the motor jumped out in front of the airframe, I immediately went to idle. Even so, the motor pulled the ESC and the battery far forward, through the firewall and almost out of the plane. The CG went forward with them. Going to high rates/full throws, I was able to successfully dead-stick a landing in the grass; without further damage to the airframe. I figure it will take 3-6 hours to rip out the damaged area, rebuild a motor mount, and re-stuff the systems into the airframe.

It threw me off my stroke, as when I flew my Rufe afterward, as a relief from frustration; I bashed it on its second flight when I lost orientation at low altitude and cartwheeled it. I have several hours of work waiting for me there, as well.

So I flew my UMX Mig 15... and it survived three flights, breaking the curse.

I'm torn between "Wah!" and "Hooray!"
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Old Jan 12, 2013, 04:35 PM
Heads up...
RMCCOR7737's Avatar
United States, VA, Stafford
Joined Jun 2009
744 Posts
Congrats on the "GOOD" news, sorry to here the "bad" news. I had a little bell 400 mounted like that and it did the same thing. Something about that one little set screw just ain't right.
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Old Jan 12, 2013, 05:22 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
Joined Apr 2012
2,920 Posts
Video of the first flight.
Blackburn Skua from Earl Stahl plans (0 min 0 sec)
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