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May 25, 2003, 08:48 PM
Thread OP

Electric 1/2A Shrike


While I'm new to electric flight, I am an experienced "wet" pilot who just doesn't have enough time to pile up to go to the field regularly. So I thought I'd build an electric for my local schoolyard that has a couple of soccer fields that should be good for a small plane. I've been spending some time lurking/investigating and have decided to build a Shrike (always liked them, just never got a chance to build one until now). Plus a belly lander would be best for these fields.

I've purchased the 1/2A (Speed 400) kit and I've also downloaded MotoCalc and started playing around with it. I want a brushless motor (might as well go for the gusto) and I didn't really like the suggested options from the wizard, and finally came to a setup that seemed satisfactory to both MotoCalc and I.

What I have cooked up is a Mega 16/15/4 brushless with a 7-cell pack...it should be OK with a 6x5, 6.5x4 or 7x4 prop. According to MotoCalc, I should get about 33MPH in level flight, which should be fine for flying around a couple of soccer fields, and it should have plenty of thrust for aerobatics.

The problem I have is the battery pack. I want enough capacity to fly for ~8 minutes per charge, but I really need to keep weight and internal resistance down. The Shrike fuse is only 1 3/8" wide and 2" deep, which makes it difficult to fit most packs. I'm entertaining the idea of widening the fuse about 3/4" (only need to make a couple of formers), which would also allow me to provide air ducts/cheeks for cooling the battery pack (the Shrike offers no cooling as designed and this setup will pull around 20A full throttle).

Any battery pack suggestions? What I found in MotoCalc that might work is the Sanyo 1100AE, but that would be a little on the heavy side. Should I go to a higher number of turns on the motor to reduce current so a smaller battery lasts longer? Is widening the fuse a little and provide air flow a good idea? Or am I off in the weeds here?

Any comments and suggestions would be most appreciated before I start building...thanks!
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May 25, 2003, 10:14 PM
Registered User
pda4you's Avatar
I used a 7 cell 600 mAh pack in my Shrike. The config was a square pack (with one cell missing). It was the only thing that I could fit into it. I had to cut the main spar from the fuse (the only way I could do it). I had my engineer friend look at it and he said it would be OK. The wing did not fail.

That 4 turn should be nice. I flew mine stock with a s400 and a 6x3 folder. Speed was OK, but it had a very short life.

But I will tell you it was fun while it lasted!

BTW I really like my Simple 400 with my mega 5 turn in it. The 4 turn would be even better. It goes faster than the stock Shrike!

Mike
May 25, 2003, 10:15 PM
Registered User
pda4you's Avatar
Shrike fall down go BOOM
May 25, 2003, 10:16 PM
Registered User
pda4you's Avatar
One more - you can see the black 7 cell pack dangeling from the wires in the above pic.

May 25, 2003, 10:30 PM
Tree? That's a Tx weed!
crashsiegel's Avatar
OUCH!
Crash
May 25, 2003, 11:36 PM
I'm Charged!
megawatt's Avatar
I have built two Shrikes(the first met with an untimely demise ) Both were powered with 6v speed 400 can motors, and 8 cell 500AR batteries. I use Graupner 4.7x4.7 cam props and these things HAUL BOOTY! Be for aware , the launch is tricky, and the plane gets small QUICK. Not really a park flyer , but loads of fun.
Your brushless combo should scoot. I have a mini 12/15/16 that I will try in mine. Let us know how yours goes!

Jeff

BTW welcome to the E-zone!!
May 26, 2003, 12:37 AM
characters welcome!
Mark Wood's Avatar
33mph??? I show 72mph prop speed and 25oz of static thrust on a 16/15/4, APC 6x5 and 7xKAN950s on P-Calc.

You're in for a big surprise, Smitty!

mw
May 26, 2003, 12:47 AM
Team 30 Micro EDF
Mike Taylor's Avatar
I like my Astro Flight 010 DD with the 6x3 prop and 3 x 560 (or 1020) LiPolys. The batteries are very small and light - a touch over 1 ounce for all three of them, and about 2 ounces for the 1020s... Just a thought...
May 26, 2003, 08:19 AM
Registered User
tekochip's Avatar
My Shrike had a Wattage Cobalt before it became a lawn dart during an inverted pass. The cobalt is cheaper than a brushless setup, so it keeps the tears down after a balsa rain.

It's fast, but not very aerobatic. Mine needed a fair amount of up elevator, and it usually snapped out of loops. Sounds like it needed even more speed?
May 26, 2003, 09:05 AM
Thread OP
Wow, thanks for the great replies...I'm a regular on another online forum, but not much electric traffic there. Anyways...

What kind of "real life" flying times would I get with a 500 NiCd? MotoCalc indicates the typical current would be in the 14A range, which would be just over 2 minutes? I think I would need something in the 1700mAh range to have decent flight times (maybe the 4/5AUP?).

Alternately, I could go with the 5-turn Mega and use 1100mAh batteries and get around 7 minutes (9A typical per MotoCalc). Of course, all this assumes that MotoCalc is real and not purely theory. How real are the MotoCalc numbers?

I briefly looked at the cobalts, but they seem relatively heavy and I'd rather put the weight into the battery than the motor.

I'm not really interested in lithium batteries...I design mobile phones for a living and have seen what lithium cells can do.

As for the 33MPH speed, I think I misread MotoCalc (still new to this tool)...it was indicating the speed at optimum Cl, the prop speed was 49MPH (7x4 prop). I want thrust more than speed due to field size and the need to hand launch this bird.

Maybe I'm overspecing this...I want a fun plane, not just going in small circles real fast. Any other powerplant configuration suggestions would be most appreciated.

Thanks again!
Last edited by snsmith; May 26, 2003 at 09:12 AM.
May 26, 2003, 09:10 AM
Registered User
pda4you's Avatar
You will want KAN 950 mAh or HE cells 1100 mAh. Anything else will simply be too large.

Mine went about 50-60 mph with the stock can s400 motor. It will haul with the Mega in it.

Mike
May 26, 2003, 09:18 AM
KLH
KLH
Pack Rat
KLH's Avatar
I use both an 8 cell 1100 mAh Hecell pack and a 8 cell KAN 950 pack in mine with a 6V s400 and a 6x3 folder, it moves out real well. Had to take out one of the spars to get the packs to fit, but didn't have to widen the fuse. A 16/15/4 should add a few mphs. That motor might give it more speed than you want.

Kern
May 26, 2003, 06:21 PM
Registered User
I say go with the 5 turn Mega and you easily get your 8 minutes. It will be plenty fast enough for a park.
May 26, 2003, 09:16 PM
Thread OP
bflinche, I'm also beginning to think the 5-turn Mega is the way to go. It will reduce the current and swing a slightly larger prop (I'm planning to use a folding prop). From what I can find, the Mega brushless is close in price to a good cobalt.

What I'm beginning to reconsider is my airframe choice. I may either seriously bash this kit or simply scratch build my own Shrike-like design. I'd love to have a rudder, even if it adds another ounce for the servo and linkage. What I think would be cool is a something like a small Patriot.
May 26, 2003, 09:41 PM
Speed Demon
GregG's Avatar
Eight minutes in the air with a Shrike is a Loooooooooong time! Mine seemed like it was doing 35 mph at idle!

The fuse on the stock Shrike 400 will comfortably fit 500AR, 600AE, KAN 950, and HE1100 but not much else. Lets do some simple math to figure out what it'll take to attain 8 minutes wide open throttle. The largest capacity cells in this size are the HE1100's.
1100 mah (milli amp hours) = 1.1 ah (amp hr.)
1.1 ah X 60 minutes = 66 amp minutes
66 ampminutes / 8 minutes = 8.25 amps current draw

So, you'll need to put together a motor, prop, battery pack combo that draws 8.25 amps or less to make your eight minute mark. However the prop does unload in flight and the amp draw will drop once the plane is at flying speed so you'll get a longer flight than that.

My Shrike was scratch built with a 6% thick NACA tailplane airfoil. It's make-up was vacuum bagged fiberglass over a blue foam core wing with a Caron Fiber spar. It had a 12 amp static current draw with a 2.33/1 geared 6V S400, 8-600AE pack, and a custom 8 X 8 folding prop. The plane would almost climb vertically from a hand launch and top speed was scary for me at the time (~50-60 mph?). I'd get 4-5 minute nerve wracking flights. Roll rates were awesome!
Last edited by GregG; May 27, 2003 at 08:26 AM.


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