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Old Jul 15, 2001, 11:57 PM
H2OFLY
Portland Oregon USA
Joined Feb 2000
2,509 Posts
What thrust line for twin Kadet Senior?

I am going to finish my twin-motored wing to go on my Kadet Senior fuselage. What thrust line would work best for this high-wing model?

Thanks,

Terry
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Old Jul 16, 2001, 12:57 AM
Speed Demon
GregG's Avatar
Antioch,CA,USA
Joined Dec 1999
12,280 Posts
I'm no expert nor am I an engineer type but it seems to me that the thrust line is angled to offset any drag induced pitch changes on an airframe. With the original plane the motor is below the center of drag. The motor would be pulling the wing (source of highest drag) and causeing a pitch up moment so they usually give it some down thrust to counter the motor incited positive piching force. With the motor on the wing, its pulling the drag straight ahead. You may get a bit of down pitching from the the fuse and landing gear drag so that maybe just a touch of up thrust would do well here. Hopefully, someone with a bit more experiance will chime in now. The drag model makes sence to me though.
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Old Jul 16, 2001, 08:26 AM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
12,788 Posts
I'd go along with Greg (I have to build one of these twin things!) and start with Zero, keeping the option to add a little "up" thrust if needed. His version of the force setup sounds real good.

Know about the thing with oily twins about angling the motors out, but assymetric deadsticks are their problems, so zero to a possible couple of degrees right thrust sounds good in that direction.

You can always have a crafty test fly before you go building sexy nacelles around the motors, too.

Dereck
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Old Jul 16, 2001, 10:22 PM
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Folsom,Ca,USA
Joined Apr 2001
992 Posts
Hi,
I'd start with zero thrust angles.

As I recall the stock Senior has quite a bit of downthrust to counteract the low engine thrust line, with the motors on the wing
the pitch up will be much less or gone.

The Senior is such a blimp that it probably won't matter, but just mount the motors so you can shim them just in case.

And, of course, dead engines are not a problem with e power.

Dave
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Old Jul 17, 2001, 01:30 AM
H2OFLY
Portland Oregon USA
Joined Feb 2000
2,509 Posts
Thanks, guys -

Wise counsel...and I had forgotten about NOT building the nacelles until after testing, Dereck...mucho gracias!

Terry
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Old Jul 17, 2001, 08:11 AM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Terry
A UK buddy of mine built a triple motored S400 flying wing thermal snoarer and came up with the neatest motor mount I've seen.

Two dowels, spaced so the motor would just sit on them. Drilled through the LE and the spar web. Motor was placed on the dowels and held on with a length of heatshrink. The wires went back into the wing just above the LE. That was with 400's...

My triple motor Lazy Bee had a ply plate from mainspar to motor frontplate. The plate, about as wide as the S400 motor, was screwed to blocks glued ahead of the spar and the back face of the LE. Two short lengths of tri-stock formed a cradle for the motors, which were then banded on. Wires run under the wing, as it was more or less removable for swapping motors around.

I recall the Bee having zero/sero thrustlines on the wing motors, the nose motor I can't remember - but my Bees never achieved straight and level for long enough for it to matter much

It flew as well on the wing motors as all three, but the noise on three was far cooler!

One side benefit - it could fly along slower and far more nose up than it did under single glow power, and that was with 6" direct drive props. Something to do with the propwash over the top wing surface maybe?

Dereck
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Old Jul 18, 2001, 02:10 AM
Speed Demon
GregG's Avatar
Antioch,CA,USA
Joined Dec 1999
12,280 Posts
Dereck, you motor mount idea sounds like the mounts on the Goldberg Mirage 550 and the GB Electra. Goldberg recommended wrapping a rubber band around the motor and mounting sticks. This was one way of making the front end a bit more begginer friendly. It works great, and helps to absorb some hard landing shock.
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Old Jul 18, 2001, 07:54 AM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Hi Greg
It's getting very hard to "invent" anything new - there's always some modeller who's been around so long they remember the last time an idea was "invented"

Not sure I'd want to trust 300 watts to some rubber bands though

If I recall right, somewhere on Ken Myers homepages there's Keith Shaw's article on twins. One shot shows the nacelle design he used on his DH88 Comet. Uses an inner frame that supports the retracts and motor, with the nacelle shell as a light cover. Blindingly simple!

Have to do one of these twin things soon...

Dereck
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Old Jul 18, 2001, 06:19 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Terry
Just got my RCMW in from UK with a freeby electric twin plan - some kind of German WW2 transports.

Anyway, the motor mounts - blindingly simple.

Two rectangles of wood, two lengths of square hardwood, though dowel would work. The rectangles are glued to the aft face of the LE and the front face of the mainspar and hang out under the wing. They have holes for the rods, which slide through them. Motor is mounted onto the front of the rods.

Nacelle is carved white fairings to the wing, bottom of a round plastic soap container as a radial cowl. One round former slips over the rods, to support the 'cowl' front.

He used square hardwood to mount Mini-Olys, dowel would do for a round motor and round holes are way easier to drill than square ones

Hope that makes sense

Dereck
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Old Jul 19, 2001, 10:29 AM
Speed Demon
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Antioch,CA,USA
Joined Dec 1999
12,280 Posts
Quote:
Originally posted by Dereck:
Know about the thing with oily twins about angling the motors out, but assymetric deadsticks are their problems, so zero to a possible couple of degrees right thrust sounds good in that direction.
Dereck
I have to say I must have all the luck. I have a twin Islander that had a motor out situation, on takeoff climbout, no less. One of the motors ate it's brushes before the other causing a one motor landing. It really wasn't that difficult a landing. I think some people expound about this more than is needed. I remember getting somewhat panicked once I figured out the problem and the shaking started in (my shaking!) but the plane came back around just fine and did a nice landing on the runway. On thinking it over later, I couldn't see why I was shaking, it must have been all the "One Motor Out" hype I had ingested over time.
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Old Jul 20, 2001, 12:29 AM
H2OFLY
Portland Oregon USA
Joined Feb 2000
2,509 Posts
Even more great ideas!

Thanks, guys. I had intended to use plastic bottle bottoms for cowls; now I am thinking that, with the right plastic bottles and some adept slicing, I can make the nacelles that way, too. Miracles of plastics!

Now I have to escape from work enough to finish this wing...had it framed some two years now!

Thanks,

Terry
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Old Jul 21, 2001, 09:35 AM
Registered User
BRAMPTON, ONTARIO,CANADA
Joined Jul 2001
11 Posts
Hi Guys,
I modified my Senioria using the articles by Bob Kopski back in 1992(?). Then in '95 I turned it into at twin using a pair of Astro 05's and 16 cells. I too was not sure of the correct thrust for the motors so I started with the motor shaft parallel with the bottom of the wing surface, this worked out just fine so thats where I left it!.
The other mod. was to add ailerons to the stock wing and this works without having to couple the rudder too.
With this setup the flying weight is about 6lbs 14ozs and it flies great.
Regards
Geoff.
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Old Jul 21, 2001, 09:42 AM
Registered User
BRAMPTON, ONTARIO,CANADA
Joined Jul 2001
11 Posts
With refernce the my previous post, there is a photo of my Seniorita in the Jan/Feb 1996 EFI page 44.
Thanks, Geoff.
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Old Jul 21, 2001, 10:02 AM
Registered User
Chilliwack, Canada
Joined Sep 2000
710 Posts
hi just a note here dead engines might not be a problem with e flight but i recently did have a prop come off in flight which is just as bad as a dead engine . I cut the throttle right away and landed.I noticed right away by the pull of the airplane and the whinning of the motor with no prop.
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