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Old Mar 16, 2012, 03:18 PM
Allways the hard way!
georgy's Avatar
South Africa, GP, Germiston
Joined Jan 2012
460 Posts
Build Log
MIG-15 Slot-jet

I've always loved early jets, & after building the Skyray I just had to try...
I used a 3-view from Wiki, cleaned it up a bit & used an old-school projector to cast the shadow directly onto the foam-board!

It is 820mm w/s & airframe weight is 120g before hardware & glue.
Power will be from a Turnigy 2508 3500kv heli motor spinning an APC 4.2x2 prop. The prop fits fully into the fuse hight, so i will be able to put bracing top & bottom to sturdy the fuse. (c/f or bamboo)

Initial tests on the power set-up looks promising. I actually can't believe how that little prop pumps!! I want to also try a 4.1x4 prop but the amps looks a bit high for the esc i want to use. (next avail esc is huge!)

Any one know where CG on this type of airframe should be?
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Old Mar 16, 2012, 11:33 PM
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Joined Jul 2009
143 Posts
Start out about one third the way back from the leading edge at the wing root. Balance it at that point with some weight on the nose. Find some tall grass and see if it glides! That will get you close.
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Old Mar 17, 2012, 03:37 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
8,589 Posts
Plenty of CoG download programs on web ... all you need is conventional swept wing.

Often it works out as 25% of wing area ahead and 75% behind ... so all you have to do is calculate wing area and then do the % to find the point on wing.

If you do 30% back as another says - you'll likely be nose heavy as the wing is swept back significantly.

Another way is to ask the EDF guys about a Mig model and where they have it ...
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Old Mar 17, 2012, 09:05 PM
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Joined Jul 2009
143 Posts
Yup, all good advice. But, you have the perfect chuck-glider right now... no electronics, minimal time invested. Make sure your elevators are neutral and glide it till you get the CoG dialed whether you start out 25% or 30% back. Remember, a little nose heavy on the maiden flight is way better than tail heavy. Sometimes it is difficult to calculate the CoG on the profile fliers as the whole flat surface acts as a wing.
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Old Mar 24, 2012, 08:29 AM
Allways the hard way!
georgy's Avatar
South Africa, GP, Germiston
Joined Jan 2012
460 Posts
Been a while... work,work...

Finally managed to finish the Mig last night. 1st thing this morning off to the park for the maiden....

Auw is a hefty 430g! Same as my SKYRAY, with half the wing area... so i was a bit worried about the launch. I even mixed in some flaps. Wasn't needed. climbed out very well. Got the cg too far back, as it was hanging its tail all the time. Easy to fix. The loop was a bit scary.... turned out to be a back-flip-stall! Got some work to do there. I'm hoping its due to the cg being out?? Any ideas?

1st flight was with the 4x2 prop. Just preparing to go back & try the 4x4.

Still, a whole lot of fun. It looks awesome in the air and the landing speed is surprisingly low. Must try & get some video. I mostly fly alone! Not too many mates into RC!
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Old Mar 24, 2012, 11:13 AM
Allways the hard way!
georgy's Avatar
South Africa, GP, Germiston
Joined Jan 2012
460 Posts
Modified the CG on the Mig. Flies a lot better, but the loop is a bit of a mystery! Fly it nicely into the loop with minimum required elevator, loop over the top all ok, but as you come out the loop towards level, it seems to flare into a bit of a stall??
Result is loss of a lot of altitude & airspeed.

The roll is also very slow despite decent throw on ailerons. (only 25mm wide, about 3/4 of wing)

Maybe the flat skinny wing?? Thinking of adding a KF-2 insert on the wing?

Any ideas?

The general flight is very jet-like, but aerobatics is a NO-NO!!

Anyway, back to the drawing board i suppose....
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Old Mar 27, 2012, 12:11 PM
Allways the hard way!
georgy's Avatar
South Africa, GP, Germiston
Joined Jan 2012
460 Posts
Added a KF2 section to the Mig's wing. Boy, what a differance. Actually got the plane to loop with-out funny antics. Still not perfect, but a lot better...
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Old Mar 30, 2012, 12:45 PM
Allways the hard way!
georgy's Avatar
South Africa, GP, Germiston
Joined Jan 2012
460 Posts
Any body know what those wing-gates do on the MIG wings? Some swept wing planes got them, some dont.

I guesss what i'm asking is does models need them?? (particularly flat-foamies like this Mig)

Progress on the MIG: I trimmed down a bit of width on the horisontal section of the fuse... about 10% & added about 20% to the area of the horisontal stabiliser.

Just waiting for a gap in the wind to test again! This bird will fly proper if it kills me... (or more likely my $$$ balance)
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Old Mar 30, 2012, 04:40 PM
Pusher jets rule!
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Mesa, AZ
Joined Jan 2006
17,638 Posts
The wing gates were added to help keep the wingtips from stalling. On these flat foamy models they would really just be there for semi-scale appearance.

I love profile jets, and have been trying to devise a few new designs based on the Century Series of US jets. I need to tinker around with those some more, and maybe an F-86 too.

Pat
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Old Apr 01, 2012, 12:28 PM
Allways the hard way!
georgy's Avatar
South Africa, GP, Germiston
Joined Jan 2012
460 Posts
Changes to the Mig worked well. Behaves more like sport plane now. Despite much impoved aerobatic performance, it still looks best flying wide smooth curves. Wot low passes... slow, low passes... very stable & landings a charm...

Only bummer is waiting for charger every 6 minutes. Gotto get more lipos
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