|Oct 16, 2010, 04:12 PM|
Alfa MiG 15 MkII
This is my second Alfa MiG15. I enjoyed the first one so much, that after the demise of the MiG21, I couldn't help myself. If there is a better looking, better flying small EDF, I haven't yet seen it.
This one was built using the tips and tricks from my first build, as well as lessons learnt along 2 and a bit years of flying my first one.
In my first one I used a single aileron servo, a HS-81 to ensure there was good torque to handle the (potential) speed as well as ensure decent centering over a 9g servo. The single servo made aligning the ailerons (especially the recommended 2mm of reflex) a pain, differential all but impossible and the servo took up valuable space inside the fuselage.
This time around I found some ultra thin servos from HK which fit inside the wing nicely. Once the control rods are removed from the wing the weight gain is minimal, only 1g heavier then using a single 9g servo or 6.6g lighter then the single HS-81 of my old MiG 15. And all with the ease of setting up a two servo wing plus the ability to use differential.
Next step is to glue the wings on. Here I used a similar method to last time. First and absolutely critical is to remove the paint from the fuselage join area. I use methylated spirits. Next, rough the surface up a little with fine sandpaper to remove the glossy finish from the Alfa mold. Then lots and lots of little holes (approx .5mm) are pricked into the foam at the join area to really key the glue into. Give the metal wing joiner a light sand where it slips into the wing spar and wipe over with methylated spirits.
The next step is to fit the joiner to the fuselage and then each wing is dry fitted. Getting the incidence right is key to a nice flying model. Following the advice of others I set the leading edge in the centre and the trailing edge at the top of the mounting area. Then pin the wings in place and tape the wing joiner to the top of the inlet ducting. Double check everything is aligned equally, the wing tips are about 15mm off the bench, unpin one wing and coat the gluing area and wing joiner with 30min epoxy, pin it back and wait for the glue to set (I let it sit overnight).
Next day repeat on the other side. In my last MiG15 I found that after a while the fuselage developed vertical cracks leading from the wing leading edge down. I put this down to the wing tips catching on clumps of grass during the take off and landing slides, not helped by the excessive andihedral I had built into it (the wing tips were almost level with the bottom of the fuselage) and the less then perfect grass strips I used.
To counter this, I first of all made sure that less andihedral was built in, and I also added a strip of balsa on the inside of the fuselage at the wing leading edge [Photo 9] to spread any bending loads.
The tailplane is then fitted - to get the incidence right the popular line of thought is to set the LE at the top and the TE at the bottom of the mounting area. Again remove the paint, and use 30min epoxy to glue the bamboo spar and tailplanes onto the fuselage. Make sure both sides have the same incidence.
That's pretty much it, the plane is otherwise a sinch to put together. I used the supplied decals for the Czech aerobatic team. Last time I used the Russian scheme, and while this is my preferred choice, it makes it a bit harder to see in the air. Alternatively you could paint the plane in something like the Russian "Red 5" aerobatic colours, but paint can add a lot of weight and I wanted to keep this in check.
This model uses my original MiG15 Alfa fan (also was used in the MiG21). I upgraded it some time ago to the 5 blade fan which sounds much better and makes more thrust then the 3 blade (less speed though, apparently). Coupled to this I have a Don's Wicked 4800kV, and for the first time (for me) have made up a new thrust tube to reduce the exhaust outlet to what Don recommends. Don very kindly designed the pattern for the trust tube and centering ring, which can be found here http://www.rcgroups.com/forums/showt...1040555&page=2 (it's mislabeled as a MiG21 thrust tube).
Lastly, there are some excellent tips around about applying decals. From what I have learnt there are only a couple of golden rules. Don't leave the decal in the water for any more then 10 secs - any longer washes away the glue the decal needs to stay on the aircraft over time. Put the decal on a non-porous surface to soak - a porous surface allows the glue to wash away. Use a good quality decal set solution such as Testors to set the decal to the foam. When it is all dry a day or two later spray the airframe lightly with a light coat of Testors gloss, then a light coat of Testors dull to help protect the decals.
Alfa MiG 15
Alfa EDF 60/25 (5 blade fan upgrade)
JR R770S SPCM RX
Don's Wicked 4800kV outrunner motor
Extreme RC 40A ESC
Multiplex Nano S elevator servo
Vigor VS-12M aileron servo (x2)
3S 2350mAh 25C / 3S 1800mAh 40C / 4S 1800mAh 40C lipo batteries
Maiden was a non-event. Fitted the 3S 2350mAh, dialed in about 3 clicks of down trim and after gathering speed on the ROG it took off itself with a gentle, positive climb. It needed a further couple of clicks of down trim, and that was it! With the new thrust tube vertical was excellent and it was really moving on a flat level pass. Nice groovy turns, not a single bad habit. Can't wait to try it again with the lighter 3S pack and the 4S pack.
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|Nov 04, 2010, 04:28 PM|
Great pics CaseySP, I am building my Alfa MiG-15 & this thread has been a big help. Question, where is your COG? I'm almost ready to balance my MiG & am wondering what works for your bird? Thanks!
|Nov 14, 2010, 09:37 PM|
Thanks Ramon. Apologies for the late reply, for some reason the email alert didn't work for me.
CG is right on the Alfa markings - what I do is transfer the markings to the top side of the wing and balance the plane inverted. The battery is above the datum line of the fuse, so it is easier to balance inverted then right-side up.
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