Yakovlev YAK55M 1520mm Aerobatic Sports Plane (ARF)

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Favourite Plane

Jul 14, 2018

15 months later.......
My Yak55M is probably the best flying, most enjoyable plane I own.
I try to be careful with it though, because I don't want to break it!
1520mm is a great size model, light and small enough, but with the
feel of a bigger plane.
What a shame they haven't restocked this aircraft.

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Yak-55M Transformed !

Jun 18, 2017

My Yak-55M flying experience was transformed by fitting a 16x10" Wooden E-Prop to the existing setup. It now flys with amazing power and control authority, so much better and more relaxing to fly without my previous fears of suddenly stalling or over-controlling.
I noticed the same behaviour on my smaller 49" Yak-55 when I finally got it propped correctly, this design seems to love a big powerful prop.

The carbon undercarriage legs are a bit short on this Yak, which has relatively small wheels under the nice looking wheel pants, so I'm mowing the taller grass on our strip when taking off with the big 16" prop !

For my Tx Profile, I simply made low rates in the UP switch position, and I don't even use full rates for normal flying at all.

Today's flight was incredible, unlimited vertical at 50% throttle, this is the most powerful plane I have ever owned, and it feels awesome to fly and a privaledge to own, I am still smiling :D

Highly recommended if HobbyKing decide to restock it and full marks for this review.

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Flight with the big motor

Jun 01, 2017

The Yak 55m was flown with the Turnigy L5055C-700kv motor, 3300mah 4S 60C-120C battery, using full size servos with a 900mah 2S lipo and a voltage regulator to power the receiver and servos, 15x8" Electric wood prop, 100a ESC for an All Up Weight of 2.966 kg.

It flys beautifully as a sport aerobatic model at the 3kg weight, but it's too heavy for 3D use in my opinion. The 4S setup as above with the 700kv motor maxes out RPM at about 3/4 throttle, so I'm going to fit a 16x10" prop soon to take advantage of all the power this setup has.

I really don't know how I could cut down on the weight, the only thing I could do is use smaller servos, but this would only save about 60 grams (2oz). If I removed the plastic housing from the Rx and the Voltage regulator, I may save another 10-20 grams, but there is not much more I can trim from the model, there is no ballast fitted at all and the CG seems pretty good.

I found the flying very scary at high rates, easy to stall at all airspeeds if you are too heavy on the sticks, even with lots of Expo, so I fly at 50% rates and the Yak is on rails, very nice and safe to fly on low rates, and confidence is high with the low control throws. I built the plane into RealFlight, and I found the same behaviour with the high rates, it's much nicer to fly on low rates in the sim as well.

At 3kg, this Yak 55M feels brutish, lots of inertia, good glide angle with a much longer takeoff and landing roll and higher than expected stall speed than you would have with the documented 2.5kg weight. The main gear is short, and it's stance on it's wheels results in a very low Angle of Attack while rolling on the deck, and the prop is close to the ground, making for longer takeoff runs until speed builds up enough for the shallow AOA to provide takeoff lift. You will want smaller diameter 3 blade prop or big wheels without the supplied wheel pants if you operate from rough grass, fortunately our strip has short grass.

My request for an engine cowl replacement was promptly authorised by HobbyKing and a new part arrived this morning, but it was the wrong part, and it appears to be an S-Bach canopy for the same size plane as my Yak, so I made yet another request for the correct cowl to be sent to me.

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Maiden Flight

May 22, 2017

Hobbyking prompty authorised my replacement engine cowl request, thank you HK.
Approx. 4-6 week wait for manufacturer to send a new one, I can wait.

The manual specified a CG point, but it was WAY too far aft and this Yak was so scary to fly that I only flew it for about 2 minutes and decided to land it before bad things could happen. CG could not be trimmed out. However, the Maiden flight was done with the
HobbyKing Donkey ST4010-820kv motor......

https://hobbyking.com/en_us/hobbyking-donkey-st4010-820kv-brushless-motor.html

and I wasn't even sure it would get off the ground with a 15"x8" Wood/electric prop, but I was shocked to find the Yak going into vertical rolls with this cheap little motor!

I'm waiting on my Turnigy L5055C-700kv motor to arrive:
https://hobbyking.com/en_us/turnigy-l5055c-700-brushless-outrunner-700kv.html
.... I only ordered the cheap donkey motor at the Aussie warehouse to fly the model while I waited for the big motor to arrive from the HK warehouse.
The big motor weighs 100g more than the Donkey motor, so I think that is going to fix the CG by itself when it gets fitted, but after seeing how much power that Donkey motor puts out, I think the new motor is going to turn this Yak 55m into a beast, I'll write more when I get it sorted :)

Flight lipo was 3300mah 4S 60-120c Turnigy Heavy Duty, with 100a Opto ESC. I thought a 70a esc would be sufficient, but it's only a 4S system, so I figured higher possible burst amps might be desirable, and the weight penalty for the 100a esc was not much. The big motor I ordered has a max amp rating of 60a, and it's rated 1600W, so it must get the higher watts with more cells than 4S, otherwise the amp rating would be more right? Anyway, the 100a esc gives me a safety margin I hope.

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Nice Aircraft

May 19, 2017

This is a well built and nicely finished model, the only issue is the faulty engine cowling that came with it. I did my research on this plane before I bought it, and I read reports of the well made cowling, but this one is obviously defective, unfortunately. I requested a replacement from Hobbyking, so we'll see how that pans out.

It looks like the flying weight is going to be well over the stated 2.3-2.5kg, I think closer to 2.8kg and I've tried to keep things light as possible. I'll post more on this review once I've flown it.