Nitro Models Yak 54 (73")

An interesting twist is that replacing the USL was going to cost $325 so the funds were allocated.  Rebuilding left extra money as covering and repairs shouldn't exceed $100, and noted was a Nitro Models Yak 54 120 size for $199 plus shipping coming to $225.  It has arrived so when the USL is repaired, I will have two planes for the price of one, though the USL has and will require considerable effort to rebuild and recover.


Another interesting twist is that the Yak is not the one ordered.  Ordered was a 69" that builds under 10 lbs.  This Yak is 72" and is claimed to build closer to twelve lbs.   The G20 will fly it but it wouldn't be the performance machine it was designed to be.  Needed is an engine capable of swinging an 18" prop and that means at least a G26.  The box has been parked in the closet until engine needs are sorted out.  Looking at the MLD 28 but have not made any hard decisions.  Intentions are to continue efforts to get all other planes in good flying condition including the Ultra Stick Lite before starting on the Yak.

Note: Nitro Models offered to have the plane returned as it was not the one ordered or give a $40 credit... I took the credit and kept the plane and will use the money saved towards an engine.  This makes it a great deal as its a larger plane than the 69 inch version and its now $40 cheaper than the 69" version.



January, 2011

Facing a forecast of a long spell of bad weather, an indoor project was needed so the Yak was put on the bench.  I'm pleased to have found the fit and finish quite good and beyond expectations of what is sometimes heard about Nitro Models.

The plane is now nearing completion but either I'm getting slower or there is more work to an Arf than meets the eye.  Some changes were made to my normal fit out.  The first is that a multi tool was used to make the hinge slots.  The second is that dual flight batteries were used.  They consist of a 10 cell brick made from a Harbor Freight tool battery pack.  Also installed a choke servo as some sort of ability to kill the engine is needed.

As expected, the plane did in fact weigh considerably more than the 9-10 range of the 69" Yak.  Total weight is 12.5 lbs. The engine is an Aero JC 28cc. Prop will be either a 18x6 or 18x8 APC.

There is a little more work to be done but the finish is close.  It's reported to fly well.  If it flies as good as the fit and finish I'll be very pleased.

The Yak is finished
The Yak has flown

Flight is reasonably good.  The engine has plenty of power to provide unlimited vertical.  It required a lot of up trim, which will need sorted out.  One click of roll was all that was needed on aileron.  Fortunately, I'd gotten good advice to slow the the throws down and the first flight showed quickly that they were still too hot.  It was a gusty day but best I could tell there were pitch issues in knife edge and up lines.  Inverted only require a hint of down.  In flight CG test produced no curl or tuck.  It did not like to taxi in taller grass... due to wheel size and not a lot of tail weight.  Out on the hard it taxied fine.

The CG was rechecked and looks good and given the very minimal down trim needed for inverted, I'm inclined to think it is ok.  The elevator however is trim up 1/4" on the aft edge so it might be that the stab needs a degree of negative incidence. One other issue was it collected a lot of exhaust debrid so it might have been too rich.    Otherwise the motor ran great and stayed cool.  Running an APC 18x6 at 8900 rpm.   






I've got five flights on the Yak and consider it a reasonably good flyer.  It is what I wanted... a taste of Yak without investing big money.

An outline might be of interest.

$182 - 72" Yak by Nitro Planes - Originally $199 + $23 shipping but was discounted because they'd sent the wrong plane
$239 - JC 28cc engine (free shipping special)
$95 -  New servos from swap fest (5 high torque @ $15 ea) (2 standard at $10 ea)
$5 - New swap fest prop
$25 - Used fiberglass gear strut
$5 - Larger wheels from swap fest
__________________________
$551 - Total (less receiver)


Trimming the Yak

As noted previous, the maiden flight required a lot of up trim, 1/4" at TE of elevator.  At issue was that the flight trim between power on and power off was different.  When the plane was trimmed for half/full power, it had too much up trim for power off flight.  The numbers on the stab were +0.5 deg so I determined to shim it towards zero in an attempt to neutralize the elevator and stab for powered flight.  After the first inrement of 1/64", the local Yak guru suggested I should leave it as that is typical to a Yak.  That meant that a mix was needed to retrim the plane for low power becuase otherwise landings were very difficult.

The mix helped but wasn't ideal because jockying the throttle on landing would cause the elevator to move some.  I concluded to keep working on the stab and shimmed it another 1/32" and hit the sweet spot where elevator was neutral to the stab and power on/off trim were the same.

I've really been enjoying the Yak.  It is easy for me to see, flies at a speed that I can deal with, has lots of power and flies smooth.  At first it was slightly difficult to land becuase of the trim issues but now that low power trim is ok, it requires the usual setup and jockying of the throttle to keep air speed and it settles down without too many issues.

The large vertical stab and elevator however are subject to injecting roll from cross wind gust so one must be very vigilant when dealing with such conditions.

So far, I've been fairly pleased with the JC-28 engine.  It starts easy, runs smooth and has very adequate power for this weight airframe.  I've had one dead stick and that was my fault for too low of an idle and pulling the throttle full off while doing a spin. 

As noted in the cost outline, the gear strut was changed because needed was a strut that angled forward some.  I also elected to go with larger wheels because of our rough field.  It is now a very fun plane to fly.