erans

A few weeks ago I was asked by a friend to find him a Petrol aerobatic aeroplane on the budget to be his first venture into "larger" petrol powered aeroplanes. I suggested a 30cc size as he has storage space constraints and my experience is that a smaller aeroplanes (20cc size) will not fly as well.
A week later I stumbled on a Seagull Models YAK 55 advertised on the Facebook Marketplace, in "as new" condition with servos and engine for $700AUD. In parts alone it was worth substantially more, so I bought it.

Quick inspection at home of what I got:
The aeroplane looked as if it was never flown and if it did, it was in perfect condition (corroborating the owned statement). New cost at the time it was available many years ago was $520AUD.
The engine received was O.S. GF30 30cc 4 stroke petrol. The engine was run previously, but looks as it may had a maximum of 2 tanks of fuel through it and looks as new. This engine will be removed as I want to maximize power for my friend intended aerobatics use of the aeroplane. New GF30 cost is $880AUD.
All servos were installed, 4x JR DS8411 (as new cost was at the time it was available $120AUD each) and 2x Hitec HS-5645MG (as new cost was at the time it was available $80AUD each).
The wings arrived in a wing bag, not a bad start...




Cheers,
Eran

erans

I apologise in advance that I do not have detailed photos for every aspect that I will be mentioning in this thread.
This YAK 55 ARF has some serious issues in design, the most serious is the fact that the pull-pull setup is not crossed, but parallel run (inside preinstalled tubes). I could not see an easy way to pull the tubes out without risking damage to formers deep inside the fuselage. I therefore decided to retain the setup for the time being. To have a full rudder deflection available I had to install the massive servo arm (which is same width as the rudder hinges). The manual calls for only 30mm deflection at high rate for the rudder...
I did a 3 way engine trade to get the desired DLE 35RA for this aeroplane, trading a Saito 30cc 4 stroke I had for the DLE 35RA from a friend and keeping the OS 30cc 4 Stroke for myself.
The engine was installed on the supplied standoffs and the holes in the firewall for the previous mount were filled with dowels.








Cheers,
Eran

erans

Cutting the cowl for the DLE 35RA was done using a template. Once the cowl was fitted it was obvious that the new engine is not aligned with the front of the cowl.







Cheers,
Eran

erans

Aligning the cowl required modified screws location at the bottom. Due to the massive gap between the cowl and the fuselage, a piece of plywood was added.
All the screw holes were re-drilled and fitted with a plastic insert which is a piece of Sullivan's Gold-N-Rod. This prevents the screws from coming out.
The cowl screws and all servo screws were replaced with socket head "servo screws" (from RTL Fasteners).







Cheers,
Eran

erans

From the very beginning it was quite obvious that this aeroplane will need weight in the nose. Therefore, the ignition module and ignition battery were mounted as far forward as possible. The battery mount is 3D printed own design, with some rubber to protect the soldered wires of the pack. A ZY Hobbies fuel tank was fitted on a mount I fabricated, replacing the smaller capacity fuel tank that was in the aeroplane when received. The optical kill switch was received with the aeroplane.






Cheers,
Eran

erans

Due to the use of large rudder servo arm, it was impossible to mount a throttle servo next to the rubber servo. It would also put the throttle servo behind the CG.
I glued plywood to the floor just behind the fuel tank and fabricated a removable servo tray (similar to what is used in many aileron servo mounting). The rod to the throttle is a Sullivan Gold-N-Rod with a ball link at both ends.
I had to be careful not to block access to the wing screws next to the throttle servo.








Cheers,
Eran

erans

I made a tray and mounted the LiFe receiver battery as forward as I can while still being able to remove it for charging. I made holes for the fuel and vent line to exit and mounted the main and remote receivers.
The receiver is the only item I mounted "willingly" behind the CG on a custom made mount (being very light weight), but also due to convenience of cable management and having the antennas as far away from possible interference. The antenna ends were routed into a clear tube.









Cheers,
Eran

erans

Control movement was set, much close to the manual hi rate for my low rate. Not from choice, but due to the factory control horns and alignment to the servo which prevented setting the recommended low rate without major rework.
First attempt to put the aeroplane on the balance machine proved almost impossible as it was extreme tail heavy for the stated 130mm CG in the manual.
I fabricated a mount to go on the stand offs and flattened lead sheet to be used as weight. The aeroplane already had some weights as received, estimated to be over 200g in total. I had to add 790g to balance the aeroplane to the factory CG. This is obviously unacceptable amount of weight and is pointing on poor design and possibly conservative CG location?












Cheers,
Eran

erans

Regardless, I took the aeroplane to the airfield and maiden it as is. It fly OK, but feel nose heavy to me. It does all the aerobatic maneuvers with ease and has plenty of power as expected. slowing down for landing was tricky. When eventually brought for landing at manageable speed in 3 point nose high decent, it violently dropped a wing which was just caught on time due to the very large aileron inputs I had.
At home, I calculated the CG range to be 132mm - 166mm (25% - 33%). The factory CG of 130mm is in front of the calculated range... Once my friend had some flights we will move the CG back a bit and see how much weight we can remove and if the performance improves (I am reasonably confident that it will dramatically).




Cheers,
Eran

erans

When originally assembling this aeroplane I forgot to cut access to the engine tuning screws. Here is how I rectified it.










Cheers,
Eran