Carf Extra 260 and MVVS 175 NP SS

Winter came, and time has come to plan experiments for the 2013 season. If my goal is to again spend more time repairing than flying, I should try something new. So to kick off I'll assemble Extra 260 with Czech MVVS 175 New Platform motor. Will we be able to do some flying? We'll about find out. 

MVVS has 90x90 bolt spacing, so I started with drilling in square, and preparing the engine mount. Engine is also 10 mm shorter than DA170, so I prepared necessary stand offs by myself, just to find out that they already came with the engine. It has also been supplied with break-in oil, spark plug tool, vast collection of stickers, and obviously - an owner's manual.

Exhaust system has been reinstalled. 

Now it’s time mount the gas tank, prepare break-in fuel recommended by MVVS, and most importantly to check the weather. If the weather is good, I’ll haul it to the gate, burn away half of the gas tank (if it runs), then compare it to DA 170. 

Weather is fairly good, so I assembled my Extra, and hit the gate. MVVS owner’s manual says how ignition should be executed, but I choose to go with the DA method: I turned on choke, few spins and engine responded, so I disengaged the choke, flip the propeller two or three times and engine came to life.  I didn’t use the throttle, it started at low revs. So it turned out that DA method works very well with MVVS.

Motor is brand new, and it needs some regulation, but it’s immediately noticeable that it's smoother than DA170, works well in lower rpm range, transitions are flawless, power is definitely higher that DA170, and what’s most important it doesn’t transfer those awkward vibrations that were noticeable in DA170. When DA170 ran, ailerons were almost torn off the wings, due to the vibrations, while with MVVS ailerons didn’t move at all. Running culture is comparable to DA150. We’ll find out how it’s performing in flight, in reverse harrier with throttle kicks, because it’s the best method to test engine usability for 3D flying. 

MVVS is narrower than DA170, due to angle in which spark plugs are mounted, so we were able to save some space under the cowling. Cowling has baffling, but I’ll put it on after 4 – 5 flights, just to save some hassle during initial regulation. Carburetor is reversed compared to DA, header obscures L and H needles, so turning them would be much more difficult, with the cowling on. After initial fly-in, I’ll regulate the motor, put on motor cowlingt and the correct propeller.  Moreover while taking the footage, engine has been deregulated, H should be on 1 ½, but it was on 2 – I initially thought that it’s the correct setting, just to find out this morning, that owner’s manual clearly states that it should be on 1 ½.

Ending of 2012 season has been successful - much to my surprise. I did some flying on the last day of 2012. It was cold, with ghastly winds, however precision flying wasn’t my intention. My intention was to perform initial flights of my model with new MVVS 175 motor. At the beginning, I took 4 15-minute flights on 1:30 mixture, and with 30x10 propeller. I flew at half of the throttle, because I didn’t want to make too much noise. Then I filled it with 1:40 mixture, and replaced the propeller to 30x12. It turned out that 30x12 successfully used with DA150 and DA170 due to high revolution count, was too noisy as well. I was stunned, because I didn’t expect it to be that more powerful than DA170.  31x12EVOL, or 32x12 (from Mejzlik, obviously – only brand I trust) should be adequate, but I left them in my house. Next time I’ll take more propellers, and even one three-blade 29x12, but I expect it to be too small. 

 

Overall, I'm satisfied with this engine:

- it starts like DA (at third try)

- smooth run, practically no unexpected jerks and vibrations

- smooth transitions from low to high revs, perfect mid range

- power is much higher than DA170, even though I’m using KS mufflers, not the ones recommended by MVVS. 

- Engine doesn’t overheat. Just after flying, I could put my hand on cylinder, with confidence. End of the engine block (just behind the propeller) was cold.  When I was starting it up next to the gate, cylinders were hot, but the section behind the propeller hub has been cold – could easily hold it with my hand (shown on footage). I’m not expecting any bearing failure, or shaft snapping, as this engine isn’t prone for overheating. 

 

What I didn’t like:

- Ignition needs 3-cell battery.

- Difficult engine regulation while the engine cowling is on. 

 

 Now what’s left is more flying. We’ll see ...


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