Yak18t engine starting advice

[MrDig]

Hi Guys, recently I purchased a Yak18T, a beautiful machine. I would like some advice on starting the engine. Im getting better at it but would like some advice from other Yak18T owners to see if Im holding my tongue in the correct position. At present I prime the line up to pressure, this takes about 8 pumps before correct line pressure. Then prime the cylinders 4 pumps, swing the prop several times and another 4 primes. On pushing the starter, it does fire normally very quickly, I then switch on the Mags. I have the throttle at about 1cm. Ive noticed if it doesnt fire within a few seconds, its not going to fire at all and best to wait 5-10 minutes before restarting. Its about 12 degrees here in NZ at present so not the best time to purchase a radial engine. Im paranoid about hydraulic lock by over priming with fuel (before starting I swing prop 20-30 times with lower cylinder valve open to drain oil). Any advice would be much appreciated

[Shaggy Sheep Driver]

I used to part-own a Yak52, with the same Vendeneyef M13P engine. Starting routine is back in the mists of time, but I did publish an article on the aeroplane in 'Pilot', and I reproduce the engine start sequence below. I was religious about 'pulling though' the prop and removing the drain plugs from the lower cylinders to preclude hydraulic oil lock, but I never heard of this happening through over-priming; that usually led to setting the nosewheel tyre on fire!

After turning on the main air valve, setting the various switches, priming the engine, and pumping up fuel pressure it’s time to start. Coaxing a big radial engine into life is part of the joy of operating an aeroplane like this, and is a bit of an art. Correct priming technique is important; not enough, and it won’t start, too much and you risk a fuel fire. Winter starting of a cold engine requires the prop to be pulled through in between primes – more easily done with the assistance of a ground helper.

I call “clear prop”, while holding my right arm vertical and rotating my extended forefinger in the air for a couple of seconds as a visual signal for those out of earshot – if a Yak is starting up anywhere near you, you need to know about it before it happens. I hold the stick back in the crook of my right arm (old taildragger habits die hard) with my forefinger on the start button to the left of the panel, having flicked up its cover. My left hand rests on the one-third-open throttle lever. A glance round to check all is clear, and I press the button. There’s a loud ‘pop’ followed by an asthmatic wheezing as compressed air is admitted to the cylinders via a pneumatic distributor to turn the engine. The prop jerks slowly round a revolution and I flick the mags to ‘1 + 2’ (you really need three hands for this) and one cylinder fires. I release the start button and pump the throttle to keep the prop turning. More cylinders join in with a sudden roar, and clouds of smoke stream from the exhausts. The prop dissolves into an invisible disc, blowing the smoke instantly backwards – but it’s not sustained and the engine dies, clattering round slower and slower, the prop becoming visible once more. I pump the throttle again, my right hand going to the primer. But before I can decide whether to prime or not, several cylinders fire up raggedly accompanied by more grey smoke which is blasted under the wing by the propwash. The engine dies again, the prop slowing, but only for a second or so. With a glorious throaty roar all the cylinders report for duty, and this time as though they mean it. The engine clears its throat with a cough or two, becomes self-sustaining, and settles into smooth regular song. The battle is won and I snap the starter button cover down.

A friend described a Yak start up as ‘biblical’ – lots of noise, lots of smoke, the ground shaking, and the smiting of lesser objects. This latter point is one to watch; anything much more than idle power can blow over a light aircraft in the propwash.

Now we have all nine cylinders rumbling away contentedly, oil pressure in the green, RPM at 50% as we wait for the oil temperature to rise to at least 25 degrees C before taxy. In winter with a cold-soaked engine, that can take fifteen minutes or so. The big radial makes a glorious sound as I complete the after start checks and do the radio calls while standing by to open the cowl flaps as the cylinder head temperatures rise faster than that of the oil.

SSD

[sycamore]

If you try `yaksource.com`,there are links to lots of sites,one especially about the myths and magic of the engine.A`must` for Yak/Sukhoi pilots..Also `yakuk.co.uk`,Mark Jefferies site..

[Amblikai]

Shaggy Sheep Driver... Thanks for that. Very cool to read! Something i wish i could see first hand!

[eharding]

At present I prime the line up to pressure, this takes about 8 pumps before correct line pressure. Then prime the cylinders 4 pumps, swing the prop several times and another 4 primes

From the Yak-52 perspective, this sounds wrong. First prime the cylinders - primer to the right - ideally one prime for every ten degrees below CHT 100C (but don't prime above 80C, and I find not required above 40C if run recently), with someone pulling a blade through between strokes on the primer. When very cold ambient conditions, leave for 90 seconds to allow the fuel to vapourise slightly - then immediately before starting, throttle open about an inch, primer to the left, pressurise the lines, then back to the right, engage the starter, as it catches mags on, and if cold encourage it with some additional strokes on the cylinder primer. I'd guess if you're pressurising the lines and *then* the cylinders, you're losing the pressure in the lines. I defer turning on the air until the manual manipulation of the prop has been completed.

Pulling the blades through 30 times is overkill - a dozen blades will either clear any oil that can be cleared by pulling through, or, by resistance, tell you if you have a hydraulic lock. If you don't have it already, consider having an inlet manifold drain fitted - standard Russian practice (without the drain) required removing the cowls and manually draining the inlet manifolds if the aircraft has been standing for more than a few days, since pulling the prop through isn't effective in removing oil in this area - the addition of the drain, and leaving the aircraft with the drain open, stops oil pooling in the inlet manifolds.

The other top tip I learned recently about 18Ts is not to park on a slope somewhere in the inner Hebrides with the right wing down, since this can apparently allow the priming system to dry out, which can only be fixed with the help of a Nanchang, a Cherokee 6 and a hell of a lot of avgas.....

Edited: to stop the OP rushing out and performing 10 times the required amount of priming...

[Wide-Body]

Hi MrDig,

Check your PMs. Eharding advice is vgood. Some of the others is good but with significant bits missing.

Wide

[TheGorrilla]

Shaggy Sheep Driver mentions 50% RPM after start, if your starting from cold this is a little too high. 38%-41% is recommended during start with a gentle initial increase to 41%-45%, then when the oil temp needle starts to rise set 44%-48%. So in a nutshell you shouldn't set more than 45% till your oil is warming up. I know this sounds like I'm being picky, but it's cheaper than damaging engine components.

Try the SkyTrace website for procedures regarding the M14. It's largely aimed at Yak 52 owners though.

[Human Factor]

Further to the above (which is good to hear as I own a tenth of the engine which eharding and TheGorilla are talking about), even pulling through the engine with care can help prolong it's life.

Hopefully you have the manifold drain modification but if the engine has been standing for some time (think days or longer) and there is some resistance to pulling through the blades, don't just pull harder. The chances are there is a significant amount of oil in the lower cylinders which may require removing the cowling and lower plugs. Also, although you are supposed to pull the blades through nine times, I always pull it through ten (I have ten fingers - even I remember that), which means if I miss one, I've still pulled it through nine.

As mentioned, the Skytrace website is the best source of info (followed by Widebody).