It is safe and is a common practice. Don't worry; with the cowl you have more friction/drag.

flying without a cowl is fine. But as a precaution I usually tape up any openings around the firewall where air can get into the fuse. I once saw a 40% plane lose its top wing covering because air got in and created pressure inside the wing - thanks to the small inside opening where the wing meets the fuse.
This is of course not to say it would necessarily happen on every model ... for whatever reason the path of the airflow in that model led to pressure build up... But then you can never be too careful, right?     

Quote from: gauravag on October 20, 2010, 03:42:26 PM
One more quick question - IS it safe to fly a the Yak without the cowl ? I am thinking I will keep the first flights without the cowl. The big frontal area has me worried though.

Check the CG again w/o cowl...

Quote from: gauravag on October 20, 2010, 06:48:37 AM
Back to the ignitiion power source. I do not have a Nicad/Nimh 4.8 . Would it be safe to use a Life with a diode power regulator (Align one from heli) ? It has 2 diodes in series, and a fully charged Life gives 6.25 volts with it. Without it the voltage is 6.8V

Would this be a safe setup to use ?

I m using 4.8vts. 2000 mah batt. w/o any probs. Manual says, below 6 vts. Above 6 vts. may damage your CDI unit.

I got the fuel today. 3 litres petrol and mixed 100 ML of LawnboyAshless. that makes a 30:1 fuel.
Whats the proper starting procuedure for this engine? From the manual i gather :

1. Choke Closed, 1/4 thorttle, Ignition Off - 5-10 flicks to pull the fuel.
2. Choke Closed, 1/4 thorttle, Ignition On - a few flicks to get the engine to fire
3. Choke Open, 1/4 throttle . ignition On - to start .

Pretty much.  I think we had to flick more times on [1], until we saw the fuel move in.  I do remember at least once we cheated by putting a few of drops of fuel directly into the carb of a 75cc 3W engine, whose engine was not started for probably couple of years or so.

Also, we kept the throttle a bit more open than 25%, from what I can remember.

We start engine with ignition 'on' from the first flip. Fires in 4-5 flips n starts in 4-5 flips.

Tip: If u flood the engine some how. Choke open, throttle full open & start flipping till u Succede.( may be 10-15 flips or so) 

Well, i started the engine this morning.
Fired up in 4 flicks ! ran it on low throttle-mid throttle for a few minutes, then shut it down,after a minute started again and it fired up again in 3 flicks !
RPM Is around 2000 at idle, and 6750 at max. I guess should be able to take out more when the needles are leaned out ?

Maiden scheduled in the afternoon today !

So breaking the engine in the air now with 30:1 fuel with Lawnboy Ashless.
Would 7 litres of fuel be enough for breakin ? What oil should i use following that ? Someone suggested Motul 800.  Any suggestions ?

Quote from: gauravag on October 24, 2010, 07:42:38 PM
So breaking the engine in the air now with 30:1 fuel with Lawnboy Ashless.
Would 7 litres of fuel be enough for breakin ? What oil should i use following that ? Someone suggested Motul 800.  Any suggestions ?

We r using all branded 2T oil with 40:1 bcoz they r not synthetic n getting idle 1600 RPM & 7350 RPM @ max.

@gaurav U can lean your H (High back needle) needle n get upto 6850 to 6950 with 22x8 prop (dont use high pitch & 23 or 24" props now, can use after 35-40 lts. of gas) you r running rich n running rich can foul your plug.

Great Planes Yak 54 DLE 55 engine setup pix....

Ok I leaned the High Needle and getting 6950 now. SHould it be leaned out further ?
I did note that the transition is OK, except sometimes it felt like it stuttered when powering up. That indicates the low needle being rich ?

Update here.
I have 2 gallons of fuel through the engine now using Lawnboy Ashless.
I switched to Castrol 2T following this. So far got 2 gallons of it through the engine as well. Ratio I am using is 1:32

Peak RPM I get is 7200. I did have to lean out the low end needle significantly to reduce the 4 stroking at low end. In fact had to slightly touch the idle adjustment screw to slow the engine down on idle.

I plan to stick to using Castrol for a few more gallons and then switch to Motul 800

Advice/suggestions are welcomed.

-Gaurav

Is Castrol 2T synthetic ?

No. Its not synthetic. The DLE, as i have read, takes a long time to break in , and I concluded that using Castrol would be better than switching to synthetic so early.
I think after 4 more gallons, i will switch to 1:40 Motul 800.

Castrol uses degummed castor oil as its base.

Switched to Motul 800 now.
Total time I spent on LawnBoy was 6.8 Lts and then Castrol 2T 7Lts.

Now using Motul 800 at 40:1 mix.

The engine RPMs are 1500-7200 and so far very, very happy.

What is the run time per litre ?

When i started I got around 25-30 minutes to a litre. This has increased gradually and is now around 60 mins a litre.

I just got a DLE-20 and what a nice little engine it is. WIll start a separate thread on it soon.
-Gaurav