ESM Bearcat - powered by Laser

[Ron Gray]

1 hour ago, Paul De Tourtoulon said:

didn't it just come back from being upgraded

Wrong motor Paul, this is the 240v not the upgraded 200 in-lines which are running perfectly both on the ground and in the air!

[Ron Gray]

Unfortunately I didn't get a conclusive answer to the issue today as the cowl-less flight was cut short and a broken prop prevented any further investigation. Fingers crossed for Wednesday.

[Ron Gray]

To give a clearer explanation it was a series of problems I introduced by trying to keep all the fuel lines and glow cables from flopping about in the now open engine bay. Basically I cable tied pipelines together nice and neatly but failed to spot that in doing so I had over tightened one thus causing a partial collapse of one fuel tube which wasn’t obvious as it was hidden behind another. As a result of neatly tying everything together it also meant that a slight kink was introduced into the other fuel tube, not really obvious unless you were looking for it! Anyway the result of this was that on starting the engine one cylinder was reluctant to fire which I immediately thought was a glow issue but soon found that wasn’t the case so then I thought that it must be a problem with the bottom end needle setting (I had reset all needles back to base the previous night) so I started to adjust those. When I realised that wasn’t making any difference, although the cylinder was occasionally firing, I swapped the fuel lines over and it started running. So I turned my attention to the fuel lines and found the problem so clipped off the ties. All good now so took off. Once in the air it was clear to me that the settings weren’t quite right as it was a bit down on power and sounded flat in the midrange but on a more positive note there was no coughing etc when I banked it round in the circuit and it seemed to perform ok when carrying out wing overs. I decided to land to adjust the needles but thought that I’d try a big loop first of all, mistake, just before pulling inverted the engine cut, no spluttering no backfiring, just cut, so I had to finish the loop and circle round towards the strip. I was going to belly land it on the grass but I misjudged it by 2’ and hit the junction of the strip/field where there is some tall grass. The only damage was a broken prop and some of the belly pan fixings pulled out.

 

The benefit of hindsight is wonderful and I can look back and say what I should have done was to take the model back to the bench, after I found the pinched lines, and reset the needles back to how they were when I arrived at the field. It is far easier to do that with the model inverted (engine is upright so mains are underneath) then slightly tweak after initial running. Hey ho, Wednesday is looking to be OK weather wise so it’ll be ready for another go then.

 

Gosh I thought War and Peace was a long (boring) read!

[Paul De Tourtoulon]

I never clip fuel lines up, I like a messy dangling approach,,,🤣;

We had a petrol plane that had the same sort of problem a few weeks ago, the 30°c + weather had softened the tygon fuel line and kinked it.

 

So is it round 4' ?.

 

 Keep it coming, it is interesting reading.

Edited July 22 by Paul De Tourtoulon

[Ron Gray]

Not really clipped Paul, well shouldn't have been, more of a loop to keep the lines together and to stop them flapping about. I've always tried to keep my engine bays tidy and no matter if it's a 100cc gasser or a 15cc glow they all get the same treatment and this is the first time I've had an issue. Still it's all been redone now so will be running the engine up in the garden tomorrow for initial tuning then up to the field on Wednesday.

 

It just goes to show that even with 60+ years playing around with model 'planes mistakes can still be made.

[Ron Gray]

I spent a while in the garden annoying the neighbours as I re-tuned the engine. On an 18x8W APC prop it's pulling 8000 and holding that for at least 10 secs. Tickover is a nice steady 2000 and transition from ticker to WOT is good, no bogging and no hunting. So all is ready for tomorrow - third time lucky I say. Im also taking a 17x8 APC with me, if the 18x8 is successful I just want to see what it's like with the smaller prop (noisy I reckon).

[Ron Gray]

An update. Well things were a lot better yesterday with the Bearcat but it still needs fine tuning as it appears to be a bit lean in flight but the motor is no longer cutting out. I didn't fly it with the cowl off as I have modified the baffling but the biggest change was to do what I did with the Super Sportster and run silicone inlet pipes back into the fuse to draw from undisturbed air (I know that I said that I wasn't going to but...). This has made the engine running a lot more stable so it is 'easier' to determine the state of tune when in the air imo. Flying it was curtailed as I had 2 depth perception aberrations (🤔) which resulted in it landing in the field when I thought I was on the strip! U/C stood up to the rough surface but it flipped at the end of the second one and broke the rear internal fuselage former which is going to be a challenge to fix in a composite fuselage!

 

I also flew the Hurricane to test out a small air scoop I fitted to the underside of the cowl. Checking and comparing the front and rear cylinder temps with that I had recorded the last time I flew shows that the scoop really works well and cuts the difference down by about 40%. This has made the decision for me that it will be converted to have a tropical filter fitted to the nose which will house an air scoop for the rear cylinder.