Man did I struggle with the DLE 55 in my 30% Yak on Sunday. Not as hot as Saturday but it was still 35 degrees, and boy did my engine hate it!

If I went straight to another flight in less than 5 minutes break it was OK, but leave it any longer than that and the heat soak into the carb meant that it just could not get enough fuel to start. I think the fuel is vaporising was the carb. In the end I added another 1/4 turn to richen the low end, but it did not really help the starting.

In flight it was performing really weird after the change to the low end. It would still hesitate when I goosed it, and would burble it's head off mid range which really confused me. The hesitation happened two times. Once over the runway (which I caught by throttling back and advancing slowly) and the second time on a long approach over the dam. This time though the aircraft was a long way over the dam I did not hear it sag and so it deadsticked! I nearly made the runway but I fell short and impacted the embankment at the eastern end. All I saw was a cloud of dust. Expecting the worst all I found was the model facing the wrong way down the embankment with a slightly tweaked LH gear leg and a punch in the chin! Just a few cracks in the fibreglass cowl. I was lucky for sure.

A frustrating day of engine issues. The reason I write this as I am constantly reminded of constantly flicking the prop by my sore RH shoulder! The constant cycle of Choke / Flip, Run/ Choke off / Flip, run and die has taken it's toll.

I'm keen to hear of any one else's experience running petrol engines in very hot days. Sunday was probably the hottest day I'd ever run a petrol engine, and in fact I'd normally just stay home but I had to get my fix and would not like to let the heat stop me. Normally my engine as sweet as a nut in all conditions, in fact I have only ever needed to adjust the needles when I have changed the prop or exhaust. Any of you guys have experience on this?

Hi Mike looks like you had a bit of luck with the bush landing.
There are lots of blogs on RCU on cooling Gas engines as you are on our site a lot i guess you have sniffed a few of them out, one of the best descriptions i have found is from
P E Reivers who is regularly on the gas site on RCU this is his own version of how to cool gas engines.
http://www.prme.nl/forum/viewtopic.php?p=506#506
There are plenty of club members who do not bother with any baffles in the canopies with gas engines.
I at least try when you have a $1200 engine in the nose you try to keep it alive as long as possible, but with the cheap Chinese engines people are not so bothered.
Its a real pain to fit tight baffles around the cylinder of an engine to force the incoming air close to and through the fins so you get contact with the hot cylinder.
One basic rule is air will take the easy way out and unless you force it through the fins with baffles it will just flow past without doing the job of removing heat.
If when running the engine next and your compression is down you may have cooked the ring ie.taken the temper out of the ring and its now longer stiff enough to hold the compressed gas in the chamber.
Sounds like me after a curry.
I use a temperature gauge and try to keep my running temp. around 100C but there are many on the RCU gas engine site that say you can go much hotter but my 3W engine book says under 100C so if it was safe to run at 150c as some do they would have put that in the book so i try to keep to under 100C

Dave.

It's a good point Dave, I don't' know how hot my engine runs. It is "baffled" but I suppose that is a loose term as it really only consists of a baffle plate around the front of the cowl (it is a Yak) with a corresponding hole in it in front of the cylinder. I did not bother going and adding more vanes to direct the airflow around the cylinder after the air goes through the plate, as I just cant figure a way of doing that while still being able to actually fit the cowl over the engine from the front. Larger aircraft can do this OK, as often the cowl will split along a lateral line.

I also paid attention to the "hot" air exhaust from the cowl, as this has quite a bit of cross sectional area and a lip in front to cause a good low pressure behind. Of the round cowl gasser installations I've seen, mine pays more attention to cooling than most. I'll keep thinking on it, as there is probably more that I can do. I need to get the cowl off for a good check over before the next flight anyway after my "mishap". I am a lucky boy for sure...

Michael.

Hi Mike,

Last year we flew at Luskintyre Giant Scale. It was a scorcher of a day. All of us who had petrol gassers found that idle went up a few notches with the heat. This meant very fast landings. If you trimmed the revs down you were in danger of a deadstick on approach when closing the throttle.

Poor Ron Clark came in very fast with his 2 x MVVS powered Mitchell B25 bomber and it flipped when attempting a go-round causing a fair amount of damage.

I nearly ran out of runway with the Storch and had to kill the engine on roll-out.

Tom Sparkes tells me by richening up the bottom end, you can elimanate fast idle on hot days.

However, on the whole I find gassers are pretty good at holding settings on "normal" days.

Good info col. I've found that even during the run in stage, my DLE needed no tuning once I'd had it set. Probably why it kinda surprised me on Sunday that it needed a tweak, and even then it still caught me out.

I'll have a look at the baffling now. Sounds like a good place to start until I try and brave the heat next time...

m.

hi Mike there are blogs on RCU that have a baffle set up for your aircraft i have seen them and studied them when i was designing the baffles on my TA152 but as i said before you may have to do a bit of real building.
What you have is not classed as a baffle. But on cooler days you most likely get away with it but dear old Murphy is always lurking.
Gas engines can take a hell of a lot of abuse i see it all the time at our club field and they mostly get away without any baffles. BUT
Dave.

This is a good example of proper baffling note the ducted fan just behind the prop boss.
On a normal cowl without the ducted fan installation you would have an opening the width and depth of the engine fins with a close baffle next to the head fins and side fines.Like pic. B1 and B2 those shots are before the front cover ducting is put on, not forgetting any hot air exit from the aircraft must be 4 times the size of the cold front aircraft air entry.
Easy ain't it!!

That must be for a pretty special application. Wow.

That is on a very well made war bird that the builder is rather fond of and does not want to wreck his engine or kill a few worms by making a smoking hole in the ground..
At the moment i am doing the baffling on my P47D it is no fun i do not enjoy doing it its tricky when you are trying to make it out of wood.
I will post some pics. when its finished but remember i am not in the Stan Begg class but it should work.
Dave.

Good stuff Dave, could you please post the link to the site where you found this baffling solution...