Anybody have any cooling issues with this aircraft? I was running a 91fx, had issues, followed by a 95ax still with issues. The engines will run for a bit, 2-3 minutes, then lose power and quit. The tank has been checked with no issues. Im at a loss. It may not even be a cooliing issue. Frustrated.

post some pics of your cowling and how you have it cut out for the enigne. Did you take any temp readings of the engine?

Unfortunately i have not taken any temperature readings. It does smell hot to me and others in the club. I know not scientific but its the best we got. Nobody has any idea why the engines are unreliable. They both work fine on the test stand.

I cant comment on the cooling problem but you should cut off the part of the cowl behind the muffler. Atleast you can takeoff and put the cowl back without removing the muffler. And a little more cooling will not hurt. Its underneath the airplane so it shouldnt be visible

Ameyam

Actually the AW Yak cooling isn't much problem.

Notice the fake engine blocks air that disrupts good cooling and lets in air that has to encounter the engine. I'd have a picture of the underside, but it's all white down there with just two moderate holes to make getting the cowl over the pitts muffler pipes easier. That huge opening AW designed in for a stock muffler works great to provide adequate exhaust for the heated air.

Todd, looking closely at your cowling showed exactly the situation I had with my Hellcat when it had a slight cooling problem. The problem with all cooling is keeping air from avoiding the hot things that need the cooling. The 91FX in that Hellcat had too much opening in the fake engine that wasn't directly in front of the engine. I added a stepped baffle in the cowl to block the too large hole in the fake engine. The arrow points to that foam baffle.

The opening can actually cause problems by letting cool air in that can easily bypass what needs to be cooled. Hot air is harder to move than cool air. So when cool air comes in it follows cool air instead of moving hot air. The hot air around the engine can just sit there. And if it wanted to, for whatever reason air might want to do something, if it wanted to go out the rear openings, it would have to push it's way into all the cool air that bypassed the engine, and hot air won't move cool air worth spit.

So you don't want openings in front of the engine that aren't in front of the engine.

Full scale engines have baffles to block air from getting around the hot cylinders. They say some of those airplanes have pressure cowls. In fact they have baffled cowls.

You want the openings in front to be about as large as what you want to get cooled. They should be in front of what you want cooled.

Best case, you want the outlet openings to be about 1.5 times larger than the inlet openings. And they should be behind what you want cooled. If they are in an area of negative pressure, you're lucky. If not, they need to be larger than 1.5.

My Hellcat has outlet openings that're probably just a touch larger than the inlet. My Corsair has maybe less. The Corsair flew through the last 2 summers without a whimper. The Hellcat only saw a month of heat. It was new the end of this summer. But with it's cowl flaps recently opened, I'm betting it'll have no problems next summer. The Corsair exit openings are in areas of negative pressure. The Hellcat has openings that had negative pressure created for them. The picture shows one of the "scale" cowl flaps after creation. They worked well on the fullscale, and will probably work good on mine.

A good rule thumb is.....if you have say 2% of fresh air coming into the cowl you should have 4% of dirty (hot) air exiting the cowl. And as Da Rock stated in his 6 posts a cowl baffle would be a wise idea.

So I guess what you guys are saying is that I have too big an opening in the front? Go figure. Guess ill be ordering another cowling and baffle from
Aeroworks.

Yeah, that was what was wrong with the Hellcat. And post #6 shows how that was fixed.

The foam that was glued into the Hellcat cowl is just house insulating foam that's glued to walls. It's about 3/4" thick and is easy to cut to fit into the cowl. The piece in the Hellcat took about 10 minutes to cut to fit. It was epoxied into the cowl and the plane was ready to go next day. I use the stuff to box gas tanks in, and build things like:

Todd - have you taken the opportunity to contact Aeroworks? They are in Denver - good people (no, I'm not a customer yet - but I'm lusting after the Yak .60 - .90...)

Yes i have talked to them, very nice. I asked how much baffling needed to be cut away and they responded with" just the part that is front of the cylinder". So me, being who I am, assumed that meant as a minimum, what harm would exposing more do. Well now I know.

Yea, I'm surprised too - very vague.

I have this YS110 just sittin' around and I luv the look of the Yak - emmmm - Christmas is just around the proverbial corner ...

Looking forward to your solution!