Aerovee quits at landing/taxi - Suggestions?

[GraemeSmith]

Making my own. Got the general dimensions from the drawing on the website. Following the intent.

[Area 51%]

My initial problem with the engine stalling on very short final or after landing was I had an overly lean condition that was needle related. I changed the profile of the needle at the idle end.......and problem solved. Solved, that is, till the temperature topped 80deg. Then it was burp-hiccup-burp. No problem during the winter months here in Florida.

Based on others having luck with a dedicated fresh air inlet, I had a go with my own solution. The assembly manual insists on the Sonex "smile" regardless of the location of the oil cooler. I have a top mounted cooler, so the necessity of the "smile" was/is a mystery to me. I made a fiberglass tunnel that picks up outside air just behind the smile (to give it purpose and make it feel better about itself), then it follows the the curve of the cowl down to the air filter and terminates an inch or two just ahead of said filter. Haven't had a burp since.

Fresh air is your friend. I am a little concerned, though, about the now missing 400CFM in cooling airflow that was created when the carb was scavenging hot air from under the engine.

10.7 trouble-free hours here @Area 51% (39.6 showing on the hobbs)

[Onex107]

My Onex had the same/similar problem on hot days. It didn't completely stop but it surged. Running lean, rpm increase, then rich, slowing down to the throttle setting. I added a blast tube in the angled front of the baffles direct to the AeroInjector to cool it. It was like day and night. The problem went away and the idle is smooth.

[pappas]

I ordered 2 small NACA ducts. I thought that I would try one like Graeme installed in the bottom of the cowl for fresh air to the Aeroinjector and one on top of the cowl to direct more to the #3 cylinder.
I also ordered a small square-ish vent to open up the bottom of the B cowl below the turbo and cylinder #3 a little bit .

The blast tube is easy to implement as a test until the parts arrive. Thanks for the ideas guys. I'll let you know what happens.

[pappas]

Onex 107,

What is the approximate diameter of the blast tube you used? I am playing around with this stuff this week.

[pappas]

Added a 1-inch scat tube from the left side baffle through a hole and plug that I already had there for plug access. That was the only change I made and it cured 90% of my landing and idle after landing problems. Thanks for the tips. Much more reliable now. Might add the 2 inch NACA duct in the lower cowl to try to get the last 10%.

[Spaceman]

Lou do have any pictures of your new setup?

Also any concerns about the extra air you're adding to the lower cowl taking away from engine cooling? ALSO, do you guys think sending cool air to the AeroInjector takes anything away from it's inherent icing resistance?

[GraemeSmith]

ALSO, do you guys think sending cool air to the AeroInjector takes anything away from it's inherent icing resistance?

This is a valid concern. Think fuel injected IFR certificated aircraft. Icing over of the EXTERNAL air filter while in IMC. Most of those setups include a sprung plate in the air induction side inside the warm cowl that will open and provide unfiltered air in the event that the air filter ices over.

For non-injected the concern is the temperature drop in the carb venturi caused by accelerated air and vaporizing fuel. The carb will ice up if the humidity is high enough to allow moisture in the atmosphere to freeze. Most commonly on warm and wet summer days - rather than cold and dry atmosphere days.

So my method of directing cold air from outside across the air filter is a sort of blend of the two situations. It might be possible to direct wet air onto the filter which might just freeze if the air was moving fast enough. Though the actual fuel (and temperature drop) is downstream inside the induction tubes and after the filter. And those tubes are well warmed by the waste heat of the engine - by conduction if nothing else).

That said - my bird is VFR only - so no plans to fly in 100% humidity (ie in a cloud). Or high enough in a cloud where freezing might be an issue - and I think the wings would be a bigger issue first. That situation - I think there would be 100% valid concern.

Which leaves the possibility of a 99% humid summer day, VFR at a decent altitude. Ice hasn't happened yet - but you know what? I have a small remote temperature probe. I'm going to stick some instrumentation on it and see the rest of the story.

[pappas]

Here is a link to Google Photos:

https://photos.app.goo.gl/9P9ruebHSX1CWqtf7

I flew this set-up twice so far. CHT's were more even, and #3 was a little cooler, than previous flights. Likely because I also added a 4 x 6 louvered vent to the cowl bottom below the turbo to increase the lower cowl exit area. I was going to do that even if I didn't try the carb cooler tube in an attempt to reduce the #3 cyl temperature a bit. My hottest cylinder, #3 is, and was, within specs but I wanted it a little cooler than it was because....well....you know how we are!

I fly in Phoenix. Temps in the 90's recently but always very low humidity. The engine did not die on short final during either flight at idle throttle setting. It did stop once on the 3/4 mile taxi back to the hangar, but that was a 90% better result than I was getting before I added the vent and SCAT tube.

I think the experiment was a success and I may replace the test SCAT with a small NACA duct ala Graeme's set-up so as not to rob any of the high-pressure air to the upper cowl.

[Spaceman]

Thanks for the pics Lou. The way that scat tube is just right next to the intake, it seems like it wouldn't suck up too much air.... I guess a little bit was all it took!!

Is there a spot you could measure the temp of the carb that could reasonably predict when icing could start to happen?

I was thinking about this the other day, and it sounds like getting fresh intake air would help everything run better, but the drawbacks are/could be, (1) interfering with the upper/lower cowl pressures and air flow by adding air to the lower area and/or taking some from the upper area, and (2) possibly making the carb more susceptible to icing.

This might be a little complicated, but has anyone tried making an airbox around the air filter that you could open and close with a cable, like carb heat on a normal plane? Like you could have a naca duct feed intake air into the box so you get all fresh air for takeoffs and landings without adding air pressure to the lower cowl, and then a second inlet that just takes air from the engine compartment that you can open once you get up to cruise altitude to keep the carb from getting too cold.