914 Temps?

[Shadowrider]

I know this is apples to oranges, but I am curious guys running 914 what are your water temps and oil temps? Hot day long climb? I am running a edge performance turbo 912 and had to mod the naca vent to clear the turbo. Airflow is reduced and wondering how close to the edge temps will be? I am just trying to get a reference to try and decide if other measures need to be made. Thanks!

[aviator79]

Hey Dustin,

My engine is pretty similar to yours - moreso than a standard 914. The differences are yours is fuel injected, and I *think* your TCU is tuned to give you more boost.

My CHTs are in the green in all phases of flight. My oil temp does get into the yellow during a high-performance climb - I've seen temps as high as 240, which would continue to climb if I maintained 65 mph. If I nose over to an 85 mph cruise climb, they cool back down to ~200 quickly. I have a 205 degree thermostat, so 200 is perfect in my opinion. I suspect at 65 mph, the AOA gives poorer flow through the NACA, in addition to the reduced mass flow rate through the cooler on account of airspeed. This is at ~8000-9000' Density altitude, and around 40-50 deg ambient temperature. The high DA means less mass flow through the cooler, so poorer cooling efficiency.

I didn't install a coolant temp sensor because the 914 Firewall Forward manual didn't call for one, and I mis-read the 914 install manual. As it turns out, if you're running conventional coolant and "without suffix -01" cylinder heads, you're supposed to measure coolant exit temp. I plan to add the coolant sensor.

[Esser]

I just ran into hot ground temps. Like 240 degree coolant. I removed my oil cooler guillotine and made my naca scoop tighter around the rad with aluminum. My temps are much better. I’ve never had an issue in the air except maybe some extended climbs.
22266

[Shadowrider]

Hey Dustin,

My engine is pretty similar to yours - moreso than a standard 914. The differences are yours is fuel injected, and I *think* your TCU is tuned to give you more boost.

My CHTs are in the green in all phases of flight. My oil temp does get into the yellow during a high-performance climb - I've seen temps as high as 240, which would continue to climb if I maintained 65 mph. If I nose over to an 85 mph cruise climb, they cool back down to ~200 quickly. I have a 205 degree thermostat, so 200 is perfect in my opinion. I suspect at 65 mph, the AOA gives poorer flow through the NACA, in addition to the reduced mass flow rate through the cooler on account of airspeed. This is at ~8000-9000' Density altitude, and around 40-50 deg ambient temperature. The high DA means less mass flow through the cooler, so poorer cooling efficiency.

I didn't install a coolant temp sensor because the 914 Firewall Forward manual didn't call for one, and I mis-read the 914 install manual. As it turns out, if you're running conventional coolant and "without suffix -01" cylinder heads, you're supposed to measure coolant exit temp. I plan to add the coolant sensor.

Thanks Brian for all the info this really helps. I will post progress, but I think we are going to install an oil to water heat exchanger like Thomas recommends. I am dropping my oil cooler all the way down to improve cooling also.

[Shadowrider]

I just ran into hot ground temps. Like 240 degree coolant. I removed my oil cooler guillotine and made my naca scoop tighter around the rad with aluminum. My temps are much better. I’ve never had an issue in the air except maybe some extended climbs.
22266

Thanks! I was going to install the oil cooler guillotine, but I got nervous because the one I was looking at, when fully open still would restrict cooling quite a bit.

Good idea. I was just getting ready to order some baffling material and do something similar.

Do you run into oil temps limits on extended climbs or water temps? From what I have read seems like most run into oil temp limits and not water temp limits?

[aviator79]

Thanks! I was going to install the oil cooler guillotine, but I got nervous because the one I was looking at, when fully open still would restrict cooling quite a bit.


From what I've read, the oil cooler door is really helpful on the 912. Your 154 HP fire-breather probably won't have any trouble getting the oil temps high enough.

[Esser]

How are you temps now? I'm finding in the summer I can hardly do circuits and I can't do super high power climbs. After mulling over this problem a bit, I decided the oil cooler needs to move. Radiators and oil coolers need a differential of pressure to push/pull air through it. In the oil coolers current location with my NACA sealed around the rad, the air will bunch up around the rad as it flows through the rad. the oil cooler will be surrounded by this air pressure both front and back without much air flowing through it. After all, air is a fluid and fluid will take the path of least resistance. Add the fact that my oil cooler is HOT (Not the best Delta T, not much air flowing through it, and the fact that it's blocking a significant portion of my rad, I think the stacked rads are a bad idea. I'm going to move it to under the gear box.

[aviator79]

Have you talked to John and/or Paul? They have been running 914s for years on their planes. It would be interesting to know if they have had any cooling issues. What are your ambient temps?

I haven't flown in a couple weeks - had an exhaust leak to take care of. The new exhaust is installed, so I'll be doing some flying this weekend in 22-25 C ambient temps. If I transition to an 85 mph, 34" cruise climb at a safe altitude, I don't have any cooling issues yet. I definitely can't do 40" and 60 mph for 5 minutes.

Have you considered a heat exchanger like Dustin mentioned? That's probably way easier than relocating the oil cooler, and I'm not sure the flow will be me much better behind that little cowl opening than it is in the NACA duct.

[desertfox1]

Hey Josh
We have about 75 hours on my new 914 Speedster now, and heating has not been a problem.
Winter testing required a shutter system in front of oil cooler to get the temps up. Last flight
was at 90 F ambient and we saw 175 F in cruise and 187 in 1500 fpm climb. We made a
rather large naca feeding a duct to a plenum at the turbo. Air is fed to the K&N and blown
over the turbo and muffler. Oil cooler is mounted in front of radiator to allow max room for
air to exhaust. All kinda shooting from the hip but it is working so far. I'll try to post a pic of
the plenum, first time try for this old man
22581

[Esser]

Interesting. I’ve never heard of the turbo needing cooling air. Your temps seem great! If I climb up 5000’ I hit 240 and it takes 30 min to get below 220 again

I do have a cold air intake for the air filter. But it’s closed off from everything else

[aviator79]

Is it possible you have a flow restriction to your cooler somewhere? The rotaxowner forums have some information about that. Roger Lee has some suggestions.

It doesn't surprise me that they get warm in an extended climb, but it seems strange they don't drop very quickly when you push over into cruise. I can hit 240 in an aggressive climb, but it comes down to where the thermostat is regulating within ~15seconds of pushing the nose into a less aggressive climb.

Phil, what MAP and airspeed are you climbing at?

[Shadowrider]

Interesting. I’ve never heard of the turbo needing cooling air. Your temps seem great! If I climb up 5000’ I hit 240 and it takes 30 min to get below 220 again

I do have a cold air intake for the air filter. But it’s closed off from everything else
Josh what are your water temps at this point?

[Esser]

I can hit 240+ Easily . I have an alarm at 230 and that’s when I start making changes. I have an alarm set on my oil at 240

i don’t think I have flow restrictions as my oil pressure is great, if not on the low side of the green when it gets hot

[Shadowrider]

I can hit 240+ Easily . I have an alarm at 230 and that’s when I start making changes. I have an alarm set on my oil at 240

i don’t think I have flow restrictions as my oil pressure is great, if not on the low side of the green when it gets hot
I don’t think an oil to water heat exchanger would help either with both your water and oil being hot. Speaking with the factory the solution they are coming up with is extending the bottom lip to create lower pressure drawing more air out the bottom and through the radiators. John said he is working on a fiberglass piece that you can attach to the stock cowl. Maybe you could try what he said they are doing is just attaching a piece of aluminum creating a lip essentially a large cowl flap? If both are running hot, water and oil, it would seem it’s an airflow issue. I also wonder about putting an scoop on the naca to help force more air through radiators?

[Esser]

The more I read, the more I think the bottom lip extension is a bandaid solution. As it stands now I think the oil cooler stacked in front of the rad is letting it do pretty much zero work except block the rad with hot air. This isn't an air cooled engine and in the installation manuals, Rotax clearing states cooling requirements for air flow etc which the Kitfox has more than enough. The lip on the exit is to actually create low pressure behind the rad. Low pressure on the one side, high pressure on the other will cause air to move through the rad. If the pressure is the same on both side, you won't get any airflow through the rad.

So the oil cooler on the stacked setup literally has the same air pressure on both sides of it(because the coolant rad is really what's blocking the air so it will have the same pressure on both the face and the back). I am going to move the oil cooler to the location under the gear box and I anticipate this will dramatically cool the oil(which will help over all engine temps) and allow better flow through the rad.

If you cool on an F18 they have a heat exchanger that is roughly 2'X8' and the inlet air to it is smaller than two of your hands. They create a huge negative pressure when not flying behind the rad by dumping bleed air behind the heat exchanger.

Looking at rotax's oil cooler requirements, I think the opening on the front of the cowl is more than adequate to cool the oil as long as I can maintain a pressure differential on the back side. I might do this with a diffuser aft of the oil cooler and a shroud that stops the ram air from spilling over. As it stands now, that opening in the cowl isn't doing much from a cooling point of view.

The 914 only requires air cooling on their cylinder walls only. They actually even state that a 4" hole is enough air cooling for the 914 if the air is directed over the walls with a plenum. My next step will be to make a fibreglass plenum (Since Rotax wants $600 for theirs). Once I have the correct cooling air directly over the cylinder walls, and I have the oil cooler working properly, I can look at my temps to see if the rad is working well enough for a water to oil heat exchanger. I think I would still like to go this way after researching everything because with no weight penalty, I could get rid of the intake hole in the cowl where I will be moving my oil cooler to. That will get rid of drag with less opening in the front of the cowl.

Why would I want to get rid of that opening? Adding the splitting lip on the bottom of the cowl is to create more negative pressure on the exit of the cowl than the positive air flowing into the cowl. Just like your wing, high seeks low. BUT if you have adequate cooling capacity and air flow as per Rotax, you may not need to create more negative pressure on the exit but actually REDUCE the positive pressure (smaller inlets) on the intake to get the same airflow through your cool.

I hope that all makes sense. I have a few more ideas I'm going to run with after I implement these things one by one.

I'm still new to all this so my logic may be flawed so I'm open to discussion!

[Shadowrider]

You hit on some good points. Speaking with John he is fully aware the lip is a bandaid, and he did mention he would like to design a new cowl but no mention of time frame. He said the cowl was designed for the lower hp engines where cooling is more than sufficient, in fact sounds like some are running to cold? As you stated the lip is creating more low pressure behind the radiators to help air flow from high to low. You can work on increasing pressure in front of cowling but if it has no where to flow won’t don‘t do you much good. John did state, and I agree the inlets to the cowling are not optimum. Also the air has to get fairly turbulent with no internal ducts. Probably just enters and swirls all over the place? I think interference from the spinner and prop play a large part also. They really need to be spaced out wider but that will be a major undertaking. I asked John if testing have they ever covered up the lower intake that hits the fuel pump and he said he had but saw no change in cooling. In the example of the 915, there is only so much exit air. You start adding naca vents for Intercoolers and intake and you are essentially reducing the amount of air that can travel through radiators because you only have so much air that can exit. I think they where running into over pressuring the cowl. One solution was to box the intake so the air coming into going to the turbo can only go to the turbo and not the cowl improving airflow through the radiators. Mic is running hot and is adding a lip as this is an easy fix. Curious to see if this helps his temps?

Its interesting that you temps seem to be fairly higher than others running 914? What’s the difference between yours? It would be awesome to have a company like LoPresti design is a new cowl to meet the higher cooling requirements of a turbo engine. Probably lose some weight and pickup a few knots also.

i also read an interesting article on the shortcomings of a naca vent. When they where first starting to be used the air-force tried them on a few turbine aircraft. I guess because they are not optimal on certain AOAs they had some compressor stalls and discontinued Naca vents for intakes. The article talked about how popular they are with home builders because of he ease of installation but may not be optimum? Just some thoughts....

[Esser]

I’m at work and will give a bigger response in a bit. You had some great points. I just wanted to clarify something I said wrong in my previous post and that was make the inlets smaller to match the negative pressure on the outlet so even though I’m making the holes smaller, the airflow would stay the same. You touched on that with your over pressurization comment

[aviator79]

I'm sure a lot of people look forward to your results Josh. Experimenting is the only way you're going to figure out if you'll get better results. As Dustin says though, your experience is not the norm, which indicates that your temps are not entirely attributable to the stacked radiator/oil cooler, because there are plenty of 914's running this way without excessive oil temps. I'm not arguing that the arrangement is optimal, just that there may be more going on than that.

For what it's worth, I pushed my climbs a little harder this morning, and found that my oil temps are well under control even in an extended 35" MAP climb at 70 mph. I think my high temps were actually just the thermostat taking some time to fully open. I climbed continuously from 8500 to 14000 feet without an issue. My CHTs did start to creep up, but pushing over to even 75 mph brought them back down into the green. Ambient temps were 65 deg F at 7500', closer to 35 up at 14,000. It would have kept climbing just fine, but I don't have oxygen.

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[Esser]

I'm not the only one but there are a couple of us. Jeff Perdue had to move his oil cooler away form the stacked config and as soon as he his temps dropped 40deg. There are a couple of things the could be affecting my sistuation. I am running fuel injection so I'm probabyl not as rich as you guys and I'm make 5% power. Not a huge thing but it might contribute. I also have my intercooler which is shooting air into the top of the cowl and like Dustin said, it may be over whelming my exit negative pressure. I may try to tape one off one of the NACA ducts and see what happens to my temps. I would have to fly with a lap top to watch my TCU show my manifold temps. So far I've never seen the waste gate open so maybe I can get a smaller intercooler that needs less air.

To respond to Dustin, it's funny you mention the Lo presti cowl because I want to at least modify Natalie's cowl to have protruding circles instead of the current setup because from those circles you can fair into the cowl and keep the air laminar easier which is definitely not happening on the current set up with that sharp ridge. I envision one intake being used for the plenum I want to make, the other for general cooling air. I think like you said, if you can direct all that swirling draggy air, it will probably have better flow and have better velocity. I may do this to mine too if it works well for her. I just loathe the idea of changing my cowl dramitcally on a flying plane. I do think the Model 6 FWF had a better design in a lot of ways. All the air going under the cowl HAS to go through the rad so it's getting loads of high pressure air. However, the Delta T isn't as good as it can be because the air is hotter after going over the engine.

Touching on the point of better flow through the cowl is trying to keep the air laminar as it leaves the cowl. I have a couple ideas for that in my head too. One of them it so actually make a diffuser box on the back of my rad that has two diverging sides to slow the air down and create a negative pressure and then inject my exhaust air into that diffuser to create a bigger negative pressure to help pull air through the rad. This is how F1 cars used to make down force(I think they still do to an extent but there are more rules about how they can do it). This idea is also touched on in Speed with Economy by Kent Paser. In the book he also adds some aluminum to have a converging diverging nozzle at the lip of the exit of the cowl. He also has it set up so the air doesn't have to go around sharp corners which should help air stay laminar and up to speed. In order to do that exhaust thing though, I would have to remove my muffler after the turbo so I could ad a 90 deg elbow right away. I'm not sure of the implications on turbo performance of doing that yet. More reading to do. I'm not too worried about noise as turboed engine's are usually quieter and the engine is small displacement and high rpm which helps too. But things to think of. Might as well put my exhaust to work!

I do have a cold air intake so all the air feeding my engine comes from a separate NACA into a box. Mic has the same intake. He also added the lip and saw temps drop I believe. He wants to switch his oil cooler position but is going to wait til after Oshkosh from what I gather.


I've been reading similar opinions on NACA ducts too. They are great for the least amount of drag but they really can't provide a huge amount of ram air. I think the big scoop on the bottom of our planes is fine because it's more or less directly in the airflow as the cowl slopes down. But it is making me revaluate my intercooler set up as that has two NACAs feeding it. I might be better with a smaller ram air intake. Gotta love experimentals!

[Shadowrider]

I wonder what the airflow is doing coming out of the back of the radiator, or how much is actually flowing out? I did some testing on the ground using an air-compressor, I know it nothing like in the air, but it was amazing how little air was coming out the back. Most of the air I could feel with a wet hand, was coming around the bottom of the radiator and I have mine pretty close to the bottom of the cowl. Wonder if you put some strings all over the back side of the radiator and mounted a go pro so you could see what its actually doing? My next thought is looking at a trophy truck and its amazing the radiators they have stacked and they are behind the cab of the truck, to help protect them, but with minimal airflow. They just run cooling fans on the back side to pull air through them. If there is not a lot of air actually making it through the radiators, I wonder if you installed two 12v cooling fans on the back of the radiator what that would do for temps? It wouldn't take much to fab up a temporary bracket and install some on the backside of the radiator, and just hook them up to a RC 3 cell lipo battery. Wouldn't take much of a battery to be able to run them for 20 or min to test?

Interesting about "Jeff Perdue". Where did he move it to and was this on a 7ss?

[jrevens]

Josh - FWIW, my CHTs were running a little high and it troubled me. I have a 912ULS of course, so it’s a little like comparing apples to oranges. Anyway, I ended up gluing a piece of thick, red silicone foam rubber to the cowl directly under the radiator. It’s then compressed slightly to form a good seal and prevent air from taking the path of least resistance and flowing under instead of through the radiator. My temps dropped considerably.

Stacked coils are common on cars of course, but the condenser for the a/c system, which is generally in front of the radiator, is usually a very thin coil which presents minimal affect on the radiator’s operation. I’m not a big fan of the way those particular oil coolers are mounted in our newer Kitfoxes, but as others have said it does usually seem to work. My oil temps are very good under all conditions, but it’s a shame to have to pre-heat the air entering the radiator.

[Esser]

Interesting about "Jeff Perdue". Where did he move it to and was this on a 7ss?

HIs was a factory built SS7. He added the oil cooler to the side of the cowl with a NACA and a door. His CHT's dropped 60 deg.


John, I do have a piece of foam to block the air on the bottom but I can improve on it. Once I move my Oil cooler, I'll be making some adjustments to the sealing of the rad.

I''ll keep everyone in the loop of my findings.

[DesertFox4]

Desertfox1 flew his 914 Kitfox yesterday morning. Asked what his conditions and temps were.
Outside temp about 90F. Long climb out @ 1500’ minute pulling just under 40” M.P.
Said oil temp never above 190F.

[aviator79]

Desertfox1 flew his 914 Kitfox yesterday morning. Asked what his conditions and temps were.
Outside temp about 90F. Long climb out @ 1500’ minute pulling just under 40” M.P.
Said oil temp never above 190F.

Wow! I wish I could do that! Did he do anything special to improve cooling? I wonder how much has to do with density altitude. I have 20-25% less cooling air flowing up here.

[fastfred]

[Why is the oil PSI so low?


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[aviator79]

[Why is the oil PSI so low?


It's at the end of a long climb where it got pretty warm and it's just cooling off. It does tend to run near the bottom of the green when the engine is at normal temps though.

[fastfred]

Mine runs around 52 psi most of he time is why I asked. It has been so cold and wet this year around here I only just removed the last of 90% of the tape off my oil cooler yesterday. Many of the grass airports are still too wet for use.

[Esser]

Mine fluctuates with oil temp. When I'm in the 240 range it's low. When I'm cold it's around 60

[SSFoxBuilder]

Thoughts on running a larger oil cooler in place of the radiator and locating a smaller radiator under the gearbox? Seems like with the turbo, oil temps are of most concern and water temps might be slightly more 'forgiving' when airflow and radiator size are an issue??

[Esser]

Water temps are way more critical. And you don’t want oil too cool either.

If the coolant boils over in flight at 255-260ish you are in big big trouble.

If oil hits 275+ it starts to breakdown but all you need to do is an oil change

[fastfred]

Doesn't the factory have the best way to solve these issues? When they used to put that in their slsa it had to work perfectly so they must have a good set up? I have had 2 7s and the factory built one has far less issues with heat problems than the amateur built. It was fun working on it trying to solve the problems but I would rather be flying . Just my experience as I am no expert.