HKS engine conversion

[rawheels]

I'm finally taxiing my HKS-Kitfox project, and am having troubles with the CHT over temping on the HKS when I have the cowl installed. It seems to be OK when I'm moving, but it will redline if I'm stopped and run it up for a short while. And once the temps get high, they won't come back down at idle.

Some baffling may help, but I've yet to find any photos of a HKS in the cowl that has any baffles attached. So, I'm looking at the air exit for now. I've read quite a few times online about a 3:1 ratio to the cowling inlet as being a good exit size, but with a large 13" round cowl opening on the front, there is no way I'd get there without removing the whole bottom cowl. Anyone else with an air-cooled engine want to tell me how large their cowl exit is?

Another thought is that the airfoil portion of the prop blade appears to start at the edge of the cowl opening, so maybe there is no airflow happening at all in the cowl when stopped. I'd like to try out a venturii lip on the bottom edge of the cowl in hopes that it would create some suction from the prop blast going across it, but I haven't been able to find any info online on how to design one. I looked at two aircraft on the field (Stinson Voyager and Piper Pacer) both of which have an exit opening lip. They both appear to be 45 deg to the cowling surface (nearly pointing straight down when the aircraft are on the ground). The Stinson's is about 1.25" tall and the Pacer is almost 2". Anyone else played around with cowl exit lips?

[Esser]

Rawhells,

Go buy a book called speed with economy by Kent Paser. He has a cool chapter on cooling efficiently. It's more for drag reduction but the principals are the same. You can buy it online in an ebook format for a few bucks.

[Mnflyer]

Hi rawheels, what prop are you using? If you go to my album you can see a couple of pic of the opening I did on the cowl, you will definitely need a venturi lip (at least I did) the exact angle is that important mine is approx 1.25" if you would like I can measure the opening and the size of the lip, I also fabricated a couple of very simple baffles that improved cooling tremulously (can also be seen in my album) Another thing you need good air flow thur the oil cooler as you know the HKS has oil cooling for the cylinder heads if the oil cooler isn't getting good air flow from the prop the CHT's will be up.

[rawheels]

Thanks Gary,

I'm using a warp drive prop (see photo on the second page of this thread). I've looked through your pictures multiple times, but can't really judge the size of the cowl exit; so yes I'd appreciate those numbers. I cut some more last night, and think I'm around 85-90 sq-in. I saw somewhere where the Jabiru 2200 recommends 155 sq-in or more. Of course it is air-cooled and has more horses, but shows that percentage wise by HP I'm still kind of low.

I've also looked at the pictures of your baffles. I was thinking more of some baffles to direct the incoming air up to the top of the cylinders (and consequently the carbs too) as opposed to something that directs the air on the back side of the cylinder, but who knows. Need to try out the new larger opening, and I also bent up a quick piece of aluminum to stick on the bottom as a lip. We'll see what happens.

Ryan

[Mnflyer]

Hi rawheels, the bottom opening in my cowl is 16" X 3" the venturi lip is 1.5" I was out flying this evening and here are some numbers: OAT 71*F, EGT's Right=1257*F Left= 1281*F CHT's L=305*F Right+ 305*F oil temp= 176*F RPM's 5500 MSL = 2000' Density alt = 2800' carb air temp = 22*C IAS 77 mph oil pressure = 64 PSI.
I looked at your pictures (I know you may not appreciate this but) the oil cooler installation looks great but you are dumping lots and lots of hot air to the bottom of the engine and loading the cowl with hot air, this may work good while in flight but on the ground with very little air flow not so good. As for the baffles the KIS system is best they do not need to be elaborate they just have to direct the incoming air around the cylinders and that's what mind do. Good luck hope you get in the air soon it was a good night for flying here in MN.

[rawheels]

I bent up some aluminum and added the venturi lip to the bottom of the cowling, but I didn't notice a significant change. The temps still crept up while idling in place. So, I finally just disassembled the oil cooler mount and clamped the cooler to the bottom of the cowl. It took a significantly longer time to heat up to operating temp, and after a few fast taxis I stopped and pulled the throttle back to idle and actually saw the oil & CHT temps tick back down. So, Mnflyer was correct about the oil cooler not getting enough airflow.

So, the next question is...Do I redesign the oil cooler mount, exhaust, and everything else at the bottom of the cowl, or is there a prop that provides more cooling at the hub than the Warp Drive prop? As I went through the hassle of adjusting the pitch on this prop, I wished that I had the simplicity of adjustment available on the IVO. Does the IVO prop airfoil go down to the hub?

[Esser]

I would say download the book speed with economy. You can get it as in ebook for a few bucks instantly and read the chapter on cooling. He has quite a few gems in there. Good luck!

[Mnflyer]

So, the next question is...Do I redesign the oil cooler mount, exhaust, and everything else at the bottom of the cowl, or is there a prop that provides more cooling at the hub than the Warp Drive prop? As I went through the hassle of adjusting the pitch on this prop, I wished that I had the simplicity of adjustment available on the IVO. Does the IVO prop airfoil go down to the hub?[/QUOTE]

Hi Ryan, No the IVO does not provide better air flow in fact it is less I tried and IVO on my Kitfox, I had the original 3 blade GSC installed and tried an IVO flew about 25 min in cruise and the CHT's went to redline landed removed the IVO reinstalled the GSC went up and the CHT's never can close to redline.
When I did my conversion I wanted the oil placed the same as you did yours but it would not work I ended up mounting just below the cowl opening (as you can see in the photos) and it has worked great. While I'd have prefered it not being there I got to thinking that where the rad is for the 582's and the 912's so what the heck.

[rawheels]

Project Update:

- I took a look at "speed with economy" in the fly market at Oshkosh. Some interesting ideas if someone wants to design a cowl, but I didn't find it usable for someone just trying to make the kitfox cowl work.

-I did end up moving the tailpipe, and mounted the oil cooler to the bottom of the firewall. Oil temps will now level off when sitting at idle on the ground (@80 deg, 197 deg oil temp).

- Finally flew the first test flight last evening. I don't have something set-up right because it was a real dog. Almost got up to 500fpm @ 50mph. Cruise @5800 was around 60-65mph. CHTs saw around 320+ deg (around 80 deg OAT). On the ground the prop is set to 5700 RPM static, but I can go past redline in straight & level flight. It was pretty hot outside, but I still expected more out of the set-up. With the 582 the plane was a 80 mph aircraft with more than 500 fpm climb rate. Not sure what the next step is, but still working on it. I'm thinking I need to get some more air to the tops of the cylinders and carbs, but not sure how to do that just yet. I'd like to add some more pitch in the prop to get more speed and reduce the rpm in straight and level flight, but I'm not sure what that will do for the climb rate. Still working...

[DLinn]

Surveyor

Might you be willing to share the mounting plate drawings?
I am look at converting my kitfox 3 from 582 to a HKS 700e.

Thank you for your time

Dana