Rotary Engine (Mazda/Wankel) conversions Hummmmmm!

[Ola]

Originally Posted by copterdoc

I just finished reading (for the first of what may be MANY times) Paul Lamars' article on engine cooling with respect to the needs of the rotary engine. If you haven't read it I've attached the link. Interesting information on duct shapes and heat exchangers. Lots of info on the site. http://www.rotaryeng.net/cooling.html

This was extremely interesting, in fact the entire thread is! I'm not considering a Wankel but a Deltahawk and will obviously run into the same issues.

This:



looked like a very nice solution. At first I thought it looked strange because the airflow would have to change direction 90 degrees twice, but when you think about it it's just a slight s-curve. The testing setup on the truck with pitots was also very impressive, looks cheap and simple yet provides valuable data.

Is the 2-3 cu.in. rad pr HP a good universal rule of thumb? (i.e. will it apply well to a DH installation still in the pen&napkin phase?)

[cobra]

Thanks for the excellent cooling article link and info about the oil pump- I hadn't seen it on Crook's site before. Ive thought about a wedge diffuser and side mount radiator, but I like the bottom mount idea even better. Im not too wild about the bottom exhaust-shutter design; a rear exhaust duct might look and perform better. Does anyone know what radiator was used?

Im still undecided on kit and engine; right now, because of higher fuel prices in the future, I'm leaning towards the 9A over 7A, and considering either Renesis or a single turbocharged version for both. FWIW, I'm thinking a cockpit adjustable-boost turbocharged 13B is probably a better choice for the 9A (lower HP requirement, extra power-on-demand for short field takeoff), the more powerful Renesis probably better in the 7A and 10. I have not seen a source or price listing yet for the Renesis yet but imagine it should be more common in a year or two. I'd really like to see a fuel use comparison between the two motors before the final choice is made.

My experience with automotive turbocharged engines has shown that oil contmination in fuel causes a real detonation problem, at least with higher boost levels (>10psi) where tuning is near the edge. The low oil:fuel concentration with the rotary is probably insignificant, but worth keeping in mind if we go with a turbocharger.

[rv6ejguy]

While some of these horizontal rad configurations are flying and cooling fine on some Ford V6s, turning air 180 degrees always involves losses and losses equals drag. Louvers also are draggy devices. Lamar has lots of great theories but little or no practical experience flying anything with a rotary in it. Food for thought though.

John Slade runs a large NACA duct on his turbo 13B cozy for the rad and intercooler air and this is working well in Florida. Not too practical on an RV probably but I have an auxiliary rad behind my baggage bay fed by a belly mounted NACA duct. This shows about 90% pressure recovery compared to a ram duct which is remarkably good. The hard part on an RV is finding a good place to exhaust that air.

[copterdoc]

John Slade runs a large NACA duct on his turbo 13B cozy for the rad and intercooler air and this is working well in Florida. Not too practical on an RV probably but I have an auxiliary rad behind my baggage bay fed by a belly mounted NACA duct. This shows about 90% pressure recovery compared to a ram duct which is remarkably good. The hard part on an RV is finding a good place to exhaust that air.Today 11:20 AM

I find it interesting that the NACA ducts will work satisfactory in this application. It seems that NACA didn't think they were exceptable because small pressure increases in the scoop would trip the air to bypass the opening. But if the heat exchanger has high porosity(low air flow restriction) a NACA duct would work ok. So my question to rv6ejguy is what kind of heat exchanger and ducting did you use to obtain the 90% pressure recovery? Also you said that this was an aux. radiator. Could you describe your eng. installation for the rest of us?

I have to agree with Ola that the heat exchanger and wedge shaped diffuser mounted under the engine is an attractive arrangment. A propery designed intake that recieved some of the prop blast while taxiing couldn't hurt. I do agree that cowl flaps are draggy but if they are only used durring taxi and climb and closed durring cruise I would personally find this acceptable. Paul Lamar does have a very good piece of advice in that article and that is to find someone with a successfull installation and copy them. Then work to improve it. By the time it's my turn to fly you guys will have a good system all figured out! Right?

[Ola]

Originally Posted by copterdoc

By the time it's my turn to fly you guys will have a good system all figured out! Right?

My plan exactly!

The drag of the open louvers should be a minor compromise as they'd be opened fully for, as you say, taxi and climb.

I wonder if a slot like this:



could provide enough exit area while the louvers are fully closed during cruise.

I still have some difficulty imagining the air molecules dancing happily through two 90 degree bends, but it does allow for a fairly large rad face with little depth.

[rv6ejguy]

It looks to me that Lamar's setup uses fixed louvers, making them moveable would help reduce drag in cruise but be a bit complicated. Conventional cowl flaps when closed don't really produce any drag. Louvers have pretty high plume drag. From years of flow bench studies, turning air this much involves high losses. The advantage of a horizontal rad is a gain in area and volume and space packaging. The disadvantage is drag and cowling revisions.

We use an Aero Classic oil cooler, rear mounted for the auxiliary rad. This is fed by a 3 inch NACA duct. For the complete story:

http://www.sdsefi.com/air41.htm

[Rotary10-RV]

Originally Posted by rv6ejguy

It looks to me that Lamar's setup uses fixed louvers, making them moveable would help reduce drag in cruise but be a bit complicated. Conventional cowl flaps when closed don't really produce any drag. Louvers have pretty high plume drag. From years of flow bench studies, turning air this much involves high losses. The advantage of a horizontal rad is a gain in area and volume and space packaging. The disadvantage is drag and cowling revisions.

We use an Aero Classic oil cooler, rear mounted for the auxiliary rad. This is fed by a 3 inch NACA duct. For the complete story:

http://www.sdsefi.com/air41.htm

The louvers Lamar suggests are supposed to be closeable. small exit slits were to remain in the closed position. I agree that this would still have a high plume drag, but is simpler than many other setups. A typical bottom exit would be less draggy. I also did a design venting the radiators in a side slot like the Thorpe. Peter Garrison's original Melmoth design used this system to excellent effect.
Bill Jepson

[cobra]

Just an idea to throw out for comment: how about an adjustable under the propeller scoop feeding, to an angled duct to a wedge feeding an angled, mostly-horizontal, radiator, exiting to a wedge shaped collecter, feeding an underslung exit duct behind/around the front wheel.

The adjustable scoop could be opened (down) to catch prop blast at idle and taxiing, closed 1/2 for low-speed climb, and closed to the smaller cruise position for lower drag at higher speeds. In the 9A, the big/open scoop might even help to work as a speed brake to some extent for landing with a fixed prop setup.

[copterdoc]

cobra Just an idea to throw out for comment: how about an adjustable under the propeller scoop feeding, to an angled duct to a wedge feeding an angled, mostly-horizontal, radiator, exiting to a wedge shaped collecter, feeding an underslung exit duct behind/around the front wheel.

Cobra you said a mouthfull! I'm no expert but I think the scoop has to be properly proportioned for the diffuser duct to work. That setup brings to mind variable geometry intakes on fighter jets and gets complicated fast! Getting more air flow through the radiators at low speeds is the key. I've read where some of the pusher installations have used fans to pull air through but shouldn't be needed on a RV. I work with turbines and dearly wish for some bleed air on my RV. I used to build crop dusters and they used bleed air to augment the oil cooler while sitting on the ground being reloaded. That PT6 could sit there all day in feather and run just fine. But when they tried going without the augmentation temps went sky high. I don't know about a variable intake but what about an aux air scoop that would feed into the existing duct durring taxi or climb and retract shut durring cruise? I'd really like to keep this simple and the less cockpit controlls and holes in the firewall the better. I'll bet that someone has allready tried some of these things and will hopefully share their results with us. It's easy to say this or that won't work untill somebody tries it. I haven't seen anything new on Tracy Crooks' site about the 20B powered RV-8. Anyone know how he is planning on cooling it?

[Rotary10-RV]

Originally Posted by cobra

Just an idea to throw out for comment: how about an adjustable under the propeller scoop feeding, to an angled duct to a wedge feeding an angled, mostly-horizontal, radiator, exiting to a wedge shaped collecter, feeding an underslung exit duct behind/around the front wheel.

The adjustable scoop could be opened (down) to catch prop blast at idle and taxiing, closed 1/2 for low-speed climb, and closed to the smaller cruise position for lower drag at higher speeds. In the 9A, the big/open scoop might even help to work as a speed brake to some extent for landing with a fixed prop setup.

Cobra,
There are several designs for wedge shaped inlets, for the EXIT to be truly effective you need space for the air passing through the radiator to start flowing again usually 2-4 times the radiator thickness. So for a 2inch thick radiator you should have at least 4-8 inches of clear box before trying to do anything with the air (LIKE TURNING IT) to get best effectiveness. The wedge shape exit would make 1/2 your radiator inneffective.
Rotary10-RV