Installing a WAM-120 diesel in an RV-9A
 

Ray clegg & Ian Bellamy have written an article in this months "Popular flying" magazine (UK) on their experiences installing a WAM-120 diesel engine in their RV-9A.

http://www.pfa.org.uk/PF/2007/Sept/DieselVans.pdf

They have taken a more complex approach to fitting the engine than I have, as they have removed Wilksch cooling pack from below the prop and mounted the intercooler and radiator on the engine mount. It takes a but more doing, but avoids the "basking shark" aesthetics of most of the Wilksch installations.

Dave

Dave,
Nice looking work. I like their graphic. Their layout is the technique I want to use for my 3-rotor powered RV-10
Bill Jepson

Engineers have more work to do.
 

I admire these poor chaps for trying to make lemonade out of a lemon. But their mistake was taking the radiators as a given. They would have done almost as well to simply bolt the radiators to the exterior of the fuselage.

Time and time again, the single most disastrous design element of water-cooled alternative engines is the shape of the radiator itself. The engineers who design engines and then slap a square radiator on it ought to be ashamed (or quit).

An engine is but one element of a whole system (RV-9A in this example). If that engine imposes undue compromises on that system, then it is no good. To illustrate extremely: if you come up with an engine that will give you 120HP, burns only 1/10th as much of the cheapest, commonest fuel but weighs 2 tons, then that engine is unsuitable for the application.

The same goes for the radiators. Why does an engine of similar power and greater efficiency need the airframe to donate a 50% to 100% increase in frontal area (compared to a standard 9A cowling) for cooling? This fails the suitability-for-the-application smell test.

Alternative engine designers must live within the same "aerodynamic budget" as mainline engines or forego some claims to efficiency. There is plenty of room inside a standard cowl for a more imaginative arrangement of cooling surfaces that is capable of using a given amount of frontal area with an efficiency comparable to a typical installation.

A Leyland bus, indeed!

Very well said, and I agree with all of your points.

But you must remember that the liquid cooled engines have a much lower Delta "T". This means more air is required to achieve an equiv level of heat transfer.

Maybe, in fact, those engineers know what they are doing.



Franklin

This has been discussed at length here on VAF and there is no flying evidence to prove this contention. This is a very complex area with multiple variables. Definitely not as simple as Delta T.

Here was some info from the water vs. air cooled thread from a couple weeks ago which actually proves the opposite may be true:

http://www.liquidcooledairpower.com/index-flash.html

http://www.liquidcooledairpower.com/...ss_arrow.shtml

Hmmm. Maybe something to this liquid cooled stuff after all.

This rad setup is similar to my thoughts for RVs.
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For those new to the discussion, here's what I posted about a year ago on VAF:

I know the air cooled guys love to say that water cooling is draggier but never produce any facts to support. Here are some tidbits I dug up:

Bristol Beaufighter. 1280hp Merlin 330 mph, 1590 hp Bristol Hercules 323 mph.

Tempest I. 2240hp Napier Sabre 466 mph. Tempest II 2520hp Bristol Centaurus 440 mph.

Reggiane RE 2001. 1175hp Alfa Romeo 337 mph. RE 2002. 1175hp Piaggio 329 mph.

DC-4/ Northstar. 353mph with 1760hp Merlins, 280 mph with 1450hp Pratt R2000s.

Note these are identical or close to identical airframes save changes for the different engine installations. In the case of the Merlin engined Beau and Northstar, these used the Rolls Royce "power egg" system of engine/ radiator in one, firewall forward- hardly the most efficient from a drag standpoint but making engine changes much quicker.

The Tempest in particular shows how much more efficient liquid cooling can be with 280 hp less and 26 mph faster at about the same altitude. The Tempest I had nicely done leading edge mounted rads.

Ross,

again....the air cooled had the frontal area of a radial...then a different cowl for liquid cooled....this in your examples.

On the other hand there is substantial evidence that for a given power or fuel flow, the liquid cooled rvs are slower....sometimes much slower...so there is the evidence.

There is a fundamental need for greater volumes of cooling air....can it be overcome? Probably, but there is not much wrong with the rv cowl now...so it won't be as easy as loosing a radial. No one has managed it yet. Your belly scoop approach may be the first.

Ross, you want your cake and want to eat it too!

You firstly state that the air/liquid cooling debate is much more complex than just the delta-T, but then quote a bunch of airframes to justify your position where there are many more factors at work than just a simple change of cooling system.

Likewise on the CoolJugs Arrow, I watched that video and when ho hum. It just doesn't tell you anything, since much is unknown about the state of either aircraft. It's pretty easy to make any aircraft go slowly - even unintentionally. Just as one possibility, poorly maintained baffles and seals on an air-cooled engine can dramatically increase cooling drag, reducing max speed in the process.

A

Just posting the info guys, take it for what it is worth.

We'll be waiting for the fully instrumented tests and side by sides sometimes in the future.

If anyone has any real world evidence where a properly designed liquid cooled setup (not cheek mounted rads) in an identical airframe with similar propellers has been inferior, I'd be interested in seeing it. I have not seen a nice installation yet on a liquid cooled RV where proper control and use of the cooling air has been fully implemented for low drag.

Under cowling space for a liquid cooled and intercooled engine is limited in an RV and intercooled engines will always produce higher drag than those without. It is a tall order to do a low drag setup on an RV, especially an A model with the gear structure in the way.

A friend just started flying his turbo EJ22 Glastar a couple weeks ago. This uses twin GM evap cores mounted at an oblique angle to the airflow and fed by a plenum arrangement with guide vanes. Despite massive area and volume, cooling is only adequate at OATs up to about 15C. He will be revamping the setup with a custom built rad and exit flap. I'll report on the success or failure of these changes.

There are at least 3 aircraft flying with belly rads now which are cooling really well with relatively small inlets and radiators. We don't know what total drag is like on these yet but this route seems to offer the best chances of success with lower drag and decent ground cooling.

Please, I didn't intend to reignite the air vs. liquid cooled engine debate nor intend to diss certain engineers. I admit I'm not schooled in the math, but the concepts behind heat transfer are simple. The devil is in the details.

I made a forest vs. trees type of observation. I'd love to have any excuse to by an engine that offers the advantages of a 2-stroke turbo diesel. It's just that I'm not willing to stick my leg out the side of the fuselage to do so.

My challenge to the engineers is to find a way to shed the necessary heat without penalizing the airframe. Since the rate of transfer is reduced, and since mass (or drag anyway) is limited, then I guess the transfer of heat must be given more time to work. This must be old hash somewhere.

I hadn't seen the liquid-cooled-air-power website before today. The pictures of their radiator are quite revealing. Its doubled over which probably serves to increase the amount of time that heat is transferred. I would guess that air exiting this radiator is hotter than a single plane radiator all else being equal.

Since the location of the propeller flange and the slice-o-wonderbread shape of the RV-9 firewall are pretty much a given, then the cowling is going to be cavernous compared to the size of the Wilksch engine. This may be sufficient space to design effective diffusers and nozzles (rather than mere passages) that work with appropriately shaped/sized radiators.

I like the idea of the Wilksch engine. I don't like the idea of handicapping the airframe. I sure wish I had the funds to p-o-c it myself.

:)

Other potential heat sinks:

;) Hammer a cowling out of 1/2" aluminum then carefully rout miles of groves/fins on it. Bond standard flat radiator tubing on the inside. Your spinning propeller will ensure that you'll never again fear having enough cooling while being 24th in line for takeoff at Oshkosh.

;) Bond a length or two of radiator tubing to the skin between each wing rib then hook em up. P.S. if you do the right combination of series and parallel connections and fly full-throtle long enough, you'll be able to generate enough electricity for a wig-wag flasher.

;) Bond surplus Carrier/York a/c tubing to the bottom of the fuselage. Don't forget to make a U-turn at the tail.

;) Bond radiator tubing to the underside of the wing. A handful of parallel loops oughta to the trick.

;) Bond radiator tubing to the top of the wing at the appropriate depth of chord. Then bond PC heat sinks to the tubing at alternating angles and call them vortex generators.

;) And if, for crying out loud, you just gotta have that massive radiator up front, at least put it on a tray that can pivot up and down. Use a cowl flap like cable and knob so the pilot can control the amount of droop. Drop it down for high power/low speed regimes and tuck it up for less demanding regimes and show times. In your spare time develop an automatic temperture sensing system to control the droop with Lego servo motors.

What drives the cooling air is the differential pressure between inlet and outlet. An underbelly scoop placed at the max pressure sone under the wing, and exit behind the wing somewhere at a much lower pressure zone, just has to be way more effective than the normal approach. I also think the original Wilksch position of the coolers, more or less at the stagnation point is a good design, even though it looks strange. With the exit at the relatively lower pressure at the sides, instead of below, this should not give very much drag either (and it will look even more like a shark :D ). Seriously, real sharks and other fish, would not have their intake at the front and the exit at the sides if this wouldn't be effective.

F1 cars (800+ hp) have forward facing intakes after the front wheels, and exit partially down in the low pressure zone under the card just in front of the rear wheels. This takes away lots of downforce, but it enables smaller rads, so they can go faster on the straights where they don't need much downforce.