Engine Cooling

[Sapphire]

It doesn't matter what whiz bang engine you get, if it isn't cooled properly then it soon becomes scrap metal. From what I have read and see, some engine setups don't seem to follow in line with theory. Some have enclosed cowls with complicated air intakes, baffles, etc. Some just have the cyl heads poking through the cowling to capture the slipstream, which I read is not acceptable, but a lot of a/c have that method. Does anyone have experience with engine life and various forms of cooling?

 

 

[Louis Moore]

Some just have the cyl heads poking through the cowling to capture the slipstream, which I read is not acceptable, but a lot of a/c have that method.

Where did you read that this system is not acceptable? It might not be efficient or effective on larger horizontally opposed engines but for other setups it is not only a working way to keep the engine cool but it looks really awesome too!

 

There are lots of ways to cool and many pro's and cons for each. It is very dependant on the particular engine, aircraft and install. As a rule I really like water cooling because the tolerances can be tighter giving you extra HP (Lycoming used to make a water cooled cyl that could be fitted STC to their engine, it gave an increase in almost 50hp just by tighter tolerances!) also water cooling can help reduce the hot end cylinder and shock cooling (by the installation of a thermostat, shock cooling is a big issue for a lot of pilots who fly GA and can not operate an engine i.e A LOT OF PILOTS!) and all around seems to be an effective way of "controlling" the cooling. Issues of course are weight, needing to have extra plumbing, radiator and other associated sections that can fail etc... etc... etc...

 

I have spent lots of time throwing various tools at Continental and lycoming engines and to be honest, if there flown correctly they seem to last just fine (minus the occasional 210 or 182!).

 

 

[eightyknots]

It doesn't matter what whiz bang engine you get, if it isn't cooled properly then it soon becomes scrap metal. From what I have read and see, some engine setups don't seem to follow in line with theory. Some have enclosed cowls with complicated air intakes, baffles, etc. Some just have the cyl heads poking through the cowling to capture the slipstream, which I read is not acceptable, but a lot of a/c have that method. Does anyone have experience with engine life and various forms of cooling?

Good question Sapphire: I'm sure there is lots of collective expert knowledge out there among the Forumites. Soon the suggestions will come flooding in.....

 

 

[Louis Moore]

http://www.liquidcooledairpower.com/cj-pricing.shtml

 

This one give you no more HP because it uses the orig cyl, still it's a cool conversion!!!!

 

 

[Sapphire]

http://www.liquidcooledairpower.com/cj-pricing.shtmlThis one give you no more HP because it uses the orig cyl, still it's a cool conversion!!!!

At the Kingaroy Soaring Club [google to aircraft and facilities] they have put a water cooled ford v6 car engine into a Pawnee. To do it commercially the cost would be prohibitive but some retired club aircraft mechnics have done it in their own time. Saw it a few years ago before I got into working on a/c engines, so don't know what modifications they did. Great workshop project to do a smaller say 1.5 litre engine for a single seater.. Though you would have to design and weld new engine mounts, etc. and welding is not my forte. Might contact them

 

 

[eightyknots]

At the Kingaroy Soaring Club [google to aircraft and facilities] they have put a water cooled ford v6 car engine into a Pawnee. To do it commercially the cost would be prohibitive but some retired club aircraft mechnics have done it in their own time. Saw it a few years ago before I got into working on a/c engines, so don't know what modifications they did. Great workshop project to do a smaller say 1.5 litre engine for a single seater.. Though you would have to design and weld new engine mounts, etc. and welding is not my forte. Might contact them

The biggest problem in using an auto engine, say the 1.5 litre example you gave, is the reduction unit so the prop turns at the right speed (up to about 2,600 rpm) from an engine revving at 5,500 or 6,000 rpm.

 

 

[Sapphire]

The biggest problem in using an auto engine, say the 1.5 litre example you gave, is the reduction unit so the prop turns at the right speed (up to about 2,600 rpm) from an engine revving at 5,500 or 6,000 rpm.

Put on a smaller prop, even a one blade prop? They add more blades if there is a clearance problem and have lots of hp., why not the reverse? The development of this might make the space shuttle look like a back yard botchup. [ It was to a certain extent]

 

 

[ben87r]

You wont get enough thrust out of it to get off the ground

 

 

[skyfox1]

We did 800 hrs with a free air 503 on a drifter we took off all the cowlins and fan it ran great

 

temps perfect.

 

 

[Old Koreelah]

As Louis says, liquid cooling is best, but most of us are stuck with the simplicity and lightness of air cooling.

 

VW heads left out in the breeze seem to work OK, amazing really, considering they are designed for the air to pass DOWN through the tiny holes near the exhaust valves.

 

I feel that the convention of exhausting the cooling air under the fuselage (into a high pressure zone) makes it hard to achieve ideal cooling. Why not locate the exit point above the wing in a very low pressure area?

 

My experiments in doing this were successful. My Jab engine runs so cool I've had to progressively reduce the intakes until they are the size of teacups. The addition of butterfly- type cowl flaps allows control of airflow during warm-up and during descent.

 

I ditched my exhaust augmentors after a few trips, and saved a couple of kgs. They sucked air through when stationary and did add about 4% to the climb rate, but the noise was intolerable!

 

We are fortunate to be able to experiment; sometimes we even get it right.

 

 

[Sapphire]

We did 800 hrs with a free air 503 on a drifter we took off all the cowlins and fan it ran greattemps perfect.

That was a two stroke. The exhaust valve in a four stroke is its own achilles heel. It runs so hot and with insufficient lubrication. I checked the valves on my Continental 0-200 and the intake valves were like new- to look at and valve guide clearance. The exhaust valves were like Dante's Inferno and wobbled in their guides like a top. Eventually got 78-80 over 80 on the leak down test. Somehow you need an oil line to feed the valve guide and huge fins for cooling that area, and a fan. Bet you could get double engine hours with that.

 

 

[facthunter]

You don't want to reinvent the wheel in this. Low powered engines like the older 65 HP Continentals were OK with cylinders out in the airflow, but you have only got to think about where the air is coming from and where you want it to go and they are often two different considerations. There are already HOT parts and colder parts of cylinders and heads. Exhaust ports are always the hottest parts. It is desireable to keep the temps even.

 

The more power you put out ( for the engines displacement) the more critical cooling becomes. This is called specific horsepower ie HP/ Litre or any other suitable units.

 

Aero engines deal more with horsepower for weight( and reliability) HP/ Lb or Lbs/ HP more often. Older engines were above 4lbs/per Horsepower.

 

High revving engines ( even the VW in it's more developed forms) needs to have a re-drive ( reduction) to reduce prop tip speed. Also a larger prop works much better on a draggy plane. You need more ground clearance.

 

Most of this is just common sense. and a bit of engineering know how.

 

Car engines ( Honda Jazz or mercedes smart) Probably OK not cheap and end up being quite complex with the engine management and quality re drive.

 

My favourite is the Continental 0-200 with first life engine and a wooden prop and baffled like they all were. You can pretty much forget the engine and just enjoy the plane, but those engines are not new anymore. You were able to get an 0-200D but I don't know the availability of those these days, and lycoming have an 0-233 which is a lightened version of the popular 0-235 115 HP.(a bit wide).

 

If you like fiddling with engines you might be more prepared to make something from something, but life can be a bit short if you are going to build a plane and a motor. The Chev Corvair is a smooth motor. You could write a book on this topic.

 

Just noted saphires comment. yes common problem with a pusher engine. You probably need a fan. jabiru's don't work as pushers, either. Nev

 

 

[Louis Moore]

Speaking of cooling system, I think the P51's cooling system actually ADDED thrust and performance to the whole plane, now thats design!

 

 

[eightyknots]

At one stage they added water injection to aircraft engines ...for several reasons. One of the reasons given was additional engine cooling.

 

You don't really hear of water injection in light aircraft engines. I wonder why?

 

 

[Old Koreelah]

Speaking of cooling system, I think the P51's cooling system actually ADDED thrust and performance to the whole plane, now thats design!

I believe that the P51 radiator contributed a significant proportion of thrust when the engine was throttled back. It was mounted on tracks and a cable system lifted it up and down about 1200mm according to need for cooling air. All this was designed and test flown in a few short months. Meanwhile here in Oz, we have squabbled for generations over whether to build a national railway or fix our national highways.

 

 

[Sapphire]

[ they seem to last just fine (minus the occasional 210 or 182!).

 

Where did you read that this system is not acceptable?

 

I've done some more reading. If you have a half vw engine with the cyl head poking through the cowling to be cooled by the slipstream, that is not acceptable on its own. You also need scoopy things that direct flow to the hottest part of the cyl head which is also where the exhaust valve is located. Some reference elsewhere about air being directed into casting holes to cool the exhaust valve area. The same would apply to other engines, I am sure.

 

 

[facthunter]

The half VW has the exhaust ports out the front so it should get away with it. You coulc easily make your own heads for a half VW. It could be a very simple casting. There is a fair bit of welding and reworking to be done to convert the original. nev

 

 

[Sapphire]

The half VW has the exhaust ports out the front so it should get away with it. You coulc easily make your own heads for a half VW. It could be a very simple casting. There is a fair bit of welding and reworking to be done to convert the original. nev

 

Welding is not my forte but I have done casting....

 

When you finally buy your dream a/c you assume every thing is set up correctly-after all the previous owner had enough confidence in it to do a demonstration flight. But is it? Reputable factory built a/c not modified by "fiddlers" should score ok but home built a/c need to be a concern. Before I bought my Varieze I researched potential problems. One builder in the USA spent four years building his Varieze but forgot to bolt down wing attachments which eventually get covered by fibreglass. Both wings fell off on his first flight. Another owner, under the influence of alcohol, crudely rebored tapered wing pin structures and then bolted them down as tight as he could [requires 3 foot pounds] He went off and did aerobatics[no no] One bolt broke away and the wing swiveled back on the remaining bolt. The winglet now produced uncontrolled yaw which flipped the plane upsidedown. His surviving relations took Rutan through an expensive court battle after which he stopped selling plans and went on to better things.

 

What has all this got to do with engine cooling? Absolutely nothing! However,when you buy your homebuilt or any a/c check if it has been built properly-cooling systems I find can be inadequate and it is you who will pay through the nose once you sign on the dotted line. Actually, in my opinion, all piston aircooled 4 stroke engines run in an over heated state. If a part of an engine fails as a result of too much heat rather than normal friction wear, then the engine is running too hot. Becomes part of the high cost of flying.

 

 

[facthunter]

Sapphire, in flying, the less you assume the longer you will live. Homebuilt can be anything from better than original (rare) to "I wouldn't fly in that for all the TEA in China. I (like you) have seen some appalling things that are supposed to fly, but everyone thinks I am too fussy.

 

IF anyone is buying a plane the best thing you can do is spend whatever it costs to get an expert on that type to look at it. You still might have to take a chance on what you can't see. I would only do that with someone I knew I could trust. I believe you make your own luck. Others believe when your time's up you go.( Someone must be doing a lot of planning and we'd have to blame him/her/it for the bad as well as give praise for the good).

 

Overheated engines do not last, but some good metallurgy and quality control makes scary things work acceptably. The exhaust valves in a turbocharged engine would be hot enough to read a paper by. Nev

 

 

[Sapphire]

I wouldn't say you are too fussy. You can be blase over airline food [i am soon to find that out againnn] but not life threatening contraptions. The next time I need a night light, I'll know where to go

 

 

[Old Koreelah]

Sapphire, in flying, the less you assume the longer you will live. Homebuilt can be anything from better than original (rare) to "I wouldn't fly in that for all the TEA in China...You still might have to take a chance on what you can't see. I would only do that with someone I knew I could trust... Nev

You are so right, FF. We fly along oblivious to what is really holding the whole damn thing together. Faith in the workmanship of others is a major component of any pilot's life.

 

As the 6th owner of my little aircraft, I once tracked down the bloke who built the wing spar and ribs to thank him for his great work and tell him how well it all turned out. He became very emotional and I regretted reminding him that his wife had caused him to sell his labour of love.

 

 

[Riley]

(quote) I've done some more reading. If you have a half vw engine with the cyl head poking through the cowling to be cooled by the slipstream, that is not acceptable on its own. You also need scoopy things that direct flow to the hottest part of the cyl head which is also where the exhaust valve is located. Some reference elsewhere about air being directed into casting holes to cool the exhaust valve area. The same would apply to other engines, I am sure.

 

Sapphire I find your "one size fits all" statement that the Hummelbird engine/fuselage design is unacceptable for proper cooling along with the "I read something, somewhere" treatise rather curious. Discussion with T. Hallet of Hummelbird in the USA reveals that there are quote, "700 to 1000" 1/2 VW-powered Hummelbirds flying worldwide with no heating problems that weren't resolved by a change to proper fuel, corrected fuel/air mixture or a review of propellor selection. Rather than to leave the above statement (specific in it's relation to 1/2 VW/H'birds et al) unchallenged and thereby a potential reference for someone in the future to quote as having "read something, somewhere", methinks perhaps more specific research or a statement qualification might be in order?

 

 

[Riley]

Apologies Louis for inadvertently including part of your post in my abv defence of the 1/2 VW-H'bird. We obviously share similar thoughts on the matter. Guess maybe I started too early this morning. cheers

 

 

[Sapphire]

There is an edit facility. I didn't specifically hunt out the Hummel Bird but more the design of having cyl heads sticking out in the slipstream with no other modification. I kept bringing up that a/c because I was investigating one that was for sale here. Cooling is a very complex subject and even the best working systems don't satisfy the requirements of aircooled engines all the time. Take a 40 C plus day and you have to taxi to the far end of a cross strip and there is lots of traffic. You are holding behind several aircraft because this aerodrome has no taxiway. You have waited what seems like eternity just to taxi on this runway so you can hold some more to back track the cross strip. The delays can go on and on while your engine is screaming for cooling.

 

 

[boingk]

Cooling 101:

 

• Aircooling is easy (no plumbing, radiator etc) but inferior. This is due to its generally higher weight (cooling ribs) and lower power (lower tolerances)
   
   
  
• Watercooling is more complex but generally provides engines with higher specific power.
   
   
  
• Both types need a suitable installation in order to work, with air being directed over the cooling surfaces (cylinders or radiator).
   
   
  
• Some airframes are not suitable to a particular installation, or offer a much more straightforward option for either type of engine.
   
   
  
• Ideally the aircraft designer will have a particular type or range of powerplants in mind when designing the aircraft.
   
   
  

 

 

The above is a reasonably straightforward guide to engine cooling. Engines are also affected by the prop fitted, mixture range and ambient temperature. Generally an idle will not be sufficient to provide adequate cooling for an engine for any prolonged period of time, and a slightly faster speed can be used in some conditions to overcome this via increased airflow. High ambient temperatures can and will cause problems for aircooled engines held on ground for excessive lengths of time.

 

As for cooling under all conditions... we're picking hairs. My car, for example, does not operate under ALL conditions... but for 99.9% of the conditions I will ever encounter it does just fine. I imagine the same for aeroplanes, with the added fact that by our study of weather conditions before takeoff we can take note of and avoid any possible trouble areas, thereby possibly circumventing any unwanted operational conditions. Being held on the flight line for prolonged periods of time is another issue and can be dealt with by a few means, notably more careful flight planning and advising the tower / traffic of any possible overheating condition to let them a) know about and b) possibly help with your situation.

 

Aircooled engines do indeed need cooling air to be directed over the cylinders. Whether this is freeflowing air of air ducted from elswhere (most notably the front or underside of the cowling) is irrelevant so long as it is there. What some people are referring to as 'cylinder head' cooling is in no way accaptable, as in reality all it does is provide marginal cooling for the valvetrain. The actual head is buried away under the cover, valvetrain, and a substantial amount of metal. Valve-cover cooling is valuable, but in no way sufficient as the sole method to cool an engine. You want and *need* airflow over the cylinders themselves to provide adequate cooling, as well as the sump/oil reservoir and any oil-cooling radiators.

 

Cheers all - Enoch