Cooling on pusher-prop designs

[Weaver]

One of the common objections to pusher-prop layouts in the piston era was the problem of getting airflow through the radiator of a liquid-cooled engine in the absence of prop-wash while the aircraft's stationary or taxiing.

Random thought: for a twin-boom pusher-prop design, why not put the radiator on the leading edge of the tailplane? Okay, so you've got to duct the coolant down the booms, but they're pretty much empty anyway. It would also move some weight to the rear, allowing more guns or armour at the front.

Thoughts?

[NARSES2]

I've no idea regarding the technicalities of such a design, but it would mean you'd have a pretty thick tailplane

[kitnut617]

I've no idea regarding the technicalities of such a design, but it would mean you'd have a pretty thick tailplane

Not necessarily, for instance the coolant lines for a Spitfire to the underwing radiators ran down in the space between the wing and the fuselage, passing though the large wing joint the main spar attached to, as you can see in this photo.

[PR19_Kit]

You could have the tailplane actually BE the radiator, or at least the upper surface of it.

A Hornet's (that's the DH one, not the usurper that the USN fly....) radiators are very slim indeed, and not much thicker than a tailplane.

[kitnut617]

Here's a better diagram showing how the Spitfire coolant lines were routed through the engine bulkhead and then down the space between the fuselage and inner wing end. This came from the Morgan/Shacklady book.



My point is, the coolant lines are not very big in diameter, not much difference between them and a commercial truck coolant lines so routing them through the rear fuselage wouldn't need a very big fuselage to the tail.

[kitnut617]

Random thought: for a twin-boom pusher-prop design, why not put the radiator on the leading edge of the tailplane? Okay, so you've got to duct the coolant down the booms, but they're pretty much empty anyway. It would also move some weight to the rear, allowing more guns or armour at the front.

Thoughts?

Just a thought, why not have the radiators in the ends of the booms, with a scoop on the inner side of the booms but downstream of the prop, to catch any airflow coming off the props. The radiator exits could be on the trailing edges of the tail planes

[jcf]

Or just put the radiators in the booms like the P-38.

[NARSES2]

You could have the tailplane actually BE the radiator, or at least the upper surface of it.

Like some of the Schneider trophy designs had you mean ?

[Weaver]

Or just put the radiators in the booms like the P-38.

Those rads are in the prop-wash from the tractor props. I'm talking about a single pusher-prop design like a Saab J-21.

Speaking of which, how did they do cooling on the J-21?

[crudebuteffective]

cooling fans on the radiators car style???

[Weaver]

cooling fans on the radiators car style???

That's the usually proffered solution, but it has some problems in a 1930s/1940s aircraft context.

1. The cooling fan is only needed during ground running, so it's dead weight and drag during most of the flight.

2. If the radiator is nowhere near the engine, then the fan needs to be either electrically powered or remotely powered in some other way. 1930s electric motors were relatively big and heavy by modern standards and mechanical/hydraulic systems would also add weight and complication.

3. For a fan-cooled radiator to be efficient, it needs to be approximately square, so that a single fan can blow over most of it. Aircraft radiators were frequently long and thin, so that they could blend into wing shapes.

4. Once in flight, the airflow will be trying to spin the fan, so it will need to either free-wheel, feather, or retract out of the airflow, all of which complicate the design still further.

[Dizzyfugu]

I've no idea regarding the technicalities of such a design, but it would mean you'd have a pretty thick tailplane

And there's lots of plumbing involved - additional and dead weight that also shifts the aircraft's CoG to the back.

The J21 had its collers in the wing roots, with several small air ducts in the lower wing leading edge - similar to the P-39, too.

The only aircraft I can remember right now that had a radiator arrangement with a fan was the Ki-78 - it had its radiators moved into a compartment behind the cockpit, with inlets on both sides of the fuselage, and internally a small "turbine driven" cooling fan - whatever that turbine had been?

[zenrat]

cooling fans on the radiators car style???

That's the usually proffered solution, but it has some problems in a 1930s/1940s aircraft context.

1. The cooling fan is only needed during ground running, so it's dead weight and drag during most of the flight.

2. If the radiator is nowhere near the engine, then the fan needs to be either electrically powered or remotely powered in some other way. 1930s electric motors were relatively big and heavy by modern standards and mechanical/hydraulic systems would also add weight and complication.

3. For a fan-cooled radiator to be efficient, it needs to be approximately square, so that a single fan can blow over most of it. Aircraft radiators were frequently long and thin, so that they could blend into wing shapes.

4. Once in flight, the airflow will be trying to spin the fan, so it will need to either free-wheel, feather, or retract out of the airflow, all of which complicate the design still further.

Don't fit any more radiators, but for extra cooling when ground running duct additional air to the in-flight rads through entries in the wheel wells using electric (or other motive source of your choice) fans.   In flight the undercarriage doors close the ducts off so there is no additional drag.

I have been told, in discussions on a model hot rod forum with a pre 1969 only rule, that electric cooling fans on cars did not come into general use until the early seventies.  However that may be a case of "it wasn't done" rather than "it couldn't have been done".

[PR19_Kit]

You could have the tailplane actually BE the radiator, or at least the upper surface of it.

Like some of the Schneider trophy designs had you mean ?

Not really, they had surface cooling pipes built into the wing and fuselage skins, S6B and MC72 etc. I meant to have a very thin radiator built into the entire undersurface of the tailplane with the upper surface being thick enough to BE the tailplane.

I have been told, in discussions on a model hot rod forum with a pre 1969 only rule, that electric cooling fans on cars did not come into general use until the early seventies.  However that may be a case of "it wasn't done" rather than "it couldn't have been done".

I'm vainly trying to remember which car types I came across with electric fans during my time in the motor industry without success. 

As I left for BR in late 1969 there must have been at least a few that had them during that period, but I can't recall which ones. Maybe the Jag XJ6 Series 1?

[perttime]

A fan out in the open, like in cars, probably isn't it. A ducted fan might do it. The ducted fan doesn't necessarily have to be in front of the radiator(s) either. I recall a drawing that showed an intake on the bottom of the aircraft, fan in the fuselage, and air exhaust somewhere near the top.

Fw 190 has a fan pushing air into the oil cooler and radial engine. A fan pulling air through engine or radiator should work well too, as long as the airflow is directed through efficient ducting.