dasintex

My Feedback: (10)

I am putting together a Top Flite Giant P-51 with a Revolution 52 Engine which fits completely in the cowl, with the only cutout being on the bottom of cowl for exhaust pipe exit and air venting; do those spinner backplates with the holes/slots cut in them allow more air into the engine compartment; additionally, these engines come with a cooling fan and shroud to help in cooling and drawing more into the narrow cowl.

alan0899

G'day Mate,
Sorry, but spinners with holes or slots don't let more cooling air in, the slots & holes are for weight reduction.
Even if the engine has a fan, the hot air has to be able to exit the cowl, so the openings for that hot air to escape need to be at least twice the size of the air inlet, fan or not.
Usually aircraft engines have a rather large fan on the front of them anyway, it's called a propeller.

aerowoof

exactly

dasintex

My Feedback: (10)

I realize that venting has to be twice as big as intake; I also realize the holes in the back plate are to reduce weight, however, take a look at the pictures of the fan and shroud set up, my thought was that if there were holes in the back plate, the fan unit would draw additional air through them, what do you think?

RCKen

My Feedback: (9)

Even if the backplate has holes in it, there will be almost no air flowing through it anyway. The spinner is a closed system. With the cone of the spinner closed there is no way that air will be able to flow into it, and then back out through the holes in the backplate. As it was stated above, the only reason there are holes cut in the backplate of the spinners is simply to save weight. Nothing more, nothing less.

Ken

dasintex

My Feedback: (10)

Just a thought, worth asking, thanks for the replies.

John Sohm

My Feedback: (9)

You got that nice little chin scoop right under the prop, give yourself some exit holes and build shroud to direct the air from chin scoop over the cylinder head and try it out.

khodges

My Feedback: (1)

You may have to open the cowl a bit around the area where the spark plug is to give an exit for airflow. It won't be too obtrusive there, but you'll have to have some place to let out the heated air. Like John said above, make some baffles to direct the air from the chin scoop downward toward the cylinder head. They can be as simple as some lite ply glued at an angle to the inside cowl sides and trimmed to fit closely to the engine. I think the fan won't do much except maybe at idle, you'll get better flow from airspeed. Make the chin scoop opening as large as scale concerns will allow for max flow.

Jazzy

If the spinner/backplate combo is fit with tight tolerances to the cowl, (almost no visible gap between the spinnerbackplate and the cowl) the engine mounted fan isn't going to do didly in that nice shroud you made for it. Get rid of the shroud otherwise the fan will basically do nothing. Where will the air come from? That big hole in the front of the cowl will be taken up by the front of the engine and the remaining gap will have a lid on it called a spinner. Get rid of the shroud and let the fan do its job!
I'm not sure what the cowl's molded muffler ports look like close up but I've drilled holes into the exhaust port exits of my P51's cowl for a little extra air flow/exit.

da Rock

You actually do have a bit of a problem.

The rule of thumb for adequate cooling used to be to have an intake area that equals the cylinder frontal area. And to have one and a half again that area for the exhaust. It worked for lots of airplanes in all temperatures.

It was understood by most that the intake area could be reduced for faster models. But the 1.5X still applied to whatever the intake was changed to. 1.5X the hole that let air in was as small as you could go for the hole that let the hot air out. And it was understood the intake hole better be in front of whatever needed cooling. And it was really good to have the majority of the exhaust area directly behind what needed cooling. When the location moved from in front and directly behind, the area needed to be increased.

The chin area is how much area compared to your engine. It is directly in front of the engine and that's good.

When you can't for any reason have enough opening in front, you need to insure that the exhausts are not only more than large enough, but that some are in areas of negative pressure. That helps somewhat to draw the air into and through minimal openings faster.

It's often pressure that moves the air, not just airspeed. Get negative pressure behind and inadequate intake and the intake works better.

There have been thousands of P51 models flown successfully.

dasintex

My Feedback: (10)

The Fan And Shroud was developed by the Engine Manufacturer 'Revolution Engines'; to address the issue of overheating in the Crankcase; apparently, when used in the P-51 utilizing this Fan & Shroud solved the overheating problem of the crankcase, I couldn't see where enough air was drawn in through the gap between the cowl and the spinner back plate, that is where I thought that holes in the back plate would allow more air to be drawn into the engine compartment by the fan through the fan shroud? and the gaps in the spinner where the prop sticks through were significant enough; wouldn't the suction force of the fan draw air through the back plate holes, if anything the holes in the back plate can't hurt, and they may allow more air passage, for lack of anything else thay will make for a lighter back plate! your thoughts would be appreciated.

saramos

I cannot comment on the Revolution setup, but I recently built a TopFlite Spitfire with a fully inclosed RCV90SP engine.
I wanted to minimize the cutting I had to do of the cowl. My solution was to have a slightly larger gap between the spinner backplate and the cowl. This is the only air intake. Then, I added a small electric ducted fan with it's own ecs and battery to exhaust the air out a 2" dia. hole in the bottom of the cowl. It's worked out well on ground tests and keeps the engine adequately cooled.

Scott

da Rock

Airflow often is the result of pressures in the right places. Positive and negative.

There have been a number of airplanes that used the opening behind a spinner for cooling air. Pressure differentials do wonders. The air that comes into our carburetors comes into them because of atmospheric pressure. It comes because the engine creates negative pressure inside where it wants the air and fuel to go. And the world pushes the air right on in.

And there have been spinners with holes in their backplates that were to allow air through to the hole behind that backplate that was purposefully there to continue the airflow. They obviously also had openings in the cone to provide that air. Like the gaps around the prop shafts. They weren't much of a solution but contributed.

Negative pressure works wonders.

Find some for the exhaust openings. Then the world will help.