Running an engine with the cowl off.

Tom-D

Tom-D

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Tom-D
why would the left side run hotter than the right side?
 
Tom-D said:
why would the left side run hotter than the right side?
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The propeller slipstream is rotating. The downgoing blade on the right forces more air down through the cylinders. The upgoing blade on the left throws air upward against the bottoms of the cylinders, inhibiting cooling flow.
 
Dan Thomas said:
The propeller slipstream is rotating. The downgoing blade on the right forces more air down through the cylinders. The upgoing blade on the left throws air upward against the bottoms of the cylinders, inhibiting cooling flow.
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I was going to say it was likely due to slipstream, but I didn’t think it could’ve been that easy.
 
Alternator, vacuum pump or something interfering with the airflow on that side maybe
 
I think it depends on type of A/C, how much cowl, how long, ‘idle power’ only, etc.. no need for an easy yes or no, it can all depend.
 
Newton's laws apply on the left side (airflow hitting the bottom), and Bernoulli's laws apply on the right (airflow hitting the top), so the faster airflow cools better.
 
There is an easy solution to this problem.
 
I saw some responses about running an engine without a cowl is something not allowed by the engine manufacturers. In NJ, I often see banner towers flying with "naked engines". Rogue operator(s) or it depends on the plane/circumstances?
 
Does a counter-rotating engine have the opposite effect?

What about pushers, for that matter?
 
Cap'n Jack said:
I saw some responses about running an engine without a cowl is something not allowed by the engine manufacturers. In NJ, I often see banner towers flying with "naked engines". Rogue operator(s) or it depends on the plane/circumstances?
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The banner tow engines that I have seen up close on the ground have a cowling specifically made for the purpose to blast air through the cylinders while at high power, high angle of attack. -Skip
 
Skip Miller said:
The banner tow engines that I have seen up close on the ground have a cowling specifically made for the purpose to blast air through the cylinders while at high power, high angle of attack. -Skip
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And...thanks for the education!
I tried to find pictures to show what I meant, but there is indeed something to direct cooling air across the engine. From the ground and a distance, they look uncowled.

As a cowling covers the engine, streamline the airflow around the engine, or direct cooling air, I consider this one cowled.

4c5b28e2068f2.image.jpg
 
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timwinters said:
I think both Conti & Lyco specifically forbid it but I'm too lazy to find a reference right now.
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It's ok for a brief time for testing, such as after an oil change to check for leaks. The cowling is part of the cooling system; it generates a high pressure above the engine and a low pressure beneath it, to get proper airflow past the cylinders and heads. The baffling is all designed for this flow. Without the cowl, the air isn't directed properly and the engine can heat up badly if run too long without it.

images
 
Ryanb said:
I was going to say it was likely due to slipstream, but I didn’t think it could’ve been that easy.
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BC-EOC-FIGURE-5.jpg


I once saw a photo of a fellow holding a long ribbon next to the forward fuselage of an airplane with its engine running. That ribbon followed the airflow and spiralled around the fuselage as shown above.
 
There is at least one fatal flaw in this discussion.

1) Have we been given all if the information needed to understand the underlying problem?

2) Does it matter whether the cowl is on or off? Does it behave the same way?

How was the temperature determined? Is this a new problem? Is it a problem at all?

The OP is notorious for not giving all the information that describes a problem.
 
I clearly recall watching a C172 land with no cowling several decades ago.
The guy was tinkering with the engine and decided it was too much trouble to keep taking the cowl on and off for each adjustment!
 
Some of you are close, but the answer is that the prop is spraying the hose water onto the right side, almost completely missing the left side. You are going to need two garden hoses.
 
Let'sgoflying! said:
I clearly recall watching a C172 land with no cowling several decades ago.
The guy was tinkering with the engine and decided it was too much trouble to keep taking the cowl on and off for each adjustment!
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A suicidal idea. Besides the overheating, imagine the drag of that big flat firewall and the shaking of the tailfeathers caused by the turbulence off the firewall.
 
Dan Thomas said:
A suicidal idea. Besides the overheating, imagine the drag of that big flat firewall and the shaking of the tailfeathers caused by the turbulence off the firewall.
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Dan, are you saying that the many banner tow pilots flying planes like the one pictured in this thread (posted by Cap‘n Jack, above) are trying to commit suicide? -Skip
 
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Cap'n Jack said:
I saw some responses about running an engine without a cowl is something not allowed by the engine manufacturers. In NJ, I often see banner towers flying with "naked engines". Rogue operator(s) or it depends on the plane/circumstances?
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If you fly close enough to those planes, you will also see a plenum on top of the engine and the word RESTRICTED on the side of fuselage. Those airplanes are highly modified for the work they're doing.

Also, I don't recommend flying that close to those airplanes. Those guys tend to not have radios (or anything else powered by electricity) and it can make them kind of nervous when a stranger gets that close to them.
 
The OP is notorious for not giving all the information that describes a problem.[/QUOTE said:
Try to focus. The OP asked a question. It’s a good question worthy of discussion. If you don’t want to contribute, are incapable of contributing or just don’t want to read Toms posts, then here’s a suggestion, don’t read them.
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Skip Miller said:
Dan, are you saying that the many banner tow pilots flying planes like the one pictured in this thread (posted by Cap‘n Jack, above) are trying to commit suicide? -Skip
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I know a few folks who would say that anyone towing a banner with a plane is trying to commit suicide regardless of cowl type. ;)
 
Juliet Hotel said:
If you fly close enough to those planes, you will also see a plenum on top of the engine and the word RESTRICTED on the side of fuselage. Those airplanes are highly modified for the work they're doing.

Also, I don't recommend flying that close to those airplanes. Those guys tend to not have radios (or anything else powered by electricity) and it can make them kind of nervous when a stranger gets that close to them.
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Yep- the picture I posted shows what you are describing (I didn't see "restricted", but I'm sure it is there).

I agree with your warning about flying close to those guys. When I flew in NJ, I stayed 500 feet above them. They had unofficial routes that they tended to use, at least down there.
 
Notice how fast this thread went astray ?
I got one answer then ?
 
Tom-D said:
Notice how fast this thread went astray ?
I got one answer then ?
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Like I said, not enough information to make a guess:

Cap'n Jack said:
There is at least one fatal flaw in this discussion.

1) Have we been given all if the information needed to understand the underlying problem?

2) Does it matter whether the cowl is on or off? Does it behave the same way?

How was the temperature determined? Is this a new problem? Is it a problem at all?

The OP is notorious for not giving all the information that describes a problem.
Click to expand...

Threads do go astray, too. Just look at your oil pressure thread.
 
Skip Miller said:
Dan, are you saying that the many banner tow pilots flying planes like the one pictured in this thread (posted by Cap‘n Jack, above) are trying to commit suicide? -Skip
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They'd have to deal with that drag. They do fly slowly anyway, and that Super Cub has a much smaller firewall than a 172, so I imagine they get away with it OK. It would have been tested. My point was that it wasn't a good idea for some dude to do just because he couldn't be bothered to re-cowl the airplane. He's a test pilot at that point.
 
Dan Thomas said:
They'd have to deal with that drag. They do fly slowly anyway, and that Super Cub has a much smaller firewall than a 172, so I imagine they get away with it OK.
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All that drag... That's rich. If you want to talk about drag, you might want to look a few hundred feet behind the firewall where you'll find a 40'x120' sail on a rope. The drag from the firewall hanging in the wind really isn't going to amount to a hill of beans compared to the banner pulling on the tail.
 
Juliet Hotel said:
All that drag... That's rich. If you want to talk about drag, you might want to look a few hundred feet behind the firewall where you'll find a 40'x120' sail on a rope. The drag from the firewall hanging in the wind really isn't going to amount to a hill of beans compared to the banner pulling on the tail.
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I've towed a banner. Once. It was enough. Just picking it up requires some unusual maneuvering to avoid stalling.

The firewall is subject to flat-plate drag, and is easily calculated. A firewall with four square feet, at 70 mph, will have a drag of around 60 pounds. Some of that firewall is blanketed by the engine, but the engine itself offers plenty of parasite drag when out in the open.
 
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