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General Question-Gas engine Fits Entirely Inside Cowl

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General Question-Gas engine Fits Entirely Inside Cowl

Old 04-21-2012, 02:36 PM
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phakur
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Default General Question-Gas engine Fits Entirely Inside Cowl

Hi all-

I am in the process of mounting a DLE 20 on a Spacewalker II (Seagull 120).

The entire engine as well as the muffler fits completely inside this very large cowl.

I realize I will need to do something about cooling air and will punch some holes strategically where they won't spoil the plane's looks, but what about the exhaust. Should I get an extension and extend the exhaust so that it is outside the cowl? Is it good enough to just put a hole in the cowl in the general area?


Your thoughts would be appreciated.

Thanks-

Larry
Old 04-21-2012, 02:53 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

I would want the exhaust just outside the cowl. You are still pushing very hot exhaust and it could burn or discolor the aircraft.
Old 04-21-2012, 03:59 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

I would make sure it exited outside the cowl as well. Often times the standard exhaust comes out in a rather "unfortunate" spot when considering the scale appearance of the plane. That's what drives the "wrap around" exhaust system sales. They nearly always allow for a much cleaner exhaust installation, leaving the outlets centered somewhere just ahead of the firewall. They're also a tad less offensive when it comes to noise.
Old 04-21-2012, 04:04 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Your strategically placed holes in the cowl might not spoil the model's looks but might also not do much in helping to cool the fully enclosed hot engine. You need to have a front opening that allows incoming air to pass around and over the cylinder head and an exit opening approx. 3 times larger that the inlet to allow the hot air to escape quickly.

Karol
Old 04-21-2012, 06:11 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Cut yourself 3 or 4 half inch wide slots so they bloe across the head and a big hole down under close to the firewall on the bottom to exit the air. It makes a big difference in temps. Just adding a spinner to my butcher bird made the temp go up about 30 to 40 degree's in no time flat
Old 04-22-2012, 03:42 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Just punching holes or slots is a very haphazard way to go about it, and likely to fry your enclosed engine. To get air blowing, you need to set up a pressure difference. Then you need to guide that air over your engine.
See http://www.prme.nl/forum/viewtopic.php?t=148 for cooling requirements and solutions.
Old 04-22-2012, 10:18 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Looks good nice baffle, lets all run out and baffle our engines. Seems to me the cowled engine has no exit area on the rear so I guess if you don't let the air out of the cowl you would need to baffle it to get as much of it to run around it to cool it. I for one willnot waste my time till I see a overheating condition. Go fly have fun and see what the engine does, with the 3 to 1 rule, then if needed ad a baffle.
Old 04-22-2012, 10:50 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrash

Looks good nice baffle, lets all run out and baffle our engines. Seems to me the cowled engine has no exit area on the rear so I guess if you don't let the air out of the cowl you would need to baffle it to get as much of it to run around it to cool it. I for one willnot waste my time till I see a overheating condition. Go fly have fun and see what the engine does, with the 3 to 1 rule, then if needed ad a baffle.
???? The first illustrations clearly show air exit area at the bottom rear of the cowl. It also illustrates how airflow tends to flow right past this exit without producing any negative pressure in the area .... so there is little air extraction from the cowl. The airdams produce low pressure behind them allowing for hot air extraction. Pretty simple really. can't see any reason to challenge Pe's logic on this and in fact thank him for publishing this some years back. Such a simple thing that works so well ... especially if coupled with the suggested baffles.

I don't baffle most of my engines but I do make sure the airflow is through the cylinder fins and that there is provision for air extraction. I've been asked more than once why my Yak has that baffle plate in the front of the cowl. Most of the time people just walk away wondering *** after my explanation. They ask the question but really don't want a real answer. Oh well, their loss!
Old 04-22-2012, 11:04 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Your thinking is pretty much like putting the cart before the horse, as the one overheating condition you see might cost you an engine.

Karol
Old 04-22-2012, 11:09 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

ORIGINAL: Truckracer


ORIGINAL: unclecrash

Looks good nice baffle, lets all run out and baffle our engines. Seems to me the cowled engine has no exit area on the rear so I guess if you don't let the air out of the cowl you would need to baffle it to get as much of it to run around it to cool it. I for one willnot waste my time till I see a overheating condition. Go fly have fun and see what the engine does, with the 3 to 1 rule, then if needed ad a baffle.
???? The first illustrations clearly show air exit area at the bottom rear of the cowl. It also illustrates how airflow tends to flow right past this exit without producing any negative pressure in the area .... so there is little air extraction from the cowl. The airdams produce low pressure behind them allowing for hot air extraction. Pretty simple really. can't see any reason to challenge Pe's logic on this and in fact thank him for publishing this some years back. Such a simple thing that works so well ... especially if coupled with the suggested baffles.

I don't baffle most of my engines but I do make sure the airflow is through the cylinder fins and that there is provision for air extraction. I've been asked more than once why my Yak has that baffle plate in the front of the cowl. Most of the time people just walk away wondering *** after my explanation. They ask the question but really don't want a real answer. Oh well, their loss!
The first pics DID NOT LOAD when i first clicked on the link. RCU bugs maybe The only cowl pic up was the round radial pic.
Old 04-22-2012, 11:16 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

ORIGINAL: karolh

Your thinking is pretty much like putting the cart before the horse, as the one overheating condition you see might cost you an engine.

Karol
I do what is needed to make sure my planes get air over the head. Some people cannot afford to buy hundreds of dollars of telemetry to monitor the conditions. Why put a baffle around an engine to fine out you done wasted your time. Most the people I see flying gas donot have baffles in there planes. I am not stupid I can hear and tell what my engine is doing. I check it on the ground with cowl for overheating. Lets hear your bright Ideas of how you go about getting your airplane intto the air the first time instead of being a smart ars My friend has been doing gas planes for ten years and have never seen any baffles or problems with his planes . all them baffles look good on paper till you try to route all your stuff through them and then still get the cowl on. I know most of you guys are engineers and metal workers so no problems getting er done
Old 04-22-2012, 11:28 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: karolh

Your strategically placed holes in the cowl might not spoil the model's looks but might also not do much in helping to cool the fully enclosed hot engine. You need to have a front opening that allows incoming air to pass around and over the cylinder head and an exit opening approx. 3 times larger that the inlet to allow the hot air to escape quickly.

Karol
But the 3 to one rule PE has pretty much shot down. You might make a high pressure area
Old 04-22-2012, 11:40 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrash

ORIGINAL: Truckracer


ORIGINAL: unclecrash

Looks good nice baffle, lets all run out and baffle our engines. Seems to me the cowled engine has no exit area on the rear so I guess if you don't let the air out of the cowl you would need to baffle it to get as much of it to run around it to cool it. I for one willnot waste my time till I see a overheating condition. Go fly have fun and see what the engine does, with the 3 to 1 rule, then if needed ad a baffle.
???? The first illustrations clearly show air exit area at the bottom rear of the cowl. It also illustrates how airflow tends to flow right past this exit without producing any negative pressure in the area .... so there is little air extraction from the cowl. The airdams produce low pressure behind them allowing for hot air extraction. Pretty simple really. can't see any reason to challenge Pe's logic on this and in fact thank him for publishing this some years back. Such a simple thing that works so well ... especially if coupled with the suggested baffles.

I don't baffle most of my engines but I do make sure the airflow is through the cylinder fins and that there is provision for air extraction. I've been asked more than once why my Yak has that baffle plate in the front of the cowl. Most of the time people just walk away wondering *** after my explanation. They ask the question but really don't want a real answer. Oh well, their loss!
The first pics DID NOT LOAD when i first clicked on the link. RCU bugs maybe The only cowl pic up was the round radial pic.
A friend has a 33% yak no baffles runs fine. He has been flying it for years. Wonder why yours needs one. All Im saying is Im not going to create something till I find a reason to do it. If I have a lean condition then I will trouble shoot it. But Im not going to create more problems for my self.
Old 04-22-2012, 11:57 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: pe reivers

Just punching holes or slots is a very haphazard way to go about it, and likely to fry your enclosed engine. To get air blowing, you need to set up a pressure difference. Then you need to guide that air over your engine.
See http://www.prme.nl/forum/viewtopic.php?t=148 for cooling requirements and solutions.
I guess I need an engineer degree to post without being jabbed at . You have to start somewhere getting air to the engine. Is not 3 or 4 slots directly in front of the head and a good size exit hole getting air to the fins. I know im not an engineer but for something is better than doing nothing. Here is what I do know most stuff I see today is way over engineered by who else the engineers. Here is just a little example of it my brothers ford. To get the alternator off you must DROP THE CRADLE for those who do not know what im talking about the whole frickin engine cradle that holds the motor in the car. Plain stupid. Just want to make it so you cannot do it yourself. A friend is a engineer for GM his own wife tells him all the time just doing stupid little stuff around the house. Honey you have way over engineered it
Old 04-22-2012, 12:04 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrash


ORIGINAL: unclecrash

ORIGINAL: Truckracer


ORIGINAL: unclecrash

Looks good nice baffle, lets all run out and baffle our engines. Seems to me the cowled engine has no exit area on the rear so I guess if you don't let the air out of the cowl you would need to baffle it to get as much of it to run around it to cool it. I for one willnot waste my time till I see a overheating condition. Go fly have fun and see what the engine does, with the 3 to 1 rule, then if needed ad a baffle.
???? The first illustrations clearly show air exit area at the bottom rear of the cowl. It also illustrates how airflow tends to flow right past this exit without producing any negative pressure in the area .... so there is little air extraction from the cowl. The airdams produce low pressure behind them allowing for hot air extraction. Pretty simple really. can't see any reason to challenge Pe's logic on this and in fact thank him for publishing this some years back. Such a simple thing that works so well ... especially if coupled with the suggested baffles.

I don't baffle most of my engines but I do make sure the airflow is through the cylinder fins and that there is provision for air extraction. I've been asked more than once why my Yak has that baffle plate in the front of the cowl. Most of the time people just walk away wondering *** after my explanation. They ask the question but really don't want a real answer. Oh well, their loss!
The first pics DID NOT LOAD when i first clicked on the link. RCU bugs maybe The only cowl pic up was the round radial pic.
A friend has a 33% yak no baffles runs fine. He has been flying it for years. Wonder why yours needs one. All Im saying is Im not going to create something till I find a reason to do it. If I have a lean condition then I will trouble shoot it. But Im not going to create more problems for my self.
If I install a baffle in a big round cowl right from the beginning, I don't have to wonder whether the engine will be getting all of the cooling airflow or not. Along with that, big round cowl planes are famous for having pressure problems that affect how the carbs work. So by installing the baffle I kill two possible problems with one quick and easy to install part. Its a peace of mind thing.

This whole baffle, airflow, cowl pressure discussion goes right along with the problems some people have with Walbro carbs and their need for a vent line from the diaphram cover plate. In many cases, the Walbro problem is telling you there is a pressure problem in the cowl. It is just a symptom of a greater problem and not a problem with the carb at all.

Yes, I have seen (and flown or owned) many planes without any sort of baffles. But as I have learned more about our engines and their environment I prefer to use at least some of the basic principals necessary to prevent problems. The fact that I don't use full baffles is just pure lazyness on my part.
Old 04-22-2012, 12:10 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrashBut the 3 to one rule PE has pretty much shot down. You might make a high pressure area
I don't believe Pe is as critical of the 3 to 1 rule (it could also be the 4 to 1 ratio or any other ratio) as much as he is critical of not making provision for air extraction from the cowl. Just providing holes in the front and rear of the cowl in a 3 to 1 ratio does not guarantee good cooling.

In big round cowl installations I regularly see where the whole 3 to 1 thing is reversed where the whole front of the cowl is wide open but there is only a small hole for air to sort of escape. Sort of like a sauna for the engine to live in!
Old 04-22-2012, 12:15 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Truck do you have any pics of how you do your setup, like to see how others do stuff. I like simplicity.
Old 04-22-2012, 12:21 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrash

Truck do you have any pics of how you do your setup, like to see how others do stuff. I like simplicity.
Off to the field to fly right now but will try to take some pics later on. Might be a few days before I can post them though. The YAK is pretty much the way Pe illustrated it though and is installed from the front with 4 nylon screws after the cowl is in place. Like you said, it was nearly impossible to permanently install the baffle in the cowl and still get the cowl on the plane. Remember what I said about me being a bit lazy? So I look for the easy way out whenever possible.
Old 04-22-2012, 12:30 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

No rush would just like to see, It must be the pic at the bottom of the page of the round cowl.
Old 04-22-2012, 01:42 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrash


ORIGINAL: karolh

Your strategically placed holes in the cowl might not spoil the model's looks but might also not do much in helping to cool the fully enclosed hot engine. You need to have a front opening that allows incoming air to pass around and over the cylinder head and an exit opening approx. 3 times larger that the inlet to allow the hot air to escape quickly.

Karol
But the 3 to one rule PE has pretty much shot down. You might make a high pressure area
The low pressure area is about three times as effective as the high pressure region. That is why radials had those large flap gills (DC3 etc etc.)
In a sound design, a 1:1.2 rule will function perfectly. Only because of cooling problems did that rule change to 1:2, then to 1:3, and nowadays even to 1:4. Changing the ratio bypasses the real reasons for bad cooling, so be my guest, try it out for yourself. You can always sell the engine on the bay.

Old 04-22-2012, 01:53 PM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Wondering why on the one example it has like the whole bottom cut out which probably is around 1 to 4 and yet it shows it as not being effective at letting the air flow out the bottom.
Old 04-23-2012, 02:02 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Air must have a reason to flow. That reason is pressure difference. No pressure difference No flow. Amount of flow is depending on the amount of pressure difference. Pulling air through a restriction like engine cooling fins needs extra pressure difference.
Large holes by themselves do not cause air to flow.
Old 04-23-2012, 02:35 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl

Well Larry !!! I have the same set up next in line for the bench !!!

about a week or 2 away befor I start on it !!!!

P/M me when you get it going need to know what way to go !!! Thanks Larry

Old 04-24-2012, 01:41 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: unclecrash

Wondering why on the one example it has like the whole bottom cut out which probably is around 1 to 4 and yet it shows it as not being effective at letting the air flow out the bottom.
its an exaggerated representation...


Pe is 100%correct re the cooling baffles. If you don't use baffles you still need a low pressure zone but also a large inlet area.
Pressure and area create force. Youneed sufficient air pressure from the front to push air out the bottom of the cowl without baffles.
No baffles works in some cases because the inlet area is large enough to drive the pressure difference.

its a case of either do baffles or don't and certainly do not blank off the front of the cowl as some people erroneously do.
Old 04-24-2012, 06:01 AM
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Default RE: General Question-Gas engine Fits Entirely Inside Cowl


ORIGINAL: TimBle
its a case of either do baffles or don't and certainly do not blank off the front of the cowl as some people erroneously do.
TimBle, are you suggesting that following Pe's example for the round cowl is incorrect? Thats the method I use for round cowls and it works great. All incoming air is directed to the cylinder. In some cases, the head fins also extend through a hole in the bottom of the cowl much like they would in something like an Extra cowl. Sometimes the engine is completely within the cowl like the topic of this thread. I would like to know more of your thoughts about not blocking off the excess frontal area on cowls.

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