Author Topic: Crankcase Cooling (Read 7687 times)

Tim Wescott · « **on:** February 29, 2016, 03:04:16 PM »

So, I'm back in the saddle building a Legacy, and I'm noticing that they plans call out a crankcase cooling vent.

How necessary is this? Is this needed by all engines, or just some? Is it better for any engine, mostly unnecessary or what?

The only other full-fuse stunter I've done is a blue-box Nobler and it did not have such a vent. I don't recall seeing them on other planes, but it's something that I might miss.

TIA.

RandySmith · « **Reply #1 on:** February 29, 2016, 04:35:38 PM »

Quote from: Tim Wescott on February 29, 2016, 03:04:16 PM

So, I'm back in the saddle building a Legacy, and I'm noticing that they plans call out a crankcase cooling vent.

How necessary is this? Is this needed by all engines, or just some? Is it better for any engine, mostly unnecessary or what?

The only other full-fuse stunter I've done is a blue-box Nobler and it did not have such a vent. I don't recall seeing them on other planes, but it's something that I might miss.

TIA.

Unless the engine is running very hot that would not be necessary , If you need that something else is wrong, the crankcase bottom has a cool fuel charge running thru it at all running times

Randy

Tim Wescott · « **Reply #2 on:** February 29, 2016, 05:54:12 PM »

Quote from: RandySmith on February 29, 2016, 04:35:38 PM

Unless the engine is running very hot that would not be necessary , If you need that something else is wrong, the crankcase bottom has a cool fuel charge running thru it at all running times

Thanks Randy.

Not trying to be a problem child here, but why does my hand-me-down Atlantis from Paul Walker have crankcase cooling vents? Was there something special about the OS 40FSR (I think that's what he said he had in there) that made it run hot? I dimly remember someone saying that one of the OS engines from around then tended to run hot in the crankcase.

I'll just finish the top without vents; I can always make some if necessary.

RandySmith · « **Reply #3 on:** February 29, 2016, 07:30:31 PM »

Quote from: Tim Wescott on February 29, 2016, 05:54:12 PM

Thanks Randy.

Not trying to be a problem child here, but why does my hand-me-down Atlantis from Paul Walker have crankcase cooling vents? Was there something special about the OS 40FSR (I think that's what he said he had in there) that made it run hot? I dimly remember someone saying that one of the OS engines from around then tended to run hot in the crankcase.

I'll just finish the top without vents; I can always make some if necessary.

Hi Tim the FSRs didn't run any hotter than any other engine, unless he ran it lean for some reason, I have ran many of them and setup 100s, The hole won't hurt, but it should not be necessary either, you don't need them, again the crankcase has a cold fuel charge going thru it, so unless the airflow is somehow very stagnate , you will be OK

Randy

Tim Wescott · « **Reply #4 on:** February 29, 2016, 08:24:42 PM »

OK. Thanks.

phil c · « **Reply #5 on:** March 02, 2016, 06:56:44 PM »

The cooler you can keep the lower crankcase, the better. A cold fuel charge gives more torque and power.

tom brightbill · « **Reply #6 on:** March 03, 2016, 02:07:54 PM »

I was just doing break-in runs on a Brian Gardner ST-51. The crankcase measured 55F. at the front bearing, 59 at the rear bearing, 69 on the rear cover, and 189 next to the plug. Ambient temp was 55F. Even if the my thermal gun from cheap a$$ tool company isn't very accurate, the relative measurements should still be in the ballpark.

rustler · « **Reply #7 on:** March 03, 2016, 03:42:46 PM »

Quote from: RandySmith on February 29, 2016, 04:35:38 PM

Unless the engine is running very hot that would not be necessary. If you need that something else is wrong, the crankcase bottom has a cool fuel charge running thru it at all running times Randy

This brings back memories of a situation we encountered when using the old ST ring piston G51 engines. For some time John Benzing (very sadly whose funeral is tomorrow) when practising was getting good engine runs on his first flights, followed by inconsistent engine runs subsequently. No analysis could find any reason. If o.k. on one flight, why not on the 2nd.? Eventually it was traced to residual heat at the cylinder head at the end of the flight travelling by conduction to the bottom, once the in-flight cooling air was no longer being ducted around the bottom of the c/case. The cause and "cure" was discovered by letting the engine cool down for 1/4 hour between flights.

This problem only became evident when practising, under contest conditions there was always more than 1/4 hour between flights.

Some of you may remember John Benzing from his and Paul Winter's trips to U.S. events. Sadly left us before his time. R.I.P. John.

Steve Helmick · « **Reply #8 on:** March 03, 2016, 03:50:59 PM »

Seems like crankcase cooling might help, won't hurt. I think I'd put some cooling ducts in. When I flew CL speed, I found that cooling improved the fuel economy over no-cooling (which was kind of the rage back then).

Steve

Chris Wilson · « **Reply #9 on:** March 03, 2016, 07:04:52 PM »

Quote from: RandySmith on February 29, 2016, 04:35:38 PM

....... the crankcase bottom has a cool fuel charge running thru it at all running times

Randy

Only if it is a two stroke and more so if its a glow engine since methanol has more of a cooling effect than petrol or kerosene.

RandySmith · « **Reply #10 on:** March 03, 2016, 07:17:01 PM »

Quote from: Chris Wilson on March 03, 2016, 07:04:52 PM

Only if it is a two stroke and more so if its a glow engine since methanol has more of a cooling effect than petrol or kerosene.

We were originally talking about a FSR, that is why I did not go into 4 stroke diesels etc..
I also was not speaking about speed engines, or running in a lean mode that isn't being done in stunt.
Bottom line is if you want to add cooling holes for the crankcase in your stuntship, do it, it most likely will not do anything, but it will not hurt anything

Randy

Air Ministry . · « **Reply #11 on:** March 03, 2016, 08:17:29 PM »

FSR ? FSR ! you mean t6he FSR . Lot of oiticals on Designs using them have two 1/4 bore outlets or ducts too the undercase area .
State the rpms on ground go up , after a lap or two the rpms drop ( with cooling ducts ) . So we thought we'd see what 's going ,
here .

Art for Arts sake . The inners about 3/4 to 1 in , with a 2 mm gap . peripheral intake .

The lower temp. should give better carge density , thus more Power . Tecnilogically .

A way to checkitout , if your spinner rings only say 1/4 " chord , would be to leave the spinner off for a few flights .
other FSR trick reputedly is to set tank down 1/8 " for even speed through manouvres .

unessesary in siberia in winter , but might help , in death valley in summertime .

Chris Wilson · « **Reply #12 on:** March 03, 2016, 10:03:54 PM »

Quote from: RandySmith on March 03, 2016, 07:17:01 PM

We were originally talking about a FSR, that is why I did not go into 4 stroke diesels etc..
I also was not speaking about speed engines, or running in a lean mode that isn't being done in stunt.
Bottom line is if you want to add cooling holes for the crankcase in your stuntship, do it, it most likely will not do anything, but it will not hurt anything

Randy

To be fair Randy, the original post was not engine type specific and your second reply used the term 'again' - as in referring back to your closet previous reply for the benefit of repetition and emphasis.
And that, again, was not engine specific either.

But I understand where you are coming from, thanks.

RandySmith · « **Reply #13 on:** March 03, 2016, 10:23:38 PM »

Hi Chris looked to me like it was..

Tim Wescott wrote " Not trying to be a problem child here, but why does my hand-me-down Atlantis from Paul Walker have crankcase cooling vents? Was there something special about the OS 40FSR (I think that's what he said he had in there) that made it run hot? I dimly remember someone saying that one of the OS engines from around then tended to run hot in the crankcase. "

Yes I think it was engine specific , Tim was the one that started the thread, but that doesn;t matter, there is not anything about that engine that would be any worse than any other engine used for stunt that would make it differant

By the way I have seen people use cooling holes in many ST46 engines as well as HP 40 and OS 35S, plus several others, I even tried them...they made zero difference in my models.
By Far you would be better off paying attention to the proper intake and exit area, the exit area is where I have seen the most heat problems with conventional muffler setups. You should have about twice the exit area in a typical setup.
In piped setups it has been problems not running cooling air over the header and first half of the pipe.

Randy

Air Ministry . · « **Reply #14 on:** March 03, 2016, 10:41:33 PM »

Heres a Baron - avanti diatribe with details .

http://www.outerzone.co.uk/download_this_plan.asp?ID=6652

hit download suppliment , see P31 .

Lauri Malila · « **Reply #15 on:** March 03, 2016, 11:09:22 PM »

Ian, I'd say that John's problem was caused by engine heat creeping into fuel tank. Heat makes the viscosity of fuel lower, it runs more freely through needle valve and engine goes richer. I do it all the time, after 1st flight the needle must be screwed in a little.
So for this reason I like the idea of creating some vertical airflow inside the engine compartment; to get some fresh air to keep fuel tank cool.

See you soon,

Lauri

RandySmith · « **Reply #16 on:** March 03, 2016, 11:50:06 PM »

Quote from: Matt Spencer on March 03, 2016, 10:41:33 PM

Heres a Baron - avanti diatribe with details .

http://www.outerzone.co.uk/download_this_plan.asp?ID=6652

hit download suppliment , see P31 .

Bob Baron caused a lot of his own problems by making such a terrible cowl, thee ones he used was just a huge opening in the fuse with an engine in it, NOT effective for cooling the motor.

Randy

rustler · « **Reply #17 on:** March 04, 2016, 04:29:55 PM »

Quote from: Lauri Malila on March 03, 2016, 11:09:22 PM

Ian, I'd say that John's problem was caused by engine heat creeping into fuel tank. Heat makes the viscosity of fuel lower, it runs more freely through needle valve and engine goes richer. I do it all the time, after 1st flight the needle must be screwed in a little.
So for this reason I like the idea of creating some vertical airflow inside the engine compartment; to get some fresh air to keep fuel tank cool.

See you soon, Lauri

Sooner than expected Lauri. Good to see you at John's funeral today, a noble effort all the way from Switzerland. I'll leave you to discuss the above with Dr. Dixon!

Brett Buck · « **Reply #18 on:** March 05, 2016, 12:22:03 PM »

Quote from: rustler on March 03, 2016, 03:42:46 PM

This brings back memories of a situation we encountered when using the old ST ring piston G51 engines. For some time John Benzing (very sadly whose funeral is tomorrow) when practising was getting good engine runs on his first flights, followed by inconsistent engine runs subsequently. No analysis could find any reason. If o.k. on one flight, why not on the 2nd.? Eventually it was traced to residual heat at the cylinder head at the end of the flight travelling by conduction to the bottom, once the in-flight cooling air was no longer being ducted around the bottom of the c/case. The cause and "cure" was discovered by letting the engine cool down for 1/4 hour between flights.

This problem only became evident when practising, under contest conditions there was always more than 1/4 hour between flights.

Sorry to hear about John, please pass along my condolences to his next of kin.

This sounds like a case of heat soak-back. That's why my airplanes have cooling holes in the nose. When it runs, the bottom end stays cool for reasons stated previously. After a flight, the hot parts soak heat into the cool parts, and it heats up the entire engine. That can have a variety of effects. On the PA (40 and 61) it caused a tendency to start up rich as the fuel got heated as it went into the engine. With no vents, it stayed a but rich until about the inverted flight. With the vents, it stabilized in the laps between the end of the level flight and the wingover. On the Jett, it starts up fast, then stabilizes about the same time as the PA.

If you just fly one flight at a time, more than about 15 minutes apart, there's no issue and it doesn't make any difference. We routinely fly two back to back (to save time of moving the airplanes on and off the circle, and to get two flights in the same conditions so you can tell if whatever change you make actually worked), so it makes a difference in that case.

Brett

Tim Wescott · « **Reply #19 on:** March 05, 2016, 03:43:47 PM »

Quote from: Brett Buck on March 05, 2016, 12:22:03 PM

If you just fly one flight at a time, more than about 15 minutes apart, there's no issue and it doesn't make any difference. We routinely fly two back to back (to save time of moving the airplanes on and off the circle, and to get two flights in the same conditions so you can tell if whatever change you make actually worked), so it makes a difference in that case.

I dunno about the Nats, but in local competition you can't guarantee that you won't be flying two flights back-to-back. It sounds worth it just for that.

Air Ministry . · « **Reply #20 on:** March 06, 2016, 07:09:47 PM »

If the engines inverted and you turned your aeroplane upside down when it landed , It wouldnt do it ( Heat soak ) .

Chris Wilson · « **Reply #21 on:** March 07, 2016, 01:58:56 AM »

I have always thought that the attached diagram always applied to two stroke IC engines in some way, shape or form - its just the emphasis that varies.

Lauri Malila · « **Reply #22 on:** March 07, 2016, 04:01:54 AM »

Ideally you should have a plenum chamber before cylinder to slow the airflow down, and from there you canguide the air to engine much easier for symmetrical cooling.
Also, it is a good thing if engine heat pre-heats the air going to venturi, it's kind of a self regulating system. (One good reason for rear intake:)
L

proparc · « **Reply #23 on:** March 07, 2016, 05:06:57 PM »

Quote from: RandySmith on March 03, 2016, 10:23:38 PM

By Far you would be better off paying attention to the proper intake and exit area, the exit area is where I have seen the most heat problems with conventional muffler setups. You should have about twice the exit area in a typical setup.

Randy

That is EXACTLY the place should be paying attention too. "Deadpanning air" or not having a proper cooling exit area, is where almost definitely, you will have problems. Heat management in cowled stunt ship is important. Do what Randy says!!

Brett Buck · « **Reply #24 on:** March 07, 2016, 08:29:32 PM »

Quote from: Lauri Malila on March 07, 2016, 04:01:54 AM

Ideally you should have a plenum chamber before cylinder to slow the airflow down, and from there you canguide the air to engine much easier for symmetrical cooling.
Also, it is a good thing if engine heat pre-heats the air going to venturi, it's kind of a self regulating system. (One good reason for rear intake:)
L

I have a PA header with a coil of copper tubing around it to regeneratively heat the fuel. It worked, after a fashion, but reducing the restriction and having a shorter fuel path is better than a long fuel path and hot and low-viscosity fuel. It *does* add some stability to the setting.

Brett

Lauri Malila · « **Reply #25 on:** March 08, 2016, 10:13:16 AM »

Brett,

My point is that it's not necessarily good to to supply fresh air directly from outside for venturi, but to let engine heat warm it up first.
That way it is possible to have a self-regulating system as warmer air causes setting to go richer and the other way round.
But propably useless in stunt, in team racing it's more usefull.

L

RandySmith · « **Reply #26 on:** March 08, 2016, 12:54:09 PM »

Quote from: Lauri Malila on March 08, 2016, 10:13:16 AM

Brett,

My point is that it's not necessarily good to to supply fresh air directly from outside for venturi, but to let engine heat warm it up first.
That way it is possible to have a self-regulating system as warmer air causes setting to go richer and the other way round.
But propably useless in stunt, in team racing it's more usefull.

L

Hi Lauri
I tried that, found nothing in stability, but only found a slight power decline, and I do not recommend heated air or winding tubing around the header, that is ripe for many problems
Brett does have a point and I do recommend keeping very cold fuel in the warm car during cold weather contest, we make a foam surround that keeps fuel temp stable , That is a big benefit in real cold weather contest. and in hot summer months
The wrap we make for gallon fuel cans, is 1 inch foam wrapped with chrome reflective metal tape, work both summer and winter, it also stops the black tarmac from overheating fuel in the hot months

Regards
Randy

Brett Buck · « **Reply #27 on:** March 08, 2016, 01:42:37 PM »

Quote from: RandySmith on March 08, 2016, 12:54:09 PM

Brett does have a point and I do recommend keeping very cold fuel in the warm car during cold weather contest, we make a foam surround that keeps fuel temp stable

I certainly don't recommend the regenerative heating. But there are very great gains to be made in reducing the drag in the fuel supply lines. We had some indications of this with 4-strokes but we proved it (to my satisfaction) when comparing the PA and Jett spraybars, and then counterboring the PA from the inlet side to increase the cross-sectional area.

Brett

RandySmith · « **Reply #28 on:** March 08, 2016, 01:51:29 PM »

Quote from: Brett Buck on March 08, 2016, 01:42:37 PM

I certainly don't recommend the regenerative heating. But there are very great gains to be made in reducing the drag in the fuel supply lines. We had some indications of this with 4-strokes but we proved it (to my satisfaction) when comparing the PA and Jett spraybars, and then counterboring the PA from the inlet side to increase the cross-sectional area.

Brett

Yes , your exactly right, that is why I posted the above, and the proof, I found, is keeping the fuel warm during cold weather contest. It does make a big difference, that makes a whopping larger difference than opening the spraybar on all my ships, and others we tested. I have feed both a 91 and a 108 with the stock PA spraybar. thats NOT to say there is no advantage to doing that, also keeping the tubing straight with no kinks, and keeping the tank close to the engine is another.
Putting warm fuel in an airplane when really cold is night and day difference.. even if you have to run the car heater...:-)

Randy

Tim Wescott · « **Reply #29 on:** March 11, 2016, 11:48:17 PM »

Brett convinced me that cooling is good for back-to-back flights, either in practice or at a contest. So there's nostrils in cowl now: http://stunthanger.com/smf/open-forum/legacy-build/msg440155/#msg440155.