downunder

Exactly, I've mentioned it a couple of times elsewhere that oil out the exhaust can only match oil in the carb. Not that I think it goes straight through the engine and out the exhaust but more likely slowly migrates its way through. But the volume going out can only equal the volume coming in. On a rough calculation with a .60 size engine there's on the order of .0006cc of oil going out the exhaust every cycle. In American terms that's 1/50,000th of an ounce.

I'd never try an experiment that I thought had a good chance of harming an engine, which is why it didn't concern me doing this prop test....or the ultra rich running of a new ABC .

I like Pe's description of a bath tub type of cooling curve with regard to pitch and I suspect the curve begins to flatten out at quite a low pitch, maybe less than 3" or so? I believe for all intents and purposes any pitch that's commonly used is fine for cooling.

pe reivers

boiling water has a temperature (not a heat) of 100C. It takes a lot of heat to bring it to boil.

Calibrating an IR device is not required if you use the same device in the hands of the same tester on measuring the same object. Only the comparison is of importance, not whether the measured value is exact to within a few degrees or not.

Some interesting reading on the difference between heat(energy) and temperature which combined with mass has a certain amount of transferrable heat (enthalpy)
From wikipedia:
In physics, heat, symbolized by Q, is defined as energy in transit.[1] Generally, heat is a form of energy transfer associated with the different motions of atoms, molecules and other particles that comprise matter when it is hot and when it is cold. High temperature bodies, which often result in high heat transfer, can be created by chemical reactions (such as burning), nuclear reactions (such as fusion taking place inside the Sun), electromagnetic dissipation (as in electric stoves), or mechanical dissipation (such as friction). Heat can be transferred between objects by radiation, conduction and convection. Temperature, defined as the measure of an object to spontaneously give up energy, is used as a measure of the internal energy or enthalpy, that is the level of elementary motion giving rise to heat transfer. Heat can only be transferred between objects, or areas within an object, with different temperatures (as given by the zeroth law of thermodynamics), and then, in the absence of work, only in the direction of the colder body (as per the second law of thermodynamics).

Sport_Pilot

Yes Pe, and IR is radiant heat which must be calculated to obtain the proper temperature that would have created that heat. It is a form of light which carries heat. Heat creats the light, and the light will convert to heat if not refelcted by a shiny surface.

I agree that an infred thermometer can give accurate readings especially if you are more intrested in the differance in temperature. However, the main problem I have with it when used to measure air cooled engine temps is that it is more and indication of surface temp, not the actual working temp of the engine. With air cooled engines there can be a very large change in internal temperature with very little change in surface temp. That is why aircraft use a head temp with a probe buried deep in the head. They do not strap a thermocouple to the surface. They do not even recommend a reading form between the spark plug and head, except as a method to help set the fuel mixture.

JNorton

My Feedback: (2)

Sport Pilot
As I see it the test that Downunder performed is perfectly adequate since as Pe Reivers has pointed out only the difference of temperature was measured. The fact that the actual temperature of the cylinder might not be correct is immaterial as long as the same procedure was used, with the caveat that the engines temperature had stabilized as was not changing.
John

EDIT-> Perhaps the duration of each test should be for 10 minutes - a typical fight time?

Sport_Pilot

The problem with the test is it had no change in the temperature. Since one had more air flow which would mean more fresh ambient air, plus an increase in the film coefficient there had to be some heat exchange. There should be some change in the temperature, but probably not at the surface. This would prove little about the exchange of heat. With no airflow the air is stagnant and there is not as much exchange of heat, but also the air temp near the engine goes up so the delta T goes down, the film coefficient also goes down so the stagnant air acts like an insulator. As the air speed goes up the temp of the air near the engine goes down, the film coefficient goes up, so with more delta T and a hugger film coefficient then the surface temp will drop, though not as much as you would think because even the stagnant air was not a great insulator. As airspeed goes up further the coefficient goes up only a little, but the average air temp near the engine goes down, thus more heat is removed but there is little change in surface temp, but the core temp will change greatly.

I alluded to this in the first test and warned that it would be invalid if he continued to measure it with an infrared thermometer. To be valid you need to measure between the sleeve and case. A thermocouple between the sleeve flange and case would work. There I suspect you would find a temp change but even there, probably not a huge one.

JNorton

My Feedback: (2)

Sport Pilot,
What I was expecting to see was a large difference in temps. The fact that the temps were the same can be resolved in my mind simply because of the inadequacies of the infra red measurements, exactly what you alluded to.

The fact that we did not see a large variance is for me all the proof needed. This whole discussion is whether you can use a low pitch prop for break-in. It seems to me that you can.

I am very curious as to how long the engine ran between measurements. Perhaps then we would see the engine overheating that Dar refers to when observing 3D flying.
John

Sport_Pilot

A moderate change in surface temp can equate to a large temperature deep inside the engine. This is because the outside is first to be cooled. As air flows over it the air becomes warmer and as travels through the fin the temperature differance drops. With more airflow the air has the same entering temperature but the leaving temp drops. But also the coeficient drops. There is not a huge differance in temp till it becomes grossly overheated. But because of the mass flow of air there is a larger loss of heat despite the modest temperature drop. This means more heat is removed but the temp doesn't rise proportiantly at the surface.

I don't think that was the argument. Rather that the high pitch prop will take away more heat. People seem to take what someone says to an extreme. Obviously more airflow will remove more heat. To have no temp difference seems too erroneous to even bother to take into account.

yallaair

Sport Pilot!

Running with a higher pitch prop does not necessary mean that the air over the cooling fins is faster. This can be affected by the propeller blade angle of attack, the rotation of the "jet stream", or the efficiency of the propeller.

This tests shows that different prop pitches does not influence on the engine temperature.

Sport_Pilot

Actually it does. At least if they were of the same make and type. I am an engineer, I would like to see monitoring of airflow, intake air volume, fuel intake, exhaust temp, ambiant air temp, and engine temp from a dozen locations or so. If I were doing this for a engine manufacturing company that is pretty much a minimum I would use, without it I would just be making assumptions, as we seem to be doing here.

JNorton

My Feedback: (2)

Sport Pilot
Last post as I'm not going to continue to beat a dead horse as we disagree. The mass in a single cylinder model engine is small with the cylinder being adjacent to the cooling fins so the heat transfer is very good. With respect your argument that you could see a large temperature difference internally without it showing on the outside is one I don't buy. For a larger multi-cylinder motor I'd completely agree with you. By the way just for the two cents it's worth I'm also an engineer which doesn't mean a hill of beans in this circumstance because my expertise is not engine related although I have a lot of experience designing and utilizing proper heat sink design for solid state devices monitoring those with both infra-red and thermocouples.
John

downunder

To avoid what seems to be a bit of confusion here, I used a contact type thermocouple probe which plugs into my tacho/multimeter so it was just a matter of flicking one switch to go from revs to temp.

On the first run with the control 10x8 prop I ran at full throttle and fiddled with the mixture until I had a steady 11,000 revs where it sounded just nice if I were to go flying, not necessarily to run in an engine. I then shut it down and waited for a minute or so to simulate the time it would take me to change a prop. I restarted and checked the revs again to be certain it would then still have the same 11,000 revs which it did. I then took the temp reading with the probe touching the cylinder head and up against the plug washer. The thermocouple readings varied a little (around 10F or so) so I used the steadiest reading as the base figure.

I then shut down, changed props and took the next set of readings. I checked revs first to be assured they were still the same and then the temp. I must admit I was surprised the temp was the same but I'd have been quite happy even if they'd been 10 or 15 higher seeing it was now running with less than half the original pitch.

This is such a simple experiment to do so I can't figure why no one takes 10 minutes at the field to try it themselves. Almost everyone has a tacho and temp guns are starting to turn up now but I don't think it's necessary to go to the extent I did of matching prop loads because I only did that to satisfy one of Dar's many objections when the results didn't match what he expected. A few more results passed on would be better than just my one set.

DarZeelon

Brian,


In the previous thread you began with a 10x6 prop.
If anything, going to the 8" pitch, should have brought the diameter to 9"; i.e. a 9x8 prop.

A 10x8, at least compared to what most sport fliers use on a .46 engine, is overloading it to begin with.

With the 10x8 and the comparison 12.25x3.75W, I am surprised the later had to be chopped down at all!


The issue is break-in, where a light load is desired and the 10x8 on a .46 engine, is not...


Also, is there any way you can monitor the fuel flow?

I believe the air-blast produced by the prop at the carburettor's intake, can influence the amount of air the engine takes in.
If air mass intake is smaller, so would fuel intake, despite the needle being open the same amount and the RPM being the same.

Less fuel burnt is less heat to get rid of.
I guess you understand my point. Both points, actually.

JNorton

My Feedback: (2)

Dar
Could you can weigh the fuel tank on a gram scale and plot the weight over time to determine fuel flow?

There are a lot of fairly inexpensive DVM with recording capabilities on the market so doing a time / weight graph should be fairly simple. I've got the stuff do do it with but with outside temperatures of 12 degrees F, -11 C - now is not the time. I think I'll try it in the spring simply because it is such an interesting experiment.
John

DarZeelon

This is possible, J., but it is Brian who is out to prove that what is correct by any common sense, i.e. that higher air-flow speed provides better cooling, is a myth....

So, it is Brian who must purchase that sensitive scale, or some kind of a flow-meter...

speedster 1919

My Feedback: (3)

DAR--- stop it---now your throwing in 6 pitch props and 9" diameter. The original sqwak was a 4" pitch and a 8" was selected to give a wide spread of pitch for a definative test. We almost all concede that a maybe a 3"-2"or 1" pitch would be a problem but not a 4" pitch and you mentioned a higher 10x8 load. Not according to his Tacko (tach)
SPORT PILOT shut up and put your money where your mouth is...........You do the test and put thermo couplers and probes between the liners and the fins and where ever you feel needed.

If Downunder test showed a 20 or more degree difference I would start to get concerned ,but from day one I said a 4" pitch provided enough flow and more flow was not needed.........That the amount of flow reached it's terminal velocity and any more was no benefit

DarZeelon

Randy,


May I remind you that Brian started this whole issue with a 10x6 prop on one hand and an 11x4 prop, which proved to be too light...

It allowed about 1,300 RPM more, so Brian wrote he would use a 12.25x3.75W and shorten the blades until it spins at the same RPM as the 10x6 did... But now he changed it to a significantly heavier 10x8.

He should change back to the 13,000 RPM 10x6 and go on from there, as he described.


It is that, or the results cannot be comparable; not that they will be perfect then either, with the equal fuel flow yet unproven.

speedster 1919

My Feedback: (3)

DAR you have not thought this out fully. First at our field are pattern flyers and 3D flyers that compete in the US NATS each year. The pattern guys have an issue to set up an engine for the long upswing manuvers for no lean runs but still run good on level flight. When you set up a fuel tank you go for a centerline level with carb setup for the most trouble free setup ,because you know even 1 inch below carb can cause problems. Now look at a 3D hover--Your asking the clunk in the tank now to pickup fuel from upwards of 12 inches below centerline on carb and not be a problem (over rich)when in level flight. It's going to get a little lean. Would your purposely mount your fuel tank 6 inches below your carb ? The answer is nooooooooo........You said foam--I said little bubbles--Keep in mind that inside a bubble is air and not fuel, which at a consistant flow will be a leaner fuel delivery..

downunder

Then one would expect the engine to get hotter than with a lighter load prop and cooling would be of even greater importance.

Why are you surprised? You're always telling everyone what load a given prop has so you should know how these two compare.

The issue is not break in but the affect on cooling by using different pitched props. What works on a well broken in engine will work on one for running in.

Yes, I understand your point. You're getting so desperate to avoid having to say you were wrong that you're coming up with even more ridiculous ideas and then trying to get someone else to prove them. Do some work yourself for a change and then maybe we'll listen to you.

errrrrrrrrrr...rant over

speedster 1919

My Feedback: (3)

Remeber DAR --Brian went for a 3.75 pitch to get under the 4 pitch and the 12.25x3.75 is a widely known 3D prop. DAR you do a scientific test. Put a 4" pitch prop and a thermo coupler on your airplane engine. Now tune for flying with that prop and run WOT for say a minute or two static and get the temp.(you do this static so you can't claim the flying air flow is a factor) Now hold up nose up for a minute and see what the temp is. By your account the temp shouldn't change because of a hover scenario........You contend the 4 pitch causes the overheat and should be a problem even when level. I say the temp will go up when pointed up because of fuel delivery..........

gkamysz

My Feedback: (19)

Why doesn't someone forget the props and put a variable speed blower on the engine to see just how much airflow makes a change in head temps.

Also do we know that the 10x8 is not stalled, or at least the inboard portion? Has anyone bothered measuring flow velocity near the engine with the props in question?

This is a very complicated question. Anyone have an Eagle Tree setup in a 3D model? One could have CHT and EGT to see whether there is a lean condition and cooling problems. I wondered why I saw so many hollow (no baffles) cowled TOC type models and why they didn't burn up hovering. but I guess you can't question what actually works.

Sport_Pilot

I don't see how the mass has much to do with it. With any heat exchanger the surface temp is going to be about the same as the leaving fluid temp, minus the film coefficient. The other side would be about the same as the source temp. Since the air is the same ambient temp then it is a matter of how much it heats up across the fins. Once a certain velocity is reached there really isn't much differance in the air or surface temp, even though more heat is removed. Kinda like heating one pound of water one degree or one hunderd pounds one degree, both are at the same temperature but one is one BTU of heat and the other is 100 BTU of heat.

The surface temp of heat exchangers will react to the fluid flow as an expontional curve. That is a little flow will have a great effect on temperature but the differance goes down as flow is increased. However the heat removed will be a flatter curve.

Sport_Pilot

This is still a surface temp, still I would have suspected a few degrees of differance.

DarZeelon

Wrong, Brian.


I used common sense to determine that a high-pitch prop, which provides a given load, will cool the engine better than a low pitch prop with the same load.

And I am surprised that you did not exhibit the same sense, but instead, you tried and are still trying to disprove it.

So I am not wrong and will not say that I am.
There is obviously something we are all overlooking, which is biasing the measurements you are making.


Randy,


I don't have any large diameter 4" pitch props...

A propeller with a pitch smaller than 40% of its diameter, is .... a rotor...

...And 3-D is not flying, BTW.

Sport_Pilot

Not going to needlessly buy a thermocouple thermometer just to avoid jerk wad posts. If you understand what I have said then show were it is wrong. If you don't understand heat transfer then you well don't.

Hobbsy

My Feedback: (102)

I dunno about that, common sense says a higher pitch presents a larger load and therefore more heat not less. Since heat is energy that is always trying to distribute itself evenly among any medium and air is a lousy heat conductor compared to an aluminum engine, changes in airflow velocity or volume aren't going to make big changes in engine temp, just like Brian discovered.