Engine temperature

[Gary Dowler]

Curious if anyone has ever paid attention to the engine temp while running?  Have one on the stand the last few days and got curious, so I got out my IR thermometer and pointed it at several spots.   Engine is pretty broke in now, and running at about where I would set it for launch, the tongue muffler was just over 200f, the venturi was 110, and the cylinder head was 240-245. 

Slowed it down to a very wet, and slow, 4 stroke and head temp dropped to about 185. 

Anyone else ever study this??

Gary

[frank williams]

The venturi should run cold.  Depending on the style of the engine, I've seem condensation dropplets from on the front end.  Of course, its humid here on the coast. The evaporating fuel drops the temperature.

[frank williams]

I measured internal pipe temp. with a thermocouple on a probe years back.

[Dick Byron]

Mr science, always on the leading edge.

[Dan McEntee]

The venturi should run cold.  Depending on the style of the engine, I've seem condensation dropplets from on the front end.  Of course, its humid here on the coast. The evaporating fuel drops the temperature.

   The intake flows quite a bit of volume of air and fuel. This has a refrigeration effect and is part of what causes carburetor icing in the summer time, when an average person might never suspect it. I have always been aware of the phenomenon,  but had never seen it in person. My first personal experience with it was on a model with an aluminum spinner. The spinner has to spin clear of any contact and not rub the air frame. As soon as the engine quits, land the model as quickly and safely as possible and grab the spinner and it will feel cold. You have to be quick about it because the aluminum in the crank case does it's job and soaks the heat from the head and cylinder and transfers it to the bottom end, and in a few seconds you will feel the spinner warm up. Before long the bottom end is as warm as the top end. This isn't so much a study but an observation when flying.
    Back in my early days flying at the SIG contest they had a Fox .35/Skyray racing event that I would participate in with some friends from our club, pitting and flying each other's models. I found out early on that a hot Fox.35 that was running full tilt boogie was hard to restart hot after refueling on the required two pits stops. I noticed when watching pit stops that sometimes you could see vapor and fuel kind of boiling out of the venturi when they choked the engine to restart. Some guys would hose down the engine with fuel to cool it off to help on restarts. Knowing that alcohol boils at a lower temp than water, changed up pmy starting routine to include having a syringe full of ice water for each pit stop. I would catch the model, hit the head right away with half the syringe before much heat could soak down the cylinder, fuel the tank, hit the engine again with the balance of the ice water, choke it and it would usually start in a few flips. It took practice to know how much of each step to do to get quick starts. The experienced racing guys had trick engines with chromed cylinders and tighter fits which help with hot restarts, but I was just using a stock Fox.35 and the Skyray I was flying was sometimes my stunt model also!! I just changed out the tank for a smaller one for racing. Again, not a specific study, just an observation from running the engine and flying the model.
    Type at you later,
    Dan McEntee

[Chris Wilson]

Curious if anyone has ever paid attention to the engine temp while running?

Define 'running.'
On the ground with zero airspeed, where I assume that these measurements where taken, is entirely different to flying speed and especially so with a good ducting system.
Ducts create pressure change and the denser and slower the air the more it has a chance to conduct heat.
So what you measure statically may only be a guide and not a Bible.
Surprisingly an engine out in the open could the worst for cooling as compared to an engine properly cowled ' in flight.'
For example, a rear exhaust air cooled two stroke has the worst cooling configuration, unducted but cowl it properly and your temps come down dramatically.
How you measure that would be directly after landing.
Chris.

[Gary Dowler]

Chris, yes, running in the open on the bench.  I have no possible way to measure this in flight. It was running on the bench , I got curious and measured the temp under those conditions.  No claim made as to how it compares to in flight temp, but I think you are correct that bench run temp might actually be higher.

Gary

[Chris Wilson]

Hi Laurie, I assume your system bypasses emissivity also?
Do you find duct design has much effect?
Chris.

[EddyR]

 Back in the 1980’s when I was doing a lot of work on the ST/46 i found that the head was running to cold during flight. I removed head fins until I was down to 3/32”. I was not looking to make the motor run hotter just to keep the heat in the head even. It worked wonders for the run. I also was running more rpm with what was a small prop at the time,11/5. I did s lot of other things to those motors but i believe the even head heating was more important than any other mod I did. I tried this same mod on ST/60’s with the same results.
 I bolted several thermocouples to the motor to check heat and the motor case never ran hotter than normal.
At the 1988 Nats Brien Eather told me about his experiments in Australia running the ST/60 with no head fins and no overheating. I did build several heads with no fins and used them on the hybrid .56 in the .40 case. Theses did not overheat as I put 500+ runs on one of those.
 I remember Frank Williams Profile Bearcat article and he was trying to get the .60 to run big props slow and ended up mounting the motor on the inside of the big profile. I often thought that was a typical cold head problem.
  I have talked about the 46 quite a bit over the years. About all the different mods I made but i do not think i have mentioned the head fins before. This has been one secret I kept to myself. I wrote a article for the Florida Modeler mag with drawings and part of it got into PAMPA many moons ago.
  Many of you may feel that what I said about head temperature goes against the grain and is not logical but it was correct for the motor that i was working with.
EddyR

[frank williams]

Gary ......  interested in what motor you ran and measured ..... a motor with an integral venturi (like a fox) might have a higher temp than one with a venturi insert,

.... you might try running the motor....... then pull the fuel line off at the spraybar to stop the motor quickly (as opposed to pinching the line and getting a prolonged lean burst to stop) ..... then quickly putting you ir detector close to the venturii and frontend to measure the temp ..... they measure better if not too far away .....

Dan ....The cold spinner check is a standard .... if the dog's nose is cold all is well

Eddie .... Too many fins on those motors was definitely true ...... however ignition is so important too .... if the motor runs with the cylinder away from "gravity" and dies with "gravity" pointing at the plug .... it probably not  the headfins (although the extra heat in the chamber is good)

Hi Dick .. long time ..... thanks, but  I consider Lauri to be "mr science" ....

Lauri ...... you do the neatest work ... you have through the years come up with some of the most sophisticated tools and experiments .... The "stunt run" is not like any other aspect of model engine analysis .... pure outright rpm or power isn't the question .... it heat temperature management issue

[Chris Wilson]

So there exists the possibility that the famous Fox 35 burp could be castor oil related rather than gas velocity related?
Chris.

[frank williams]

Chris .... no

Lauri .... 40 deg down, I assume outboard .... Did you ever try an inboard cylinder either at 90 deg or 40 deg
beautiful machine work ... rear intake is good for stunt applications I agree .... "Fragile Harmony", I like that