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Cylinder Head Temps.

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Old 10-07-2011, 04:08 AM
  #1
JUGFLIER
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Default Cylinder Head Temps.

I have a DLE 111 on a carden Edge. When I bought my motor, troybuilt gave me a temperature gauge with it. Immediately after landing, (looking from the front), the right cylinder will read about 195, the left will read slightly above 200. If you give it about a minute, the right drops to the low 180s and the left to the low 190s.
What is a reasonable temperature on cylinder heads?
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Old 10-07-2011, 05:05 AM
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Default RE: Cylinder Head Temps.

Anything you like with that sort of temperature measurement. They really are close to meaningless.

A direct thermocouple close to the top of the head (idealy under the spark plug base) whilst flying is the only true measure to be concerned with.
However the temps you are seeing with the method being used is about right.
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Old 10-07-2011, 06:37 AM
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Default RE: Cylinder Head Temps.

This has been covered many times before but I'll do it once more.

First we'll address the means of measurement. If you cannot obtain the CHT while the engine is in flight you measurement device is useless. Reading what CHT's are post recovery simply tell you what CHT's are now. You know nothing about what the engine was experiencing in flight, which is the most critical phase of operations. So anything like a temp gun or visible read out mounted on the plane without previous temperatures is a waste of time, money, and effort. With those, what you know versus what you don't know is a very dangerous condition. Better off not knowing anything at all because at least then you know what you don't know and you'll be more careful. Currently you really know nothing useful at all.

You need an active cylinder head temperature measurement device. The best is akin to an Eagle Tree telemetry system where you have the option of down loadable information after recovery or live telemetry that can be consulted anytime during flight. The next in line is something like a Venom Temp Monitor which records the high and low of the flight for post recovery review. If you are serious about your engines you go for the Eagle Tree. If you only have a casual interest the Venom works ok.

It's normal for twins to run different temps per side. The design of the crankcase and positioning of the cylinders pretty much assures a temperature delta between cylinders. How much is only partially up to the user. I'll toss something out here that most are unaware of. MVVS handles this delta better than anyone with the induction design of their twins. They compensate for the crankcase counter balances by separating the induction plenums to permit offset induction charge flows to the cylinders. An engine during taxi never runs as hot as an engine in climb or hover.

Safe, or "normal" CHT's run between 110C and 150C. Any of our engines see a noticable and progressive loss in RPM as CHT's exceed 150C-155C. The hotter they get the more RPM is lost. At 180C you will generally be causing some kind of permanent damage to the engine. I say some kind because such damage is dependant on the quality of the various components and metals used in the engine. The last part to experience permanent damage is the case bearings, with cylinders next to last. Rings, pistons, and wrist pin bearings are generally the first. Rod ends follow the wrist pins.

Use what you have to perform a short experiment. Run the engine up at wide open throttle on the ground until the temps hit 150C, or 302f. Then quickly throttle back and see how quickly temperatures fall. Next, run the engine up to 150C again and again throttle back. This time after throttling back, "blip" the throttle several times like you might during a taxi or landing approach. Observe how much faster the temperatures fall than during the previous expriment. Those two experiments will provide you with all the proof necessary for you to conclude your temperature monitoring equipment is useless, unless the only temps you care about are those experienced on the ground.

Hobby dealers will sell you anything you are willing to pay for. Whether or not it is suitable for the task is a decision left up to the buyer and the buyer's level of sophistication. Dealers make money either way, be it the sale of monitioring equipment, engine repairs, or new engines. What you don't know can become quite expensive.
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Old 10-07-2011, 06:59 AM
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Default RE: Cylinder Head Temps.

The Aurora 9's telemetry system is a 3rd way to meausre head temps in flight. I find myself more interested in in-flight rpm & temps of both heads on my engines than I ever thought I would. It's cool to watch while flying, and you can mount the sensors in the most accurate position on the head. Being able to read in flight temp is amazing! I found I needed to baffle my Yak after seeing in flight temps, even though they were just fine on the ground for example. I was able to further drop my temps 30*C on that plane!

I've also discovered (though it's likely due to good cooling) that insanely long uplines on my DLE's only produce 6-7*C increase in head temp over normal level flight. Tom is very correct in speaking about useless head temps taken on ground after landing. My heads have dropped just over 20*C by that time, depending on throttle after landing.

Here's another tidbit most people don't know that I'?e discovered through my live telemetry. WOT flat and level flight on my 55, 100, 111 all pull just a shade over 1000rpm greater than they do statically on the ground! That means if you're propping a 111 at 6900rpm on the ground, it'll be unloading to 7800-8000 in flight flat and level! If you do any type of dive at WOT add another 4-500. As you can see, it's easy to exceed any engine's redline specification (though usually harmless in small bursts) of any engine if not propped carefully.

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Old 10-07-2011, 08:25 AM
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Default RE: Cylinder Head Temps.

Thank you for the comments about the Aurora's telemetry capabilities. I failed to consider that several newer radios provide that capability. Until recently it was only available on very high end radios.
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Old 10-07-2011, 03:08 PM
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Default RE: Cylinder Head Temps.

I used to use my Eagle Tree FDR but now my Spektrum DX8 does the job quite nicely. I don't really ever look at the temps much but I have an alarm set for 320 degs F so just in case I do a really really long hover it'll warn me to punch out and cool it back down before I do permanent damage.
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Old 10-13-2011, 03:49 AM
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Default RE: Cylinder Head Temps.

Thanks TOM,

You just made the most comprehensive temperature guide ever!

My tow plane goes up to 190°C in a flight. To make the MVVS engine live through this repeated ordeal, I replaced the wrist pin roller bearing by bronze bushings, and add a boost port in the rear cylinder wall which gets its mixture flow through a small piston port just below the ring. This added scavenging flow cools the piston crown and carries extra oil to the wrist pin bearing. Low end torque is enhanced as well.
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Old 10-13-2011, 09:28 AM
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Default RE: Cylinder Head Temps.

I think all two strokes should be made that way; with a boost port that feeds through the piston. Cooling the piston head and oiling the rod small end that way is great.

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