EGT Probe?

-- Chris W ==========================================

Unless you are racing, this seems pretty extreme.

Carrell

I use an infared temerature gun for my engines. Costs about $100 with the case and an integrated laser aiming light. I find it useful for all sorts of things and use it in my Podiatry practice on a regular basis. Andy

We can make a box of wood.....FLY!!

Sounds like killing flies with a sledge hammer to me.

Well a friend of mine and I are trying to see how high we can fly. At

20,000+ feet you need all the power you can get and since fuel supply is limited we need to use as little fuel as possible. Since EGT is the best indicator of how lean the mixture is, and we need to keep readjusting it as we climb, that seems like the best way to go.

-- Chris W

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

Well a friend of mine and I are trying to see how high we can fly. At

20,000+ feet you need all the power you can get and since fuel supply is limited we need to use as little fuel as possible. Since EGT is the best indicator of how lean the mixture is, and we need to keep readjusting it as we climb, that seems like the best way to go.

-- Chris W

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759 Historical Review of Pennsylvania =========================================

Everything I've seen is sized for cars and would be too big and heavy for a plane that will fly on a 50.

An obvious question; how will you fly it?

A 'standard' RC transmitter/receiver likely doesn't have 20,000+ foot range, and a plane that will fly on a 50 will be pretty hard to see at that distance.

Carrell

"John Alt" wrote > If you still want to make your own, one way to test your system is to

Good plan, except for one thing. The exhaust should be seeing the same altitude as the inside of the box.

-- Jim in NC

I hope you are coordinating this effort with the FAA. I would look into one of the fuel injected engines like the OS FI series

Pricey, but it will save you a lot of bench time. I would confer with OS (not just tower tech support) on what limitations their system has. They might not have designed the operational envelope to account for such thin air, but may be able to help you get around that.

If you still want to make your own, one way to test your system is to mount the engine in a large box. Now, seal the box except for a small ball valve or other needle valve to let a small amount of air in. Mount the motor so the exhaust exits the box through a sealed tube. Hook up a gauge to your box to record the air pressure (Hint: make the box clear or have a window in it, and place an altimeter inside). Voila, a poor mans altitude simulation chamber for the engine. Alternatively, you could simulate the same thing with a pipe to the inlet, but with just a little less certainty as to what the altitude density is. As far as probes go, their everywhere. Look at any of the meter manufacturers websites and get a temp probe for their meter, or try any of the electronic part supply catalogs, like Digi-Key. Get one with the narrowest range that covers the temperature you are trying to hit. One last note is you may want to employ cable drive to the needle valve. At 20,000 ft you are going to be a lot more than a 1/4 turn lean, so plan on making a few turns on the valve, and design your travel accordingly. One of those chain drive servo set-ups from servo city, or a sail winch servo, might do the trick.

And, how will you cool the engine in the box? Air at 20K is going to be very cold!

True, but I don't know of a simple way to simulate this, other than altering the exhaust restriction by way of an educated guess. That's for the original poster to work out.

Details, Details, Details ;)

I didn't cover it all in one post. I'm not talking endurance here. He just needs to see if his system will function at lower atmospheric conditions. The colder temps will only make him want to run the engine richer, which should be more to the "inside" of the operating envelope. But it does bring up a point, that he might want to use the hottest plug the engine will tolerate.

Carb icing will be a very big problem because no matter how fresh the fuel is, methanol always has some water in it. Some kind of carb preheat is going to be needed. Also, restricting the amount of cooling air getting to the engine.

The altitude record was set about 30 years ago by Maynard Hill (same man associated with the transatlantic model flight)with whatever was available then, and that didn't include EGT for models. The details were in the model magazines at the time. The library at AMA headquarters should be helpful.

Andy- I know you don't need one, but maybe somebody else.... FWIW, RatShack has one on sale now for 29.95. No laser pointer though. I got one to check engines and Eflight motors/batteries, and will use it to check on the Moneykote irons too.

Abel

John -

You can get the temperature probe from Omega. You'll have to figure out how to drill the hole and install it into the exhaust stream yourself. Then there's that pesky telemetry issue...

have fun - Rob Glover

Your right, but with the four stroke I thought the cowl radiant heat and the rear intake would negate the problem. I haven't had the chance to fly below zero since I was a kid, so I'll have to pass on that one. Don't see much of that weather here in South Louisiana, and when we do, it's gone by the time the car is packed :)

No telemetry issue just feed the probe signal to a Pic micro chip and use the PWM output to drive the servo controlling the NV.

Anybody tried using a gas waterheater / furnance thermocouple as a temp sensor? They are cheap but would require an amp to boot the output signal?

Hugh

I looked at Omega and they have a fair number of very small (.5 mm) very high temperature (2000+ F) probes and they don't cost too much either. Since I'm not really interested in the actual temperature, just the peak, I am guessing I can just use a multimeter to read the prob. But just for the sake of curiosity, is there any chart that gives what reading would correspond to what temperature? Also I have seen some high temperature ceramic adhesives and plan on using them to glue the probe into the exhaust pipe, anyone see a problem with that?

-- Chris W

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

No, even with the rear induction there is significant heat loss when the fuel vaporizes. Second issue is that the outside temperature is not going to be the issue with carb icing as much as the FUEL temperature. I very strongly suggest some sort of fuel prewarmer as the Saito 50 and 80 both had a stand off induction manifold and I KNOW the 80 would ice up in moist cool (less than 90 degrees) air. BTDT and repeatedly almost ate a nice plane until I figured out what was happening and how to stop it!

Third item is that high altitude record is something like 26 or 27 thousand feet (I am too lazy to look it up right now) and to be certified you must exceed it by a verified 3 percent.

I am not sure the header pipe temperature is as elegant as the actual gas temperature, but that is closer to how most GA birds measure EGT. The sensor and processor combination needed to drive the servo needs some peak seeking mechanism and recovery for when your system over leans during operation. I think John Alt had a reasonable idea of how to find out if you need a cable drive or just a direct drive system and you should test that early.

Good luck,

-- Jim Branaum AMA 1428

Six_O'clock_High Target snipped-for-privacy@Guns.com

Why not have a box with engine and exhaust all sealed up in it with a needle valve to let a small amount of air in and then have a powerful fan to suck the air out. You may even be able to set up with a pusher prop and just use that to suck the air out. That way the whole system is seeing the same pressure. You could also have a coil of copper tubing in ice water to cool the incoming air through the needle valve. You will want to have something to deal with condensation in the tubing though so it doesn't spray water in the "altitude chamber", maybe one of those centrifugal air oil separators that some older engines use would work?

-- Chris W

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759 Historical Review of Pennsylvania