EGT Probe?

Has anyone tried to use Exhaust Gas Temperature to lean their engine? If so where can I get a good EGT probe to use with a Saito 50?
-- 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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Has anyone tried to use Exhaust Gas Temperature to lean their engine? If so where can I get a good EGT probe to use with a Saito 50?
-- Chris W ========================================Unless you are racing, this seems pretty extreme.
Carrell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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!!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@aol.com (RCPILOT48) wrote in message

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Carrell wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@comcast.net says...

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
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXALM8&P=7
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
And, how will you cool the engine in the box? Air at 20K is going to be very cold!
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@mcintoshcentral.com says...

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@mcintoshcentral.com says...

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 :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Like I said, you are using a sledge hammer to kill flies. The use of an EGT probe is so much vast overkill in this case. Besides, how are you going to calibrate it for 20k altitude? How do you know what the EGT should be at that altitude?
If you want to be real accurate, you need an oxygen sensor. That will tell you how rich or lean you are. The temp can change with load, air temp, etc.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Paul McIntosh wrote:

You make it sound like an EGT probe is hard. The probes are inexpensive and all you need to install them is some high temp adhesive and a very small drill bit. As far as setting it. You don't set it to a specific temperature, you lean the engine till the temperature peaks and starts to drop off again (that is how real planes lean). As far as knowing what it should be at altitude I will have to use a transmitter to transmit the reading from the probe so I can make adjustments every few thousand feet. It shouldn't be that hard to transmit back since I will already be transmitting back GPS data so I know where it is and how high it is (there is no way you are going to see anything smaller than a 747 at that altitude (ok so that's a slight exaggeration but only slight). I think the reason cars use O2 sensors is because they are easier for the computer to use and I think they also aid in the emissions control systems that are irrelevant in this case. I will have to have some method of determining how much to lean while I climb because if the setting is for 2,000 feet, long before you get to 20,000 your engine will be running so rich it will probably die. So why not use the most direct method of determining how much to lean which is EGT?
-- 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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The basic advantage of an O2 sensor is that it can be used with a simple PIC device to automatically adjust the carb for optimum mixture. Adjusting by reacting to an EGT has the disadvantage that if you overshoot your adjustment, you can easily kill the engine at those extreme altitudes. Adjustments become much more sensitive when the engine is barely running! Remember, at 10k feet, half of all the air on the planet is below you!
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Because the EGT max may not be the best mixture. Simple EGT measurements do not take into account advanced or retarded timing or other combustion factors. O2 sensors directly measure the unused O2 in the exhaust stream and can be calibrated for best combustion for any given situation. It will also automatically compensate for elevation or air pressure changes.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
EGT has been the way you set the mixture in full scale airplanes for years. I would peak the EGT when at altitude and then richen the mixture for a drop of 50 degrees. This would produce the most efficient fuel burn without damaging the engine. Some people would richen 100 degrees depending on how much power they were running or if they were turbo charged.
Also carburetor ice is caused by humidity in the air passing over a cold venturi. The lowering of air pressure when air goes through a venturi and the evaporation of gas causes the carb to become very cold in that area. If flying in warm humid air the water vapor freezes in the venturi thus creating the dreaded "carb ice" and the need for carb heat. The problem is exacerbated when power is reduced for landing and the engine is not producing it's normal heat. That's why carb heat is used when landing.

simple
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That may be the case for full scale where millions of hours on each engine has determined where to set them. In a tiny, glow powered engine operating WELL outside its design envelope, how could you POSSIBLY determine where to set the mixture using EGT? An O2 sensor doesn't care how or where the engine is operated and can be used as a feedback device for automated systems. That's why they are used in automotive EFI systems. The sensor puts out a voltage (or resistance) depending on the O2 content of the exhaust gas. This content is used to determine the optimum mixture for best burn. The % content is very constant throughout elevation and humidity changes.
I am not saying that an EGT will not work, just that you will be operating it in an environment that there is no data for.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
OK, do it the hard way. A PIC pocessor is a lot lighter than a telemetry transmitter with the power to transmit over 5 miles! You gotta carry all that stuff up to the altitude where you will be generating only about 10% of the lift and power that you do at sea level. I was only trying to make the system lighter.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.