912 Egt temps

[Gundy]

Gday all. I monitor my Egts through a Dynon Skyview which is very accurate. My engine is a 912S which ran a constant 760c on the rear exhausts. Now I decided to wrap all my exhaust headers with special heat wrap to help keep inside cowl temps a bit lower. Since the headers have been wrapped my Egt temps have rising to 850c. I wonder is the higher temps caused by the wrap keeping the temps in the exhaust and the air when unwrapped help cool the exhaust. Any help much appreciated. Gundy

 

 

[facthunter]

That's a significant increase. I have always believed that wrapping the pipes( and therefore insulating them) MUST raise the temp of the valve. There is an argument that hotter gases flow easier, which is true as they are less viscous. 912's don't have much trouble with valves but yours will be hotter. How far are you measuring them from the head ? nev

 

 

[Gundy]

Thanks Nev. they are exactly as Rotax say 100 from flange. I never herd of it causing hotter valves. I was looking at wrap for safety as anything that touches the pipes don't burn (nothing surpose too touch I know). Plus my racing mates say its better for motor. Now I have doubts. Gundy

 

 

[Guest Maj Millard]

There has been some debate in the past about wrapping exhaust pipes. Some say the additional high temps crystalize the metal, and cause early failures/cracking of the pipes themselves. Then of course there's the added difficulty in inspecting the exhaust system closely, both during a daily insp, and at each 50 0r 100 hourly. A serious crack can appear during one flight, and not be picked up before the next. The wrapping has to be removed each time for a complete and through inspection for cracks etc....Unwrapped exhaust pipes, (normal), do dissapate a lot of heat from the pipes, into the engine bay. Obviously your temp rise is due to that heat not being dissappated from the pipes. Heat coming from the pipes within the engine bay is controlled, and removed, by the flow of cooling air through the engine bay. This same flow of heat also assist in engine warm up, and in helping the engine to maintain a constant, and consistant warm condition throughout it's operation............................................................Maj...

 

 

[facthunter]

Gundy , generally if the gas is hotter at a point ( where you measure it) than it was before it will be hotter upstream too and the valve is in that gas. This principle is used in measuring Turbine temps too. You can't always locate the probe at the hot spot (as it won't last) so you use a downstream temp that equates to the ones you want to measure. ( Does that make sense?)Nev

 

 

[Gundy]

Thanks Maj and Nev for your responses. After an hour of flying and a Google on the subject plus your info I'm going to remove it. From a safety point of view it sounds good but as Maj and google say it ruins the exhaust metal and fatigues it so a crack can appear with out notice. And Nev I don't need a engine failure from hot valves so off comes the wrap. thanks again. Gundy

 

 

[pudestcon]

Thanks Maj and Nev for your responses. After an hour of flying and a Google on the subject plus your info I'm going to remove it. From a safety point of view it sounds good but as Maj and google say it ruins the exhaust metal and fatigues it so a crack can appear with out notice. And Nev I don't need a engine failure from hot valves so off comes the wrap. thanks again. Gundy

That's what I like, and is so valuable about these forums; you can get quality information (sure you gotta sieve some chaff out) to help make educated/knowledgeable decisions. Great stuff.

Pud

 

 

[Gundy]

Yep I agree Pud. I thought I'd put the wrap on, then found Egt got hotter so by asking the question I get some good answers from people who have seen this before( this is called EXPERIENCE). This is why I'm a member of this forum to get good honest help. Gundy

 

 

[eightyknots]

Yep I agree Pud. I thought I'd put the wrap on, then found Egt got hotter so by asking the question I get some good answers from people who have seen this before( this is called EXPERIENCE). This is why I'm a member of this forum to get good honest help. Gundy

I'm glad you are taking the wrapping of because I am worried that due to an unseen crack (being under the wrapping, and brought on earlier by the increased heat), you could get carbon monoxide problems.

 

That's what I like, and is so valuable about these forums; you can get quality information (sure you gotta sieve some chaff out) to help make educated/knowledgeable decisions. Great stuff.Pud

I really like that about these forums as well.

 

Now, Gundy, I think your experience with Air Master props in the Savannah is called for in another thread too:

 

http://www.recreationalflying.com/threads/savannah-cs-prop.40939/#post-223906

 

 

[facthunter]

A graphite pencil line can make an exhaust pipe fail. The graphite is an allotrope of carbon that can infuse into the metal and make it go brittle. another cause of metal failure is plating. Unless anything that is plated is heat treated soon after plating it can suffer from hydrogen embrittlement. CASA wensite has somethinng on it or try Wiki.. Nev