Engine temperature monitoring

[Antoni]

It's important to look at engine temperature instruments periodically.

The length of the period may depend upon your degree of paranoia, wot the instructor said, the quality of available landing areas, whether you have a passenger, a recent engine rebuild and [insert particular reason]. Here's one of my reasons:

Changing from a power setting which has been held for a while, to another.

Particularly with two-strokes.

Any other reasons to be cheerful?

 

[Peter Twissell]

A useful addition to todays digital instruments would be a warning (flashing light etc.) which shows up if the rate at which engine temperature is changing exceeds a preset limit.
If something changes, e.g. an induction leak causing lean mixture or a cooling system failure, it may take only a few seconds for engine damage to occur.
Unless the pilot has eyes fixed on the instruments (not recommended!) the damage may be done before the temperature change is noticed.

 

[BobH]

Because I fly 2 stroke powered aircraft I tend to watch the EGTs like a hawk. I've trained myself to do a sweep of the engine instruments (EGTs, Water temp, tachometer) about once every minute. It only takes a second or two, and lets me see if there's anything developing that might need my attention. I also do a sweep of the flight instruments (ASI, altimeter, compass) at the same time, and the rest of the time my attention is outside of the cockpit.

 

[ginge]

I found that with a Jab the CHT is a pretty vital instrument as overheated heads can loosen the valve seats (different expansion rates of the steel seats and alloy heads I guess) leading to all sorts of problems. Easy to avoid as it mostly seems to occur on high power climbs on a hot day, just throttle back a bit and all will be well.As Bob said nothing beats a regular scan, othwise why would you have the instruments fitted?
One interesting thing I found with my good ole TST (503 powered) that in a sustained high power climb on a hot day the CHTs would sometimes climb a bit close to the red zone on the dial. I found that by altering the angle of climb I could change the airflow into the ram air duct an temps would reduce at the same power setting. I never got around to trying it with a Jab, but maybe it would work there as well.

 

[BobH]

Ginge,

When you say you changed your climb angle do you mean you used a flatter trajectory? I tend to do that anyway, as I was taught that on climb out, whatever angle you're going up at is the angle you'll go down at if the engine stops. So I prefer to keep the speed up and the angle shallow. That way if it all goes quiet at least I have some airspeed and I can quickly adjust the trim to minimum sink while I look for a landing spot.

 

[Antoni]

An interesting difference between Jab and Rotax 2-stroke there.

With Rotax 2-stroke you are generally in guarnteed safe territory on full throttle because they are designed to over-fuel the engine at that setting. it means they run cooler. That assumes that all else is reasonably sound - air cooling, forced air cooling, radiator plumbing and so on.

That's why I always pull back a long way from full power at the top of the climb. Reduce the RPM a lot so that the engine does not have as much energy and heat (entropy) to handle.

There was another student pilot's faulty XL447 I flew once where it always seized at the top of climb during his ownership of the aircraft. Except for the two times I flew it - once with a passenger and once without.

I'm not trying to say I'm a saint, only that there is some logic in positively backing off a Rotax 2-stroke in case all is not well with its condition or its installation. If all is well, then no problem backing off a bit. After all they are reliable.

 

[Antoni]

The mechanics of this forum is wierd.
It doesn't seem to let you edit your posts at all. I abandoned the above post completely (move the browser to another page without "sending") because I wanted it to quote one of Ginge's posts within mine to make it clear what I was on about, and to make the story of the XL447 a little clearer. Even tho I did not click 'Post reply', the post above was posted!

Now that could cause embarrassment in future for those of us who like a drink in the evening!

This forum engine is not easy to use. Maybe some settings can be changed.

Clicking on Post reply ..............now


[edit, and now I see an edit option at the bottom of the page, which I am using here, but I certainly did not 'Post' the above post, as described.]

[edit2 Maybe there is a time delay for the forum engine to sort itself out re editing, still doesn't explain posting without posting.]

 

[ginge]

I was taught, in a TST, that on climbout to maitain full power at 45kts for 500ft then reduce power and increase speed to 50kts. That is 6200-6500rpm backed off to about 5850rpm. On hot days on a prolonged climb I noticed the CHT start to climb towards the red zone. So at first I just reduced power a bit and that worked, then I noticed that if I over compensated for the nose up tendancy as I reduced power, due to high thrust line, the temps dropped whether I reduced power or not. I put this down to the change in airflow through the ram air duct. That of course is with air cooled two strokes I know Bob likes his water cooled units which of course are a different ball game
With the Jabiru I never tried it I just eased back the power and reduced the climb and if needed, in a suprisingly short time the CHTs dropped and all was comfy again. The damage done by overheating Jab heads takes a while to get back at you but unless you catch before it bites you'll end up with loosened valve seats and the nasties that can cause. Nice engines Jabs but you do need to be aware of the things that can cause you hassle.