CHT's Lower with Wheel Pants

Does this make sense? I flew my RV-8A with the main gear leg fairings and wheel pants installed for the first time today.
My cylinder head temps had been running a bit high, however today they were almost perfectly in line with what they should be.
Has anyone else experienced this?
Please let me know. Any comments are welcome.

jeffmoreau said:

Does this make sense? I flew my RV-8A with the main gear leg fairings and wheel pants installed for the first time today.
My cylinder head temps had been running a bit high, however today they were almost perfectly in line with what they should be.
Has anyone else experienced this?
Please let me know. Any comments are welcome.

Click to expand...

Same thing happend to me. In my mind the equation went something like:
Gear leg fairings and wheel pants = higher airspeed = more cooling air through the cowl = lower CHTs

Makes complete sense. If you've gained 10 to 15 knots or more, that is about 10% more cooling air for the same power. These RV's, fortunately, do not have excess cooling (i.e., drag).

This is one reason I have never understood Van's recommendation to do initial flights without gear/wheel fairings. Why try to break in an engine with even higher cht's? It makes sense if the engine is already broken in, to find out if the airplane itself is rigged properly, to fly without the fairings. Perhaps the recommendation came at a time when most flew with run-in engines. My perception is that most are newly overhauled or new now.

Define "a bit high" as with numbers.

Definition

I was seeing temps just over 400 in the climb on the number 1 and 2 cylinders.

I see 420 F or higher in a climb.

jeffmoreau said:

Does this make sense? I flew my RV-8A with the main gear leg fairings and wheel pants installed for the first time today.
My cylinder head temps had been running a bit high, however today they were almost perfectly in line with what they should be.
Has anyone else experienced this?
Please let me know. Any comments are welcome.

Click to expand...

Jeff,
Unless the OAT was exactly the same for both observations, you don't know for sure if there was an improvement. A 20? difference in OAT will result in about that much CHT difference.

Ron Lee said:

I see 420 F or higher in a climb.

Click to expand...

Now I feel better....

How do you get 300 and anything in climb on a 100 deg day in an RV?

...and for comparison...

...the coolant temperatures actually drop in the Me-109 when you partially close the radiator doors. Decreased drag provides more speed and better cooling. Surprising, at first.

Rob

There is some logic is reduced CHT's with the fairings on. At any single condition, climb or cruise, since the fairings reduce drag, the engine requires less power to maintain the same speed, therefore lower CHT's.

This would actually be more pronounced at higher speeds, as drag varies proportionally to the speed squared. In climb I would think the difference would be rather small. I can quickly get to 400F and even 415F in climb at 120 mph. A climb at 140 mph will stay below 400. Your engine is still breaking in and you could be experiencing lowering temperatures as internal frictions decrease.