I am doing the same with my Renesis, except I have not found the energy to install an adjustable cowl flap.  I just install an open cowl flap for summer flying and block it off for winter flying.  :>)

I somehow seem to gain about 3 knots in the winter…..

Bill

Well, the second flight occurred last night with same results as before; one short low-level circuit due to insufficient cooling … looks like Al Wick made the correct prediction.

There are 3 things I can try with the current configuration: 1) Increase inlet area 2) Increase outlet area (adjustable cowl flap) 3) Re-profile the pinched diffuser.  I will do all 3 and see what happens.

If all of the above show remarkable improvement then repositioning the radiator is the only alternative.

Jeff

 

From: Bobby J. Hughes [mailto:flyrotary@lancaironline.net]
Sent: Wednesday, May 06, 2015 12:36 PM
Subject: RE: [FlyRotary] Re: Return to Flight

 

Al,

 

“Sorry to say, the pressure you see has no significant effect on cooling efficiency (heat transfer). The next time you fly, since you’ve removed most of that air, you will still see 210F. Just like before”.

 

If the air was trapped at the top of the heat exchanger I would expect improved temperatures. Could be wrong.

 

Bobby Hughes

 

 

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Wednesday, May 06, 2015 11:15 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Return to Flight

 

Hi Jeff. I’ve done lot’s of experimenting with cooling sys. Tough to explain all this, but I’ll give it a try:

Pretty clear you saw 6 psi only because you took off with 3+ cups of air in the system. If you’d taken off with 2 cups of air, then pressure would have been 9 psi. 1 cup, 14 psi. No air in system, then you would have seen rated cap pressure (16 psi in your case).

 

Sorry to say, the pressure you see has no significant effect on cooling efficiency (heat transfer). The next time you fly, since you’ve removed most of that air, you will still see 210F. Just like before. There’s one huge exception to that statement, that’s if you have air in sys that can’t move to a high point out of the flow. In that case air in sys has huge negative effect. Causes local boiling when it passes hot areas and inflates cooling temp.

 

You don’t have to fly to prove these concepts. Ground running at idle is all that’s needed. Let’s assume all air is removed. Then letting engine warm up to 180 F will result in rapid pressure rise to 16 psi (rated cap pressure). Fluid will exit system. With 2 cups of air in sys, that same 180F will yield slow rise in pressure to only 9 psi. No fluid will leave sys.

 

A good cooling design pretends air is stuck in block, so you add a path for that air to rise out of the block coolant flow. This is called a dynamic bleed. Air is automatically removed from engine coolant flow. Super low risk way to fly as you no longer care if air is in system. It’s can’t affect cooling.

 

It’s a bit higher risk to fly without dynamic air bleed, you just make darn sure you purge all air from block sys prior to flight. Applying vacuum to rad cap is great way to remove air.

 

One of the ironies about cooling design is that air that resides above engine flow is a safety asset. For example, your cap is highest point in sys and you have 2 cups of air under cap. Big safety advantage simply because your pressure gage is then a great predictor of how well your sys is doing. A leak will be detected long before overheating. A bunch of other assets to this design.

 

Conversely, air in engine flow has overwhelming negative affect. Temps soar and risks boil over.

 

Clear as mud eh?

 

Fwiw

 

-al wick

 

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