Mailing List flyrotary@lancaironline.net Message #39856
From: Ed Anderson <eanderson@carolina.rr.com>
Subject: Re: [FlyRotary] Re: FW: [FlyRotary] Re: Coolant Water Pressure
Date: Fri, 12 Oct 2007 20:38:39 -0400
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Perhaps for an "normal" automotive use, the cavitation rpm was not seen as critical as it would be  as normal use of  an Rx-7.  Apparently just buzzin the engine to 8000 rpm in the auto could be tolerated for brief periods.  But, naturally in aircraft operation, we might run at 6500-7000 rpm for hours - would like be a bit more critical.
 
But, as I mentioned, that data out of the Racing Beat technical catalog (1992) might well be dated.  I feel fairly confident that the Renesis must be able to cope with much higher rpm as Tracy has had his up to 7500 rpm (don't know for how long), but without any ill effects.
 
Ed
----- Original Message -----
From: Al Wick
Sent: Friday, October 12, 2007 5:49 PM
Subject: [FlyRotary] Re: FW: [FlyRotary] Re: Coolant Water Pressure

That's quite the surprise. Japanese engineers are expert at making sure the design has extra safety margin. Even back in the 70's. Although they are much better at it now. I can't imagine they are rpm sensitive 33 years later.
 
I have heard of a lot of guys adding flow restrictions on pump inlet, not aware they are increasing pressure drop. Particularly true with fuel systems.
 
-al wick
----- Original Message -----
Sent: Friday, October 12, 2007 2:14 PM
Subject: [FlyRotary] Re: FW: [FlyRotary] Re: Coolant Water Pressure

Hi Al,
 
Racing Beat's Rotary Tech catalog specifies that for 1974 and later pumps using stock main and water pulley, that  engine rpm above 6300 rpm would cause the stock water pump to cavitate.  .  This is of course with OEM size hoses.  That cavitation beings gradually and becomes worst as rpm and temperature increases and if full throttle operation is maintained under those conditions "...the engine will not last long."
 
Now that information is somewhat dated (my catalog is dated 1992).  I strongly suspect  that, the Renesis for example would be able to handle a higher sustained rpm.  And perhaps the later 13B's as well, I just have not seen any information more recent on the topic. 
 
I fly with a main pulley sized for 20% less water pump rpm and my alternator has a 20% reduction as well. So my top engine rpm (sustained) around 6500 rpm hopefully keeps me out of the bubble zone.
 
Ed 
 
 
 
----- Original Message -----
From: Al Wick
Sent: Friday, October 12, 2007 4:29 PM
Subject: [FlyRotary] Re: FW: [FlyRotary] Re: Coolant Water Pressure

Where does the fear of pump cavitation come from? Is that speculative or have some guys inadvertently choked off the pump inlet with small diam hose instead of OEM size?
 
 
 
-al wick
----- Original Message -----
From: Al Gietzen
Sent: Friday, October 12, 2007 11:31 AM
Subject: [FlyRotary] FW: [FlyRotary] Re: Coolant Water Pressure

This was rejected because of the photo files being too large, so I’ll send one of the pics separately.

Al

Subject: RE: [FlyRotary] Re: Coolant Water Pressure

 

Bill;

 

Here is the setup I use. On the first photo, the filler neck is on the left, and connects to the line going to the inlet side of the pump.  The two small lines (3/16”) coming into the side are air bleed lines going from the high points of my two radiators (note that the pressure at the filler neck will be near the lowest in the system.)  The ‘overflow’ from the filler cap goes to the bottom of the accumulator bottle on the right (made from a discarded fire extinguisher).

 

The accumulator bottle overflow goes over board, but coolant only goes out here once on first heatup.  When cold, there is only about 3 – 4” coolant in the bottom of that bottle, so there is air in there that compresses as things heat up.  Coolant forced out of the filler neck on heat up is draw back in on cooldown.

 

The idea is that whenever the engine is running, there is positive pressure on the system – at the pump inlet; reducing the chance of pump cavitation at high RPM.  And positive pressure is maintained at altitude even when throttling back and the coolant temp is decreasing.

 

Originally I had a 23# cap on the filler neck, and 15# on the accumulator bottle.  I later reversed the two to lower system pressure on initial heatup (as soon as the engine heats up at all the pressure goes to filler cap pressure), but it still gives me the sum of the two caps under any extreme condition to protect against boiling.  Keep in mind that the caps are ‘differential pressure’ so at altitude the max absolute pressure in the accumulator bottle is reduced by the reduction in the ambient.

 

Al

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry
Sent:
Thursday, October 11, 2007 8:49 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Coolant Water Pressure

 

Lynn, I don’t know what we would do without you.

I have several questions. 

Where can I get a good accumulator tank? 

I was thinking of making one out of a used fire extinguisher  and was also looking at one from Moroso that looks like a flat canteen.  The one from Moroso has an inlet on the bottom and one on the top side as well as one for the pop off of the radiator cap.  Due to space constraints, I will probably try and make one. I need something about 3” diameter and maybe 12” or so long.   Will I need the inlet on the top side?  If so, where does it plumb to?

I suppose I will still need an overflow tank from the pop off of the radiator cap?

After talking  with Tracy yesterday, I tried to see if the engine would stabilize temp somewhere below 230* at 2600 rpm.  No joy!  I suspect that I will need to increase air flow to get this to happen.  I will try an leaf blower on the cowl today.

My pressure stabilized at 22 lbs (cap in constant blow off relief) but the temp would not hold.  If I had this same condition with the system you described, what would prevent the air from blowing off and then water from the accumulator?

It seems to me that no matter what system you have, the pressure has to stabilize below the pressure rating of the radiator cap, else you will be losing first air, then water????

 

Bill B

 


From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Lehanover@aol.com
Sent:
Wednesday, October 03, 2007 10:28 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Coolant Water Pressure

 

In a message dated 10/3/2007 9:08:53 A.M. Eastern Daylight Time, bbradburry@bellsouth.net writes:

I think that I would see air under the radiator cap if I had a compression gas leak?  I never see any air.

To check a piston engine for head gasket leaks, you would put the cylinder at TDC and pressurize the cylinder to about 150 lbs with compressed air and check the radiator for air bubbles…How do you check a rotary?

I will check the pressure sender against a mechanical gage. 

There is obviously a heating problem, but I think the pressure is higher than it should be until just ready to boil.  I shut the engine off at 210*, and at 22+ lbs, the boiling point should be well above 250*??

 

Thanks for the suggestions of where to look, guys…

 

Bill B

It is extremely difficult to remove all of the air from a rotary engines cooling system. It is also extremely important. If air is under the pressure cap in a static situation, it will remix with other coolant when the engine is at speed. The coolant moves very quickly through the system. The coolant volume appears to increase slightly because much of the air is reintroduced into the water. This coolant then becomes a poor conductor of heat. You need the anti foaming agent in Antifreeze. Just a bit, perhaps 10%. The system with the relief cap right on the radiator or filler point, starts to offload coolant as soon as the engine is started. It is in hydraulic lock, and has a small volume. The actual boiling point calculated for this coolant makes no difference at all. The cap opens a bit when the trip pressure is attained, the pressure drops to 22 PSI or whatever for your cap, and a bit more heating trips the cap again. It is exactly the same as most cars.

So, at first in each heat cycle, there may be no correlation between coolant temperature, and the actual amount of coolant dumped by the cap. This is only true closer to a constant operating temperature. And then pressure may be alarmingly unstable with power changes. The accumulator system makes pressure rock solid. 

 

 

Make the pressure cap into a filler cap, sealing only the top lip of the radiator or filling port. Connect only a  bleed hose and run it to the bottom of a recovery bottle, and put the pressure relief cap on that bottle. Keep the bottle about 1/3 full. Note after several heat cycles, the amount of water you need to add to keep that bottle 1/3 full is reduced each time. Once all of the air is out of the cooling system, no more coolant need be added to the bottle.

 

Heating and cooling of the system, makes sweeping changes in coolant volume. The air cushion in the bottle acts as an accumulator (used in thousands of aircraft) to maintain a constant pressure and coolant supply.

 

Race cars use a Rolairtrol or spin bottle in the hose from the top of the engine to the radiator. Water enters the bottle at about half height on a tangent and adds a spinning motion. Water leaves through a center hole at the bottom.

Trapped air pops to the top of the bottle and that is plumbed to the bottom of the accumulator as above.

You used to get the plans for this thing when you buy a Cosworth race engine. Does Cosworth know something you don't? 

 

Anyway, after about three heat cycles (operating temperature and back to room temperature) the coolant system will be solid coolant with all of the air removed. It will not be hydraulically locked against the cap.

It will have the relief cap pressure, and will hold that for as long as the engine is hot.

 

I have a Shrader valve installed in my accumulator tank, and before I start the engine I charge that bottle with compressed air until the cap relieves at 22 PSI. Now I know it has pressure, and I know it has 22 PSI.

 

This was the stock system on all Mazda cars in the 70s. I didn't invent it.

 

It is unlikely that you have leaking compression seals, unless there is coolant blowing out of your makeup tank, or coolant is running out of your exhaust system after shutdown.

 

My recovery bottle is mounted where the passenger foot well would have been. Even with the bottom of the engine. So long as the hose ID is less than 1/4" and the hose enters the bottle on the bottom of the coolant supply, it matters not at all where that bottle is located. There is a money back guarantee with this system. 

 

Lynn E. Hanover 

 


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-Al Wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam timing.
Artificial intelligence in cockpit, N9032U 240+ hours from Portland, Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
-Al Wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam timing.
Artificial intelligence in cockpit, N9032U 240+ hours from Portland, Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
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