Jack, your experiment below would be interesting but there is one caveat you must remember: The engine has to be under load for that to be a good test. The engine can produce next to no horsepower and be revving 2000 rpm in neutral. It won't be producing rated horsepower. On a piston engine, the way to measure the load is the BMEP (brake mean effective pressure). See http://www.tsrsoftware.com/bmep.htm for an explanation. I don't know exactly what the equivalent formula for a rotary.

Think of it this way: Without a load, all that the engine needs to put out to hit 2000 (or 3000) RPM is enough HP to revolve that rotating mass of the rotors a little faster. That will be really nominal HP and a nominal cooling load.

That's why engine dynos have to be harnessed to water brakes to get valid data.

Barry Gardner
Wheaton, IL

Jack Beale wrote:

All,

 

    Been following the EWP thread with interest....

 

    Sooooo...., actually knowing little, but suspecting much:

 

    I'd suspect that Mazda designed the water pump and flow characteristics to provide adequate cooling for an idling engine in Phoenix in the summertime.  I'd also bet that the majority of time, a car is sitting at idle, as opposed to cruising down the freeway at 70 mph.

 

    My suspicion is that the water pump is designed for some arbitrary flow rate that will be adequate at idle - and at normal cruise (with it's attendant increased airflow).  I'd guess that the pump is flowing a much greater volume of water at high RPM's than is really necessary, because the pump impeller is not variable.  The engine temperature does not remain cold, because the thermostat closes, either completely or partially to keep the block temperature at 180-deg.

 

    Have ya-all ever driven a car with a stuck-open thermostat...?  The engine never warms up.  Runs OK, but builds-up sludge and carbon inside.

 

    Therefore (if all that's correct) an EWP will not have to pump a correspondingly greater volume of water as engine speed increases.  I agree that it will take more flow for a higher horsepower, the question remains: "What MASS of water per unit measure of time will cool 180 HP...?"

 

    Here's a suggested test for someone with an engine:

Run a rotary with an EWP and radiator combination (no temp regulator) (may need a fan).

Run the engine at idle, until the temperature stabilizes at (say) 180-deg.

Measure the flow rate required.

Increase the RPM's to 2000, and increase the flow rate (if nec) to stabilize the temperature at 180-deg.

Measure the flow rate required.

Increase the RPM's to 3000, and increase the flow rate (if nec) to stabilize the temperature at 180-deg.

Measure the flow rate required

 

Jack Beale

---

----- Original Message -----

From: Russell Duffy

To: Rotary motors in aircraft

Sent: Monday, November 08, 2004 3:31 PM

Subject: [FlyRotary] Re: EWP Info- Lynn?

As I’ve suggested before, I don’t see saving power consumption as a reason for considering an EWP, especially considering the losses in converting mech energy to electrical and back again.   

 

I think the biggest chance to save power on cooling is if Mazda is providing way more than is necessary at our cruise rpms.  I have to suspect that's the case, since Todd is running just fine with only 9.X gpm.  

 

Al (I swear I will not say another word about EWPs; that beheading thing is just too scary) 

 

Ha.  Don't worry, my wife would kill me if I stained the carpet :-)  

 

As for EWP's saving power, you'd think that the first people to jump on that would be the racers.  I know that these pumps are sold to drag racers, but I can't say that I've heard of other types of racers using these pumps. 

 

Hey Lynn,

 

-Are EWP's against the rules?

-Has someone determined that they don't save any HP? 

-Has someone determined that they won't cool the engine in racing conditions?

 

Cheers,

Rusty (just can't have any fun on this list)