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Date: Fri, 4 Mar 2005 16:40:02 -0700
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Bill Schertz's cooling analysis
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Hi Ernest,

My plan is to start with much more than 50 square inches of opening.
That's bad for drag, but I want to cool first and optomize later.  I
will start with two openingsof 8X7 for a total area of 112 square
inches.  That happens to be the frontal cross section of my radiators
as they are installed.  Also, we need to consider the climb speed rather
than top speed. Normal climb for me is 120 MPH.  If I take the 262 MPH
and adjust for 112 sq. in., that should bring it down to 117 mph.  But
I still need 20 GPM per Bill's analysis.  I'm at 12 GPM with cold
water.  I've got to figure out some way to check the flow with hot
water.

Bob W.

On Fri, 04 Mar 2005 17:58:06 -0500
Ernest Christley <echristl@cisco.com> wrote:

> I've been working through Bill Schertz's example analysis that he did of 
> Todd's system, trying to divine an answer to the question "How much flow 
> is enough?"
> 
> Let's simplify everything and just arbitrarily look at 200Hp.  I've 
> followed Bill's example and assumed a 100F day, and a max temp of 180F 
> for the coolant.
> 
> The first step is getting a dT for the water going through the engine at 
> a specified flow rate. 20GPM will produce a 37F dT and 30GPM move it 
> down to 27F dT.  From that point on, the curve starts heading to the 
> stratosphere, with ridiculous amounts of flow required to produce any 
> worthwhile reduction in dT.  Going up to 40GPM only reduces the dT to 
> 20F.  You have to boost the flow another 15GPM to 55GPM in order to get 
> another 5F dT.
> 
> But lowering the dT gives us more headroom to heat the air.  At 55GPM, 
> the water leaving the radiator is still 165F.  That allows us to heat 
> the air from 100F all the way up to 165F.  Stepping to the second graph, 
> we see that it doesn't continue up to a 65F dT, but the graph has 
> bottomed out, so I'll extrapolate and say that the airflow required is 
> 5000CFM.
> 
> If we're only flowing 30GPM, with it's dT of 27F for the water, then we 
> can only heat the air to 153F.  The second chart says that we'll need 
> about 6000CFM.  For the 20GPM and 37F dT, we'll need 8000CFM since there 
> is only 43F of headroom.
> 
> For a 50in^2 intake, the 8000CFM results in a 262MPH intake velocity for 
> the air.  30GPM/6000CFM will result in an intake velocity of about 
> 196MPH.  At 55GPM, the air only has to move at 164MPH.
> 
> 200Hp will push a typical RV size plane at just over 200MPH (using 
> Tracy's performance at Sun'n'Fun as my only point of reference).  From 
> these numbers, however contrived they may be, I would say that somewhere 
> around 30GPM is sufficient unless you're building a drag queen.
> 
> Lowering the OAT, or increasing the coolant temp will change the 
> numbers.  An engine exit temp of only 190F would mean that the 20GPM's 
> coolant dT of 37F will tranlate to a air dT that matches the 30GPM at 
> 180.  That is, if you can accept coolant temps of 190F, then you only 
> need a 20GPM pump for sustained max power cruise.  With a 30GPM pump, 
> you could maintain a max power climbout at 165MPH.  However, we're 
> playing on the bottom part of a log curve.  Increasing the dT of the air 
> is having less and less of an effect on the outcome.
> 
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
> 
> 


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