Sender: <marv@lancaironline.net> (Marvin Kaye)
To: flyrotary
Date: Sat, 07 Dec 2002 16:56:24 -0500
Message-ID: <redirect-1896786@logan.com>
In-Reply-To: <list-1895518@logan.com>
References: <list-1895518@logan.com>
From: "Stone Tool" <owly@ttc-cmc.net>
Subject: Re: [FlyRotary] Torque??
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Tommy:
	Torque is a non-issue.  A given horsepower at a given RPM requires a given=
 amount of torque be produced.    Torque is a static measurement of force.=
  Horsepower is the ability to do work.   An example would be carrying=
 water up the stairs by the bucket.  Torque would be the amount of water=
 you could carry per trip, and horsepower would be the amount of water you=
 could carry carry per hour.   If  you can carry two five gallon buckets of=
 water per trip you  have twice the torque as someone who can only carry=
 one five gallon bucket, but if the guy with one bucket can make twice as=
 many trips he does the same amount of work as you do.  A million pounds of=
 torque at zero RPM does no work at all.... it just sits there.   
	Horsepower can be defined as   Torque * RPM / 5252       

If a 13B produces 140 horsepower @ 6000 RPM          140 * 5252 / 6000 =3D=
  122.54 lbs torque @ 6000       Put that through a 50% redrive and you end=
 up with 245 foot pounds at 3000.     

	You must think in terms of generating horsepower......   Horsepower is the=
 ability to do work..... Oops I'm repeating myself.  

GENERATING TORQUE:
 	
	There is only one way to increase torque....(aside from gearing down)=
  that is to increase air / fuel flow PER REVOLUTION.  This can be=
 accomplished by improving induction design which generally assists only in=
 a limited range.... most such measures work primarily at high RPM.  The=
 reason for this is that the resistance to airflow increases as the airflow=
 increases.   You will note that peak torque is found at low RPM where=
 maximum airflow can be achieved.  This can also be achieved by=
 supercharging an engine..... which has other undesirable effects including=
 increasing the compression to the extent that detonation is an issue, and=
 of course weight, and higher stresses.

GENERATING HORSEPOWER

	To increase horsepower we need to increase airflow PER UNIT OF TIME.  I=
 use cubic feet per minute as a standard measure of airflow.   It takes=
 very close to 1.62 cubic feet per minute to produce one horsepower.    We=
 can increase horsepower by increasing RPM.    Simple...... open the=
 throttle.      By using the appropriate gear reduction we can run our RPM=
 up to where we have the horsepower we need....... there's your increase in=
 torque.  The extremists resort to such measures as peripheral ports and=
 turbocharging to achieve much higher than rated horsepower, and much less=
 than normal life expectancy and greatly reduced reliability.  

	There are a lot of pie in the sky claims out there, and a lot of=
 mis-conceptions....... unfortunately we must operate in the real world=
 with real world limitations.    You have about 140 horsepower to work=
 with..... all you need to do is determine what your optimum prop RPM is=
 based on diameter which you determine from gear clearance and your=
 intended operating speed...... do you want lots of low end thrust or a=
 high cruise speed?   High cruise speed does not require nearly as large of=
 a prop as good climb out, static and low speed operation.    You then spec=
 out your reduction to match the desired prop RPM.  Don't bother your head=
 about "torque"..... 

	Interestingly you can convert horsepower directly into thrust at a given=
 forward speed if you know prop efficiency.   Assuming a prop efficiency of=
 80% which is realistic from around 100 mph upward through most of our=
 cruise ranges,   you can use the following formula to work out your=
 thrust.   (note that it does not work much below 100 mph because=
 efficiency falls off increasingly)

Thrust =3D horsepower * (300/speed in mph).    Thus your 140 horsepower=
 should give you 280 pounds of thrust at 150 mph

	Actually Thrust =3D horsepower* { (375*prop efficiency) / speed in mph }=
      Horsepower has to be real honest American Society of Automotive=
 Engineers Brake Horsepower for this to work.   Note that at very low=
 speeds prop efficiency drops to near zero values, and in fact at zero=
 forward speed efficiency is at zero for all intents and purposes.  

 
	Hope this helps clarify the issue...... there are way too many people out=
 there trying to cloud it.


									H.W.

*********** REPLY SEPARATOR  ***********

On 12/5/02 at 6:06 PM Tommy James wrote:

>Hi Guys and Kathy,   Happy Christmas!
>
>Does anyone have ideas about how much torque@rpm the typical aviation
>installation makes with a NA 13B?  Also some elementary principles on the
>variables of generating torque would be helpful.
>
>TIA
>Tommy James<><
>
>
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