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Date: Mon, 9 Jul 2012 13:11:25 -0500
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Subject: Re: [FlyRotary] On the step
From: Mark Steitle <msteitle@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Brian,

What's your fuel burn at 140-150 mph?  How long are your intake
runners?  I assume you've checked and verified your static timing?
What airframe is this?  How does your performance compare to other a/c
of the same make/model, but running certified engines?  As Lynn H. has
stressed many times before... the devil's in the details.

Mark S.


On 7/9/12, bktrub@aol.com <bktrub@aol.com> wrote:
>
> I commented on here recently about how I took a cross- country flight to
> Walla Walla from Everett, Wa recently and was only seeing 140-150 mph cruise
> at 11,500 feet. It got me to thinking- I was getting about 6200 rpm on the
> engine which is 2175 at the prop. So, I'm a little overpropped/
> underpowered.
>
> So, there's the old chestnut about how you can get a few more knots from an
> airplane in cruise if you go a little above your cruise altitude and then
> descend to your cruise altitude, thereby getting "on the step" . Some pilots
> swear by this, others dismiss it. I have a theory- if I climb to a cruise
> altitude and stay at full throttle while doing so, I will only get the
> engine to run up to a certain RPM and therefore a certain hp will be
> achieved, and no more and so the airplane will settle into an equilibrium at
> a certain speed- say at whatever hp/speed - 140 mph at 6200 rpm- lt's say x
> hp.
>
> Now, If I were to descend to my cruise altitude in a shallow dive, I will be
> acheiving a higher rpm and hence horsepower, say 6800 rpm and horsepower
> will be x + 9%x for a hp of 109% of the hp achieved at 6200 rpm, so I should
> be able to achieve and maintain a higher cruise  speed if I descend to my
> cruising altitude. ( I picked 9% arbitrarily for the sake of argument) .
>
> Anyone want to shoot me down on this one?
>
> This is just an theory, If I want to go faster first I have to clean up my
> drag. My cooling scoop is effective, but obviously draggy. And It needs a
> flap on it. That's a project for this winter.
>
> Brian Trubee
>