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

From: Charlie & Tupper England

Sent: Tuesday, April 06, 2004 9:03 PM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: : Percent Power, Throttle position, & RD-1Cperformance

 

OK, how about a 'real world' cruise power fuel burn? My 160hp fixed
pitch Lyc powered -4 burned ~92-9.5 gph of avgas at ~190-195 statute
mph. What are you burning down around 190 mph (allowing a little wiggle
room for 'work in progress' aerodynamics of your plane)?

Tracy Crook wrote:

> Took closer note of throttle position on todays flight. At 2000 ft the
> throttle was only about 1/3 open (position of throttle quadrant, but
> it closely mirrors butterfly position) at economy cruise setting which
> was 6.0 GPH. This is about 42% power, 82 HP according to the EM2 which
> is fairly close but not perfectly calibrated yet. The same power
> setting with the -B drive would bave been a bit further open.
> I did a quick check of MAP at 1000 ft at full throttle and found I was
> not getting any drop at 150 MPH and had .5" boost at 220 MPH (ram air
> recovery I assume). I did not get around to checking it in slow climb
> which would more accurately compare to what you would see on a dyno.
> Finally got some reasonably calm air to do performance comparisons of
> -C drive vs -B drive. Without the prop blade cuffs it looks like the
> break even point is at 203 MPH. Above that -C burned more fuel than
> the -B. After installation of the cuffs, the break even point was off
> the scale! i.e., above top speed with -B drive. I had a good data
> point on the -B drive while burning 17 GPH (209 mph during SUN 100
> race). At the same speed, the C drive was burning 15.8 gph. This was
> better than I had hoped for.
> Tracy
>
>     Thanks, Tracy. I was hoping there would be someone out there
>     flying with the same TB diameters.
>
>     Like most things, TB diameter is a tradeoff. My conclusion from
>     the dyno data is that 44mm per rotor (1 ¾) is a bit small as the
>     MAP is dropping off over 5000 RPM. But if you want to idle at
>     1500, and have a decent transition from there to 3000; 1 ¾ is
>     good. For a 2.85 to redrive, I’d want to increase that flow area
>     by 30% or so – to about 2” dia for each rotor.
>
>     My data may not be representative because of restricted flow to
>     the TB. The ‘airbox’ size is restricted by the cowl, and may have
>     restricted the flow a bit. In hindsight, it would have been smart
>     (and easy) to make a run with the airbox off and see what
>     difference it made.
>
>     Al
>



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