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Actually, they all have a lot of windmill. My Velocity idles at 800
or so, and on final, at idle, my rpm is around 1200-1300 minimum.
There really IS some thrust there. It'd be really REALLY difficult
to calculate the residual thrust, but I guarantee it's significant.
Try landing no flaps on a paved strip some time and check how far it takes
to stop the airplane. Then go back up and make another no flap approach,
only this time, shut the engine down right at flare and let the airplane
roll as far as it can. Bet dollars to doughnuts you can't MAKE
it roll much over 2000' with the engine off.
A real eye opener .... try it and report back to us ... Jim S.
Charlie & Tupper England wrote:
I agree with Jim about this. I've had similar problems
with a Lyc
powered RV-4. Anything over about 800 prop rpm caused a lot of
float.
I'd be interested to see the calculations on whether a really highly
pitched cruise prop is producing thrust at 800-850 rpm &
60-70mph. I
think that it's at least safe to say that the airflow isn't driving
the
prop disc & producing drag like a climb or c/s prop.
I wonder what engine-stopped glide angle would look like compared to
the
angle we get used to while being pulled along by the engine on final.
This could be a significant safety issue if there's an engine failure
when we have become acclimated to unknowingly carrying power (thrust)
on
final.
Charlie
Jim Sower wrote:
> <... I need to get the idle speed way down ...>
> You sure do. I've regaled you several times about my EZ with
an O-235
> idling at 800-900 rpm that could NEVER be slowed down enough to land
-
> floated 1000' or more down every damned runway I encountered.
Landed
> fine when I set the idle down to 500-600 rpm. Ran rough as
a cob at
> that speed on the ground (which is why it had been set so high),
but I
> could advance it to 800 for ground ops, and go to the idle stop on
> final. With all your power, I would emphatically recommend
that you
> back the idle down till it will just barely idle on the ground.
You
> can always taxi above the idle stop, but you can never land below
it.
> I would also strongly recommend a shutdown switch (injectors?
pumps?)
> near the throttle quadrant for convenient shutdown on final.
A
> guarded switch (guarded ON) would satisfy safety considerations,
and
> be convenient enough that you could shut down nearly as easily as
> pulling the mixture.
>
> That way, you have all the bases covered ... Jim S.
>
>
> John Slade wrote:
>
>> Last week we had some discussion on idle speeds, and I think the
>> consensus
>> was to keep it around 2000 or a little under. Just for information
>> for other
>> canard pusher people, I think 2000 is going to be a real problem
for
>> me. At
>> the current 1850 setting with the big 3 66/84 prop I have on she's
>> pushing
>> hard against the brakes. I think I could taxi the length of the
>> runway at
>> idle and be doing 30/40 kts at the end. On a short (3400) runway
the
>> only
>> way to stop might be kill the engine once on the ground, or even
on
>> short
>> final. So I need to get the idle speed way down.
>> John Slade (more power than I know what to do with)
>>
>> >> Homepage: http://www.flyrotary.com/
>> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>>
> --
> Jim Sower ... Destiny's Plaything
> Crossville, TN; Chapter 5
> Long-EZ N83RT, Velocity N4095T
>
>
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
--
Jim Sower ... Destiny's Plaything
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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