Today's Message Index:
----------------------
1. 09:05 AM - Re: Mt-Prop From the Owner (flyv35b)
2. 10:43 AM - Re: Mt-Prop From the Owner (Eric Finley)
Message 1
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| Subject: | Re: Mt-Prop From the Owner |
--> TeamGrumman-List message posted by: "flyv35b" <flyv35b@juno.com>
> Funny how that works isnt it, grab a 172RG manual or POH, look at the
cruise
> perfomance numbers.
> The difference between 25"MP and 2500 and running the plane at 23"MP 2300
> RPM is only 1 knot TAS, but wait reducing power that much and dropping the
> RPM another 200 surely would slow the airplane down drastically wouldnt
it?
Very interesting. I don't have a 172RG POH to look at but the POH for the
V35B Bonanza shows a 10 kt slower speed at 2300 rpm than at 2500 rpm at sea
level and 11 kts. slower at 6000 ft. And that is with the SAME MP!
Reducing the MP 2" would increase the difference even more.
> It's not rocket science, developing extra horsepower simply doesnt produce
> huge increases in TAS, come on it goes back to your private pilot days and
> simple aerodynamics. To put it simply, as you know parasite drag
increases
> as you fly faster, right? Oh and wait doesnt your prop create drag too?
But
> now with a constant speed prop, you have control over that drag. Now let
me
> think by slowing the prop down are we decreasing or increasing drag, well
> that would be decreasing drag. Meaning decreasing the overall drag of the
> airplane, finally resulting in less power to maintain the same TAS or
> slightly below within 1 or 2knots max. Grab the book " Aerodynamics for
> Naval Aviators " and you can read all about it. After all would you really
> argue with the NAVY.
>
> Eric
Sure, I understand that reducing EITHER or BOTH engine speed and prop spreed
will increase efficiency. But looking at Lycomings engine curves for the
IO-0360A1B6 (the C172RG engine) shows that power output is 154 hp (77%) at
sea level for 2500 rpm/25" and 124 hp (62%) for 2300 rpm/23". The prop
would have to be very inefficient at 2500 rpm vs. 2300 rpm to account for 30
hp less power and only 1 kt. speed reduction. I can't believe that there is
that much difference between the C172RG and V35B planes that one would have
a 1 kt. speed change and the other a 10 kt. change (and more at altitude).
Actually, assuming that % speed increase is proportional to % power increase
cubed results in a 7.5% change in speed or about 10.5 knot speed change at
140 kt. (same prop efficiency). Amazing, about the same as the V35B POH
shows!
And I'm not arguing with the NAVY or the theory on aerodynamics, just that
you said your plane didn't slow down AT ALL with a 200 rpm and 2 " MP
reduction in power. Maybe you should keep reducing the power even more and
save even more fuel and not loose any speed in the process. After all the
prop efficiency will increase fast enough to overcome the reduction in
engine power output, right!
Cliff A&P/IA
----- Original Message -----
From: "Eric Finley" <finleyn254@hotmail.com>
Subject: Re: TeamGrumman-List: Mt-Prop From the Owner
> --> TeamGrumman-List message posted by: "Eric Finley"
<finleyn254@hotmail.com>
>
> "Do you really believe that you can substantially reduce the power output
of
> the engine and the plane will fly just as fast as it did at the higher
power
> setting? Believe me, the speed will not remain the same with 2" less MP
> and 200 rpm less unless you are still slowing down or descending."
>
> Funny how that works isnt it, grab a 172RG manual or POH, look at the
cruise
> perfomance numbers.
> The difference between 25"MP and 2500 and running the plane at 23"MP 2300
> RPM is only 1 knot TAS, but wait reducing power that much and dropping the
> RPM another 200 surely would slow the airplane down drastically wouldnt
it?
> It's not rocket science, developing extra horsepower simply doesnt produce
> huge increases in TAS, come on it goes back to your private pilot days and
> simple aerodynamics. To put it simply, as you know parasite drag
increases
> as you fly faster, right? Oh and wait doesnt your prop create drag too?
But
> now with a constant speed prop, you have control over that drag. Now let
me
> think by slowing the prop down are we decreasing or increasing drag, well
> that would be decreasing drag. Meaning decreasing the overall drag of the
> airplane, finally resulting in less power to maintain the same TAS or
> slightly below within 1 or 2knots max. Grab the book " Aerodynamics for
> Naval Aviators " and you can read all about it. After all would you really
> argue with the NAVY.
>
> Eric
>
> Tired of slow downloads? Compare online deals from your local high-speed
> providers now. https://broadband.msn.com
>
>
Message 2
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| Subject: | Re: Mt-Prop From the Owner |
--> TeamGrumman-List message posted by: "Eric Finley" <finleyn254@hotmail.com>
Well im not saying an airplane wont slow down at all when power is reduced,
and vice versa obviously if you add enough power the airplane speeds up, but
depending on altitudes and OAT's, the difference of inputing an extra 200
RPM may not result in much of a change when using a constant speed prop. My
results were 138 TAS at 25" 25RPM, i also saw the same result at 23 squared,
reealistically it was probably around 137 TAS, so one knot difference.
Personally 1 KNOT isnt worth running the engine 200 RPM faster, which means
more fuel being burned, and more decibals in the cabin. Now as for my plane,
no doubt about it, i'll run 25 squared all the time, my only point i was
trying to make, was that running the MT prop passed its specified limits
(2500 RPM), wont gain you that much more in terms of TAS, maybe a knot or 2
at the most.
>From: "flyv35b" <flyv35b@juno.com>
>Reply-To: teamgrumman-list@matronics.com
>To: <teamgrumman-list@matronics.com>
>Subject: Re: TeamGrumman-List: Mt-Prop From the Owner
>Date: Sat, 3 Jan 2004 09:04:34 -0800
>
>--> TeamGrumman-List message posted by: "flyv35b" <flyv35b@juno.com>
>
> > Funny how that works isnt it, grab a 172RG manual or POH, look at the
>cruise
> > perfomance numbers.
> > The difference between 25"MP and 2500 and running the plane at 23"MP
>2300
> > RPM is only 1 knot TAS, but wait reducing power that much and dropping
>the
> > RPM another 200 surely would slow the airplane down drastically wouldnt
>it?
>
>Very interesting. I don't have a 172RG POH to look at but the POH for the
>V35B Bonanza shows a 10 kt slower speed at 2300 rpm than at 2500 rpm at sea
>level and 11 kts. slower at 6000 ft. And that is with the SAME MP!
>Reducing the MP 2" would increase the difference even more.
>
> > It's not rocket science, developing extra horsepower simply doesnt
>produce
> > huge increases in TAS, come on it goes back to your private pilot days
>and
> > simple aerodynamics. To put it simply, as you know parasite drag
>increases
> > as you fly faster, right? Oh and wait doesnt your prop create drag too?
>But
> > now with a constant speed prop, you have control over that drag. Now let
>me
> > think by slowing the prop down are we decreasing or increasing drag,
>well
> > that would be decreasing drag. Meaning decreasing the overall drag of
>the
> > airplane, finally resulting in less power to maintain the same TAS or
> > slightly below within 1 or 2knots max. Grab the book " Aerodynamics for
> > Naval Aviators " and you can read all about it. After all would you
>really
> > argue with the NAVY.
> >
> > Eric
>
>Sure, I understand that reducing EITHER or BOTH engine speed and prop
>spreed
>will increase efficiency. But looking at Lycomings engine curves for the
>IO-0360A1B6 (the C172RG engine) shows that power output is 154 hp (77%) at
>sea level for 2500 rpm/25" and 124 hp (62%) for 2300 rpm/23". The prop
>would have to be very inefficient at 2500 rpm vs. 2300 rpm to account for
>30
>hp less power and only 1 kt. speed reduction. I can't believe that there
>is
>that much difference between the C172RG and V35B planes that one would have
>a 1 kt. speed change and the other a 10 kt. change (and more at altitude).
>Actually, assuming that % speed increase is proportional to % power
>increase
>cubed results in a 7.5% change in speed or about 10.5 knot speed change at
>140 kt. (same prop efficiency). Amazing, about the same as the V35B POH
>shows!
>
>And I'm not arguing with the NAVY or the theory on aerodynamics, just that
>you said your plane didn't slow down AT ALL with a 200 rpm and 2 " MP
>reduction in power. Maybe you should keep reducing the power even more and
>save even more fuel and not loose any speed in the process. After all the
>prop efficiency will increase fast enough to overcome the reduction in
>engine power output, right!
>
>Cliff A&P/IA
>
>----- Original Message -----
>From: "Eric Finley" <finleyn254@hotmail.com>
>To: <teamgrumman-list@matronics.com>
>Subject: Re: TeamGrumman-List: Mt-Prop From the Owner
>
>
> > --> TeamGrumman-List message posted by: "Eric Finley"
><finleyn254@hotmail.com>
> >
> > "Do you really believe that you can substantially reduce the power
>output
>of
> > the engine and the plane will fly just as fast as it did at the higher
>power
> > setting? Believe me, the speed will not remain the same with 2" less
>MP
> > and 200 rpm less unless you are still slowing down or descending."
> >
> > Funny how that works isnt it, grab a 172RG manual or POH, look at the
>cruise
> > perfomance numbers.
> > The difference between 25"MP and 2500 and running the plane at 23"MP
>2300
> > RPM is only 1 knot TAS, but wait reducing power that much and dropping
>the
> > RPM another 200 surely would slow the airplane down drastically wouldnt
>it?
> > It's not rocket science, developing extra horsepower simply doesnt
>produce
> > huge increases in TAS, come on it goes back to your private pilot days
>and
> > simple aerodynamics. To put it simply, as you know parasite drag
>increases
> > as you fly faster, right? Oh and wait doesnt your prop create drag too?
>But
> > now with a constant speed prop, you have control over that drag. Now let
>me
> > think by slowing the prop down are we decreasing or increasing drag,
>well
> > that would be decreasing drag. Meaning decreasing the overall drag of
>the
> > airplane, finally resulting in less power to maintain the same TAS or
> > slightly below within 1 or 2knots max. Grab the book " Aerodynamics for
> > Naval Aviators " and you can read all about it. After all would you
>really
> > argue with the NAVY.
> >
> > Eric
> >
> > Tired of slow downloads? Compare online deals from your local high-speed
> > providers now. https://broadband.msn.com
> >
> >
>
>
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