Today's Message Index:
----------------------
1. 04:01 AM - Re: speed, weight, and engine power output (Brian Lloyd)
2. 04:36 AM - estimating percent of power (Brian Lloyd)
3. 05:18 AM - Re: estimating percent of power (Jim Griffin)
4. 05:32 AM - Re: estimating percent of power (Craig Payne)
5. 06:18 AM - Re: estimating percent of power (Brian Lloyd)
6. 07:48 AM - Prop Spinner (Jeff Linebaugh)
7. 10:28 AM - Prop Strike (Ernie)
8. 04:09 PM - Re: Prop Strike (Terry Calloway)
9. 04:54 PM - Re: Prop Strike (Ernie)
10. 06:04 PM - Re: Prop Strike (Gus Fraser)
Message 1
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| Subject: | Re: speed, weight, and engine power output |
--> Yak-List message posted by: Brian Lloyd <brian@lloyd.com>
Jim Griffin wrote:
> --> Yak-List message posted by: "Jim Griffin" <jgriffint28@cox.net>
>
> Hi Brian,
> All of my instruments are standard US except the Manifold Pressure. I assume
> the numbers are atmospheres of pressure but I really don't know what they
> are.
They are mm of mercury. 760mm hg = 29.92" hg
> My home made POH that I got with the plane says to take off at 2350 RPM
> and full throttle which is usually over 9 chinese thingys, climb at 8 Ch Th.
You had better test your manifold pressure guage then. The book says that the
maximum manifold pressure is ambient pressure + 85 mm. If you are at sea level
on a standard day that will be 760+85 or 845mm-hg. That is all the manifold
pressure a stock engine will generate at full throttle normally.
> and cruise at 7 to 7 and a half. 9 would work out to just under 39 inches.
And that is way overboosted. Something is wrong and I would suspect the gauge.
While sitting on the ground with the engine not running it should read 760 mm
at sea level. That value reduced by 25mm for ever 1000' of altitude. If you
live at 1500' MSL your static MAP should be 760-37 or about 723mm.
> Other than some mods for inverted flight, I'm pretty sure the engine is
> stock.I am use to 48 inches on take off in the T-28 but it has a two stage
> super charger. If that is higher than this engine can generate, then the
> guage must be reading something other than ATM or is mis -calibrated. I have
> a lot of throttle left at 7CTs and it doesn't feel like it's working hard.
> Whadduya think?
Check your MAP guage. Do try to adhere to the engine limitations for long life.
--
Brian Lloyd 6501 Red Hook Plaza, Suite 201
brian@lloyd.com St. Thomas, VI 00802
+1.340.998.9447 - voice +1.360.838.9669 - fax
Message 2
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| Subject: | estimating percent of power |
--> Yak-List message posted by: Brian Lloyd <brian@lloyd.com>
I have a simple method for figuring out an approximate percent of power from an
engine. An engine will produce 100% power at 100% RPM and 100% of manifold
pressure. For the Housai engine this would be 840mm-hg (33") and 2250 RPM. Now
hp decreases linearly with RPM assuming that torque remains constant which it
does for quite a wide range of RPM. So if you leave the MAP at max and reduce
the RPM from 2250 to 2000, you have reduced HP from 100% * 2000/2250 or 88.9%.
This is actually quite accurate.
You can do the same thing for MAP but it isn't quite as accurate. Still, it
will get you into the ballpark. So if you reduce the MAP from 33" to 21", and
you reduce the RPM from 2250 to 1950 you get the following estimate for % power:
100% * (1950/2250) * (21"/33") = 55%
It isn't exact but I would bet it is within 10% (which means that my 55%
estimate could really be as little as 50% or as much as 60%) and suitable for
making gross performance estimates. As you go higher and exhaust back-pressure
is lower, the %power will be slightly higher than it will be down low since down
low you will have higher pumping losses (sucking against a closed throttle
valve) and higher exhaust back presure.
This technique is useful for figuring out how much faster you will go if you
open up the throttle. Remember speed is a function of the cube root of hp. If
you increase the hp by 30% you can expect a 9% increase in speed. This is God's
way of telling you to spend time reducing drag, not increasing hp in order to go
faster.
--
Brian Lloyd 6501 Red Hook Plaza, Suite 201
brian@lloyd.com St. Thomas, VI 00802
+1.340.998.9447 - voice +1.360.838.9669 - fax
Message 3
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| Subject: | Re: estimating percent of power |
--> Yak-List message posted by: "Jim Griffin" <jgriffint28@cox.net>
That is a great rule of thumb for estimating your brake horsepower. I don't
think it will have an exact linear correlation with your performance because
of prop efficiency at different RPM.
The T-28 would surge forward when the RPM was dropped from 2600 to 2400 RPM
after take off to climb settings. In a section take off you can tell if the
lead has reconfigured and you hadn't done so yet.
Thanks for your input on my MP gauge as well.
Jim Griffin
----- Original Message -----
From: "Brian Lloyd" <brian@lloyd.com>
Subject: Yak-List: estimating percent of power
> --> Yak-List message posted by: Brian Lloyd <brian@lloyd.com>
>
> I have a simple method for figuring out an approximate percent of power
from an
> engine. An engine will produce 100% power at 100% RPM and 100% of
manifold
> pressure. For the Housai engine this would be 840mm-hg (33") and 2250
RPM. Now
> hp decreases linearly with RPM assuming that torque remains constant which
it
> does for quite a wide range of RPM. So if you leave the MAP at max and
reduce
> the RPM from 2250 to 2000, you have reduced HP from 100% * 2000/2250 or
88.9%.
> This is actually quite accurate.
>
> You can do the same thing for MAP but it isn't quite as accurate. Still,
it
> will get you into the ballpark. So if you reduce the MAP from 33" to 21",
and
> you reduce the RPM from 2250 to 1950 you get the following estimate for %
power:
>
> 100% * (1950/2250) * (21"/33") = 55%
>
> It isn't exact but I would bet it is within 10% (which means that my 55%
> estimate could really be as little as 50% or as much as 60%) and suitable
for
> making gross performance estimates. As you go higher and exhaust
back-pressure
> is lower, the %power will be slightly higher than it will be down low
since down
> low you will have higher pumping losses (sucking against a closed throttle
> valve) and higher exhaust back presure.
>
> This technique is useful for figuring out how much faster you will go if
you
> open up the throttle. Remember speed is a function of the cube root of
hp. If
> you increase the hp by 30% you can expect a 9% increase in speed. This is
God's
> way of telling you to spend time reducing drag, not increasing hp in order
to go
> faster.
>
> --
>
> Brian Lloyd 6501 Red Hook Plaza, Suite 201
> brian@lloyd.com St. Thomas, VI 00802
> +1.340.998.9447 - voice +1.360.838.9669 - fax
>
>
Message 4
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| Subject: | Re: estimating percent of power |
--> Yak-List message posted by: Craig Payne <cpayne@mc.net>
Jim,
That surge you feel when reducing RPM is from the inertia of converting
prop RPM to coarser pitch. When the CJ-6 is fitted with an M-14, this
surge is more noticable as there is a greater reduction in RPM (2900 to
about 2200) and greater blade area.
Craig Payne
>
> That is a great rule of thumb for estimating your brake horsepower. I don't
> think it will have an exact linear correlation with your performance because
> of prop efficiency at different RPM.
> The T-28 would surge forward when the RPM was dropped from 2600 to 2400 RPM
> after take off to climb settings. In a section take off you can tell if the
> lead has reconfigured and you hadn't done so yet.
>..
> Jim Griffin
Message 5
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| Subject: | Re: estimating percent of power |
--> Yak-List message posted by: Brian Lloyd <brian@lloyd.com>
Jim Griffin wrote:
> --> Yak-List message posted by: "Jim Griffin" <jgriffint28@cox.net>
>
> That is a great rule of thumb for estimating your brake horsepower. I don't
> think it will have an exact linear correlation with your performance because
> of prop efficiency at different RPM.
That is true but I didn't say it was exact, only that it would get you in the
ballpark. Given that there are no power tables or performance specifications
available with the CJ6A, this is better than nothing.
Still, over the normal range of RPMs and cruise speeds, prop efficiency is
amazingly constant, probably within a couple of percent, enough that all the
other errors, e.g. guage readings, are probably greater than the error in
calculating prop efficiency.
> The T-28 would surge forward when the RPM was dropped from 2600 to 2400 RPM
> after take off to climb settings.
Yes, any CS prop will do that. You have extra rotational energy in the prop
disk and it is turned suddenly into thrust. But once that goes away (after a
second or so), you will find your new steady-state airspeed is lower because the
engine really is producing less power.
> In a section take off you can tell if the
> lead has reconfigured and you hadn't done so yet.
> Thanks for your input on my MP gauge as well.
You are most welcome.
--
Brian Lloyd 6501 Red Hook Plaza, Suite 201
brian@lloyd.com St. Thomas, VI 00802
+1.340.998.9447 - voice +1.360.838.9669 - fax
Message 6
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--> Yak-List message posted by: "Jeff Linebaugh" <jefflinebaugh@earthlink.net>
Jim,
I would be very interested in seeing the spinner on your
airplane....pictures?
Thanks!
Jeff Linebaugh, N621CJ, Memphis, TN
--> Yak-List message posted by: "Jim Griffin" <jgriffint28@cox.net>
I have a spinner on my 2 blade prop on a Housai engine.My CJ was built by
Steve Culp. He had a cut down P-51 spinner adapted to it. Engine temps are
good Winter and Summer and it will cruise at about 155 knots. I am not sure
but I believe it was Nelson Ezell that made the spinner.
I am very happy with it.
Jim Griffin
CJ6-A 273SC
Jeff Linebaugh
jefflinebaugh@earthlink.net
Message 7
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--> Yak-List message posted by: "Ernie" <ernest.martinez@oracle.com>
Well guys.
A very close friend of mine (wink wink) was practicing dead stick landings, the
other day and didnt stick to procedure and brought her in on her belly. No damage
except to his pride and prop. He put her down very very gently on a grass
strip and the engine was at idle so the tips curved back ever so gently. Absolutley
no damge to the airframe, even the transponder antennae survived.
My engine manual states chapter 5 Procedure in special cases not covered by the
operating instructions.
5.2 "In case of properllor blade damage /broken or cracked at distance exceeding
1m / 3.3ft from the engine axis without sharp braking due to striking against
ground irregularities - the engine may be used after replacement of propeller."
I'm assuming this means that if the damage is further than 3.3ft from the center
of the shaft and was not caused by a sudden stoppage (sharp braking) that the
engine can be returned to service.
The prop didnt stop suddenly they slowly rotated to a stop and it was in dirt.
The bends start right at about 3 ft from the center of the shaft and gradually
arc back untill the tips are facing about 75 degrees aft. There are no sharp
bends in the prop.
My questions are;
Is my interpretation above correct?
Does my case meet the above scenario?
If not, what is the approved inspection procedure that I can hand over
to an A&P which would allow him to inspect and certify the engine as airworthy.
My engine manual just says send to an authorized service center. Is there
an overhual manual?
Ernie
Message 8
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--> Yak-List message posted by: "Terry Calloway" <TCalloway@datatechnique.com>
Ernie,
Was this your CJ?
Sorry to hear about it either way.
Concerned,
tc
Message 9
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--> Yak-List message posted by: "Ernie" <ernest.martinez@oracle.com>
Thanks Terry,
No it was my very good friends CJ, you see he doesnt want to say who he is
on the list since the feds might be listening.
Ernie
----- Original Message -----
From: "Terry Calloway" <TCalloway@datatechnique.com>
Subject: Re: Yak-List: Prop Strike
> --> Yak-List message posted by: "Terry Calloway"
<TCalloway@datatechnique.com>
>
> Ernie,
> Was this your CJ?
> Sorry to hear about it either way.
> Concerned,
> tc
>
>
Message 10
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--> Yak-List message posted by: Gus Fraser <fraseg@comcast.net>
In the years I have been flying I have learned that the sayings in this game
are taught by bitter experience. Therefore I remind everyone of the saying:
"There are two kinds of pilot. Those that have landed gear up, and those
that have yet to do so."
Sorry to hear about it Ernie.
Gus
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com]On Behalf Of Ernie
Subject: Re: Yak-List: Prop Strike
--> Yak-List message posted by: "Ernie" <ernest.martinez@oracle.com>
Thanks Terry,
No it was my very good friends CJ, you see he doesnt want to say who he is
on the list since the feds might be listening.
Ernie
----- Original Message -----
From: "Terry Calloway" <TCalloway@datatechnique.com>
Subject: Re: Yak-List: Prop Strike
> --> Yak-List message posted by: "Terry Calloway"
<TCalloway@datatechnique.com>
>
> Ernie,
> Was this your CJ?
> Sorry to hear about it either way.
> Concerned,
> tc
>
>
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