Value of a knot

I got an idea from a recent thread.

I would like to know what you guys would spend to go a little faster. This
would seem to be interesting information, and a fun topic.

Please note the present speed of your plane, because 5 knots means a lot
more at 100 than 200.

Personally, It seems to me that a speed mod less than $1,000 a knot is
likely a good deal. I presently fly about 142 in a hurry, and 120 when I am
not.

I know the people selling the mods often over advertise, but lets assume we
know the real increase of a given mod from an expert. What's it worth to
you?

In article ,
Dude wrote:
Personally, It seems to me that a speed mod less than $1,000 a knot is
likely a good deal. I presently fly about 142 in a hurry, and 120 when I am
not.

They're probably not worth much of anything until you're talking about
airplanes with stock speeds in the 160kt+ range. That seems to be the
speed aircraft designers can easily get by going to 250-300hp. Getting
beyond that requires smarter aerodynamics.

For example, the price difference between a similar vintage Piper
Cherokee 235 and Comanche 250 is $10-15,000 (based on a quick look
at TAP). If you put $15,000 worth of speed mods (ie all of them) on
a 235 it still doesn't go as fast. The same is probably true of the
Warrior - 235 upgrade.

Once your stock speed is up around 160kt it might cost less to add STCs
than to upgrade to a faster model, but the returns have diminished
significantly. I'm not aware of any combination of mods that take a
160kt stock airplane and give you 180kts (with the possible exception
of an aftermarket turbo, if any still exist). Even that only saves you
20 minutes on a 3 hour trip.

If you're flying long distances and want to cut the total time, the most
cost effective way is to carry enough fuel that you don't have to stop.
If you can cut a 30 minute fuel stop out of a C-172 flightplan it's like
adding 15kts.

--
Ben Jackson

http://www.ben.com/

On 6-Sep-2004, (Ben Jackson) wrote:

If you're flying long distances and want to cut the total time, the most
cost effective way is to carry enough fuel that you don't have to stop.
If you can cut a 30 minute fuel stop out of a C-172 flightplan it's like
adding 15kts.


I don't think I have ever in my life been able to turn a fuel stop in 30
minutes, taking into account the time to fly the pattern and climb out after
the stop. 45 minutes is probably more realistic, and probably at least an
hour if IFR. And the speed penalty is more pronounced on higher performance
airplanes. For a 140 kt plane on a 600 nm trip, the penalty (of a 45 min.
stop) would be more than 20 kts.

This illustrates why having small tanks in order to obtain high "full fuel"
cabin load is such a stupid idea.

--
-Elliott Drucker

Amen brother. Range was one of the main reasons we chose our Beech
Sierra---only 135-ish knots, but 6+ hours aloft make us faster than a
Bonanza on some trips. Not all, but some. Heck, if you have a Mooney
you get higher speed AND more range (but less headroom).

To answer the original question, if I could spend $1000 to get 5 knots I
would do it, but not 1. If I could spend $5000 and be guaranteed 5
knots I would think about it. If I could spend $10,000 on a turbo that
would take me up higher when I need to climb to be safe, I would
seriously think about it, but I wouldn't count on it to give me lots
more speed.

Regarding range---I have found that for our plane at least, a LOT of
fuel savings can be had by flying at 10,500 rather than 6,500. Speed is
very nearly the same while fuel use drops to about 8.9gph, vs. 10.5 at
the lower altitude. This is not a linear relationship and drops off
above about 13,500. I will leave it to the math weenies to tell me
exactly how long I have to fly for a given leg to get a positive return
from amortizing the climb, but on really long legs I always go up high
and it always pays off.

I am no math weenie, but I read an article once than basically said that
climbing higher always pays off, no matter the distance. In other words,
level cruise was less efficient than a plan where top of climb was the same
as the beginning of the descent.

I can't prove it though, so I will leave it up for debate like you.



"Elwood Dowd" wrote in message
...
Amen brother. Range was one of the main reasons we chose our Beech
Sierra---only 135-ish knots, but 6+ hours aloft make us faster than a
Bonanza on some trips. Not all, but some. Heck, if you have a Mooney
you get higher speed AND more range (but less headroom).

To answer the original question, if I could spend $1000 to get 5 knots I
would do it, but not 1. If I could spend $5000 and be guaranteed 5
knots I would think about it. If I could spend $10,000 on a turbo that
would take me up higher when I need to climb to be safe, I would
seriously think about it, but I wouldn't count on it to give me lots
more speed.

Regarding range---I have found that for our plane at least, a LOT of
fuel savings can be had by flying at 10,500 rather than 6,500. Speed is
very nearly the same while fuel use drops to about 8.9gph, vs. 10.5 at
the lower altitude. This is not a linear relationship and drops off
above about 13,500. I will leave it to the math weenies to tell me
exactly how long I have to fly for a given leg to get a positive return
from amortizing the climb, but on really long legs I always go up high
and it always pays off.

"Dude" wrote in message
...
I am no math weenie, but I read an article once than basically said that
climbing higher always pays off, no matter the distance. In other words,
level cruise was less efficient than a plan where top of climb was the
same
as the beginning of the descent.

I can't prove it though, so I will leave it up for debate like you.

I've thought about this when paying tach time for a rental...climbing full
rpm
which isn't too far over the 1 tach hour = 1 clock hour mark but uses lots
of fuel (highish MP, but you don't get to see it on a fixed pitch machine
usually). Then you pull to idle to descend...1 tach hour = maybe 3 clock
hours. So you pay less! :-) Don't suppose it does the engine and fuel bill
much good though.

Paul

Dude wrote:

I am no math weenie, but I read an article once than basically said
that
climbing higher always pays off, no matter the distance. In other
words,
level cruise was less efficient than a plan where top of climb was the
same
as the beginning of the descent.

True for jets, not so for non-turbocharged piston aircraft.

--
Marc J. Zeitlin
http://marc.zeitlin.home.comcast.net/
http://www.cozybuilders.org/
Copyright (c) 2004

Dude wrote:

I am no math weenie, but I read an article once than basically said that
climbing higher always pays off, no matter the distance. In other words,
level cruise was less efficient than a plan where top of climb was the same
as the beginning of the descent.

Maybe that's true, as far as it goes, but I've seen many days when I can make 90
knots at 1,000' AGL and 50 knots at 6,000' AGL. You'd be a fool to climb under those
conditions.

George Patterson
If you want to know God's opinion of money, just look at the people
he gives it to.

I think that this is only true in still air. Obviously you don't want to be
climbing into a rapidly increasing headwind.

Mike
MU-2

"Dude" wrote in message
...
I am no math weenie, but I read an article once than basically said that
climbing higher always pays off, no matter the distance. In other words,
level cruise was less efficient than a plan where top of climb was the
same
as the beginning of the descent.

I can't prove it though, so I will leave it up for debate like you.



"Elwood Dowd" wrote in message
...
Amen brother. Range was one of the main reasons we chose our Beech
Sierra---only 135-ish knots, but 6+ hours aloft make us faster than a
Bonanza on some trips. Not all, but some. Heck, if you have a Mooney
you get higher speed AND more range (but less headroom).

To answer the original question, if I could spend $1000 to get 5 knots I
would do it, but not 1. If I could spend $5000 and be guaranteed 5
knots I would think about it. If I could spend $10,000 on a turbo that
would take me up higher when I need to climb to be safe, I would
seriously think about it, but I wouldn't count on it to give me lots
more speed.

Regarding range---I have found that for our plane at least, a LOT of
fuel savings can be had by flying at 10,500 rather than 6,500. Speed is
very nearly the same while fuel use drops to about 8.9gph, vs. 10.5 at
the lower altitude. This is not a linear relationship and drops off
above about 13,500. I will leave it to the math weenies to tell me
exactly how long I have to fly for a given leg to get a positive return
from amortizing the climb, but on really long legs I always go up high
and it always pays off.

wrote in message news:he7%c.3530$Va5.1196@trnddc01...
On 6-Sep-2004, (Ben Jackson) wrote:


This illustrates why having small tanks in order to obtain high "full fuel"
cabin load is such a stupid idea.

Anybody know of a mod to install a lavatory in place of the back seat in a 172?

-cwk.