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1. 10:50 AM - Re: Re: changing props (Dear Jim why MT?) ()
2. 09:26 PM - Re: Re: changing props (Dear Jim why MT?) (LessDragProd@aol.com)
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| Subject: | Re: changing props (Dear Jim why MT?) |
Jim:
No disrespect, but I am done. I get what you recorded is what you believe. I
know you think it's correct, and I will never convince you. Ask MT engineering
to analyze you data and see what they say. That is all I can say, but let me
try to make my point one more time, and the -59d or -59b has noting to do with
it.
It is impossible for any RV to go faster at 12,500 feet than at 2,500 feet. There
is NO prop in the world, dash-59b/d or not, that MAKES more thrust than HP
available. The only way this could be true is if you had a super charger or
turbo charge. I DON'T care what dash number you are talking about NO prop could
do this.
That is all I can say about that. If going faster on less HP makes snese to you,
read nop further.
YOUR HARTZELL DATA IS SLANDER
As far as Hartzell I can tell you your data does not match the analytical data
or the experience of may self or a handful of other pilots. This again has NOTHING
to do with -59b/d. The Hartzell data is just wrong. IF THIS HAPPENED the
the Hartzell would loose say 14% efficiency!!!!!!!!! You know if that was true,
Hartzell would have gone out of business long ago. A "2 by 4" could do better.
This is really an insult to the Hartzell and not fair. Hartzells are great
props and very efficient, basically the most efficient constant speed props
you can get for light planes. Not only do you claim the MT is faster (as well
as smoother) the Hartzell is a piece of cr%#p. If that happened I would sue them
for my money back, damages and emotional stress.
That is quite a sales pitch you got, and if true I would buy a MT. If I accepted
your data as fact. Fortunately for Hartzell and their employees their company
makes a great prop and from a pure performance, value and low maintenance
stand point, they have a great product, which takes nothing away from MT.
That is all can say but let me try to illustrate it one more time.
*It is impossible for a Hartzell to loose 6 mph with a 200 rpm increase in RPM
(at any altitude). Let me make it clear
1) A Hartzell is more efficient at 12,500 than 2,500 feet.
2) A Hartzell looses very little efficiency at higher RPM at high speed and even
gains efficiency with higher RPM at low forward speed.
3) A Lycoming HP always goes UP with RPM (if leaned properly)**
**At sea level (5 HP / 100 rpm), at 12,500 (2.5 HP / 100 RPM)
From experience and analytical data a gain of engine power of 5 HP (minus about
.25 HP for loss in prop efficiency) for a net gain of 4.75 HP will increase
speed about 1 MPH. There is no argument about this in my mind, your data is
wrong.
Why did you get the results you did?
May be you did not re-lean after every RPM change?
May be you just messed up the calculations or made a recording error?
Did you install spinners on every prop?
What was the weather, vertical gust, turbulence?
For the Hartzell to be given 5 more HP and loose enough thrust to slow the airspeed
but 6 MPH is more than unlikely. IF ANY prop performs like this, than it
is not suited for that airframe. This might happen if the aircraft is going
say REAL FAST say MACH 0.60, but at for little planes with TAS less than 250MPH
this is not an issue. Remember the faster you go (airplane speed) the faster
the PROP-TIP MACH number. Thinner blades have advantage at higher tip speeds.
LOOK AT A JET. The wing is thin for a reason. Slow aircraft have fat wings.
ITS YOUR BUISNESS BUT........................
If you want to tell your customer's that their MT prop gains MORE speed at 12,500
feet fine. If you want to tell them MT prop will be the same speed or faster
than a Hartzell at 7,500 feet and above, go a head, it is not true but go
ahead. If the -59b/d has wood core blades and three of them, right off the bat
it is at a disadvantage over ANY thin metal blades and props with 2 blades vs.
3. Those are hard facts.
Even the -59b/d can not make it's own HP. Going faster on less HP is a great
trick I wish was true.
All I have to say is "do you want to race". I am not quite flying my current
project but I will call you when I am ready. Basically if you have faith in your
data, prove it. Challenge some 180HP, RV's with Hartzells. Enter some races
like the sun-n-fun or air-venture or copper-state dash. I know what the results
will be.
I guess we agree to disagree.
The old Hartzell, even though designed 30 plus years ago, was made to be efficient
at 190-210 MPH, with a 180-250 HP engine and from 0-20,000 feet; in other
words well suited for RV's. The blended tweaks this just a little more and
is about 1.5% more efficient. That is reaching the limit of prop efficiency. EVEN
the Sensenich is faster than the MT at 8,000 feet, 2500 RPM. Props just can't
get more efficient than say 0.85. It is just the laws of physics. Most props
are close in efficiency, but to claim huge changes in efficiency over the operating
envelope is ridiculous. A MT prop way slower at 2,500feet will not BECOME
way efficient, nor will the Hartzell BECOME way inefficient with small changes
in RPM and altitude. SMALL changes are 200 rpms, 10,000 feet and 40HP.
With that said the MT will be smoother and that counts for something. The MT
on the other hand is made for either slower speeds or higher HP (with the much
greater blade area). If you can get the DATA form MT I can calculate efficiency
for any speed, hp, altitude, RPM or airspeed. That way we can compare apples
to analytical apples. The nice part of Hartzell is you can call engineering
and speak English with them. Can you call MT engineering and ask for DATA?
Again Jim show the data you have for the MT-12 and ask MT engineering if it is
possible, knowing the performance of the engine and airframe. IF YOU DON'T BELIEVE
ME FINE, BUT ASK SOME REAL EXPERTS, LIKE MT AND SEE WHAT THEY SAY. If they
say no it is not right, what are you going to do? Do you want to PROVE you
data or are you happy to let it stand, despite my protest?
Not that MT engineers can not design a fast prop but they are restricted by the
materials they are using, wood. A modern composite props use SOLID laminates
and dense man made resin cores. The good part is the blade can be thinner. The
bad part the props are stiffer and have less ability to dampen vibration like
wood, so they feel more like metal props than a wood based prop.
RETEST AND HAVE OTHERS VERIFY IT:
Bottom line is MT props are wonderful, well engineered and made props, but speed
is not the reason to by one. I know you recognize speed is a major issue with
selling MT props to experimental pilots. Try as you may and want to trust
your results and want to make it LESS of an issue, your conclusions are based
on incorrect data.
Get better data and re-test the Hartzell and the MTV-12 dash any-one-you-want.
Do just 3 altitudes, 3 RPMs on the same airframe. Make sure you use the 3 -leg
constant track method (and reduce the data with a spread sheet to give airspeed
which is ground speed with wind component removed). Lean with every RPM change.
Test early in the morning and try to do a quick prop change to the 2nd prop and
test within say an hour. Fly the next morning with the 2nd prop again to validate
the test and change back to the 1st prop, test the first prop again, which
I assume will be the one the owner will keep on.
The other idea is to find two matched RV's, HP, weight, fit and finish and the
same in every detail except one, the props. One with MT and one with a Hartzell
(new or old).
Van just flew the proto type RV-10 with a Hartzell next to a new RV-10 with a
MT and a hot rod engine. The Hartzell was faster even though the customers RV
was set to a higher MAP and higher FF. With some assumptions of what power the
high compression engine was making makes the Hartzell 8-12 MPH faster!!!!!!!!!!!!!
I keep seeing 8 MPH come up when a two RV's, one with a MT the other with a RV,
fly next to each other. How can every one but you be wrong?
LAST WORDS:
I appreciate your enthusiasm and effort to use analytical and flight test methods
to prove your point, but the results have to be valid. Any one looking at
this data who knows anything about light piston plane performance will question
your data and it does you no good. If you where an individual I would not
care, but since you sell the product you are representing you should be held to
a higher standard. One flight test will not do it. You need to retest and also
may as well get a Hartzell Blended airfoil and Sensenich to test while you
are at it.
Best of luck, when I am ready for a MT prop on my future Pitts I want to buy,
I'll buy a MT from you. Smoothness does count Jim, don't get me wrong that is
a real selling point.
Cheers
George
LessDragProd@aol.com wrote:
Good Evening George,
I copied out the section at the bottom of this page for your reference.
I show the MTV-12-B/183-59d propeller at 2300 RPM & 25" MP at 2,500' going 186
mph tias.
I show the MTV-12-B/183-59d propeller at 2300 RPM & 18.9" MP at 12,500' going
191 mpg tias.
Please check your calculations with this more complete data provide for your
benefit.
The MTV-12-B/183-59d propeller is an improved model of the MTV-12-B/183-59 propeller.
The MTV-12-B/183-59b propeller is a farther improvement over the MTV-12-B/183-59d.
I don't believe Van's (or anyone else at that time) had the MTV-12-B/183-59d
propeller available to test.
Regards,
Jim Ayers
In a message dated 12/12/2005 10:29:23 AM Pacific Standard Time, gmcjetpilot@yahoo.com
writes:
SWEET SPOT? You show the MTV-12 at 2300 RPM at 2500 going 186
mph, but at 12,500 you are going 191mph????? Impossible! Why? You have
156HP @ 2300 RPM at 2,500 ft. At 12,500 ft the best you could do is
115HP (@ 2300 RPM). 6 MPH faster on 40HP less power!
---------------------------------
Message 2
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| Subject: | Re: changing props (Dear Jim why MT?) |
In a message dated 12/13/2005 10:52:43 AM Pacific Standard Time,
gmcjetpilot@yahoo.com writes:
Why did you get the results you did?
May be you did not re-lean after every RPM change?
May be you just messed up the calculations or made a recording error?
Did you install spinners on every prop?
What was the weather, vertical gust, turbulence?
Dear George,
Why are you now asking questions? By your attitude, I could have no
credible answers for any of your questions.
You have claiming repeatedly that my data is wrong and I should remove it
from my website.
Until now, you didn't seem to care in the least what I did to establish a
repeatable test program.
Maybe we need to establish some ground rules.
Payments due from discussions are not made by purchasing MT Propellers.
They are paid in Strawberry shakes at Sun'N'Fun.
A perspective:
Empirical data is always subject to measurement errors.
Engineering theory is based on empirical data.
(An opportunity for continual learning by reducing error in obtaining
empirical data and improving theory.)
I spent yesterday working with two different friends on their aircraft, and
working on my RV-6A.
I spent today working on my RV-6A.
I have 6 different propellers that need to have test data gathered, and I
need to get my RV-6A completed to do this.
You can expect much more empirical data on my website in the near future.
You have spent an inordinate amount of time bashing my company. Quite
frankly, as a lobbyist, you have failed.
Regards,
Jim Ayers
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