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1. 10:23 AM - Re: changing props (Dear Jim why MT?) ()
2. 08:45 PM - Re: Re: changing props (Dear Jim why MT?) (LessDragProd@AOL.COM)
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| Subject: | Re: changing props (Dear Jim why MT?) |
>From: LessDragProd(at)aol.com
>Date: Dec 08, 2005
>Subject: Re: changing props (why?)
>Hi George and All,
>
>It amazes me, sometimes, on how much can be said
>just on an opinion, and a scattering of engine and
>propeller theory.
First of all Jim it is not opinion it is facts.
Second for someone who calculates the drag of one bent whip COM antenna
having 30% of the drag of the whole wing needs to be careful whom you say
that to. By the way one COM antenna is worth less then 1/2% of the aircraft
total drag at 200 mph or about 0.48 mph or 1.25 hp. You just happen to sell a
cap for a vertical stabilizer antenna? No thanks I don't want to add 1.5lb of
coax to add an antenna that only works in the pattern. I am not
criticizing you for trying to make aerodynamic calculations Jim, but
engineering is more than just getting an equation and plugging in numbers.
You have to understand what you are doing. When you came up with 3
comm. antennas equaled the drag of the WHOLE WING! You should have
known something was a miss.
Just like the prop data you have on our site. Just coming up with numbers is
not the solution; they have to be right and checked. I can tell you with out a
doubt your data is way off and not correct. Although I don't work
as an aerospace engineer anymore as an airline pilot, I can tell you my
opinion is more than "scattering of engine and propeller theory", which I
take offense to. I am not trying to sell anything. I am trying to help you.
I will be blunt; your data on your web site is incorrect and miss leading. Also
when you are told this you make wild claims or impugn the person pointing
it out to you. You seem to imply you have some understanding of
engineering and aerodynamics, which is clear you do not. I think you try but
you don't have the education to apply the math, OK.
However like your antenna drag calculations, your prop data seems
to have something to do with what you are selling? There is a pattern here.
As far as a scattering of engine and propeller theory Jimmy, I have 1000 hrs
in RV's. I have raced my old 150HP RV-6 successfully against 160 and a
few 180 hp RVs, and believe me when racing I turn my Hartzell +2700
RPM. Also in +10,000 flight hours I have at least another 2000 in props.
If you don't know what J, Ct, Cp means and what units they are calculated in,
we are at different levels of understanding. Sorry just being honest.
J= advance factor and is Airspeed / RPM * Prop diameter
Ct = coefficient of thrust = Thrust / (air-density * rpm
2 * dia
4 )
Cp= coefficient of power = Power (watts) / (air-density * rpm
3 * dia
5 )
If you know J and Cp you can find Ct, efficiency with proper theoretical data.
I have the data for the Hartzell and can confirm your results don't fit the
data or my personal experience or flt data from 3 other sources.
It amazes me your data on your web site is invalid but you keep
pointing to it with authority. No offense, your data is not correct and does
not fit the (empirical) results of others, including Van's aircraft. I know Van's
aircraft data has more validity. Sorry :-) Also your data does not match
the theoretical either. In fact like your other "calculations" the prop data
is several orders of magnitude off.
You sell MT props, so does Van and he has compared prop performance and
it is very different from your results. Van's is much more meticulous and
honest with his data than anyone in the kit plane industry.
Look let me simplify if for you. You are trying to draw a favorable
comparison of MT props, the MTV-12 and MTV-15 to a Hartzell. THAT
was the reason of your data, was it not? That's cool. You want to say your
products are great! Also the metal MTV-15 data is also not correct.
Lets just look at the MTV-12 vs. the Hartzell.
You are also a proponent of this theory or assertion that the MTV-12 prop,
although much slower at lower altitudes, any RPM's, some how by magic
gets real fast at higher altitudes. The MTV-12 gets so good in fact, it defies
the laws of aerodynamics, such as going 6 mph faster with 40 HP less power.
Your data also shows the Hartzell just stops flying at 12,500 feet. That is
absurd. Actual numbers (data from the manufacture) show the Hartzell gains
efficiency with altitude. In fact it LOVES altitude. As far as higher RPM,
going from 2500-2700 rpm results in a loss of 1 percent prop efficiency
(about 1/2% per 100 rpm).
ALL PROPS AT CRUISE SPEED ARE slightly LESS EFFICENT WITH
HIGHER RPM, INCLUDING ANY MT PROP MODEL.
However higher RPM means more engine power. In this case 200 RPMs at
12,500 ft is 5 hp more. 5 HP will give 1 to 1.5 mph faster speed, even with
the 1% efficiency loss. Again all props loose efficiency with RPM at cruise.
You will NOT slow down 6 mph like your data shows. What ever you did
you did it wrong. The data does not FIT real world predictions and known
performance. I know, I raced my RV-4 and ran at 2,700 RPM the whole
time. The F7666 loves speed and is certified to 2900 RPM!. In fact the
fastest RV, Dave Anders 250MPH RV-4 turns 2900rpm.
Now some how the MTV-12 gains SPEED with altitude? You should loose
about 10% cruise speed (TAS) with a 10,000 ft change from 2,500 to 12,500
feet, but instead you claim you went 5 mph faster, from 186 to 191
mph, a 2.5% increase. NO WAY. The above will never happen unless you
have a turbo-charger. You cannot maintain HP as you climb? Did you
measure TAS or ground speed? Again engineering data must pass a test,
a test that it is reasonable and repeatable. Your data is a little suspect.
Yes airframe drag is less and prop efficiency goes up a little with altitude
(lower air density). The down side (and a big one) is less HP. Less HP,
means less speed which reduces prop tip speed, but than the speed of sound
goes down with altitude. The prop performance is somewhat a wash. Bottom
line is you will see a steady loss of speed with altitude until you don't have
enough thrust to maintain airspeed and will stall. Engine power is key not
the prop.
>Let's try taking one single point I had hoped to
>get across from the empirical data obtained.
Look Jim let me be honest with you and not waste your time and mine, I get
that fact that reduced RPM means more miles per gallon. No kidding, this is
true for all pistons / props, but it has more to do with the airframe and
engine. In fact my one point is the prop is a very small factor. Lower RPM
means less
HP, less fuel burn and the airframe closer to its best range speed. (Sorry I am
using a scattering of engineering theory; I know you don't want to be
encumbered with facts, so substitute your reality) Prop efficiency DOES
change with air speed, rpm, and altitude, but it's effect on airspeed for a
given altitude is small. You data shows incredible (impossible) increase in
speed at 12,500 and other wide aberrations is the data. To be blunt your data
is useless and at best dubious.
A prop that is faster than another at 2,500 and 7,500 feet will not
be slower at 12,500.
Engine HP or airframe drag dominates. In your "test" you used the same
airframe and engine. How do you explain your data?
Also if you want to be gas efficient you would fly at best L/D, but no one
does that because people want to go fast. The MT is just slower. PERIOD.
Slower at all altitudes and claiming the Hartzell goes into "speed brake"
mode is just plan silly. OK, the MT is smoother. That is great but don't
mitigate the speed penalty with bogus data.
The altitude and power you choose for max ECON depends on leg length,
winds, gross weight, and temperature. Assuming winds and long leg length,
in a RV 8,000 ft is the base line (+/-500ft) is a good starting point. However
higher altitudes from 12,500 ft to 15,000 ft will provide best miles per gal
(no wind, long leg, lighter weight)? What RPM? Well in general as slow as
you can turn it with WOT, typically 2300-2400 RPM works. The downside
of high altitude is the need for supp O2.Also your average speed will be less.
There fore the getting out of town going somewhere makes 75% power at
8000ft a good base line in most piston planes (high perf, piston). Flying
higher really just reduces HP with the lower air density while allowing wide-
open throttle. However with big head winds flying 1000 ft AGL at wide
open may be the best way to go, but the above assumes, standard
atmosphere, no wind.
Jim, MT's have FAT (thick) blades and three blades on some models are one
too many for best efficiency (you know that right?). For other reasons the
wood blades and 3 -blades have advantages but speed is not one of them.
Their low mass and gyroscopic inertia is great for hard-core aerobatics, like
with a Pitts, where top speed or cruise efficiency is important. In my opinion
MT markets to the US home-built market as an after though with props they
make for other planes. To be fair Hartzells C2YK/F7666 was made for high
Perf retracts like the Mooney and Comanche. However Hartzell and
Sensenich makes props specifically for the experimental market and
specifically for RV's, like the Hartzell Blended air foil and the Sensenich
Fixed pitch prop, which also outperforms the MT. Sorry this is FACT not
opinion. Unless MT starts to make props just for the RV's they will never
make more then a small dent in the market.
On Pitts Special the MT is a great prop, where top speed is not an issue and
would not hesitate to buy one for a Pitts special. On a "fast" RV it is not as
desirable (and that is an opinion), and you are not going to convince me at
some low RPM or high altitude the MT becomes hyper-efficient beyond all
belief. In fact I estimate to make your data work the MT would be
theoretically be 99% efficient. This is a miracle. I hope it's true because I
will sell my house, cars, and plane, empty my 401K's and buy MT prop
stock. Unfortunately it is just wishful thinking.
It does not matter what conclusion you think your data shows. There is no
way the MTV-12 matches the speed of a Hartzell at 7,500' and 2500 RPM,
on the same 180HP RV-6. The data is clear from Van and others the
Hartzell's are 5-8 mph faster than the MTV-12. How do you think your data
is more valid than Van's aircraft flight test? Van sells MT props as well as
Hartzell. He has
no agenda but engineering data. I do value Van's flight test data more than
yours, I am sorry just being honest.
REF: Van's Aircraft: RVator 1st issue 2004 page 5
HC-C2YR-1BF/F7496; 208.9 MPH
HC-C2YK/F7666A-4; 205.4 mph
MT MTV12B/183-59; 200.7 mph
(WOT, 2,500 RPM, 8,000 feet, RV-8 with 180HP)
"Over the 8 runs, the AC averaged 4.4 kts faster
than the MT."
http://www.lazy8.net/proptest.htm
Even Randy Lervold verified and collaborated with Van's Aircraft. A third
source that confirms your 7,500 ft data is not correct.
LETS FORGET 2,500 feet and 7,500 RPM. Your data at 7,500 is off by 5-8
mph, compared to other data (Van's, Randy's and my data).
Here is YOUR mystery data?
You seem to think there is some magic that at low RPM or higher altitudes
the affect makes the MT oh so much better than a Hartzell. All props are
affected in similar ways by RPM and altitude. The Hartzell gets VERY
efficient with altitude and lower RPM. In fact from actual analytical models
from Hartzell the HC2YK/F7666 is seeing efficiency of about 0.83! That is
approaching about as good as you can get, BUT get this, the NEW Blended
is even better. WHY? Because it was engineered specifically for the RV's
with 180-200HP engines.
Look at your data for 2,500 feet and 12,500.
Look at the 2300-RPM data for the HC and MT.
What you see there is IMPOSSIBLE.
You show the Hartzell going 7 mph faster at 2,500 feet than the MTV-12,
but at the same 2300 RPM, at 12,500 feet, the MTV-12 is going 4 MPH
faster, for a total 11 MPH change! JIM, that is impossible. That represents a
6% change in speed difference? HOW DID THAT HAPPEN? If it where
true it would be FANTATASTIC. Sadly it is not true, wish it was, I'd buy a
MT prop tomorrow. No doubt that is the intent of your data, to sell props, but
be honest. Don't misrepresent the data.
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! WOW. I don't
give a gosh darn how great you think the MT prop is, this will never happen.
Not only that you show the Hartzell is like going in reverse. I know that is
not true and from both my flight test, which match the actual analytical data,
going form 2500rpm to 2700 rpm will produce may be 1 mph increase.
4 mph faster on 40 HP less. DOES THAT SOUND RIGHT to YOU JIM? If
it is true I will buy 20 MT props. It is so wrong it is hard to believe you did
not notice and still you post the data on your site. You are doing yourself,
MT and your customers a disservice. Ask the MT engineers if a MTV-12
will go 4 mph faster at 12,500 on 40 HP less.
AIRSPEED WILL DECREASE WITH ALTITUDE ON A RV -6 WITH A
NORMALLY ASPERATED ENGINE! Fact. Yes airframe drag does down
and prop efficiency goes up (a little), but the HP is the big factor, not the
props.
AIRSPEED WILL INCREASE WITH RPM INCREASE. In general:
more RPM = more HP = more Thrust = more speed.
Despite less efficiency with higher RPM again HP makes the plane go
(thrust). HP will in general overcome prop efficiency loss. Jim you got to
look at your data and realize it is not correct by now.
I don't know how you did it, when, where, why you went wrong, but the
results are not cutting the REASONABLE or SANITY checks.
I suggest you take the data off your web site, but that is your business. I don't
think it is doing you or MT any good creditability wise. I have pointed out
just a few discrepancies, there are many more inconsistencies. Just look at a
few of the plots. Lines never cross like this for the same prop, and the trends
between props don't flop back and forth by altitude and RPM.
http://img203.imageshack.us/my.php?image=jimspropdata2qe.jpg
*1st chart: HC-Bogus, especially 2700 rpm is bogus
*2nd chart: MT-2300 rpm some how "magic" happens
*2,500 ft: between 2500-2700 rpm "the wall" (impossible)
*7,500 ft: Vans data HC 4.7mph faster than MT at 2500rpm
*12,500 ft: HC takes a 6mph dump, from 2500-2700rpm
(Should result in about 1 mph gain not a 6 mph loss)
I have the actual data for the Hartzell HC-C2YK/F7666 produced by
Hartzell (no I don't work for them). The Hartzell LOVES 12,500 feet and
2300 RPM. IN fact the prop efficiency goes up about 3% from sea level.
Why, well because you are going slower (TAS) and thus have slower tip
speeds. Even though prop efficiency is better you are still going slower
because the engine is making less power. It does not matter as much how
efficient the prop is if the engine is making a lot less power.
So for your MTV-12 to gain and pass the Hartzell speed by a total delta
(difference) of 11 mph, also considering the Hartzell is 3% more efficient
(from actual data), means the MT is gaining getting more efficient. The
MTV-12 would have to produce a 19% gain in efficiency!!!!! Basically
110% efficiency. Did I say that is impossible yet. Well it is impossible.
Most props are lucky to be 80% efficient. The Hartzell is in the ballpark of
0.75 to 0.85 in typical range of RV-6 flight conditions. BTW the .83 is
fantastic and happens to be the Hartzells efficiency at 12,500ft and 2,500 rpm.
The Hartzell is good but the new Blended airfoil Hartzell is even better and
designed specifically for the RV series of aircraft. Efficiency is even better
Please ask MT engineering if that is possible. Props LIVE in a narrow band
or efficiency from .75% to about .85%, mostly around 0.80 +/- 2.5%, and
that is if you are lucky and have a good prop. For a prop to do what your
data says means a 19% efficiency gain. It's not possible.
I know you want to say to customers the MT props
are not slower or have some advantage high-up but
that is not correct. They may have less of a speed
disadvantage, but not an advantage. Your data has
this strange increase in at 12,500 ft for the MT
and this huge loss for the Hartzell? Makes no sense
if they props where bolted to the same airplane and
flown in the same conditions. The reason the
Hratzell wins is the thin metal blades and it's
designed for high-speed flight.
Analytically prop data is easy to compare. You can calculate efficiency for a
given J, Cp. J and Cp are functions of airspeed, air density, RPM,
prop diameter and engine power. Do you have the MT prop performance
data for Ct, Blade angle and efficiency for given J's and Cp's? I have it for
the Hartzell.
>To quote you: "Van only had to do one altitude
>(8000) and one RPM (2,500), which is
>representative of normal flight conditions."
>
>Regardless of the propeller, my data shows that
>2,500 RPM is NOT the best propeller speed to
>obtain the best performance from the aircraft.
No one said 2500 RPM it was BEST. It is just a STANDARD Jim. A
standard we all can use to compare, not a BEST of any kind.
Why 8000 feet. Well it is the typical altitude that you can fly WOT and make
75% power or less. Why is 75% a good thing? Because you can lean at 75%
pwr. Why is WOT good, because there are less pumping losses in the engine
(easier for the engine to suck air past an open throttle vs. partially closed
throttle.)
Why not higher? Leaning becomes CRITICAL and no doubt one reason
your data is off at 10,000 and 12,500 feet. Every time you make a power
(RPM) change above 8000 ft you need to re-lean for best power.
Why 2500 rpm? No reason it is just the typical high cruise RPM on would
choose. It could be 2400 rpm would be fine to. ITS A STANDARD.
For most flying, the let's get out of town base-line altitude is 7500-8500 feet,
75% power (which is about 2400 rpm on a O-360). 8000 feet is where you
get a good compromise between speed and economy. This is why we use
8000 ft, 2500 rpm, WOT, full rich or lean to best power for a BASE LINE or
Bench mark. It has nothing to do with what it best ECON.
IT is too difficult to measure 100 data points on different days and hope that
it will be accurate. WE SHOULD ALL CONSENTRATE ON THE BENCH
MARK. The best benchmark to compare performance is 8,000 feet (density
altitude), WOT at 2,500 RPM. It has nothing to do with the props BEST or
the airframes BEST or the engines BEST. From the above condition you can
draw conclusions. There is no magic change in prop efficiency with altitude
or RPM. A fast efficient prop is efficient all the time when comparing props.
If the prop was not designed properly you could have a big drop off with
RPM but that does not apply to the Hartzell's and I have the data to show it.
I know you think there is some magic for the MT prop at 12,500 feet but
that is just wishful thinking. The lack of speed (efficiency) at 2,500 or 8,000
ft will not magically disappear at 12,500 feet. Your data has miss led you.
Confer with MT engineering and show them the data. If you can get me the
MT prop data I can run the numbers for you.
>2,300 RPM was 4 mph slower. However, the aircraft
>was consuming 2 gph less fuel. What do you really
>want? 203 mph at 10 gph? Or 199 mph at 8 gph?
>To put this into perspective, after flying for 3
>hours at 199 mph, you will have flown 12 miles
>less distance with 6 gallons
>of additional fuel on board.
I agree with you 100%. I get it. Lower RPM means less fuel burn for a little
reduction in speed. It is not the prop it is the airframe drag and engine that
goes into the mix. However apples and apples Jim. Efficiency at the
"BENCH MARK" is a good indicator of all performance. That is why most
flight test pilots use 8000 feet and 2500 rpm.
>2,500 RPM is an engine thing, not an aircraft
>system thing.
Jim I have no idea what you are talking about. Prop tip speed is a one of the
critical factors in prop efficiency. Obviously RPM is a big factor in tip
speed. Prop analysis is way more complicated because the interrelated
factors.
Engine power vs. altitude vs. rpm/map is a known. The best L/D and drag
characteristic vs. airspeed is known for the airframe.
The prop efficiency is known (to engineers) thru models and flight test.
Equations or tables are provided to calculate efficiency from the following:
RPM,
ENGINE POWER,
FORWARD AIRCRAFT SPEED,
PROP DIAMETER,
AIR DENSITY
Change one of the above, changes several other things.
Since many of these are interrelated and complex. With the Hartzell data I
have, it takes me 12 interpolations of the prop data and three calculations
(engine pwr, tip speed and air density) to come up with the prop efficiency
for that one point.
I would suggest you concentrate on ONE CONDITIION (the "bench mark"
one RPM, one altitude) and may be just two props, tested early in the
morning on the same day as close to the same time as possible, or in two
consecutive days. You would have a direct comparison. From the analytical
data (MT should provide you) you can do a sanity check.
With the Hartzell data I have I can mathematically predict any condition I
want, and adjusted it to the test condition. Can you get the data for the MT?
All I need is to calculate air density, engine power, tip speeds, J and Cp. The
tables will have efficiency vs. Cp and J. (Coefficient of power and advance
factor J).
If MT will not give you that, have them predict speed vs. altitude vs. RPM.
Give der MT engineers the data for the RV-6, you know top speed at sea
level, 7,500' at 75% and 55% power from Van's specifications:
http://www.vansaircraft.com/public/rv-6per.htm
Also give them this:
http://www.cafefoundation.org/aprs/RV-6A%20Final%20APR.pdf
Last give them the % HP from sea level to 12,500 for different RPM's of a
Lycoming O-360, 180HP engine. The MT engineers can predict speed vs.
altitude vs. RPM. You will see two trends. Speed decreases with altitude;
speed should increase with RPM (due to greater HP). Your data shows
some odd reversed trends and flip-flops. Does MT apporve you data?
Get data from MT and post that and leave the Hartzell data off, it is not true.
>Best Regards,
>Jim Ayers
>PS I can hardly wait for your response. :-)
Regards George (please take that incorrect data off your site)
---------------------------------
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| Subject: | Re: changing props (Dear Jim why MT?) |
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!
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