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Background & Objectives |
When planning my RV-8 I knew right from the
start that I wanted a constant speed prop. Any aircraft with the speed
envelope of an RV (50-230 mph) would be operating under a considerable
compromise with a fixed pitch prop. Therefore I planned on installing the
Hartzell compact hub constant speed prop that Van's offers it's builders
right from the outset. My Hartzell has performed admirably and I really have
no complaint with it, but... if you have an experimental aircraft that
you've built yourself you know about that little voice in your head that
keeps talking to you. "Gee, if I just made this change I could (substitute
any of the following here: make it go faster, make it more efficient, make
it more functional, make it look better, etc. ad nauseum)". That little
voice has been talking to me about propellers. My engine/prop combination is
probably the single most common RV power train there is, and I'm sure there
will be many builders interested in what can be achieved with a prop switch,
hence this section of the site.
My interest in upgrading my prop began by reading an article in the December 2000 issue
of Custom Planes Magazine by Larry Olson titled "Constant-Speed Pitch
Distribution". In this very interesting article Mr. Olson explains that even
though a constant speed propeller changes its pitch to suit the condition,
there is more that must be considered in assessing efficiency. Although the
whole blade does indeed change pitch, the twist of the prop at any
point on it's blade can only be optimized for one airspeed and rpm.
Therefore inefficiencies are introduced under any other condition. To be
sure, a constant speed prop is a quantum leap in efficiency over a fixed
pitch model, but this twist profile (aka pitch distribution) concept made
sense and got me curious. After a bit more reading I learned that the
Hartzell HC-C2YK-1BF that Van's sells for the O-360 family, and that I have
on my plane, is optimized for airframe speeds slower that the typical RV
cruises at and therefore the whole blade is not providing optimum thrust at
all stations under that condition. Hmm.
Also, while I have the standard 8.5-1 pistons
in my O-360, I do have electronic ignition, Unison's LASAR system
specifically. Hartzell's recent position on higher compression ratios and
electronic ignition systems pointed out that with either higher compression
or electronic ignition systems there would be a greater power pulse being
generated that introduces additional resonance modes. In addition to
observing the NO CONTINUOUS OPERATION FROM 2,000-2,250 RPM restriction, they
explained that there was another vibration zone at or above 2,600 and that
time spent in that range should be minimized while at high power settings if
you have either high compression pistons or electronic ignition. Following is Hartzell's "position letter" on
this issue obtained from Brad Huelsman at Hartzell Propeller in Ohio:
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The Hartzell propeller
Model HC-C2YK-1BF/F7666A-2 has been vibrationally approved per FAR23.907 on
the standard production Lycoming Engine Model O-360-A1A, and similar
models, rated at 180 H at 2700 RPM with a restriction to avoid continuous
operation between 2000 and 2250 RPM. The propeller vibration
characteristics and stress amplitudes on a reciprocating engine installation
are primarily mechanically generated by the engine. Any modification
to the standard engine configuration to include high compression pistons,
electronic ignition, FADEC, tuned induction and exhaust, and turbocharging
or turbonormalizing have the potential to adversely effect the propeller
vibration characteristics and stress amplitudes. Hartzell Propeller,
therefore, does not endorse any such engine modification unless the specific
engine and propeller configurations have been tested and found to be
acceptable vibrationwise.
The Lightspeed
electronic ignition is not certified for use on any aircraft engines so its
use is limited to the experimental/amateur built market. Hartzell recently
conducted a test with the propeller model HC-C2YK-1BF/F7666A-2 installed on
a standard Lycoming O-360-A1A engine, except for a modification to equip it
with the Lightspeed ignition in place of one magneto. The results of
this test show an increase in the propeller vibratory stress amplitudes
within the 2000-2250 RPM range currently covered by the operating
restriction noted in the first paragraph, and additionally above 2600 RPM
with high power settings. Based on this data, continued safe use of
this propeller on O-360-A1A and similar engines equipped with Lightspeed
electronic ignition would require the following:
1. Continuation of the
current restriction to avoid continuous operation between
2000 and 2250 RPM.
2. An additional
restriction to limit operations above 2600 RPM to takeoff. As soon as
practical after takeoff the RPM should be reduced to 2600 or below.
3. The propeller blades
are life limited (with electronic ignition or higher compression) to 20,000
hours of operation.
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Well, there are just some times when I want
to go fast, and to do that it's balls-to-the-wall which means continuous
operation at 2,700 rpm. While I will of course observe Hartzell's
recommendation of this extra restriction, coping with this
vibration/resonance problem can be added to my quest for an optimized pitch
profile. Now as long as I'm motivated to deal with these issues, which means
looking at alternative propellers, wouldn't it be nice to shed some weight
as well? And so began my quest for prop alternatives. Before beginning
however, lest I get distracted, I thought it would be a good idea to
establish some clear objectives to be achieved with a possible prop swap...
- Increase performance:
If pitch profile is optimized for the RV speed range, and with the latest
thinking in blade aerodynamics, I would expect the following performance
increases:
- Increase of at least 5-10 mph at 75%
cruise or above.
- Increase of ~200 fpm climb at 130 mph
below 8,000 ft.
- Reduction of noise and perception of
"smoother operation".
- Eliminate vibration concerns -
Since composite materials tend to absorb vibration by their nature then
virtually any composite prop should eliminate the resonance issue
experienced with the Hartzell. While I don't have much need to spend time in the 2,000-2,250
range, I am more concerned about the newer advice against high power high
prop rpm operation. The simple fact of the matter is that our engines put
out more horsepower at 2,700 and when you want to get to your 10,500
cruise altitude at gross weight you want to keep it spinning to get there
as quickly as possible. I don't want to have to pull the prop speed back,
and thus the power produced, for fear of shortening my prop's life.
- Lower weight - Every RV builder
wants the lightest plane possible to enhance it's flying qualities and
maximize its carrying capacity. Most of the composite prop options would
allow me to lower the empty weight of my plane by 10-30 lbs. This
reduction would also shift the CG aft a bit which in my case would be just
fine, I'm still forward of the aft CG limit with a 240 lb. pax and 40 lbs.
of baggage in the aft baggage compartment. RV-8s are nose heavy when flown
solo to the point that many examples cannot be trimmed to approach speed
when solo. A lighter prop would go a long way toward providing better
balance here.
Now that I'd established my objectives the
search began. With these objectives the first decision I could make was to
go with a composite prop instead of an aluminum alternative. After all, the
vibration and resonance issues raised by Hartzell are largely due to the
natural properties of aluminum which can resonate somewhat like a tuning
fork. Any composite prop would be inherently more damp and therefore less
susceptible to sympathetic resonances.
Initial research into the composite prop
options indicated that at this time (fall 2002) there
were four alternatives. They are from MT Propeller, Aero Composites, and Whirl Wind Propellers. Below is an overview of the three options. For
comparison, the Hartzell is 55 lbs plus the Van's spinner assembly which
adds another 4 lbs. Therefore all three options would be lighter than
the Hartzell's system weight of 59 lbs. Since then Whirl Wind has developed
another significant option, a prop designed specifically for RVs, the model
200RV. Click here to see a
comparison table.
The first decision was to go with a two or three blade design. In doing my
research I learned that there are
inherent advantages and disadvantages to each. As part of my investigative
process I exchanged e-mails and had phone conversations with each
manufacturer. While at AirVenture 2002 I visited with the Aero Composites
and MT Propeller folks at their booths, Whirl Wind did not display.
I was initially attracted to a 2-blade design
for the simple intuitive reason that there is less blade area and therefore
less drag. We have all heard that 3-blade props improve climb, it's a
popular retrofit for Cessnas and Bonanzas, but since I was more interested
in improved cruise speeds and not necessarily improved climb (RVs climb
pretty darned well already!), this became my initial direction. As I learned
more and more from various sources however it turns out there's a very small
difference in efficiency with the 3rd blade, something on the order of .5%
loss due to the increased area. There are also offsetting factors in favor
of a 3-blade design. When I distill down what I've gleaned I get the
following summary.
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2-blade props: |
Feature |
Result/benefit |
Less wetted surface |
- Less drag, improved cruise & top speed,
especially with slippery airframes where it would be a higher portion
of total drag
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Fewer blades |
- Less weight (in theory, not
necessarily in practice)
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3-blade props: |
Feature |
Benefit |
More blade area |
- Better dissipation of engine vibration
- More area to transfer power to the
air: faster acceleration, improved climb
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Less horsepower per blade |
- Lower amplitude pulses, less vibration
|
Frequency of pulse passes
increased |
- Frequency of noise shifted up (at
2,700 rpm 2-blade = 5,400 passes, 3-blade 8,100 passes): less
perceived noise in cockpit.
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Admittedly this is a fairly simplistic
lay summary of some fairly sophisticated engineering and aerodynamic principals,
nevertheless this is how it sorts out from my point of view. Deciding on a
prop however is not as simple as just looking at the features and benefits,
there are a lot of other important considerations such as the reputation and
support of the manufacturer, weight, and cost. Every manufacturer uses
different techniques which can alter the fundamental balance of
characteristics. For example you can see from the table that the Whirl Wind
150
is the lightest prop of the group yet it is also a 3-blade design. The Hartzell is a 2-blade with less drag than a 3-blade, yet it will likely not
be the fastest on an RV because of the pitch profile. So, many factors must
be looked at simultaneously in selecting the right option for your
application.
Assessing the manufacturer is an important
consideration as well. As important as a prop is, I want the manufacturer to
be credible and to be there down the road should my prop need service or
parts. From this standpoint clearly MT comes out on top with a long
history of high-performance props and certified designs. Clearly their track
record is best, they have the most complete testing (required for
certification), and an established network of service centers. Whirl Wind and
Aero Composites are newer companies but with significant technical expertise
in each case. I believe Whirl Wind has been around a few years longer and does
have more props in the field. I was impressed with the fact that the 150
design has been in "test period" for a full two years before being released
for full production just a two months ago. They sent eight props out for installation on
various aircraft, including several RVs, and had the pilots return the props
periodically for inspection. The 150 was put into production and offered for
sale only after this period was completed. They report there were
a few relatively minor changes (none
to the blade or hub) made to the design as a
result of the test period data.
In
doing my research I learned some interesting things from all the vendors,
but especially from Whirl Wind: Whirl Wind blades are dynamically balanced, not just
matched by blade weight. The reason for this is that the moment of
any imbalance is more important than the outright amount. Once the blades
are dynamically balanced the prop is assembled, then statically balanced.
Builders should still have their props dynamically balanced in the
traditional method, but the measures taken by Whirl Wind ensure that the
prop won't contribute to any imbalance, rather it will be in the engine
assembly.
So,
which one to choose? All three of these props have pitch profiles
suitable for the RV so that's not a point of differentiation, and each manufacturer has
certain characteristics that are appealing. In the end though it was the
light weight, the fully finished spinner assembly, reasonable lead time,
apparent quality of both the design and construction, positive reports from
their beta pilots, the candor of Jim and Patti Rust
(proprietors), and the overall value that caused me to pick Whirl Wind.
With my initial decision made and my order in
it was time to collect some baseline performance data and think about
testing methodology. Testing is important because if I can't make an
accurate comparison of any performance differences then I'll never know if
switching props was worth it.
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Installation & testing |
In speaking with other builders, but especially
with the prop vendors, I learned that there is a real lack of real world empirical
propeller test data. Without good data how can one make an objective decision? The
answer is that you can't, therefore I resolved to do the best job of testing
I could, not only for myself but for others in the RV community as well. Props are an important element in the performance of our
aircraft and the more we know about how these various props work with our
airframes the better decisions can be made. Therefore the extra time and
effort here should pay dividends for me, and also the rest of you making
decisions on propellers. 12/29/02 saw a break in the weather here in
the Northwest so out we went to collect the "before" data on the
Hartzell. I chose to do the
testing near gross weight because A) it would allow me to take a passenger
to assist with data collection, and B) most performance figures are shown at
gross weight in order to be conservative and show worst case. Frequent backseater Randy Griffin was drafted for the task and we planned for the
test to be close to my plane's 1,800 lbs gross weight. Fuel was noted for
each test and gross weight at that time computed. Contents of aircraft
(people, equipment) were weighed post-flight to verify weights. In all I
think this is fairly sound data. |
Test equipment:
Prop Tach 3 optical tachometer, guaranteed to be accurate within 1 rpm.
Radio Shack Sound Level Meter with several scales as well as A and
C weighting.
Heuer analog stopwatch.
Tanner Racing digital race car scales guaranteed accurate to within 1
lb.
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Scope creep
As with many projects, the scope of this one has crept. Instead of simply
installing and testing the Whirl Wind 150 against the Hartzell, I have
entered into an agreement with Whirl Wind to expand the scope of the test to
include a two-blade model as well — a non-counterweighted version of their
model 200C would also be included in the test. Other new models under
development could be included as well, which turned out to be the case with
their new 200RV.
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Installation & testing of Whirl Wind 150 Series
I have a Woodward Model B210776-A prop governor as purchased from Van's.
Whirl Wind recommends that Woodward or McCauley governors have their
pressure relief value reset to 475 lbs due to the smaller piston in the prop
hub. This is done to avoid overspeeding under high-temp conditions.
Apparently under high speed and high power settings with the oil very hot it
can thin out to such an extent that adequate oil pressure to move the blades
to the coarse pitch needed cannot be maintained. Consequently I removed my
governor when I removed the prop and sent it to Sullivan Propeller in
Hayward, CA which was the shop Jim Rust recommended. In talking to Brian
Sullivan I learned that the Woodward governors can be reset where the
McCauley's cannot. Be so advised if you plan to make this type of swap.
Hanging the prop was made quite a bit easier by
the light weight. Picking up this prop compared the Hartzell is truly a
shock. The spinner parts including the backing plates and fill plates behind
the blade roots, are very high quality pieces. The precision of both these
fiberglass parts and the the hub assembly is truly impressive. There is a
front bulkhead in the spinner that engages the front flange on the hub --
this can only work with very precise manufacturing.



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One bit of advice for those who remove their
props: I noticed quite a buildup of film in the crank center, visible with
the prop removed. My guess is that it was either lead or carbon that had
deposited itself on the inner walls of the hollow crank from centrifugal
force during operation. My engine/prop only had 287.5 hours on it, I can
only imagine what that would look like at 500 hours or more. The moral to
the story is to always inspect that area, and clean as necessary, if you
ever remove a prop. |
Installation & testing of Whirl Wind 200C
For background on the performance of the 200C, there was an article comparing the 200C to
several other aerobatic props run in the June 2001 issue of Sport Aerobatics
magazine that you might find interesting. Download it (Word doc) by right
clicking here.
The 200C was
installed on 3/16/03. On 3/24/03 the weather broke and we were able to
launch our prop testing mission. The testing went well and we feel like we
have solid comparison data depicted in the tables below.
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Installation & testing of Whirl Wind 200RV
The
200RV is Whirl Wind's brand new 2-blade prop, this time
designed specifically for the RV series airframe, and I have been asked to test it.
The new 200RV uses a McCauley 215 hub which is smaller and lighter than
the 200 hub used in the 200C. It also features an all new airfoil designed
specifically for the RV series airframe that they are calling Opti-Q. WW engineer/design Jim Rust
consulted with two outside aerodynamicists on this model and it incorporates
some new thinking in the airfoil. Note the very small chord at the tip as
compared to both a Hartzell and WW's previous designs. There will be more
complete info on this prop on the WW web site as they get closer to making
it available, but the price has been established at $7,500
with their usual fully completed spinner. The spinner is the same shape as
that on the 150 and is a splash of the Van's design. This prop is 6 lbs lighter than the 200C
and 18 lbs lighter than the Hartzell. While the plane was out of service for
the prop change I also changed batteries from a Concorde RG-25XC to an
Odyssey PC680 resulting in another 8 lb reduction for a total of 14 lbs. I
noticed this during my very first landing, much of that nose heaviness
characteristic of the RV-8 when solo was reduced. Test data is in the tables
below. |
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Test results |
Testing was performed for five parameters:
weight, climb performance, max. cruise, top speed, and noise. Test
methodology is detailed in each section.
WEIGHT
Test: weigh each propeller assembly complete with spinner using
digital race car scale.
Notes: this might seem an obvious test, but I wanted to verify the
exact difference in weight and not rely on manufacturer's claims.
Reductions are all relative to Hartzell baseline.
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Manufacturer's claim |
Actual weight |
Note |
Hartzell |
55 lbs
for prop alone |
59 lbs
prop & spinner |
|
WW 150 |
29 lbs
prop & spinner |
31 lbs
prop & spinner |
28
lb reduction relative to Hartzell |
WW 200C |
47 lbs
prop & spinner |
47 lbs
prop & spinner |
12
lb reduction relative to Hartzell |
WW 200RV |
41 lbs
prop & spinner |
41 lbs
prop & spinner |
18
lb reduction relative to Hartzell |
Since
weight is an important parameter I wanted to get accurate data here too. I
calibrated the scales twice and also measured other known weight items and
it all crosschecked accurately. Stainless steel spinner screws weigh
nearly a pound (laying under the prop in the pic) so if you ever weight a
prop don't forget them. See the Interpretation and Conclusion comments at
the end for comments on the impact of the weight and CG change.
CLIMB
Test: time climb 2,000' to 5,000'
Conditions: W.O.T., full rich mixture, 2,700 rpm, maintain 120 mph (Vy)
Notes: RPM measured with optical prop tach, time measured with
stopwatch, ROC then computed from time data. This is the most difficult
test to fly correctly which is why I thought more runs would yield a more
reliable result. In retrospect I wish I had taken more runs with both the
Hartzell and the WW 150.
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Time |
rpm |
OAT |
Avg.ROC |
Weight |
Note |
Hartzell |
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|
|
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|
Run 1 |
1:48 |
2,695 |
39° |
1,666 fpm |
1,716 lbs |
Max rpm allowed by governor |
Run 2 |
1:49 |
2,695 |
40° |
1,651 fpm |
1,692 lbs |
Max rpm allowed by governor |
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|
Average: |
1,659 fpm |
1,704 lbs |
|
WW 150 |
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|
|
|
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|
Run 1 |
1:50 |
2,705 |
36°/35° |
1,636 fpm |
1,667 lbs |
Tests run 2/8/2003 |
Run 2 |
1:44 |
2,700 |
40°/35° |
1,730 fpm |
1,640 lbs |
|
Run 3 |
1:48 |
2,700 |
39°/35° |
1,666 fpm |
1,637 lbs |
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|
|
|
Average: |
1,677 fpm |
1,648 lbs |
Note lighter avg. test weight |
WW 200C |
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|
|
|
|
|
Run 1 |
1:51 |
2,700 |
40°/32° |
1,621 fpm |
1,672 lbs |
Tests run 3/24/2003 |
Run 2 |
1:53 |
2,700 |
40°/33° |
1,592 fpm |
1,666 lbs |
|
Run 3 |
1:47 |
2,700 |
43°/32° |
1,682 fpm |
1,660 lbs |
|
Run 4 |
1:43 |
2,700 |
43°/32° |
1,747 fpm |
1,634 lbs |
|
|
|
|
Average: |
1,661 fpm |
1,658 lbs |
|
WW 200RV |
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|
|
|
|
|
Run 1 |
1:47 |
2,700 |
39°/27° |
1,682 fpm |
1,697 lbs |
Tests run 12/06/03 |
Run 2 |
1:43 |
2,700 |
39°/28° |
1,747 fpm |
1,689 lbs |
|
Run 3 |
1:36 |
2,700 |
40°/28° |
1,875 fpm |
1,683 lbs |
|
|
|
|
Average: |
1,768 fpm |
1,690 lbs |
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This is the most difficult test to fly
correctly, airspeed control is critical to the result and difficult to do.
This is why I thought more runs would yield a more reliable
result. In retrospect I wish I had taken more runs with both the Hartzell
and the WW 150.
TOP SPEED
Test: note IAS and TAS
Conditions: W.O.T., 1,000' msl
Notes: RPM measured with optical prop tach. Results consistent with
previous top speed measurement of 217 mph TAS taken on 65° day -- lower OAT
will yield higher power.
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|
IAS |
TAS |
rpm |
OAT |
Weight |
Note |
Hartzell |
Run 1 |
219 mph |
219 mph |
2,698 |
39° |
1,698 lbs |
Max rpm allowed by governor |
Run 2 |
220 mph |
220 mph |
2,696 |
40° |
1,674 lbs |
Max rpm allowed by governor |
WW 150 |
Run 1 |
215 mph |
215 mph |
2,705 |
41° |
1,625 lbs |
|
Run 2 |
215 mph |
215 mph |
2,702 |
41° |
1,622 lbs |
Note lighter test weight |
WW 200C |
Run 1 |
219 mph |
219 mph |
2,700 |
40° |
1,701 lbs |
|
Run 2 |
219 mph |
219 mph |
2,700 |
42° |
1,676 lbs |
|
Run 3 |
219 mph |
219 mph |
2,700 |
44° |
1,636 lbs |
|
WW 200RV |
Run 1 |
220 mph |
221 mph |
2,700 |
42° |
1,665 lbs |
Local airport humidity 82% |
Run 2 |
220 mph |
221 mph |
2,700 |
44° |
1,658 lbs |
|
CRUISE
Test: note IAS and TAS
Conditions: W.O.T., 2,500 rpm, 8,000' msl pressure altitude, leaned to 50° rich of peak
Notes: RPM measured with optical prop tach. M.P. measured with ship's
gauge (Van's Aircraft), OAT measured with ship's OAT gauge (previously
verified accurate).
|
|
IAS |
TAS |
rpm |
M.P. |
OAT |
Weight |
Note |
Hartzell |
Run 1 |
186 mph |
206 mph |
2,500 |
22.5" |
15° |
1,698 lbs |
|
Run 2 |
187 mph |
207 mph |
2,500 |
23.0" |
16° |
1,660 lbs |
|
WW 150 |
Run 1 |
181 mph |
203 mph |
2,500 |
22.75" |
26° |
1,685 lbs |
|
Run 2 |
181 mph |
203 mph |
2,500 |
23" |
27° |
1,628 lbs |
Note lighter test weight |
WW 200C |
Run 1 |
184 mph |
205 mph |
2,500 |
22.75" |
24° |
1,687 lbs |
|
Run 2 |
187 mph |
208 mph |
2,500 |
22.75" |
25° |
1,651 lbs |
|
Run 3 |
186 mph |
207 mph |
2,500 |
22.75" |
24° |
1,642 lbs |
|
WW 200RV |
Run 1 |
187 mph |
208 mph |
2,500 |
22.5" |
18° |
1,711 lbs |
|
Run 2 |
187 mph |
208 mph |
2,500 |
22.5" |
16° |
1,681 lbs |
|
Run 3 |
187 mph |
208 mph |
2,500 |
22.5" |
19° |
1,670 lbs |
|
NOISE
Test: note sound pressure level meter reading at head level position
in cockpit at various prop speeds
Conditions: 20.0" manifold pressure cruise setting
Notes: The Hartzell has always exhibited a "droning" at certain rpm.
I was curious to note whether this was measurable or not -- as you can see
from the data it is. Takeoff SPL with the Hartzell was measured twice at 114 db.
|
|
SPL
C-weighted |
M.P. |
Note |
Hartzell |
|
|
|
2300 rpm |
112 db |
20.0" |
Acoustic resonance at 2300 rpm |
2400 rpm |
110 db |
20.0" |
|
2500 rpm |
108 db |
20.0" |
|
2600 rpm |
108 db |
20.0" |
|
WW 150 |
|
|
|
2300 rpm |
107 db |
20.0" |
5 db quieter! |
2400 rpm |
107 db |
20.0" |
Absence of acoustic resonance. |
2500 rpm |
107 db |
20.0" |
|
2600 rpm |
106 db |
20.0" |
|
WW 200C |
|
|
|
2300 rpm |
107 db |
20.0" |
|
2400 rpm |
110 db |
20.0" |
Acoustic resonance between 2400 & 2500
rpm |
2500 rpm |
110 db |
20.0" |
|
2600 rpm |
107 db |
20.0" |
|
WW 200RV |
|
|
|
2300 rpm |
106 db |
20.0" |
|
2400 rpm |
106 db |
20.0" |
|
2500 rpm |
108 db |
20.0" |
Resonance is not noticeable without
meter |
2600 rpm |
106 db |
20.0" |
|
About
A and C weighting: Since the
ear is not equally sensitive to all frequencies we need to take this into
account when we measure sound. This is usually done with "weighting" curves
by giving less weight to the frequencies to which the ear is less sensitive.
Several different weighting networks have been developed over the
years. The one which has been found to best describe human hearing is the
A-weighting network. This reduces the low frequency response and some of
the high frequencies as shown in the diagram.
Another weighting curve, more useful in
estimating the attenuated noise when personal hearing protectors are used,
is the C-weighting network. Note that the C-weighted curve is a more
accurate representation of actual sound pressures and hence it a better
predictor of hearing damage. Personally, I would always look for a
C-weighted measurement when evaluating headphones or anything related to the
audio system in your aircraft since that the actual energy your hearing
organs are physically subjected to.
|
|
Interpretation & conclusion |
Results ranking:
|
Hartzell |
WW 150 |
WW 200C |
WW 200RV |
Top speed |
2 (tie) |
2 |
2 (tie) |
1 |
Climb |
2 (tie) |
2 (tie) |
2 (tie) |
1 |
Cruise |
2 (tie) |
3 |
2 (tie) |
1 |
Weight |
4 |
1 |
3 |
2 |
Noise |
4 |
2 |
3 |
1 |
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Hartzell HC-C2YK-1BF:
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- Heavy, and due to it's weight yields a
very fwd biased CG in the RV-8 application. This can be mitigated
partially by locating the battery in the aft baggage compartment but this
is a compromise due to reduced accessibility and the longer/heavier cables
required.
- Performs remarkably well given it's pitch
profile which is designed for slower aircraft
- Not well suited for non-counterweighted
crank O-360s due to vibration and resonance issues, especially if
electronic ignition or high-compression pistons are used.
- Spinner assembly from Van's must be fitted
and installed.
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Whirl Wind 150: |
- Significantly lighter, 28 lb net weight
reduction. This yields virtually the ideal CG location for the RV-8. With
the heavier Hartzell when flying solo I could only trim down to about 90
mph when on approach and then had to hold back pressure on the stick to
get approach speeds below that. With the 150 I could trim right down to 75
mph and still have one turn left on my trim knob. My spreadsheet shows
that I can still put a 240 lbs pax in back plus 40 lbs in the aft baggage
compartment and not exceed the aft CG. Lastly, and this is subjective, the
plane feels more responsive in trim (not that it needs to), probably due
to the mass reduction up front.
- Significantly quieter, 2,300 rpm resonance
is completely gone. I wouldn't necessarily say it is any smoother, both
props are smooth, but definitely quieter.
- Spinner assembly comes fully finished,
just needs paint.
- This prop needs a high pressure governor.
I recommend you only use this prop with the the Jihostroj (Czech)
governor. I've seen one in person and it appears to be a very nicely built
item. The simple fact of the matter is that due to it's smaller hub piston
the 150 needs the higher pressure to operate reliably. There is no
apparent downside to operating with higher pressures.
- The 150 is essentially a match with the Hartzell in
climb. The data suggests the 150 may be slightly better but the test
weight was also 56 lbs less, therefore calling it a tie seems reasonable.
- The 150 is 3.5 mph slower in cruise
- The 150 is 4.5 mph slower at top speed
- In all, the 150 is an excellent choice for
many builders, especially where light weight and quiet operation are
priorities. The small performance differences will not be measurable or
noticeable to many (most?) RV pilots. The weight reduction, and resulting
improvement in CG and increase in useful load, is significant and
should not be overlooked for the small speed differences. Is the 150 right
prop for me given my objectives? I won't know until I test the 200C, but I
sure like the way it feels on the plane!
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Whirl Wind 200C: |
-
12 lbs lighter than the Hartzell. This
difference was not as noticeable as the 28 lb reduction with the WW 150, but
is there nevertheless to decrease the empty weight and increase
the usable load of the aircraft.
-
When flying solo approaches I was only able to
trim down to 86 mph with the 200C which is slightly better than the Hartzell
at just over 90, but not as good as the 150 at 75 mph. The plane was simply
better balanced with the 150.
-
The 200C was a dead match with the Hartzell in
all three speed parameters: top speed, climb, and cruise with no measurable
difference.
-
The 200C is slightly quieter, but not obviously
noticeable like the 150. It's interesting that the acoustic resonance is at
a higher rpm than the Hartzell, I have no explanation for it, maybe the
shape of the blade?
-
Deceleration during any mode of flight is subjectively
very noticeable with the 200C. Pull the throttle back with the
prop spinning fast and it'll throw you forward right now! I'm sure
this braking is due to the wide blade chord and is a desirable
characteristic for aerobatic maneuvers. It can also be used to good
advantage in an RV to slow down in the pattern or for steep approaches. Any constant speed prop will provide good deceleration
compared to a fixed pitch, but the 200C takes it to another level. Take-off
acceleration seemed a bit snappier too but was not measured. I'm told that
if I had checked Vx performance the 200C would likely have shown an
advantage, but I did not test it, nor do I fly in that mode much because it
yields such a nose high attitude and also heats up the engine fairly
rapidly.
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Whirl Wind 200RV: |
- Lighter weight noticeable: 18 lbs lighter
than the Hartzell, 6 lbs lighter than the 200C. This definitely helps the
plane feel better when solo.
- When doing this installation I also
replaced my Concorde RG-25XC battery with an Odyssey PC680 for additional
net reduction of 7 lbs. The lighter 200RV plus the loss of the battery
weight now put me almost exactly where I was with the 150... the best
"feel" of all.
- Weight is now such that when solo I can
trim to proper approach speed.
- Subjective aspects: this prop accelerates
and decelerates more like the Hartzell -- gone is the remarkable
acceleration and deceleration of the 200C. The quiet and smoothness is
immediately apparent. Frequent passengers in my plane noticed it right
away without being prompted.
- This prop excels in every respect: it's lighter,
quieter, and faster. I think it will end up being quite popular with RV
builders for those willing to pay a premium over the Hartzell in exchange
for lighter weight, better performance, and no vibration related
restrictions.
|
Summary thoughts: |
So what have I learned through all of this?
Primarily two things: first, that it's a heck of a lot of work to do all
this testing, maybe more than it's worth. Second, that the performance
window (the differences between these props) is surprisingly narrow. I'm
sure the aerodynamic gurus out there are snickering "I could've told you
that" to themselves, but us homebuilders just have to keep pushing in
our quest for optimization. I also
learned that there are factors that may be more important than mere speed
numbers. Weight and noise have a considerable impact on the way the
plane feels, and the instantly
noticeable noise difference.
Even though the Whirl Wind 200RV tested the
best, that doesn't mean it's the right prop for you. Rather the
best prop for your plane would depend on
what your own priorities reflect. The cheapest is the Hartzell, but there are issues
with vibration if you have electronic ignition or high-compression pistons.
(my LASAR system is a huge step forward in efficiency and I'm not willing to
give it up) The lightest by a wide margin is the WW 150, which happens to
benefit the RV-8 particularly CG-wise. The WW 200C aerobatic prop is as fast
as the Hartzell, also lighter and slightly quieter, but more expensive. For
those of you looking forward to more frequent acro this might be the best
choice. It's hard to beat the 200RV as the best overall prop however. I
suppose that's what results from a no-compromise design for the RV.
Hopefully the
information presented here will be useful to you in making the right selection for your own
aircraft and typical mission profile. For me the 200RV now has the perfect combination of qualities that I've
been looking for so it's a keeper for me. Propellers are a fascinating and important part
of our aircraft. Understanding them is integral to getting the most out of
your particular set-up and fulfilling your mission profile. To learn more
about the fundamentals involved check out these links:
http://members.eaa.org/home/homebuilders/authors/bingelis/The%20Fixed%20Pitch%20Propellor%20Dillemma.html
http://www.auf.asn.au/groundschool/propeller.html
http://www.aerospaceweb.org/question/propulsion/q0039.shtml
http://naca.larc.nasa.gov/reports/1939/naca-tn-698/index.cgi?thumbnail1
http://www.djaerotech.com/dj_askjd/dj_questions/fourblade.html
NEW DEVELOPMENT - Jan/05 - The aviation division of
Whirl Wind Propellers has been sold to the owner of Titan Aircraft, John
Williams, who has formed a new company called Whirl Wind Aviation. My
understanding is that he will be manufacturing and selling WW props from
Titan's Ohio facility. I do not know anything about their credentials,
intent for the future of the product line, or support policies.
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