Remi,
The Tests were done over a short period of time swapping blades and rebalan
ce over a couple of weeks at as close to the same conditions as possible.
Then flown again to try to verify the test points about a month later. The
scatter of the points I will discuss below.
It has been a while, and the data Jim and I used was different because of t
est aircraft and location. He has a mono with early 914, and mine is a tri
gear with a new TCU on the 914.
Of course each experimental plane is slightly different from builder to bui
lder, model to model, and so is our test data. Heck, the same day test in
the same airplane gets frustrating also. For instance, setting 35 inches o
ne day may look like 35 inches on my gauge, but it is actually my Rotax def
ined stop for the 100% throttle position. In reality even though the test
conditions were relatively close in temperature and pressure altitude, I ch
ose to record the temp and fly pressure altitude and let the density altitu
de be up to you all to decide if you wanted to use. Jim flew at the same co
mputed density altitude. The Tach setting in the Airmaster is fairly accur
ate, but as any analogue system, has a dead band of plus or minus about 50
RPM, so each setting is going to vary day to day or run to run. I only fl
ew to 15,000 feet (the operational ceiling by Rotax) as the temp, throttle
position, TCU computer settings, turbo cable setting and other factors such
as cowl heat, does cause a variation in test data. I did runs at 1000 fee
t, 2500 and each 2500 foot increment to 15,000. I flew for at least two mi
nutes or as required to get steady state results at each power setting for
each altitude trimmed for steady flight with limited thermals.
I have an EI fuel flow meter and it is quite accurate over 10 years of flyi
ng. But the throttle position used by setting a MP by eye, varied only a t
iny bit, but that made fuel flow variations at the higher power settings es
pecially. You are right, that better economy comes from the increase in sp
eed with the same power setting not the same power setting and RPM.
As I only have 914 engines to test with stock intake and cowls, it is true
the 912S especially took a back seat to my testing, as I just didn=92t have
aircraft available. Few 912S owners have constant speed propellers over h
ere unlike in Europe. I started using a local Experimental Pipestral for 9
12S tests. Testing is not complete, as the test was done against a Woodcom
p that shed a blade. The other has hit its 300 hr. mandatory removal and f
actory inspection and is out of service for an unknown time. So I am still
stuck with my 914s for the time being.
I tested the two blade Sensenich, the three blade Warp and the Whirlwind ag
ainst each other on my Europa. All have their good and bad points. Jim Bu
tcher was lent my Whirlwind test blades to see if there is a correlation of
data.
In general, at low altitude and low RPM you can put any club on the front o
f a Europa and the speeds do not change appreciably. That is a nasty thing
to say, but the static thrust difference between 6 different manufacturers
is virtually the same in head to head tests. Comparing ground adjustable
LSA aircraft (Breezer) using various blades (GA, Woodcomp, Sensenich, Whril
wind and Warp Drive) the Breezer dealer settled on the Sensenich and Whirlw
ind for his clients as they were nominally better at cruise.
For me I stuck with blades that would fit the AP332 hub (the Sensenich and
Woodcomp would not fit due to their shank size), the GA was not considered
as it was terribly slow. The 332 hub is tried and true, 2000 Hr TBO, only
annual maintenance required, and the blades can be cleaned up here in the S
tates for little cost. Only blades that could meet the 2000 Hr. TBO were
considered. Flight performance was documented, not takeoff distance. Time
to climb was tested only from 1000 feet to 10,000 MSL. (It was 30C and te
mps were starting to climb.) To keep the cost of the testing down, I stuck
with only the 64 inch blade lengths and that screwed the Warp Drive guys a
bit as when you cut the constant chord Warp, the total twist decreases, so
=93the twist is in the hub=94 as we say in the constant speed world. The
Whirlwind has a fairly small visual angle of twist but its airfoil shape go
es from a high lift section at the root to a flat thin airfoil at the tip.
It is like comparing apples to oranges so I settled for just flying the pr
op blades head to head and doing analytical tests on blade length vs speed.
See my paper on choosing the right propeller for your experimental on my
website.
I found the following over all three propellers tests on 6 different days o
ver two months but at nearly the same temperatures and pressure altitudes.
As you can see, the low altitude low speed runs are virtually identical. T
his made Airmasters point that the blade type in a low slow airplane does n
ot differ the top end much. The constant speed prop improves the climb mor
e than a fixed cruise prop and cruises faster than the fixed climb prop whi
ch is exactly what you want. What does become a factor is the spin up from
idle as lighter blades spin up faster due to lower inertia, the residual t
hrust on landing will vary due to blade and idle settings but the flat pit
ch decreases float distance, cruise will be as close to optimum for the bla
de and engine chosen, and finally subjective looks. Each aircraft design h
as a sweet spot. The Europa is very efficient at low speed cruise (110 KIA
S), where the 80 HP 912 and fixed pitch prop is very efficient. Just not a
s fast as most of us would like to fly. However, for those of us who desire
speed and long range, a blade that is 5-7 knots faster at 10,000 + feet de
nsity altitude is going to be very tantalizing. Provided it is reliable, e
asy to service and repair, doesn=92t throw blades, and you can talk to some
one who speaks your language at the factory, then it is worth the money. T
he 914 Europa can get to 10,000 MSL in about 12 minutes, use 1.5 gallons of
gas from engine start to level off, and cruise at 143KTAS without using ox
ygen. I can=92t get to 160 knots without running at 5500 RPM at 15,000 MSL
. The airframe is capable of 170 KTAS at 10,000 feet if the engine can pro
vide the power, and the prop can absorb it, so some will say why not fly th
ere.
If I were a 912S owner with an Airmaster AP332 flying off lumpy grass pastu
res, I would use a Warp Drive blade as you can mow the grass with it on tax
i out, turn around and take off. Your plane will look like a Chia Pet, but
the prop will take it. A nicely painted blade with a clear coated nickel
tape leading edge will be fine on clean hard surfaces or well maintained gr
ass and because it has a more advanced profile will perform slightly better
. Unfortunately, the clear coated leading edge tape will start to look a b
it worn as the clear coat wears from sand, rain and bugs, so more touchup m
ay be necessary. Since at low RPM and low speed the blade choice does not
significantly change the speed of the aircraft, it may be prudent to stick
with the blade one has and use the money to lower your aircrafts drag and i
mprove the efficiency. However, if I were a 912S owner flying at higher d
ensity altitudes, using a Hacman leaning kit for better efficiency, or a 91
2iS owner and most of my cruising was above 10,000 foot density altitude, I
would consider the Whirlwind for the slightly better speed I will get with
a properly leaned engine. Landing at high density altitude may be improve
d also as the fine pitch stop of the Whirlwind is slightly shallower and yo
u get a bit more braking from the prop without lowering your idle to unacce
ptable levels when confronted with shorter strips.
Finally, as the chart attached shows, the Whirlwind at a cruise climb of 90
Knots does climb very slightly faster than the Warp Drive. Takeoff roll d
idn=92t seem to vary much, but the 90 and 75 knot climb rates and best angl
e of climb were very slightly better. If I was out in the high desert, I w
ould look hard at a blade swap rather than considering buying a new propell
er.
Attached above is my raw data from 2015 on the initial tests with my old ca
rbs (yes I had to change carbs as one became quite scarred in the sleeve ar
ea and wouldn=92t match the other). The carb change caused me to have to t
hrow out my fuel flow data on my latest attempts at prop testing and the 15
000 foot test with the Whirlwind was running about =BD inch low on MP when
I tested the Whirlwind blades. With the new carbs I have different jets, EG
Ts are off as you would expect and due to work load I have not been able to
retest with the new carbs.
Overall, I stand behind what I have said above. I encourage comments. It
will take me a while to get back to everyone as the shop is full of airplan
es that are hard broke.
Bud Yerly
Sent from Mail for Windows 10
From: Remi Guerner<mailto:air.guerner@orange.fr>
Sent: Sunday, May 14, 2017 9:29 AM
Subject: Europa-List: Re: Airmaster whirlwind blades
Yes the article by Bud and Jim in EF 89 is interesting. Those Whirlwind bla
des are beautiful and the new ferrules are not protuding outside the spinne
r anymore as they do with the WarpDrive blades, adding drag without thrust.
The possibility to upgrade an existing Airmaster/WrapDrive prop with the ne
w blades is very tempting.
However the article is disapointing regarding the compared cruise performan
ces of the WD and WW blades. Both Bud and Jim say they see a few more knots
at the same power setting. I have analyzed in details the figures shown in
the charts for the Monowheel and here are my comments:
1. Some speed figures are very wide spread, sometimes 10 knots for the same
conditions, probably because the air mass was not as stable enough during
the testing. As we are looking for a few knots differences, that makes the
comparison a little bit doubtful.
2. The tendency is a speed increase of 2 knots with the WW blades at altitu
des up to 14000 ft.
3. The testing was done on the Rotax 914 only. I assume there would be some
similar speed improvement also with the normally aspirated 912S.
3. Surprisingly at 17000 ft. figures show that the WW are slower than the W
D for 3 out of the 4 power settings used for the test.
So to summarize, sorry Bud, I do not see the 5 knots increase you are talki
ng about. Regarding the alleged reduced fuel flow with the WW blades at a g
iven power setting at the same density altitude, this is just not possible.
That is the law of physics. If the fuel flow is lower, that is due to eith
er a lower power setting or an inacurate fuel flow meter, not to the better
prop blades.
To conclude I pass the following message to Airmaster: with the Airmaster/W
D blades on my Monowheel, 912 ULS, one on board, full fuel, I consistently
get 140 kts TAS at full throttle, 5000 RPM at 8500ft density altitude. If I
could get the proof that those WW blades would increase my cruise speed b
y 5 knots in those conditions, I would place an order immediately!
Remi Guerner
F-PGKL
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http://forums.matronics.com/viewtopic.php?p=469294#469294
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