Hi Bud et al,
As a representative LAA inspector to the Europa Club and in this instance I
refer to UK Permitted aircraft (probably of no significance outside the UK)
I have to add a further comment that slightly countermands what Bud has
said.
For certification purposes within the UK Permit system, aircraft fitted with
variable pitch or ground adjustable props must be set up such that the max
permitted engine RPM cannot be exceeded up to Vfe. For the Europa this
speed is 83 kts. This fine pitch setting refers to the absolute finest
pitch setting that can be achieved with the prop controller set to manual
and fully fine.
In practice this will result in a max static full throttle RPM of around
5,300 to 5,600 (even in auto T/off). This figure can vary with different
props.
The reasoning behind this requirement is to avoid the possibility of a pilot
fully opening the throttle for T/off or go around with the prop either too
fine (ie manual full fine) or because of relatively slow auto responce, or
failure of the auto system, exceeding the max rpm limit of the engine. THE
ROTAX ENGINE and your wallet, and your neck, REALLY DO NOT LIKE RPM
EXCEEDANCE.
Best regards
Pete Jeffers
I Now copy in part of a letter that I received from Andy Draper at the LAA.
Apart from his position with the LAA Andy used to be part of the design team
at Europa Aircraft as it is known today.
'Bud touched on something else, which I think is key to the answer to
William's question and that is pilot technique. Gaining a few hundred RPM
by setting the prop's fine pitch stop to 5800, or close to it, would quickly
be eradicated by less than efficient pilot technique. It would be very
interesting to know the difference in take-off performance with a propeller
set-up as we require and one set-up to develop 5800 RPM static. I don't
suppose that it would amount to much and climb performance should not be
affected at all, as both would be running at the same speed at Vy.
Pumping the tyre up should be acceptable, now that the undercarriage is
sprung and damped. In the early days we relied solely on the tyre for
suspension and wanted to avoid it acting like a spring.
Out of interest, I was recently checking out the new owner of G-MIME,
912-ULS, Airmaster AP332, Warp Drive blades 64" diameter. We finished off
with some circuits at the owner's home field, Grove Farm near Coventry,
400m grass with an 8ft hedge at one end and we safely operated out of it
with little in the way of a head wind. We weren't at max gross, but two
guys and reasonable fuel load would probably compare well with William's
described loading.
As I alluded to earlier, we are about to open discussions with all the
in-flight adjustable prop manufacturers the issue of mechanical fine pitch
stops.'
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Bud Yerly
Sent: 26 September 2016 01:11
Subject: RE: Europa-List: 912ULS to 914?
William and others,
Takeoff performance and cruise performance are significantly different in
the 912 ULS and 914 provided we are equipping them both with constant speed
props.
A fixed pitch prop on the 914 leaves much performance wasted. Also, an
improperly set up constant speed prop can waste performance as well.
If you have a 450m strip, fully loaded at 1370lb. or even 1450 lbs. over
gross max takeoff recommended by some in the US, one only needs to look at
the engine performance charts to see that without the Rotax turning near
5700 RPM you are not achieving maximum acceleration and climb potential.
Conversely, we all know that one's cruise will be severely impeded with a
fixed pitch prop set at 5700 static as the throttle will have to be
retarded significantly to prevent an engine over speed as the airspeed is
increased. The 912S vs the 914 is 72KW to 85KW respectively at full rated
RPM. That is 15% more power delivered by the 914...
Should one set his fixed pitch propeller to only spool up to 5200 RPM
maximum static, one can see that the power output of the 912S and 914 are
68KW and 67.5KW respectively. A dead heat.
In my own testing and reading test reports, on many fixed and variable pitch
propellers, I have found the following:
The thrust at full 5700RPM does not vary noticeably between any of the blade
types at sea level. From Bolly, to Kiev, to Warp Drive, Whirlwind,
Sensenich, Woodcomp, GA and on and on when attached to an aircraft with the
same length prop and cowl shape. The thrust scales do not lie. Nothing
good happens after 67 inches or so on a Rotax (due to torque limits) and the
thrust difference of a 64 and 67 on a constant speed prop hub shows no
difference on a Europa XS except the 64 inch prop pitches a bit more. The
engine just doesn't have the torque to spin larger props and deliver the
performance one has been traditionally. So what is the perceptive
difference?
It is dependent on propeller setup, i.e. pitch and the airframe setup.
Propellers are driven by torque not HP (high RPM engines require a gearbox
to generate the torque and direct drive engines require a long crank arm to
generate the torque). As for the prop, the twist, inertia and airfoil shape
of a blade in the low speeds we fly (up to 160-170KTAS on the high end to
120 KTAS on the low end) will achieve slight advantages in speeds at higher
altitudes and will achieve a faster spin up on takeoff and or better braking
on landing than a plain flat Hartzell or Warp Drive Clark Y airfoil prop but
very little difference in reality. I will not degenerate into bragging
rites as some prop blades are better in some specific areas as two blades
and others as three blades at different altitudes and power settings. Each
airframe and pilot technique is slightly different but in testing using one
aircraft and the same technique and measuring tools, there is just no
significant speed or climb difference between blades in low altitude
operations if the setup and pilot techniques are the same... You are
looking at 100fpm climb and within 8 knots of cruise from sea level to
15,000 MSL. Example: 12AY will do 140-145 at 5500 rpm and 35 inches MP
with any blade at 1000MSL much to my surprise. At altitude, the higher
cambered lighter props such as the Whirlwind do perform better than a Warp
Drive by about 5-10 knots.
For best performance a constant speed prop is essential in a slick airplane
like a Europa to take advantage of takeoff, climb and cruise performance
potential. A constant speed prop set up for a max RPM of 5750 ground static
at zero airspeed and full power is essential for maximum acceleration and
best angle of climb, especially important for short field operations. On a
short field approach with the prop set to a fine pitch (constant speed prop
set for a maximum RPM of 5750 or so, or said another way, the fine pitch
limit stop is very fine), allows the prop to act as a brake on landing.
Excess thrust in the flare is the last thing you want on a short field
landing. Note: I use 5650 as my static RPM as my clients, during training
will rapidly advance the throttle during high speed go-arounds or inflight
high speed dives and quick throttle operations, and this gives me a cushion
to prevent over speeding the engine.
Another note, ground cooling is enhanced by setting the prop to a courser
setting while on the ground to improve flow over the cowl and enhance ground
cooling... It took a field trip to the airport to convince the guys of
this. Old ideas die hard.
The airframe setup is important also.
Many use low tire pressures for softer landing on a trigear or mono wheel.
Flat tires resist rolling.
The mono is limited to full flaps on takeoff which slows acceleration.
Rough field nose high attitudes during the initial acceleration phase
detract from ideal acceleration potential.
Getting the tail up on a mono improves acceleration potential but very
difficult to measure as control inputs are larger...
Rolling the nose gear along on a rough field in a trigear just adds drag but
not as much as the aft stick required to hold the nose fully up. Heavy
nosed aircraft do not rotate as well and put excessive weight on the nose
tire as well. A more aft CG helps get the nose up with less drag from the
stabilator angle needed to get the proper attitude and proper acceleration
angle which is slightly nose up and nose wheel nearly off the tarmac...
Half flap or about 10-15 degrees of flaps lowers takeoff speed without
increasing drag significantly or causing the aircraft to exhibit that old
sinking feeling when out of ground effect after liftoff and considerably
shortens the takeoff run.
I can routinely get 12AY (Trigear, 914, Airmaster with any blade (Whirlwind,
Sensenich, or Warp Drive) off the ground in 200m (600 feet or so) fully
loaded without snatching it off. My takeoff roll off grass is about 250m
using soft field techniques at a local soggy grass strip. With 12AY
equipped with a fixed pitch prop (5200 Static) in LSA testing, the aircraft
took nearly 250m to get off the ground on a hard surface being snatched off,
and fully loaded was a pig. On a similarly equipped 912S aircraft, I am
seeing 250m takeoffs minimum fully loaded on a hard surface also. That is
about a 20 % increase in takeoff run. Note: Even the 120 HP Jabiru
equipped aircraft with fixed pitch props set at 2650 static can only get off
the ground in 350m.
If you want a short takeoff, get a constant speed prop, set it up properly,
inflate your tire(s), use half flaps if you can, accelerate tail high (once
you have rudder control) if you can, and she'll come off the ground in
200-250m normally.
Landing is a different story. The prop has to be in fine pitch or you will
have excessive thrust on landing roll out. Approach speed is critical. If
your plane is controllable at 45 knots in level flight flaps down I would
not recommend an approach speed below 55 Knots as power off, the sink rate
is high and if in ground effect, the deceleration is at a controllable rate.
Fully loaded on approach at 55 requires only a bit of power, and if the
power is not reduced prior to the intended landing site, a long float will
ensue. Typically if one crosses the threshold of the runway 5 feet in the
air at 55 knots, and the power is pulled at the threshold, the float
distance can be 300 meters or more. After touchdown roll out is nominally
200m with hard braking and 400 meters using only aerodynamic braking and
light wheel braking at the end of run below 30 knots. Of course a soft
field will decrease landing roll and increase roll out deceleration rate.
If you have read my posts on my three mistakes rules, I'm afraid your grass
strip is a bit short for what I would call normal full gross continuous
operations. I prefer to determine my normal runway length as follows:
Acceleration to takeoff, get airborne for 3 seconds, decide to abort and
land from that point and glide to an intended landing using normal roll out
techniques. That is 1000 meters for me or about 3000 feet more or less.
Doing the math: 600 feet for takeoff, 3 seconds or 300 feet of climb to 50
feet and push over to approach at 55, an over 50 foot landing approach to
touchdown is 1100 feet, plus an additional 1000 foot roll out using light
braking for the turn off only. For a real short field operation as you have
1300 feet or 450m or so, you barely can stop if you abort at 45 knots or
minimum takeoff speed and stop by the fence.
Engine choice is personal. Like many of us, I have a very old 914 with the
1000 hour TBO and endured constant minor problems. Every SB applies to my
engine. These were design equipment problems and properly maintained, the
engine still delivers excellent performance. What has it cost me: A
stator, fuel pump, both carbs, and starter replacement, rebuild of my turbo,
and repair of the turbo bracket, new hoses, and required education on carb
and TCU maintenance and service training. What have I gotten in return,
140-150 knot plus cruise performance at 10,000 feet plus 700-800 fpm climb
all the way to 10,000 ft. I never fear a hot day high density altitude
takeoff and I spit on carb icing and shock cooling.
The early 912S have had the following: Rough starting, requiring new or
modified ignitions, exhaust failures due to harmonic vibrations and that
ugly shaking on start and stop, cracked engine blocks, carb heating
concerns, stator problems, starter cranking problems, and carb problems
also. They do not perform well above 7500 feet due to poor leaning and
significant power loss due to altitude is evident.
The brand new engines of both 914 and 912S are much better engines. Much
has been learned and incorporated in the last 20 years. The 912iS is not
very maintainable in the field due to its proprietary electronics, but it
performs superb in comparison to the 912S in economy at cruise. No
difference on takeoff performance at sea level to speak of, but better
performance at higher takeoff density altitudes...
Bottom line:
If you want good takeoff, climb and cruising performance, get a constant
speed with either engine. Research maintenance problems and servicing for
the prop of choice. If you are concerned about high altitude operations,
get a 914. If you just intend to fly at lower altitude and short hops, a
912S is an excellent value. Even equipped with a fixed pitch prop, it is a
nice $100 hamburger cruiser to join your Light Sport buddies at a nearby
airport. I prefer high and fast in my area of operations where I need to
get to 10,000 feet to clear clouds, and find some cool air and a comfortable
range of 300nm. Cruise efficiency is at my choice, from 25-35anmpg (air
nautical miles per US gallons) depending on power setting.
Full disclosure, I am a dealer for Airmaster and somewhat predujudiced after
10 years of replacing other brands here in the US.
See my website (www.customflightcreations.com) and click on the techniques
section on many topics from cooling to maintenance as well as performance
testing and an article on choosing the right propeller options for your
aircraft. This section works for other brands of props as well (not the
Ivo as friends don't let friends fly with an Ivo) MT, Airmaster, Woodcomp
are all very close in performance but differ in weight, maintenance and
operational problems such as time to mandatory overhaul and servicing
requirements, corrosion and rot problems, blade wear due to weather and
foreign object damage, component life limits, finish problems (peeling paint
and cracks), controller operations, failure rates, factory/dealer assistance
and availability, finding an English speaking service rep, etc..
An airplane is 20,000 compromises flying in close formation, the choices are
yours. Choose wisely.
Best Regards,
Bud Yerly
Custom Flight Creations, Inc.
US Europa and Airmaster Dealer
www.customflightcreations.com
Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for Windows
10
From: William Bliss <mailto:william@wbliss.co.uk>
Sent: Sunday, September 18, 2016 3:58 AM
Subject: Europa-List: 912ULS to 914?
Dear All
I am struggling to get out of a 450m grass strip 2 persons and full fuel
(no baggage).
Has anyone got experience of the improvement in take off performance
with the Rotax 914 over the 912ULS?
I expect this has been debated before but I cannot find a way to search
the matronics website for it.
Thanks
William Bliss G-WUFF
Mono Classic XS firewall forwards. 912ULS, Woodcomp SR3000, Smartcontroller
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