Wow! If there were a Nobel prize for Matronics contributions, that would
be a leading contender! David Joyce, GXSDJ
On 2016-09-26 01:10, Bud Yerly wrote:
> 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 [1]) 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 [2] for Windows 10
>
> FROM: William Bliss
> SENT: Sunday, September 18, 2016 3:58 AM
> TO: europa-list@matronics.com
> 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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