---------------------------------------------------------- Europa-List Digest Archive --- Total Messages Posted Sun 09/25/16: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:15 PM - Re: 912ULS to 914? (Bud Yerly) ________________________________ Message 1 _____________________________________ Time: 05:15:12 PM PST US From: Bud Yerly Subject: RE: Europa-List: 912ULS to 914? William and others, Takeoff performance and cruise performance are significantly different in t he 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 imp roperly 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 gr oss max takeoff recommended by some in the US, one only needs to look at th e engine performance charts to see that without the Rotax turning near 5700 RPM you are not achieving maximum acceleration and climb potential. Conve rsely, we all know that one=92s cruise will be severely impeded with a fixe d pitch prop set at 5700 static as the throttle will have to be retarded s ignificantly 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 maxim um static, one can see that the power output of the 912S and 914 are 68KW a nd 67.5KW respectively. A dead heat. In my own testing and reading test reports, on many fixed and variable pitc h propellers, I have found the following: The thrust at full 5700RPM does not vary noticeably between any of the blad e types at sea level. From Bolly, to Kiev, to Warp Drive, Whirlwind, Sense nich, 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 h appens after 67 inches or so on a Rotax (due to torque limits) and the thru st difference of a 64 and 67 on a constant speed prop hub shows no differen ce on a Europa XS except the 64 inch prop pitches a bit more. The engine j ust doesn=92t have the torque to spin larger props and deliver the performa nce one has been traditionally. So what is the perceptive difference? It is dependent on propeller setup, i.e. pitch and the airframe setup. Pro pellers 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 ge nerate 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 1 20 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 brakin g 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 on e aircraft and the same technique and measuring tools, there is just no sig nificant speed or climb difference between blades in low altitude operation s if the setup and pilot techniques are the same... You are looking at 100 fpm climb and within 8 knots of cruise from sea level to 15,000 MSL. Examp le: 12AY will do 140-145 at 5500 rpm and 35 inches MP with any blade at 10 00MSL 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 kno ts. 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 p otential. 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 pro p 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. E xcess thrust in the flare is the last thing you want on a short field landi ng. 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 s etting 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 th is. 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 detra ct from ideal acceleration potential. Getting the tail up on a mono improves acceleration potential but very diff icult to measure as control inputs are larger... Rolling the nose gear along on a rough field in a trigear just adds drag bu t not as much as the aft stick required to hold the nose fully up. Heavy n osed aircraft do not rotate as well and put excessive weight on the nose ti re as well. A more aft CG helps get the nose up with less drag from the st abilator angle needed to get the proper attitude and proper acceleration an gle 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 incr easing drag significantly or causing the aircraft to exhibit that old sinki ng feeling when out of ground effect after liftoff and considerably shorten s 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 l oaded without snatching it off. My takeoff roll off grass is about 250m us ing 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 ne arly 250m to get off the ground on a hard surface being snatched off, and f ully 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 airc raft 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 (onc e you have rudder control) if you can, and she=92ll 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. I f 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 rat e. 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 dista nce 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 w heel 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=92m afraid your gra ss 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: Acc eleration 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 tech niques=85 That is 1000 meters for me or about 3000 feet more or less. Doin g the math: 600 feet for takeoff, 3 seconds or 300 feet of climb to 50 fe et and push over to approach at 55, an over 50 foot landing approach to tou chdown is 1100 feet, plus an additional 1000 foot roll out using light brak ing for the turn off only. For a real short field operation as you have 13 00 feet or 450m or so, you barely can stop if you abort at 45 knots or mini mum 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 stat or, fuel pump, both carbs, and starter replacement, rebuild of my turbo, an d repair of the turbo bracket, new hoses, and required education on carb an d 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 mo dified ignitions, exhaust failures due to harmonic vibrations and that ugly shaking on start and stop, cracked engine blocks, carb heating concerns, s tator 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 h as been learned and incorporated in the last 20 years. The 912iS is not ve ry maintainable in the field due to its proprietary electronics, but it per forms 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 sp eed with either engine. Research maintenance problems and servicing for th e 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 nic e $100 hamburger cruiser to join your Light Sport buddies at a nearby airpo rt. 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 rang e of 300nm. Cruise efficiency is at my choice, from 25-35anmpg (air nautic al miles per US gallons) depending on power setting. Full disclosure, I am a dealer for Airmaster and somewhat predujudiced afte r 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 t o maintenance as well as performance testing and an article on choosing the right propeller options for your aircraft. This section works for other b rands of props as well (not the Ivo as friends don=92t let friends fly wit h an Ivo) MT, Airmaster, Woodcomp are all very close in performance but dif fer in weight, maintenance and operational problems such as time to mandato ry overhaul and servicing requirements, corrosion and rot problems, blade w ear 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 se rvice rep, etc.. An airplane is 20,000 compromises flying in close formation, the choices ar e yours. Choose wisely. Best Regards, Bud Yerly Custom Flight Creations, Inc. US Europa and Airmaster Dealer www.customflightcreations.com Sent from Mail for Window s 10 From: William Bliss 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 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message europa-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Europa-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/europa-list Browse Digests http://www.matronics.com/digest/europa-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.