Pietenpol-List: Scimitar Prop

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Original Posted By: Galen Hutcheson
Subject: Pietenpol-List: Scimitar PropI'm going to see if I can kick up any interest in the design of a 'Scimitar Prop'. I've brought up this subject in years past on this list, but had only limited interest. As we all know, a propeller absorbs the energy of the fuel burned in the engine, and dispenses it in the form of thrust. Whenever energy is transformed from one form to another, some energy is transformed to some otherform which is lost to intent of thrust. Energy cannot be created nor destroyed...it'sa fact of physics. Therefore, the more efficiently the 'Potential' energy of the fuel that is burned, can be transformed into thrust, the less fuel will berequired to perform a given amount of work. A given fixed pitch prop is most efficient at a specific r.p.m., and a specific forward speed. This is why adjustable props came into play, and high performance airplanes usually have Constant Speed Props. Here is where the Scimitar Prop comes in. The blades ofthe Scimitar Prop will twist to a lower blade angle for the high thrust required for takeoff and climb, then once airborne and power is pulled, the propunloads and flexes back almost to the blade angle it was carved at. Hence youhave an adjustable blade angle prop, with No Moving Parts !! Pretty cool, huh?Wood is the chosen material for this design, because it will not fatigue, it'sreadily available, and it's relatively easy to work with.Here are the forces imposed upon a Propeller:1. Centrifugal Force - Most powerful force, tends to pull the blades outward away from the hub.2. Thrust Bending Force - Blade tips bend forward when put under a load.3. Torque Bending Force - Blades bend opposite the direction of rotation.4. Aerodynamic Twisting Force - Twists the blade at the aerodynamic center of pressure. Tends to twist the blades to High Pitch.5. Centrifugal Twisting Force - The Mass of the blade, under a centrifugal force, tends to twist the blades to a Lower Pitch.6. Vibration Force (Resonance) - Everything has a resonant frequency, according to the mass, and the location of the mass. A Scimitar design prop takes advantage of these forces to twist the blades to a lower blade angle for takeoff and climb, and then when in cruise flightand power is pulled back, and the prop unloads, the blade angle relaxes back to a higher blade angle, and you have a cruise prop. Steve Wittman certainly understood the potential of a scimitar design, as evidence on the wall of his hanger in Oshkosh. I still can't understand why all props aren't of scimitar design. With enough Research and Development, then mass production could easily bring the additional labor involved, down to a competitive cost. I have searched the library at Oshkosh, lots of web sites, and asked lots of people about scimitarprops. By far, the best info I've found on it, is the couple of pages in EricClutton's book. I did, however, discover that the concept came about in W.W.Iaircraft. The design showed potential, but what happened on several occasionswas that in a dogfight, the lead plane would go into a dive, in an effort to escape the aggressor, and the engine / prop would overspeed, then the blades would begin to flutter, and disintegrate. You can imagine the vibration of a broken prop blade, and if power wasn't pulled and shut down the engine, it wouldthen shake the engine right off the plane, and now, with a tail heavy CG condition, the plane would spin to the ground. Even if the pilot was able to shutdown the engine in time, he was then a glider pilot...easy prey. I believe when you over-run the prop of a scimitar design, the aerodynamics are what cause the flutter. I have heard stories about how props de-laminate when usingthin laminates of wood, however these props had the width of the planks in theconventional direction. The cause of these de-laminations could also have beenthe technique of construction. The big question, is if any successful props were built using the parameters that Eric Clutton set forth. I do not know the answer to that question. I still plan of building one, but haven't began construction, yet. The method of construction I would use, is laminates of 1/4" or less, bend each laminate in a jig, to match the 'S' shape of the prop, and use T88 exclusively,but to avoid squeezing too much of the adhesive out, by using either scrim cloth between the laminates, or glass beads in the mixture of epoxy. The typeof wood would I'll use, is still undecided yet, but the type of types of acceptable prop wood is called out in the AC 43.13-1A. Now, the challenge of designing a reliable Scimitar Prop, using the mass of the blade to twist the blade to a lower blade angle for takeoff and climb, then back almost to the blade angles that they were cut at, when the prop unloads. The laminations would be perpendicular to the direction of conventionalprops, so as to achieve the dramatic arc of the blades, as set forth by Eric Cluttons design. I'm looking for any input, pros or cons, and especially if anyone is aware of an aircraft that has used this design prop successfully.Chuck GantzerPietenpol AircamperNX770CG________________________________________________________________________________Date: Tue, 28 Sep 2004 21:56:17 -0700 (PDT)

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Original Posted By:
Chuck,If you need one more reason to build ascimitar prop it is this,they look REALLY COOL!Greg CardinalMinneapolis----- Original Message -----

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Original Posted By: Michael D Cuy

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Original Posted By:
ChuckI would like to know more about this. If you plan on pursuing this, keep mein mind. Maybe this could be a Sun N Fun project.Dick N.----- Original Message -----

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Original Posted By: Clif Dawson

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Original Posted By: Galen Hutcheson
Subject: Re: Pietenpol-List: Scimitar PropGang, What are you guys using for leading edge protection on your carved props.?Ken Conrad, in sunny Iowa with the beans in the bin________________________________________________________________________________Date: Tue, 5 Oct 2004 19:28:25 -0700 (PDT)

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Original Posted By: Rcaprd(at)aol.com
Subject: Re: Pietenpol-List: Scimitar PropIn a message dated 10/5/04 7:54:16 PM Central Daylight Time, Wizzard187(at)aol.com writes:>Ken,After all the carving, sanding, balancing and re-checking blade track and blade angle at each station, I use Kevlar tipping on the leading edge, and putfiberglass cloth on the entire blade. I could go into more detail of this process, if you like.Chuck G.Good to hear the beans are in...that leaves the fields open for a possible off field landing !!________________________________________________________________________________

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Original Posted By: Galen Hutcheson

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Original Posted By: "Steve Eldredge"
Subject: Re: Pietenpol-List: serious smoke advice (now Tomahawk)A very dear friend of mine by the name of Bob Sears introduced me to inverted flight in a Decathalon. Bob was a commercial pilot and CFII and the adventurer I took my flights into Mexico and Central America. (Plenty of storiesfor these trips, no time to explain.)Bob used to fly in various air shows in the late 80s and early 90s and actually flew in a few events that some really topnotch performers appeared in.The first show I went to with Bob was in Lakeland, Florida, where Bob flew a SuperViking as the Avenger.He developed a routine especially for kids and was actually dressed up like a super-hero. After his routine in the Super Viking, he would hand out pictures and autograph them for hundreds and hundreds of kids. He introduced me to a handful of airshow pilots and among the most impressive (personally) was PattyWagstaff and her husband. Bob had four airplanes he flew in different airshows, to include a 300 HP Pitts Special. I never saw anyone do in a Pitts, what Bob did and he was a legendat the ABQ Balloon Festival when he flew is Pitts upside down in a drainage canal. From the audience perspective, it was quite alarming to see him do thisbecause he appeared to look like he flew into the ground. The audience could not see the canal and it was startling to see him disappear into the canal.He also flew his Pitts upside down through a WWll hanger near Monahans, TX. The hanger was very large and part of a training base for B-17s. It was abandoned and simply out in the country as a vacant building. I'll try and finda copy of Bob flying upside down through the hanger so I can scan it and send itout on e-mail.The least impressive upside down flying was done in his Decathalon and he practiced his routine at his (Sears, DFW Sectional) ranch, not too far from myplace, (5TA6, Knot-2-Shabby, San Antonio Sectional). I proudly can say I neverblew chow on the three occasions I did with him in his Decathalon when he was practicing out here in the boon docks, but it hurt like the devil. The harnessreally digs in to the shoulders (at least for me, when holding a camcorder). Wanna see my video from inside the Decathalon, upside down? I still have a copyaround here somewhere. He clipped ribbons on poles as he flew upside down about 25 feet off the ground.Bob also had a Yak and he was working on a routine for that, but be became ill from lymphoma and he died in 1995. I think had Bob not become ill, he wouldhave made the airshow circuit in a very big way. His flying skills were extraordinary and he made friends where ever he went. He really made an impressionwith kids as the Avenger in his Super Viking and one interesting note for Pietenpol folks... Bob especially liked the Super Viking for aerobatics becauseit was made out of wood and gave him the strength he needed for the budget he hadin finding an airplane that looked cool for kids. A black airplane with red and yellow lightning bolts.S.B.________________________________________________________________________________Subject: RE: Pietenpol-List: Scimitar PropDate: Wed, 6 Oct 2004 05:58:08 -0600

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Original Posted By: Michael D Cuy