Date: Thu, 20 May 1999 23:10:34 -0400 From: "Marc J. Zeitlin" Subject: COZY: Fwd: Prop Info Nigel Field (an ex-mailing list member who developed the prop-fabrication methodology listed in the archives and used by Nick Ugolini and Lee Devlin to build props for their L.E.'s) writes: >Hi Marc, > >Been helping Gilles Graton (gratton@magma.ca) make a prop for his Velocity >173 Elite powered with a 225 HP Franklin 6 cyl. This is the first higher HP >prop that I have been directly involved with and we learned a few things. >Thought I would pass this on. > >The prop is a 3 blade 67 inch dameter constructed with pine core with glass >spars and skins with carbon re-inforced tips, same as the ones we discussed >on the mail list. We used a carbon tube insert in the centre to fit the >centering boss on the prop extension. There was room to loop the spars >around this tube and between the bolt holes. > >The prop came out at 10 lbs and quite flexible in torsion, I was concerned >but we decided to run it anyway to see what it would do. It was great until >2000 RPM when it went into flutter and howled. The tip path made a blurred >pattern about 4 inches wide. No damage to the prop so we stripped off the >primer and added 2 bias plies at + and - 45 degrees of uni glass right up to >the hub full span of the blades. This really stiffened up the blades in >torsion. The added blade weight was not a concern as we used large spars >with a calculated centripital blade load safety factor of 7 at 3000 RPM >overspeed. > >It now runs perfectly giving 2750 static which was our design objective. >The aircraft will soon have its final inspection and then go on to flight >testing where we can further evaluate propellor flight performance. > >So what did we learn? The spars can be fitted around a centering boss >insert, we used carbon but machined aluminum would be easier. The higher HP >props with longer blades need a 2 ply torsional bias layup of + - 45 degree >uni to ensure sufficient blade stiffness to prevent blade flutter. > >Hope this is usefull, > >Nigel -- Marc J. Zeitlin mailto:marcz@ultranet.com http://www.ultranet.com/~marcz/ From: "Schuler, Larry" Subject: RE: COZY: Fwd: Prop Info Date: Fri, 21 May 1999 08:33:00 -0500 > >>It now runs perfectly giving 2750 static which was our design objective. >>The aircraft will soon have its final inspection and then go on to flight >>testing where we can further evaluate propellor flight performance. The final test will of course come after the baldes are fully loaded in flight testing. Static run up is not the same, unless it's an airboat prop. Keep us posted PLEASE! Larry From: cdenk@ix.netcom.com Date: Fri, 21 May 1999 16:19:06 -0500 (CDT) Subject: Re: COZY: Fwd: Prop Info One of the props I have been testing fluttered, I added 2 plys of fiberglass BID at 45 degrees to length of blade, and the prop worked fine, except for a little too flat of a pitch. The object of that prop was to try to find a minimum blade thickness, which we found. Date: Wed, 26 May 1999 09:38:23 +0200 From: "Rego Burger" Subject: COZY: Propeller Construction I'm entering a new field here and need education please. With Ref. to Bates and other printout packages. Can someone tell me ( and other interested parties) what the difference (or definition) is between "Geometric Pitch" and "Absolute Pitch" In anticipation. Régo Burger Date: Sat, 22 May 1999 11:34:08 +0200 From: Jean-Jacques CLAUS Subject: Re: COZY: Propeller Construction Rego Burger wrote: Hi Rego and all, > > Can someone tell me ( and other interested parties) what the difference (or definition) is between "Geometric Pitch" and "Absolute Pitch". In relation with the Bates's program, the geometric pitch is the distance a propeller should advance in one revolution; effective pitch is the distance it actually advances. Jean-Jacques CLAUS France Date: Sat, 10 Jul 1999 10:34:58 -0400 (EDT) From: Nigel Field Subject: Prop Flight Report Hi Marc, A follow up on flight testing on Gilles Graton's Velocity 173 225 HP Franklin 3 blade prop. First I must correct a typo in my initial report. The prop turned up 2650 static not 2750 as posted. Seems my fingers don't work like they used to, or is it my eyes, anyway sorry about that. The aircraft and prop first flew mid June and now has 22 hrs. We expect the 25^2 restrictions to be lifted next week. The prop is performing perfectly throughout the entire flight envelope up to 165 kts IAS so far. It and the engine run very smoothly although the downward facing exhaust is pretty loud, we got to work on that later. We had to try a few things to lower the oil temp which would go to 265F at 2600. We ended up adding a FG baffle around the oil sump fed with inlet air which helped a bit but the biggest improvement came by increasing the spring tension in the bypass valve to force more oil flow through the cooler. That got the oil temp down to 220F with CHTs at 210F for all 6 at 2600 RPM cruise. That downdraught cooling plenum with armpit inlets really works well for this engine. I was honoured to fly the aircraft 2 weeks ago and was very impressed with it and the prop. We were airborne with a 2500 ft roll from our grass field and climbed out at 100 KTS IAS giving 1200 ft/min on a 30 deg C day at 2060 lbs gross (2 pilots 30 imp gal fuel) up to 3000 ft where we leveled and accelerated to 155 KTS cruise with 2600 RPM set on. The throttle was reduced from WOT so there was power to spare. The airplane is very happy at 2600 where the prop was designed to cruise. We studied the flight data to see if the prop needed modification. We considered more pitch to lower cruise RPM but that would degrade the TO and climb. We also considered the opposite to provide for a better max gross TO from a short grass field but that would degrade the cruise. So we concluded that it was just right as it is. It will soon get a nice Imron paint job as its still in primer. Past experience using Propopt has resulted in most props turning a little faster than designed. This is probably due to use of thinner carbon re-inforced tips which have lower drag than the thicker pure wooden tips that the design application optimizes for. This skews the calculations somewhat. The solution has been to add 1/2 degree of pitch if diameter limited, or add some diameter. In this case we left the pitch as specified and added 1/2 inch blade length (1 inch diameter) knowing that it could be easily trimmed off later if required. It turned out that the extra diameter was needed in this example so the prop remains as initially built. Gilles has reams of flight data if needed. He is an active member of the Velocity builders' mail list. His Email is gratton@magma.ca So to conclude, yes a homebuilder with composite skills can build a light yet very strong 200+ HP high performance 3 blade prop with a centering boss insert, for about $100 that will perform as well, or better, than anything on the market. Good flying, Nigel Field