REFLECTOR: Metal prop on Velocity
Andrew Ellzey
ajlz72756 at yahoo.com
Mon Apr 10 20:14:55 CDT 2006
MessageScott Baker, and all,
I sent the following e-mails to Hartzel. I haven't received a reply to my last e-mail as of yet. I will forward Richards response if I get one.
Andy Ellzey
----- Original Message -----
From: Andrew Ellzey
To: Bowerman, Rick
Sent: Monday, April 10, 2006 1:28 PM
Subject: Re: Velocity aircraft pusher props
Richard,
I am sad to hear that Hartzel is taking a negative and more conservative view on pusher prop aircraft. I agree that all of your worst case scenario's are true with stones and ice. I know that Velocity fliers would be very vigilant to any damage that might occur to their props, and would also except a lower TBO to be able to fly a more reliable prop than the MT prop has provided. I believe that any issues that you have stated could be resolved by Hartzel if they were looking at our airplanes for what they truly are and that is an experimental aircraft. Your prop could be provided as an experimental prop. I know that none of this will probably matter, but I thought that it should be expressed. I wish that Hartzel would reconsider. I believe that the market for your prop is larger than Hartzel believes, and that any of these issues could be resolved.
Best Regards,
Andy Ellzey
----- Original Message -----
From: Bowerman, Rick
To: Andrew Ellzey
Sent: Friday, April 07, 2006 8:50 AM
Subject: RE: Velocity aircraft pusher props
Dear Mr. Ellzey,
The propeller tests that we recently completed on the velocity revealed that the propeller vibratory stresses were above certifiable limits. Pusher propellers operate in the wake of the aircraft. Each time a blade chops through the wake the thrust and torque on that blade changes momentarily. The unsteady blade loading leads to reduced propeller efficiency, high vibratory stresses and increased exterior noise levels. The severity these maladies depends partly on the proximity of the propeller to what lies ahead of it. In the case of the velocity, the prop is very close to the trailing edge of the wing. That feature is beyond our control, so we decided not to pursue the installation any further.
Other issues to consider with pusher props deal with exhaust impingement, ice impact and FOD. These are addressed in Part 23.905. The amount of heat generated by a piston engine is usually not enough to elevate the propeller temperature to a level of concern. Pusher props on turbine engines, however, can experience temperatures in excess of 200 degrees F so the exhaust configuration of a turbine engine becomes part of the pusher propeller approval. Exhaust gases, whether from a piston or turbine engine can be corrosive to aluminum, so extra propeller maintenance is needed to ensure that the blade paint is always intact.
If the airplane is likely to be flown in icing conditions, any part of the airplane that lies directly ahead of the propeller must also be protected to prevent the buildup of ice. An ice impact is potentially more damaging to the propeller than a bird impact even though the mass of the ice may be much less than that of a bird. Due to the difference in speed between the airplane and a bird, the blade slices through the bird like a knife and little or no damage will result. However if ice collects at the wing leading edge or the corner of the windscreen and then releases into the propeller, the ice is traveling at nearly the same speed as the aircraft at the time of the impact. The blade does not slice through the ice, but will impact on its flat surface. The energy of the impact can be sufficient to bend an aluminum blade and cause the entire propeller to be scrapped.
Foreign object damage is also higher with a pusher prop. Sand, stones, water and debris that are lifted by the tires find their way into the prop during every takeoff and landing. There is also increased probability that the prop will ingest loose nuts, bolts, washers, safety wire, hand tools and anything else that may be left in or on the engine cowl or on the wing when the engine is started. Above average maintenance costs should be expected.
Pusher aircraft look unique and many are very comfortable in the cabin since the primary noise source is behind. The idea that a pusher configuration is aerodynamically more efficient than a tractor is somewhat of a myth. The airframe has no slipstream drag with a pusher prop, but the loss in prop efficiency tends to be greater than the gain from eliminating slipstream drag. The high performance of the Velocity is more likely a result of being a good clean design and from the induced drag benefits of the canard configuration.
Best regards,
Richard D. Bowerman
Certification Manager / Senior Integration Engineer
Hartzell propeller Inc.
tel: (937) 778-4359
fax: (937) 778-4365
rbowerman at hartzellprop.com
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From: Andrew Ellzey [mailto:ajlz at cox.net]
Sent: Thursday, April 06, 2006 9:54 PM
To: Bowerman, Rick
Subject: Velocity aircraft pusher props
I understand that Hartzel was doing some testing on a 3 blade CS prop for Velocity aircraft. I am interested in using one of your props on my Velocity XLRG IO-540 E1A5 290hp @ 2575 RPM. Do you have a prop that would work for my application? If not what are the issues that prevent your supporting this type of instillation? There are a lot of Velocity builder/owners looking for a better prop than MT for their aircraft.
Andy Ellzey
479-631-2851 home
479-531-5139 cell
----- Original Message -----
From: Scott Baker
To: amillin at sbcglobal.net ; Velocity Aircraft Owners and Builders list
Sent: Monday, April 10, 2006 2:57 PM
Subject: Re: REFLECTOR: Metal prop on Velocity
Hello Andy,
You are correct. Hartzell performed extensive testing of the propeller on our Velocity XL with Continental IO-550N engine. The folks at Hartzell tested the aircraft/engine/propeller combination for 2-days ... found a harmonic situation that only instruments could detect ... worked on solving the problem ... and finally gave up. The situation, as you say, might be entirely different with a Lycoming engine. We have not made plans to test other aircraft.
SB
----- Original Message -----
From: Andy Millin
To: 'Velocity Aircraft Owners and Builders list'
Sent: Wednesday, April 05, 2006 10:44 AM
Subject: RE: REFLECTOR: Metal prop on Velocity
It was very disappointing to hear.
Velocity had flown with it for a while and it was looking very good. I believe they only tried it with one engine. It was possible, if not probable, that the prop might have worked in other combinations.
I believe it was run with the large Continental. Scott Baker would be able to say.
I have the 260HP Lycoming and would have liked to have seen it tested in that configuration.
Andy
-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Andrew Ellzey
Sent: Wednesday, April 05, 2006 2:45 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Metal prop on Velocity
That's disappointing to hear. I wonder if they tried to balance their prop to get rid of the vibrations, I guess it doesn't matter it sounds like they aren't interested in finding a solution.
Andy
----- Original Message -----
From: Andrew Millin
To: Velocity Aircraft Owners and Builders list
Sent: Wednesday, April 05, 2006 12:26 AM
Subject: REFLECTOR: Metal prop on Velocity
The prop was from Hartzell. It had their semi-scimitar blade. Velocity noticed an increase in airspeed with it. Things were looking good at OSH last year. Scott Baker reported that MT was anxious that there might be another option for us.
Unfortunately, after OSH Hartzell went to Velocity to perform some vibration tests on the aircraft. There were problems and the prop was withdrawn and will not be made available.
It appears they were able to provide the prop from existing parts. I.e., they didn't develop it specially for us. It was probably sitting on a shelf somewhere. And is probably back on that same shelf now.
They do not have plans to start a program to get a prop for us.
Andy
Andrew Ellzey <ajlz72756 at yahoo.com> wrote:
When I purchased my kit last April after sun & fun, Velocity had a aluminum pusher prop that they were showing and testing. Has anyone heard of the results of these trials? It was supposed to be priced competitively with MT.
Andy
----- Original Message -----
From: Ron Brown
To: Velocity Aircraft Owners and Builders list
Sent: Tuesd! ay, April 04, 2006 6:56 PM
Subject: Re: REFLECTOR: Aerocomposite Prop
I was talking to a long time Mix Master owner and asked him about the rear prop blades. He said he never had a problem with the rear prop, just the engine - running hot back there.
I asked the question about metal props back there, and no one could give definitive info about the problem (canard and Velocity lists). Someone said that Mike Melville had a metal prop on of his first pushers (Vari?), he flew it and said that "damn" metal prop is vibrating and has to come off. But beyond that, no one had any real data.
Ronnie
----- Original Message -----
From: HYTEC45 at aol.com
To: reflector at tvbf.org
Sent: Tuesday, April 04, 2006 6:19 PM
Subject: Re: REFLECTOR: Aerocomposite Prop
In a message dated 4/4/2006 2:52:17 P.M. Pacific Standard Time, michalk at awpi.com writes:
They sell props for tractor
airplanes, and I assume Lycoming 4 cylinders, why do they have problems
here?
One thing we have to deal with that tractors don't is the trailing edge wake from the wing hitting the prop. Someone smarter than I may be able to chime in if this has anything to do with prop performance. I know the mix-masters from Cessna had problems with the rear prop even though it was basically the same as the front, but with pusher blades.
TEC
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