We get many questions from builders regarding the propeller that is used for the Falco in our kits. They are:
Propeller & Spinner for 150-160 hp engines
Hartzell HC-C2YL-1BF/F7663A-4 propeller with A2476-19 spinner mounting kit installed.
Hartzell A2298-2 spinner assembly.
Propeller & Spinner for 180 hp engines
Hartzell HC-C2YK-1BF/F7666A-2 propeller with A2476-19 spinner mounting kit installed.
Hartzell A2298-2 spinner assembly.
From "Construction Notes" Falco Builders Letter, March 1996
Stanley Harper is completing his Falco and wants to install a fixed pitch propeller. He asked for the specifications of the prop used on the production Falcos.
As I recall from some long-ago document from Hoffman, the German propeller manufacturer, there were two fixed-pitch propellers specified for the Falco. One was a 'climb' prop and one was a 'cruise' prop. I remember noting some years ago that the propeller on my Falco was the 'climb' prop. After years of flying behind it, I would describe it as a 'cruise' prop to anyone. I can't imagine flying behind a prop with more pitch than mine.
The flight manual for the Aeromere Series III Falco calls for a Hoffman propeller with a pitch of 70.86" (180 cm) and a diameter of 68.89" (175 cm). This is the only fixed pitch propeller mentioned in the flight manual. I believe this is the 'cruise' prop mentioned in the Hoffman document.
However, the actual propeller installed on my Falco is a Hoffman HO23 HM - 175 170. From this part number, I believe we are looking at a propeller with a diameter of 175 cm (68.89") and a pitch of 170 cm (66.96").
With this propeller, my Falco gets off the ground slowly, but it will get off my 2500' grass strip when the ground is dry. When the grass is long, when the ground is a little soft, or when the Falco is filled with fuel and two pilots, it is very marginal. On takeoff roll, the engine turns about 2200 to 2300 rpm, so you can see that it is not developing full power.
It tends to cruise at about 2700 rpm at 5,000 feet, and perhaps at 2500 rpm at 8-10,000 feet. With the carbureted engine, I always find the engine runs smoother with the throttle wide open, so I always cruise with a fully open throttle, and only retard the throttle for descent or low altitude flying. So unless you have a very long strip, I'd suggest sticking with the 'climb' prop I've got on the Corporate Disgrace if you must use a fixed pitch propeller.
From "Construction Notes" Falco Builders Letter, September 1989
I can also report another perplexing problem that Pawel Kwiecinski has had with his propeller governor. Pawel and Irek have been doing a lot of inverted flying with the Falco, in fact, they are the only ones to ever have flown the Falco inverted for any length of time.
The propeller that we use is a standard, non-aerobatic propeller. This means that it uses oil pressure to increase pitch. This is the standard type of propeller used on single-engine aircraft because it is the lightest. The only difficulty with this type of prop is that when you do aerobatics, you may experience a momentary oil pressure loss-in that case the propeller goes to flat pitch, and the engine overspeeds.
Aerobatic propellers have counterweights on the blades and use oil pressure to decrease pitch. Any momentary oil pressure loss causes the engine to go to a high pitch and the engine slows down. Aerobatic propellers are heavier and the counterweights prevent the use of the nice looking spinner that we have.
Pawel reported that his engine would overspeed after 15 seconds of inverted flight. Pawel heard that Woodward Governor made special type of governor that uses an accumulator. We decided to switch to that system and see what it would do.
The way a governor works is that it takes oil from the back of the engine, pumps it to a higher pressure and then regulates this pressure. The regulated-pressure oil is fed to the propeller through a tube that passes below the cylinders on the right side of the engine. The tube puts oil in the front of the engine and is directed to the propeller. The important thing to remember is that the governor takes pressurized oil from the oil galleries of the engine. The oil is picked up at the bottom of the sump, goes to the oil pump that then sends the oil under pressure to various parts of the engine that need lubrication.
If this supply of pressurized oil is interrupted, the governor is unable to supply oil pressure to the propeller. The accumulator is plumbed so that it is between the engine and the governor's oil pump. During normal operation, the accumulator fills with oil and if there is an interruption in the flow of oil, the accumulator pushes oil to the governor, which doesn't care where the oil comes from.
The accumulator is a cylinder about two inches in diameter and twelve inches long. You mount it on the firewall with a hose to the governor. Inside the accumulator is a piston, and you pump about 100 psi of air into the end. It is this pressurized air on the other side of the piston that supplies the pressure. When the engine is not running, the air pushes the piston to the far end of the accumulator and all oil is pushed from the accumulator. When the engine is running, the oil pressure of the engine is greater than the pressure in the accumulator, so oil flows into the cylinder.
The first problem that we encountered was that the governor supplied by Woodward has a different housing than the one we normally use. Our governor has a head with a number of screws on it, which we use to mount the governor bracket. The type Pawel received did not have the screws. We inquired of Woodward if they could just supply us with the same type of housing.
This turned out to be one of those absurdities that only makes sense when you rely of government approvals for insuring safety. To provide for the installation of the accumulator, Woodward drills and taps the housing of the governor. There is no difficulty at all in drilling our standard governor since the housing are internally identical and only have the slightest differences on the outside.
Unfortunately, this hole in the governor is what is known as an Engineering Change Order, for which Woodward has a minimun charge of $1800.00. The reason is simple, any changes must be in accordance with certification requirements, so they have to do a new drawing, define an inspection procedure, make changes to the operation and service manuals, mail all these to their distributors, etc. Woodward is embarrassed by all of this, but sees no way out. They readily admit that a homebuilder can drill his own hole and adapt the present governor-but you should be careful to make sure all chips are cleaned out. This certainly calls for the governor to be taken apart, drilled, cleaned and then re-assembled.
So Pawel kept the governor and made a clamp to go around the governor housing. This provided the screw holes for the governor control bracket. I have a copy of his drawing and CNC milling machine program should you need a copy.
Pawel reported that the accumulator increases the inverted time from 15 seconds to one minute and 15 seconds before the engine overspeeds. That is enough for him, since they don't normally fly inverted for any extended periods of time.
Now we get to the part that makes no sense. With his inverted oil system and accumulator, Pawel should be able to fly inverted until the fuel is exhausted. The symptoms that Pawel describe exactly fit those of an inverted oil system that is not functioning properly. You would expect that when going to inverted, there would be a short interruption in oil, but once inverted the inverted oil system should pick up oil again. Pawel insists that his oil pressure gauge reads normally throughout the inverted flight, but this makes no sense at all to me.
I think what is happening is that once he goes inverted, the engine oil pressure drops to zero and the accumulator supplies a minute of oil to the governor. I think Pawel has no pressure at all when the engine is inverted.
I have talked about this to Lycoming representatives, Al Hadaway of High Performance Engines and aerobatic pilot Clint McHenry. All agree that the description makes no sense and that it sounds like the inverted oil system is not functioning correctly. Clint was interested to know if it made any difference if you rolled to the right or left, pointing out that the interruption occurs at knife-edge and that competition aerobatic pilots set things up so that they can maintain oil pressure in knife-edge flight to one side.
I have talked to Pawel about this, and he says that he understands what we are saying and is as confused as the rest of us. He doesn't have any answers and plans to investigate the matter.