I started a new thread to float this topic to the top, rather than continue the already long thread,
http://www.vansairforce.com/community/showthread.php?t=13269
wherein many of us were having prop surging difficulties when MT governors were involved.
The executive summary of my experiences is that an MT remains on my -7, the surging is acceptably controlled (but can be induced), though for a new installation I would use a PCU5000 and avoid an MT. Along the way to this conclusion, however, MT has provided stellar customer service and diligently followed through with every offer of assistance.
The rest of the story. During first four hours of Phase I, the -B serial number version overspeeded and surged plus/minus 100 rpm at low airspeeds, high power, hot oil, e.g., a stop-'n-go or transition from cruise to climb.
MT brought this governor up to -D configuration at no charge. The surging, if anything, was worse.
Hartzell suggested increasing the high speed (low pitch) stop from the 180hp spec as shipped to the 200 horsepower pitch as my parallel valve 360 is producing over 200 hp. This adjustment did not help the surging, but I've left it in.
MT prepared a second unit and shipped it to me to swap out with the first, trusting I'd send one back, rather than again ground the plane while governors travelled to and fro. In conversations leading to this, Juergen (MT governor honcho) said that he'd have to modify a variant unit as it was the only one in house at the moment. All other new -D stock had been shipped to other pilots who were having similar difficulties but none as yet had come back for reissue. Yikes!
This modified second govenor works well, but I can still induce a bit (+/- 25 rpm) for up to ten seconds. I'll keep it for now, but I've not yet tried its response in acro. I'm just happy to have it perform normally in flight regimes that would find my most critical pax aboard - my wife.
I can only conclude that MTs with Hartzells are a poor combination on the knife edge of unacceptable as evidenced by my cherry picking, and others' experiences in the thread noted above. One criticism I have of the MT is that a few degrees of arm travel yield a large rpm change. This sensitivity means that the prop vernier shaft only has to move 3/16" from 2700 to 2400 rpm. Worse, Van's MT bracket requires setting an acute angle between the shaft and control arm at the high rpm stop. This means a little shaft travel pulls the arm through many degrees of rotation. You could mitigate this by adjusting the prop control so the knob sticks out 1" from the panel at high rpm, thus positioning the arm and shaft at 90 degrees in the most used rpm range, but that looks goofy in the cockpit.
I talked to a couple of prop/gov shops and several RV and Rocket drivers. Here's the collected hearsay. Several pilots have gone from MTs to PCU5000s and surging has been eliminated. Even though the PCU5000 is another Jihostroj knock-off (MT and Avia house brand it), Aero Technologies hired an ex-McCauley engineer who redesigned the pump gearing and pressures. I'm not received a negative comment from anyone regarding the PCU5000 in many different applications.
No amount of good customer service can make up for marginal performance. Next project (or if the MT doesn't wear well) I'll try the PCU5000.
John Siebold
Boise, ID
http://www.vansairforce.com/community/showthread.php?t=13269
wherein many of us were having prop surging difficulties when MT governors were involved.
The executive summary of my experiences is that an MT remains on my -7, the surging is acceptably controlled (but can be induced), though for a new installation I would use a PCU5000 and avoid an MT. Along the way to this conclusion, however, MT has provided stellar customer service and diligently followed through with every offer of assistance.
The rest of the story. During first four hours of Phase I, the -B serial number version overspeeded and surged plus/minus 100 rpm at low airspeeds, high power, hot oil, e.g., a stop-'n-go or transition from cruise to climb.
MT brought this governor up to -D configuration at no charge. The surging, if anything, was worse.
Hartzell suggested increasing the high speed (low pitch) stop from the 180hp spec as shipped to the 200 horsepower pitch as my parallel valve 360 is producing over 200 hp. This adjustment did not help the surging, but I've left it in.
MT prepared a second unit and shipped it to me to swap out with the first, trusting I'd send one back, rather than again ground the plane while governors travelled to and fro. In conversations leading to this, Juergen (MT governor honcho) said that he'd have to modify a variant unit as it was the only one in house at the moment. All other new -D stock had been shipped to other pilots who were having similar difficulties but none as yet had come back for reissue. Yikes!
This modified second govenor works well, but I can still induce a bit (+/- 25 rpm) for up to ten seconds. I'll keep it for now, but I've not yet tried its response in acro. I'm just happy to have it perform normally in flight regimes that would find my most critical pax aboard - my wife.
I can only conclude that MTs with Hartzells are a poor combination on the knife edge of unacceptable as evidenced by my cherry picking, and others' experiences in the thread noted above. One criticism I have of the MT is that a few degrees of arm travel yield a large rpm change. This sensitivity means that the prop vernier shaft only has to move 3/16" from 2700 to 2400 rpm. Worse, Van's MT bracket requires setting an acute angle between the shaft and control arm at the high rpm stop. This means a little shaft travel pulls the arm through many degrees of rotation. You could mitigate this by adjusting the prop control so the knob sticks out 1" from the panel at high rpm, thus positioning the arm and shaft at 90 degrees in the most used rpm range, but that looks goofy in the cockpit.
I talked to a couple of prop/gov shops and several RV and Rocket drivers. Here's the collected hearsay. Several pilots have gone from MTs to PCU5000s and surging has been eliminated. Even though the PCU5000 is another Jihostroj knock-off (MT and Avia house brand it), Aero Technologies hired an ex-McCauley engineer who redesigned the pump gearing and pressures. I'm not received a negative comment from anyone regarding the PCU5000 in many different applications.
No amount of good customer service can make up for marginal performance. Next project (or if the MT doesn't wear well) I'll try the PCU5000.
John Siebold
Boise, ID
