Henshaw Challenge: Success! (Now includes photographs)
Congratulations Chalkie on a great achievement, and in being in the vanguard of bringing the capabililties of homebuilt/permit aircraft to the authorities' attention.
Skua
Skua
Join Date: Mar 2009
Location: Jeffreys Bay, EC, South Africa.
Age: 75
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ZU-CLC and the autopilot.
The GP4 is fitted with an MGL EFIS and this has software to drive an autopilot that can be programmed in flight, in 'real time' with the autopilot active. The autopilot was a late addition and was tested and adjusted a few days before departure.
It worked OK in pitch at low weight and more fwd CG, but on the London flight at high gross weight and CG approaching the aft limit the autopilot could not handle pitch inputs. I did spend hours trying to find a happy point of control input; control authority and control lag but after having the autopilot try to eject me through the canopy more than once, I elected to tell the EFIS that a pitch servo was not fitted. This allowed me to use the roll channel as a wing-leveller. I do agree that this reduced my workload, but the aircraft had to be flown every single second till the ferry tank was empty as this allowed the CG to move forward a bit and I could then relax a bit.
Remember that the GP4 is designed to be neutrally stable and as the aircraft was designed for the Lycoming IO-360 (angle valve heads) and CLC has parallel valve cylinders, it actually has a more fwd CG than design
and we only went back to 34% MAC where the limit is 35% MAC, even at this CG, the aircraft had to be flown all the time. Any pitch disturbance had to be corrected, before it became exponential.
So I did fly many of the hours without an autopilot, and at times, simply to keep myself busy and awake. I also logged more actual IF time than I care to remember.
To the purists: there is only one Mew Gull in the word and I doubt it will fly to the Cape and back again in its life.
Regards, Chalkie.
It worked OK in pitch at low weight and more fwd CG, but on the London flight at high gross weight and CG approaching the aft limit the autopilot could not handle pitch inputs. I did spend hours trying to find a happy point of control input; control authority and control lag but after having the autopilot try to eject me through the canopy more than once, I elected to tell the EFIS that a pitch servo was not fitted. This allowed me to use the roll channel as a wing-leveller. I do agree that this reduced my workload, but the aircraft had to be flown every single second till the ferry tank was empty as this allowed the CG to move forward a bit and I could then relax a bit.
Remember that the GP4 is designed to be neutrally stable and as the aircraft was designed for the Lycoming IO-360 (angle valve heads) and CLC has parallel valve cylinders, it actually has a more fwd CG than design
and we only went back to 34% MAC where the limit is 35% MAC, even at this CG, the aircraft had to be flown all the time. Any pitch disturbance had to be corrected, before it became exponential.
So I did fly many of the hours without an autopilot, and at times, simply to keep myself busy and awake. I also logged more actual IF time than I care to remember.
To the purists: there is only one Mew Gull in the word and I doubt it will fly to the Cape and back again in its life.
Regards, Chalkie.
Join Date: Oct 2003
Location: uk
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Chuck,
I found your experience with the pitch/stability problems very interesting. Would you care to share any other experiences/issues or anecdotes about the flight with us? How much help did you receive from A.T.C. with weather avoidance and direct routings? Any more detail on the problems encountered on the ground? What were the most difficult challenges to overcome?
I found your experience with the pitch/stability problems very interesting. Would you care to share any other experiences/issues or anecdotes about the flight with us? How much help did you receive from A.T.C. with weather avoidance and direct routings? Any more detail on the problems encountered on the ground? What were the most difficult challenges to overcome?
Join Date: Mar 2009
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Ja Nee Japie, 
Just read my own posting again and what is not clear is the lighter engine pushed the CG back, but we moved the battery FWD to counteract this force and ended up with a less AFT CG for the design at light weights. Heavy with fuel, pilot and survival gear, pushed the CG aft, but not beyond limits.
ATC in Africa (RSA) gave direct routings, but the routes are close to direct at any rate. France gave direct routings and wished me "Bon Voyage" through Military airspace, but this only saved a few miles, if any.
Luanda demanded that I route over VNA, but to any / all who know this airspace, it is about the most congested and also the worst controlled airspace in Africa, so I elected to stick to my flight plan and route direct.
This made me a nervous boy, but prevented a long detour over Luanda.
Regards, Chalkie.
Just read my own posting again and what is not clear is the lighter engine pushed the CG back, but we moved the battery FWD to counteract this force and ended up with a less AFT CG for the design at light weights. Heavy with fuel, pilot and survival gear, pushed the CG aft, but not beyond limits.
ATC in Africa (RSA) gave direct routings, but the routes are close to direct at any rate. France gave direct routings and wished me "Bon Voyage" through Military airspace, but this only saved a few miles, if any.
Luanda demanded that I route over VNA, but to any / all who know this airspace, it is about the most congested and also the worst controlled airspace in Africa, so I elected to stick to my flight plan and route direct.
This made me a nervous boy, but prevented a long detour over Luanda.
Regards, Chalkie.
