Post by bil438 on Aug 7, 2011 16:35:56 GMT -5
Those of you who have followed the Sonerai lists for some time, may remember that I installed a Jabiru 2200a engine, 50 lbs lighter than the VW, in My Sonerai II LS. It is rated at 80 hp. To get the CG right the new engine required a new mount which was placed 10" forward of the firewall. Also the battery was placed near the firewall.
The simple story is that neutral yaw stability became divergent. Sonerai is a great plane to fly if you accept it as designed. I made one change, to start with. ThenI coined the name Wild Weasel.
I've been seeking information, drawings and making preparations for 2 years. Thanks to all those who replied and provided help.
After 8 months of work and delays, I was able to fly my Sonerai II today, the first time in 2011. It's like flying a different aircraft, one that fun and friendly.
Yesterday I did some taxi runs and I noticed that slowing down from 40mph, there was a spot where it wanted to be come squirrely. I was able to hold it straight but it wasn't automatic. Somehow this seemed different from 2010, but a small price to pay for improved flight stability.
All this matters because I have increased the Vertical Fin by 1/3 area, and the Rudder by 40% greater area. The rudder also was the recipient of a 10 sq in Rudder Tab with an incidence of 5 degrees left. I already have a 90 sq in Ventral fin from 2008.
Lastly the mechanical stabilizer trim mechanism (2009) was removed (it slipped) and a new electric trim mechanism installed. It consists of a Jabiru Flap Actuator operating the stab trim through a bell crank to reduce output travel. 2" input = 1/2" output. It works just beautifully.
The test flight went this way. The takeoff remains unchanged, at least in summer weather. The engine pulls as strongly as ever and showed no faults. The EGT did not exceed 1100F and the cylinders never exceeded 225F. Cowl flaps are full open.(another mod) Oil temp stays at 190F. (Oil cooler installations are my specialty. )
I climbed out straight to Hwy 401 and paralled the Highway until 3000 ft. There were nice fields just north of the highway so I did my air work there.
I began with pitching the aircraft up and down 45 degrees but not above 150 kts. The pitch control of the aircraft remained unchanged. I may have seen +2g's when I pulled out. The aircraft structure and tail feel solid. With both Stablilizer and Rudder mods plus elevator trim, solid feels great.
So I tried some reversing 45 degree turns. Those of you who know my aircraft may know that it used to be subject to divergent yaw when rolled briskly. If the rudder was used aggressively to stop the yaw things quickly got wilder.. With the increased fin area, this yawing tendency has stopped. I expected improvement but a total elimination of assymetric yaw comes as a nice surprise.
Third, I set the speed to 130 mph and increased pressure on the rudder pedals, right rudder first to 10 degrees and released the pedal at 10 degrees. I was astonished when the aircraft ball indicator returned to neutral. So I did the same to the left rudder with the same result. Amazing. Just to be sure of what I was seeing I took my feet off the pedals and the ball indicator stayed centered and the compass indication stayed the same. Then I increased the right rudder to 15 degrees of yaw. The aircraft remained stable and I did not experience any pre-stall buffet as I had in 2007. Then I repeated this with 15 degrees left rudder and released the pedal. The result was the same. Very nice and also a first for me.
I wanted to know whether the aircraft had improved any when medium then steep reversing turns are made. To my satisfaction, the aircraft turns nicely at 90 degrees and shows no unusual tendencies. Then I made reversing 90 degree turns and the ball remained centered. This was very good news. I did perhaps 6 or these. The assymetric yaw is gone.
The rudder tab was installed to reduce the pilot workload in cruise. It seeemd a shame to rebuild the rudder and not incorporate nut-plates to accommodate a rudder tab. I sped up to say 140 mph to see what the yaw stability was like. With the 5 degree rudder tab, the aircraft flies straight with the ball centered and at every airspeed throughout the airspeed range. Amazing. Sore feet and knees are past.
While I was in cruise I tried to adjust the elevator trim to see whether it had enough travel at the 3/4" Stabilizer Leading edge down position, my usual neutral setting. The answer was that the elevator trim runs out, before the aircraft is trimmed level.
That being the case, I switched the Electric stabilizer trim on and pressed the trim switch to up, perhaps 1/2 second. I could feel the change. It was quite noticeable. Then I tried to retrim the elevator and found that the aircraft trimmed for pitch with the elevator trim in the neutral position. That's very nice to have. I estimate that the aircraft flies level for pitch with the stabilizer front spar 5/8" down from the square steel tube above it.
Throughout the later approach the elevator trim was sufficient to keep the aircraft trimmed the way I like it, which is slightly aircraft nose down. In did not have to re-trim the stab during this flight though I burned off an hours fuel from the aux (rear) tank.
I tried an overshoot at Lancaster Airpark as friends were there, but they say I am silent and invisible at 1000'.
Those nice long fields beckoned again so I repeated some of the maneuvers north-west of Lancaster, ON.
I'd been up for say 45 minutes so I returned to Cornwall. All the engine numbers were in the green. My plan was to enter the circuit and fly one missed approach which saw the final quite a bit lower than I wanted so I went around at 100'. The second approach went better and I touched down say 200' past the threshold.
But there were 2 students in the circuit and one guy apparently from China. I saw him on short final just before he called on downwind.)
Unintelligible.
The aircraft lands straight ahead and stays straight until say 40 mph, then it wants to squirm on the tailwheel. My conclusion is that the bigger rudder becomes ineffective by about 40 mph, so that is where things get twitchy. It's better if I reduce the braking below 45 mph. Touchdown is at say 65 mph.
With the 2.5" x 4" tailwheel,(I made the wheel) when I round off to a 3 point position, the tailwheel touches down first. As it touches the wings stall and the main wheels drop in from say 6". You can feel the drop but there is no bounce and it rolls out straight. Good enough.
After returning to the hangar line, I inspected the aircraft and checked the tires and oil quantity. Both are unchanged from before flight. The oil streaks I had before are no more. Especially important the canopy is clear.
Structurally all is well. The Horizontal Stab has no play. (Oh yes. I designed and installed a Stabilizer Centering and flutter damper.) The stick was steady throughout the speed envelope.
So what does all this mean? When I bought this aircraft I thought I was buying a fun aircraft, with light controls, one that was fun to fly, easy on fuel and fast in cruise. In 2007, I had much more than I bargained for.
With these 4 changes: Fin, Rudder, Stab Trim, & Rudder Tab, the aircraft now flies the way I hoped and expected the aircraft to fly in 2007. I now have the sport plane I thought I'd bought. I am able to trim it for pitch reliably and the rudder tab trims it for neutral yaw all the time. In turns I need to use rudder but that is true for all taildraggers. Yet the rudder needed is much less than before this rudder mod. The aircraft will roll if the stick is left unattended but this occurs gradually and one can see how roll is developing. The changes are slow and easy to correct. With one's hand on the stick, the aircraft now flies straight and level. Most of all I can relax my feet in cruise. Aug 5 is a banner day in my Hangar.
The Flight Stability guys and local test pilots tell me this. As it was the aircraft required so much attention just to fly it, that if an emergency arose there would be very little concentration left to deal with the emergency. Before, If I wanted to do something else (navigate) I had to get it straight and level. Now, the neural circuits I have fly the plane, so I can do everything else that airmanship requires.
Admittedly today the wind was generally calm. The sock just hung. I will need to see what it will fly like in mild turbulence and when stronger thermals are present.
Thanks once again to those who gave me good engineering advice: Most of them are local flight stability engineers, but several from this list sent drawings and ideas. One member sent me a report on the handling of his SII after the Fin and Rudder mod.
No doubt someone has helped me whose contribution I cannot recall. Thanks to all of you.
My plan is to fly Papa Gold Sierra every flyable day this summer and fall.
Bill
The simple story is that neutral yaw stability became divergent. Sonerai is a great plane to fly if you accept it as designed. I made one change, to start with. ThenI coined the name Wild Weasel.
I've been seeking information, drawings and making preparations for 2 years. Thanks to all those who replied and provided help.
After 8 months of work and delays, I was able to fly my Sonerai II today, the first time in 2011. It's like flying a different aircraft, one that fun and friendly.
Yesterday I did some taxi runs and I noticed that slowing down from 40mph, there was a spot where it wanted to be come squirrely. I was able to hold it straight but it wasn't automatic. Somehow this seemed different from 2010, but a small price to pay for improved flight stability.
All this matters because I have increased the Vertical Fin by 1/3 area, and the Rudder by 40% greater area. The rudder also was the recipient of a 10 sq in Rudder Tab with an incidence of 5 degrees left. I already have a 90 sq in Ventral fin from 2008.
Lastly the mechanical stabilizer trim mechanism (2009) was removed (it slipped) and a new electric trim mechanism installed. It consists of a Jabiru Flap Actuator operating the stab trim through a bell crank to reduce output travel. 2" input = 1/2" output. It works just beautifully.
The test flight went this way. The takeoff remains unchanged, at least in summer weather. The engine pulls as strongly as ever and showed no faults. The EGT did not exceed 1100F and the cylinders never exceeded 225F. Cowl flaps are full open.(another mod) Oil temp stays at 190F. (Oil cooler installations are my specialty. )
I climbed out straight to Hwy 401 and paralled the Highway until 3000 ft. There were nice fields just north of the highway so I did my air work there.
I began with pitching the aircraft up and down 45 degrees but not above 150 kts. The pitch control of the aircraft remained unchanged. I may have seen +2g's when I pulled out. The aircraft structure and tail feel solid. With both Stablilizer and Rudder mods plus elevator trim, solid feels great.
So I tried some reversing 45 degree turns. Those of you who know my aircraft may know that it used to be subject to divergent yaw when rolled briskly. If the rudder was used aggressively to stop the yaw things quickly got wilder.. With the increased fin area, this yawing tendency has stopped. I expected improvement but a total elimination of assymetric yaw comes as a nice surprise.
Third, I set the speed to 130 mph and increased pressure on the rudder pedals, right rudder first to 10 degrees and released the pedal at 10 degrees. I was astonished when the aircraft ball indicator returned to neutral. So I did the same to the left rudder with the same result. Amazing. Just to be sure of what I was seeing I took my feet off the pedals and the ball indicator stayed centered and the compass indication stayed the same. Then I increased the right rudder to 15 degrees of yaw. The aircraft remained stable and I did not experience any pre-stall buffet as I had in 2007. Then I repeated this with 15 degrees left rudder and released the pedal. The result was the same. Very nice and also a first for me.
I wanted to know whether the aircraft had improved any when medium then steep reversing turns are made. To my satisfaction, the aircraft turns nicely at 90 degrees and shows no unusual tendencies. Then I made reversing 90 degree turns and the ball remained centered. This was very good news. I did perhaps 6 or these. The assymetric yaw is gone.
The rudder tab was installed to reduce the pilot workload in cruise. It seeemd a shame to rebuild the rudder and not incorporate nut-plates to accommodate a rudder tab. I sped up to say 140 mph to see what the yaw stability was like. With the 5 degree rudder tab, the aircraft flies straight with the ball centered and at every airspeed throughout the airspeed range. Amazing. Sore feet and knees are past.
While I was in cruise I tried to adjust the elevator trim to see whether it had enough travel at the 3/4" Stabilizer Leading edge down position, my usual neutral setting. The answer was that the elevator trim runs out, before the aircraft is trimmed level.
That being the case, I switched the Electric stabilizer trim on and pressed the trim switch to up, perhaps 1/2 second. I could feel the change. It was quite noticeable. Then I tried to retrim the elevator and found that the aircraft trimmed for pitch with the elevator trim in the neutral position. That's very nice to have. I estimate that the aircraft flies level for pitch with the stabilizer front spar 5/8" down from the square steel tube above it.
Throughout the later approach the elevator trim was sufficient to keep the aircraft trimmed the way I like it, which is slightly aircraft nose down. In did not have to re-trim the stab during this flight though I burned off an hours fuel from the aux (rear) tank.
I tried an overshoot at Lancaster Airpark as friends were there, but they say I am silent and invisible at 1000'.
Those nice long fields beckoned again so I repeated some of the maneuvers north-west of Lancaster, ON.
I'd been up for say 45 minutes so I returned to Cornwall. All the engine numbers were in the green. My plan was to enter the circuit and fly one missed approach which saw the final quite a bit lower than I wanted so I went around at 100'. The second approach went better and I touched down say 200' past the threshold.
But there were 2 students in the circuit and one guy apparently from China. I saw him on short final just before he called on downwind.)
Unintelligible.The aircraft lands straight ahead and stays straight until say 40 mph, then it wants to squirm on the tailwheel. My conclusion is that the bigger rudder becomes ineffective by about 40 mph, so that is where things get twitchy. It's better if I reduce the braking below 45 mph. Touchdown is at say 65 mph.
With the 2.5" x 4" tailwheel,(I made the wheel) when I round off to a 3 point position, the tailwheel touches down first. As it touches the wings stall and the main wheels drop in from say 6". You can feel the drop but there is no bounce and it rolls out straight. Good enough.
After returning to the hangar line, I inspected the aircraft and checked the tires and oil quantity. Both are unchanged from before flight. The oil streaks I had before are no more. Especially important the canopy is clear.
Structurally all is well. The Horizontal Stab has no play. (Oh yes. I designed and installed a Stabilizer Centering and flutter damper.) The stick was steady throughout the speed envelope.
So what does all this mean? When I bought this aircraft I thought I was buying a fun aircraft, with light controls, one that was fun to fly, easy on fuel and fast in cruise. In 2007, I had much more than I bargained for.
With these 4 changes: Fin, Rudder, Stab Trim, & Rudder Tab, the aircraft now flies the way I hoped and expected the aircraft to fly in 2007. I now have the sport plane I thought I'd bought. I am able to trim it for pitch reliably and the rudder tab trims it for neutral yaw all the time. In turns I need to use rudder but that is true for all taildraggers. Yet the rudder needed is much less than before this rudder mod. The aircraft will roll if the stick is left unattended but this occurs gradually and one can see how roll is developing. The changes are slow and easy to correct. With one's hand on the stick, the aircraft now flies straight and level. Most of all I can relax my feet in cruise. Aug 5 is a banner day in my Hangar.
The Flight Stability guys and local test pilots tell me this. As it was the aircraft required so much attention just to fly it, that if an emergency arose there would be very little concentration left to deal with the emergency. Before, If I wanted to do something else (navigate) I had to get it straight and level. Now, the neural circuits I have fly the plane, so I can do everything else that airmanship requires.
Admittedly today the wind was generally calm. The sock just hung. I will need to see what it will fly like in mild turbulence and when stronger thermals are present.
Thanks once again to those who gave me good engineering advice: Most of them are local flight stability engineers, but several from this list sent drawings and ideas. One member sent me a report on the handling of his SII after the Fin and Rudder mod.
No doubt someone has helped me whose contribution I cannot recall. Thanks to all of you.
My plan is to fly Papa Gold Sierra every flyable day this summer and fall.
Bill
