Aussie_Paul
06-25-2010, 03:46 AM
Reading Roger's drop keel Raf experience got me reminiscing!!!!!:sorry:
Aussie Paul’s 2002 story of RAF 2000 to Hybrid and Raf mods
I am a very lucky fella. I have been fortunate enough to have conducted probably the most R&D on Raf pitch stability than most. I had to. I “spent me money” and received a pitch unstable quite dangerous machine that was almost impossible to teach productively in. I trusted the Raf management that the "magical" bush and the control geometry worked as an H/stab. I was concerned as I had proven over the years that a stab made training much more productive.
I found eventually that I had been lied to and fitted a stab. I worked up from the too small flat plate stabs to effective airfoil shaped stabs, and was quite happy with the results. The forum guys back in the days of Norm’s forum told me that my "bandaid" fix was better than nothing but that the real problem lay with the high thrust line to CoM offset. Their explanations made sense to me and so I developed Hybrid. Hybrid uses the Raf cabin and quite a bit of the airframe and control systems etc. I replaced the Raf belt drive with a Hirth or Autoflight gear box and turned the gearbox around compared to almost everyone else and placed the thrust line beneath the engine crank line. I stepped the keel and was able to lower the thrust line 5". That meant that the engine was now attached to the mast 7" higher. Not a bad scenario to be able to lift the engine and redrive weight(approx 270 lbs) up 7” and lower the thrust line 5” all with the one modification!!!!
Because the prop is now going in the opposite direction a new tail had to be made. As the Raf with the doors on is quite yaw unstable we made the tail 30% larger. That solved the doors on yaw instability. The first test flights were conducted with a Raf rotor head and Raf blades. I had to hand spin the Raf blades as I did not have a pre rotator. At this point Hybrid did not have a stab fitted.
Hybrid without a stab flew much more stably that a Raf with a stab!!!! Wow I was pleased. We added a small stab and I could fly circuit after circuit with the stick locked against the dash. After lift off and attitude set for 55 mph I would lock the stick against the dash with an adjustable, for various speeds, bar. I could fly the circuit using power, roll and rudder BUT no pitch control at all. I would begin the flare and the lock would drop out and I would finish the landing. I would take off and repeat the performance. I must tell you that this was a very exciting time for me.
Since then we have experimented with various rotors, pre rotators, props, gearboxes, rotor heads with various offsets, and some different designs of h/stabs etc. We have now found that since we have the airframe stable with CLT and an h/stab, that various brands of rotors can have quite different stability/instability characteristics.
I have developed a set of modifications that make a Raf a much more use friendly and productive training gyroplane than just adding a stab. These certainly are not necessary for reasonably safe flying as Stan and the stabbed Raf guys are finding. I have developed the next level of safety for the extremely large thrust to Centre of Mass (CoM) offset of the Raf. These extra mods make a Raf a much more productive training machine, as I can let the student get closer to the “edge” without worrying. A lot of instructors have to take over too early. I like to have my training machine set up, and know my machine so well, that I can let the student go to the point that he thinks he will lose it, and still be able to talk him back without running the risk of dying. That is what I call a very productive learning environment for any training scenario.
These mods require very little financial outlay. Just some cutting, drilling, and spanner work, and a couple of 3/8” rod ends and some ¼” plate approx. 8” X 12”.
I believe using my mods and a stab with vertical fins to help with the "doors on" yaw instability, is the best a Raf can be made without major expense.
Wow!! I have got carried away a bit, but there have been numerous new members to the ever growing Todd’s forum, so I hope that the old timers will put up with my ramblings for the benefit of the new members.
Aussie Paul. :)
Aussie Paul’s 2002 story of RAF 2000 to Hybrid and Raf mods
I am a very lucky fella. I have been fortunate enough to have conducted probably the most R&D on Raf pitch stability than most. I had to. I “spent me money” and received a pitch unstable quite dangerous machine that was almost impossible to teach productively in. I trusted the Raf management that the "magical" bush and the control geometry worked as an H/stab. I was concerned as I had proven over the years that a stab made training much more productive.
I found eventually that I had been lied to and fitted a stab. I worked up from the too small flat plate stabs to effective airfoil shaped stabs, and was quite happy with the results. The forum guys back in the days of Norm’s forum told me that my "bandaid" fix was better than nothing but that the real problem lay with the high thrust line to CoM offset. Their explanations made sense to me and so I developed Hybrid. Hybrid uses the Raf cabin and quite a bit of the airframe and control systems etc. I replaced the Raf belt drive with a Hirth or Autoflight gear box and turned the gearbox around compared to almost everyone else and placed the thrust line beneath the engine crank line. I stepped the keel and was able to lower the thrust line 5". That meant that the engine was now attached to the mast 7" higher. Not a bad scenario to be able to lift the engine and redrive weight(approx 270 lbs) up 7” and lower the thrust line 5” all with the one modification!!!!
Because the prop is now going in the opposite direction a new tail had to be made. As the Raf with the doors on is quite yaw unstable we made the tail 30% larger. That solved the doors on yaw instability. The first test flights were conducted with a Raf rotor head and Raf blades. I had to hand spin the Raf blades as I did not have a pre rotator. At this point Hybrid did not have a stab fitted.
Hybrid without a stab flew much more stably that a Raf with a stab!!!! Wow I was pleased. We added a small stab and I could fly circuit after circuit with the stick locked against the dash. After lift off and attitude set for 55 mph I would lock the stick against the dash with an adjustable, for various speeds, bar. I could fly the circuit using power, roll and rudder BUT no pitch control at all. I would begin the flare and the lock would drop out and I would finish the landing. I would take off and repeat the performance. I must tell you that this was a very exciting time for me.
Since then we have experimented with various rotors, pre rotators, props, gearboxes, rotor heads with various offsets, and some different designs of h/stabs etc. We have now found that since we have the airframe stable with CLT and an h/stab, that various brands of rotors can have quite different stability/instability characteristics.
I have developed a set of modifications that make a Raf a much more use friendly and productive training gyroplane than just adding a stab. These certainly are not necessary for reasonably safe flying as Stan and the stabbed Raf guys are finding. I have developed the next level of safety for the extremely large thrust to Centre of Mass (CoM) offset of the Raf. These extra mods make a Raf a much more productive training machine, as I can let the student get closer to the “edge” without worrying. A lot of instructors have to take over too early. I like to have my training machine set up, and know my machine so well, that I can let the student go to the point that he thinks he will lose it, and still be able to talk him back without running the risk of dying. That is what I call a very productive learning environment for any training scenario.
These mods require very little financial outlay. Just some cutting, drilling, and spanner work, and a couple of 3/8” rod ends and some ¼” plate approx. 8” X 12”.
I believe using my mods and a stab with vertical fins to help with the "doors on" yaw instability, is the best a Raf can be made without major expense.
Wow!! I have got carried away a bit, but there have been numerous new members to the ever growing Todd’s forum, so I hope that the old timers will put up with my ramblings for the benefit of the new members.
Aussie Paul. :)