3 hours ago
If anyone is not flying with the longer aluminum skids with the steel reinforcement on both sides, they need to in my opinion and experience.
Only days after writing the November article I was flying with a student here at my training center in Missouri. He was beginning his phase two flight training and was very excited to begin practicing autos. Larry had taken his 162f to Mark Peterson for his hover training and Mark had installed one of the first cog drives to be installed on Rotorway helicopters, it was produced by John Spurling and called the Pro-Drive. The kit was a new cog belt, Drive sprocket for the 30mm secondary shaft, and the large cog sprocket that mounted on the main shaft to replace the chain drive sprocket. Removing the chain drive opened up the access to the engine compartment, cut the weight of the chain out, and got rid of the ever-leaking chain bath that would leak chain oil over the drive belts causing them to slip.
The instructions for installing the Pro-Drive gave the set up tension that must be held on the cog belt and this tension was accomplished by shimming the secondary back enough to hold that tension at 70 degrees F. Mark set the cog drive up correctly and then he provided Larry with his hover training. Larry then took his helicopter home and practiced his hovering until he was confident and proficient in his skill set.
He called me and asked me if I would give him his phase two altitude training as I was closer than Mark and I agreed to do so. I had not seen the new cog drive before so I gave it a really good inspection for my own learning. It looked great. The helicopter was in my heated hangar during my initial inspection and once I determined that all was good we rolled it outside into the cold winter air. After fueling we got in, started the engine, and lifted to a hover. Larry showed me that he had achieved the needed hover skills so we decided to take off and head to the local airport for some initial pattern work.
As we were climbing out and increasing our airspeed the helicopter wanted to nose over and it took progressively more aft cyclic to keep the nose from dropping. I informed Larry that this was not a desirable condition so I turned the helicopter around and headed back to the hangar. Upon inspection I noticed that the horizontal stabilizer was set at an angle with the leading edge up higher than the specs called for. We modified the mount holes to allow the stabilizer cord line to be in line with the top of the tail boom. This should give us a good cyclic position in forward flight.
The day before we had installed the extended reinforced skids and flipped the front landing gear leg for more support in case of a run on landing.
As we were beginning our next take off from my helipad, we were accelerating through about 10 to 12 mph and were about 5 feet skid height when all at once the engine raced, the ship did an immediate rotation to the right and dropped. This one was a real surprise and happened in a hear-beat.
I informed Larry “I have it” at which time he let go of the controls. Larry and I had just installed the extended reinforced skids with the front gear leg reversed and it was what saved the ship. As the ship dropped and spun I to the right, chopped the throttle, applied full up collective, cyclic opposite to the direction that we were traveling, and full left anti-torque pedal. The helicopter dropped onto the front of the left skid, where the stock skid will snap off, and pivoted around to the 180 degree position of our original take off direction of travel.
![[Image: Cog%20break%201.jpg]](https://rotorwayforums.com/flywithorv/www.flywithorv.com/images/Drive%20Train/Cog%20break%201.jpg)
We were then sliding backwards and the ship rocked back onto the tail rotor and slid to a stop. We surely would have rolled over had it not been for the extended reinforced skids which allowed the ship to pivot the 180 degrees to where the tail boom acted as an outrigger preventing the ship from rolling over backwards.
Upon inspection we found that the new factory cog belt with only 21 hours on it had snapped. This was the first instance of a ship equipped with the tensioned cog drive that I was aware of the cog belt breaking. When the belt broke, the power to the main rotor was disconnected so all of the engine power went to the tail rotor, snapping the nose of the ship 90 degrees to the right. We were very fortunate to have not experienced a rollover but we sure came close.
![[Image: Cog%20break%202.jpg]](https://rotorwayforums.com/flywithorv/www.flywithorv.com/images/Drive%20Train/Cog%20break%202.jpg)
I have included several photos of Larry’s ship following the belt break. There is some damage but not nearly as much as would occur from a rollover. The belt manufacturer engineers stated that the break was most likely from the belt being run with too little tension allowing the cogs to ride up the driving cog wheel which can hyper extend the reinforcing fibers causing a belt failure.
![[Image: Cog%20break%203.jpg]](https://rotorwayforums.com/flywithorv/www.flywithorv.com/images/Drive%20Train/Cog%20break%203.jpg)
![[Image: Cog%20break%204.jpg]](https://rotorwayforums.com/flywithorv/www.flywithorv.com/images/Drive%20Train/Cog%20break%204.jpg)
Shortly after this incident I received a call from Bruce in Main. He told me that the exact same thing happened to his AP cog drive belt as he was in a hover and setting down. He told me that the hard set down also damaged his ships tail rotor and tail boom as well as the landing gear and skids but he was also able to keep the ship upright.
The reason the cog belt broke was the change in temperature in the operating environment. When Mark set up the cog belt to spec it was set up at 70 degrees f. When I checked it in my heated shop it was at 70 degrees F. We then rolled the helicopter outside into the 40 degree f air and began our flight training. In the cold air the large aluminum cog wheel would shrink relaxing the tension on the cog belt. Pro-Drive's response was that we should re-shim the secondary for the cooler temps to maintain proper cog belt tension. That is a royal pain.
I did some research and found that cog belts in this application should always be run with a tensioner to keep the cog belt at the proper tension at all operational temperature ranges. From that point on we began installing tensioners onto all of the cog systems as they were converted from the original chain drives.
As always, only fly your ships over areas that are safe to auto into. If this should happen at altitude, it would give the pilot more time to get to the ground safely with no damage.
Only days after writing the November article I was flying with a student here at my training center in Missouri. He was beginning his phase two flight training and was very excited to begin practicing autos. Larry had taken his 162f to Mark Peterson for his hover training and Mark had installed one of the first cog drives to be installed on Rotorway helicopters, it was produced by John Spurling and called the Pro-Drive. The kit was a new cog belt, Drive sprocket for the 30mm secondary shaft, and the large cog sprocket that mounted on the main shaft to replace the chain drive sprocket. Removing the chain drive opened up the access to the engine compartment, cut the weight of the chain out, and got rid of the ever-leaking chain bath that would leak chain oil over the drive belts causing them to slip.
The instructions for installing the Pro-Drive gave the set up tension that must be held on the cog belt and this tension was accomplished by shimming the secondary back enough to hold that tension at 70 degrees F. Mark set the cog drive up correctly and then he provided Larry with his hover training. Larry then took his helicopter home and practiced his hovering until he was confident and proficient in his skill set.
He called me and asked me if I would give him his phase two altitude training as I was closer than Mark and I agreed to do so. I had not seen the new cog drive before so I gave it a really good inspection for my own learning. It looked great. The helicopter was in my heated hangar during my initial inspection and once I determined that all was good we rolled it outside into the cold winter air. After fueling we got in, started the engine, and lifted to a hover. Larry showed me that he had achieved the needed hover skills so we decided to take off and head to the local airport for some initial pattern work.
As we were climbing out and increasing our airspeed the helicopter wanted to nose over and it took progressively more aft cyclic to keep the nose from dropping. I informed Larry that this was not a desirable condition so I turned the helicopter around and headed back to the hangar. Upon inspection I noticed that the horizontal stabilizer was set at an angle with the leading edge up higher than the specs called for. We modified the mount holes to allow the stabilizer cord line to be in line with the top of the tail boom. This should give us a good cyclic position in forward flight.
The day before we had installed the extended reinforced skids and flipped the front landing gear leg for more support in case of a run on landing.
As we were beginning our next take off from my helipad, we were accelerating through about 10 to 12 mph and were about 5 feet skid height when all at once the engine raced, the ship did an immediate rotation to the right and dropped. This one was a real surprise and happened in a hear-beat.
I informed Larry “I have it” at which time he let go of the controls. Larry and I had just installed the extended reinforced skids with the front gear leg reversed and it was what saved the ship. As the ship dropped and spun I to the right, chopped the throttle, applied full up collective, cyclic opposite to the direction that we were traveling, and full left anti-torque pedal. The helicopter dropped onto the front of the left skid, where the stock skid will snap off, and pivoted around to the 180 degree position of our original take off direction of travel.
We were then sliding backwards and the ship rocked back onto the tail rotor and slid to a stop. We surely would have rolled over had it not been for the extended reinforced skids which allowed the ship to pivot the 180 degrees to where the tail boom acted as an outrigger preventing the ship from rolling over backwards.
Upon inspection we found that the new factory cog belt with only 21 hours on it had snapped. This was the first instance of a ship equipped with the tensioned cog drive that I was aware of the cog belt breaking. When the belt broke, the power to the main rotor was disconnected so all of the engine power went to the tail rotor, snapping the nose of the ship 90 degrees to the right. We were very fortunate to have not experienced a rollover but we sure came close.
I have included several photos of Larry’s ship following the belt break. There is some damage but not nearly as much as would occur from a rollover. The belt manufacturer engineers stated that the break was most likely from the belt being run with too little tension allowing the cogs to ride up the driving cog wheel which can hyper extend the reinforcing fibers causing a belt failure.
Shortly after this incident I received a call from Bruce in Main. He told me that the exact same thing happened to his AP cog drive belt as he was in a hover and setting down. He told me that the hard set down also damaged his ships tail rotor and tail boom as well as the landing gear and skids but he was also able to keep the ship upright.
The reason the cog belt broke was the change in temperature in the operating environment. When Mark set up the cog belt to spec it was set up at 70 degrees f. When I checked it in my heated shop it was at 70 degrees F. We then rolled the helicopter outside into the 40 degree f air and began our flight training. In the cold air the large aluminum cog wheel would shrink relaxing the tension on the cog belt. Pro-Drive's response was that we should re-shim the secondary for the cooler temps to maintain proper cog belt tension. That is a royal pain.
I did some research and found that cog belts in this application should always be run with a tensioner to keep the cog belt at the proper tension at all operational temperature ranges. From that point on we began installing tensioners onto all of the cog systems as they were converted from the original chain drives.
As always, only fly your ships over areas that are safe to auto into. If this should happen at altitude, it would give the pilot more time to get to the ground safely with no damage.
