Kolibri
FW and Gyros
- Joined
- Oct 17, 2014
- Messages
- 1,636
- Location
- Wyoming
- Aircraft
- Cessna 152, 172, 172RG, 177, 206 -- Piper 180 -- RV-7A -- Calidus -- RAF2000 -- Sport Copter II and
- Total Flight Time
- 1000+
Many RAF owners have partially or totally upgraded to the Sport Copter rotor system.
Along the way since 2008 there have been many threads wondering aloud how to null out the new and strong stick forces required when flying with SC rotors.
This can be a confusing installation since the stick forces can be up or down, depending on if the RAF rotorhead is still being used.
I've read through all those threads, and composed what I hope is a succinct digest of what to expect and how to solve it.
In my summation, I may surprise potential customers by recommending that they either install the entire Sport Copter upgrade
for RAFs (rotors, hub bar, rotorhead, mast plates, and 4-way air-trim) . . . or none at all (i.e., not merely the SC rotors and bar, on the RAF rotorhead and trim).
Let me know if this has been useful to you.
Safe flying!
Kolibri
P.S. My original 2015 thread when I installed my SC upgrade is here:
converting RAF2000 to the superior Sport Copter rotor system
and:
Why I fly with Sport Rotors
IF ADDING ONLY SC ROTORS/BAR TO THE RAF ROTORHEAD AND TRIM SYSTEM:
TRIM EFFECT: With trim still set from the old RAF rotors, you will likely experience strong nose-DOWN forces, requiring strong back stick pressure. This has been universally commented on by owners, and so should not surprise any recent customer by now ( such as in March 2016 ).
TRIM CAUSE: the SC blades have more negative pitching moment than the RAF blades, which reduces the cyclic flapping angle and requires more nose-UP trim. (Note: ALL offset gimbal gyro heads require some amount of nose-UP trim, as the rotor disk is always wanting to pitch downward.) This may be near/at the limits of the RAF cable/spring trim system.
TRIM SOLUTION: First, change the mast setting to the next more vertical, e.g., from #3 to #4. This reduces pitch offset, and, in effect, increases the cyclic flapping angle which reduces necessary trim pressure.
If you still cannot trim out the remaining nose-DOWN force, then you will need to install stronger trim springs.
TRIM CAUTIONARY NOTE: RAF trim chains and springs have been known to break. If this occurs during a point of flight when you've cranked in a lot of trim force, the sudden absence of that force will be very dramatic, likely resulting in a sudden and severe down pitch. This happened to CFI Ron Menzie, and it took all his experience and physical strength to pull out of it. Quick reflexes for power reduction and aft stick are vital.
I highly recommend that RAF owners considering the excellent SC rotor/hub bar go "the full Monty" and install the entire SC package (rotorhead/mast plates/air-trim) as this system (which I've flown for 125+ hours) properly trims at the head vs. through RAF's non-robust control system. Although this $4,000 expense may seem like a lot, do keep in mind that the RAF was designed and made very cheaply, full of low-time and risky components (torque tube, gimbal arm, etc.). I cannot quite describe the peace of mind I've enjoyed having dumped those rickety RAF components for the SC rotor package.
Now, those who "can't afford" or don't desire to pay for the complete SC upgrade and continue to rely upon the RAF trim system, I would caution them to immediately inspect and beef up their RAF trim and control systems components. RAF PN40 has some good ideas there, and I would disassemble and carefully inspect the lower control yoke arm components. Replace the skinny OEM gimbal arm with a beefier version. Definitely replace all RAF original cheap control rod ends with Heim HM-6Ms, and don't forget to beef up the lower control rod with the Jim Mayfield mod (which replaces those tiny 1/4" shanks with 5/16").
Also, you simply must replace the OEM "dog collar" trim chains with stainless links of at least 300 lbs tensile strength, as well as steel (not OEM aluminum key fob quality) Quik-links. Procure top quality new springs (and you'll need heavier ones for the SC rotors, and you might add an equal pair on each side for safety, not relying upon just one). I would replace the trim spring washer mounts with a pair of SS on each side, and replace all AN4 bolts down there. Carefully inspect the trim cable lengths and eyes, and keep the cable sheaths lubed to prevent corrosion. Inspect the cabin trim wheels.
Even with all of the above done, you'd still be relying upon RAF's trim-through-the-control-system, and I cannot recommend that. In my opinion, there's a general unwillingness of RAF owners to more than minimally maintain their gyros, an observation commonly evidenced by rusty trim chains, original Grade 0 control rod ends, pre-2004 crack-prone hub bars, etc. For this reason, I must now discourage owners of such RAFs from adding merely the SC rotor/bar and not the entire SC upgrade.
On this point, I will recommend to Jim Vanek that in the future he not supply anything but the full SC rotor package to RAF owners unless he is personally confident that the customer has already carefully inspected/upgraded the OEM RAF trim/control system. I say this not to sell more parts from SC, but as a frank appraisal of the average RAF owner and his financial unwillingness to tackle the weaknesses inherent to his gyro.
Those who wish to reroute the RAF trim properly to the rotorhead might use the below idea of adding an arm to the rear of the torque tube:
Owners should inspect their torque tubes, and if not upgraded then at least replace them when in doubt of condition.
However, with the SC upgrade your RAF now has the very best rotor system of any other gyro. Sport Copter gyros can be flown vigorously, and even looped and rolled (if the pilot is qualified to do so). No other gyro rotor system can be flown so hard and hold up. Sport Copter constructs extremely robust machines. Yes, they do cost more, and although gyros are often thought of as "toys" any gyro can kill you, so it makes more sense to fly something not built like a toy.
IF ADDING SC ROTORS/BAR/HEAD/MAST PLATES, BUT STILL USING RAF TRIM SYSTEM:
EFFECT: With trim still set from the old RAF rotors, you will likely experience strong nose-UP forces, requiring strong forward stick pressure. (I saw this myself on a taxi-test prior to hooking up my SC air-trim, and still using the RAF cable/springs trim.)
CAUSE: Different pitch offsets of the rotorheads. The RAF trim system is now likely overly sprung, which applies unwanted nose-UP trim by pushing up the front of the torque tube.
SOLUTION: Gradually slacken out the RAF trim springs. The cable/springs might need to be slackened so much that they seem even loose at rest. You may need to even add an extra link in the chains. If you have an effective horizontal-stab (e.g., Martin, or Boyer), the you may also consider reducing by 1° its negative incidence (e.g., from -2° to -1°). With a negative angle-of-attack, the H-stab is designed to push up the nose, and not as much force is needed now.
NOTE: Since the SC rotorhead/blade combination hasn't the strong nose-DOWN forces of SC rotors on an RAF rotorhead, using RAF's trim system is not as remarkable. If something in the trim linkage broke in flight, you would likely be at/near zero trim and little stick correction would be required. I would nonetheless inspect and upgrade the RAF trim components as described above.
IF ADDING THE COMPLETE SC ROTORS/BAR/HEAD/MAST PLATES/AIR-TRIM:
CONGRATULATIONS! You've eliminated the previous trim forces from the non-robust RAF control system, greatly de-stressing those components. You're now safely "trimmed at the head", and the air-trim can be used as a secondary control system if something ever broke in the RAF primary controls.
You now enjoy a double roller bearing gimbal, and a stronger torque tube, gimbal arm, and mast plates.
The RAF torque tube, for example, has little margin of material strength.
Its spindle AN8-36 bolt is just "a half-penny away" from the AN6-44 pitch bolt.
That's a lot of stress within a very small bit of aluminum.
Along the way since 2008 there have been many threads wondering aloud how to null out the new and strong stick forces required when flying with SC rotors.
This can be a confusing installation since the stick forces can be up or down, depending on if the RAF rotorhead is still being used.
I've read through all those threads, and composed what I hope is a succinct digest of what to expect and how to solve it.
In my summation, I may surprise potential customers by recommending that they either install the entire Sport Copter upgrade
for RAFs (rotors, hub bar, rotorhead, mast plates, and 4-way air-trim) . . . or none at all (i.e., not merely the SC rotors and bar, on the RAF rotorhead and trim).
Let me know if this has been useful to you.
Safe flying!
Kolibri
P.S. My original 2015 thread when I installed my SC upgrade is here:
converting RAF2000 to the superior Sport Copter rotor system
and:
Why I fly with Sport Rotors
IF ADDING ONLY SC ROTORS/BAR TO THE RAF ROTORHEAD AND TRIM SYSTEM:
TRIM EFFECT: With trim still set from the old RAF rotors, you will likely experience strong nose-DOWN forces, requiring strong back stick pressure. This has been universally commented on by owners, and so should not surprise any recent customer by now ( such as in March 2016 ).
TRIM CAUSE: the SC blades have more negative pitching moment than the RAF blades, which reduces the cyclic flapping angle and requires more nose-UP trim. (Note: ALL offset gimbal gyro heads require some amount of nose-UP trim, as the rotor disk is always wanting to pitch downward.) This may be near/at the limits of the RAF cable/spring trim system.
TRIM SOLUTION: First, change the mast setting to the next more vertical, e.g., from #3 to #4. This reduces pitch offset, and, in effect, increases the cyclic flapping angle which reduces necessary trim pressure.
If you still cannot trim out the remaining nose-DOWN force, then you will need to install stronger trim springs.
TRIM CAUTIONARY NOTE: RAF trim chains and springs have been known to break. If this occurs during a point of flight when you've cranked in a lot of trim force, the sudden absence of that force will be very dramatic, likely resulting in a sudden and severe down pitch. This happened to CFI Ron Menzie, and it took all his experience and physical strength to pull out of it. Quick reflexes for power reduction and aft stick are vital.
I highly recommend that RAF owners considering the excellent SC rotor/hub bar go "the full Monty" and install the entire SC package (rotorhead/mast plates/air-trim) as this system (which I've flown for 125+ hours) properly trims at the head vs. through RAF's non-robust control system. Although this $4,000 expense may seem like a lot, do keep in mind that the RAF was designed and made very cheaply, full of low-time and risky components (torque tube, gimbal arm, etc.). I cannot quite describe the peace of mind I've enjoyed having dumped those rickety RAF components for the SC rotor package.
Now, those who "can't afford" or don't desire to pay for the complete SC upgrade and continue to rely upon the RAF trim system, I would caution them to immediately inspect and beef up their RAF trim and control systems components. RAF PN40 has some good ideas there, and I would disassemble and carefully inspect the lower control yoke arm components. Replace the skinny OEM gimbal arm with a beefier version. Definitely replace all RAF original cheap control rod ends with Heim HM-6Ms, and don't forget to beef up the lower control rod with the Jim Mayfield mod (which replaces those tiny 1/4" shanks with 5/16").
Also, you simply must replace the OEM "dog collar" trim chains with stainless links of at least 300 lbs tensile strength, as well as steel (not OEM aluminum key fob quality) Quik-links. Procure top quality new springs (and you'll need heavier ones for the SC rotors, and you might add an equal pair on each side for safety, not relying upon just one). I would replace the trim spring washer mounts with a pair of SS on each side, and replace all AN4 bolts down there. Carefully inspect the trim cable lengths and eyes, and keep the cable sheaths lubed to prevent corrosion. Inspect the cabin trim wheels.
Even with all of the above done, you'd still be relying upon RAF's trim-through-the-control-system, and I cannot recommend that. In my opinion, there's a general unwillingness of RAF owners to more than minimally maintain their gyros, an observation commonly evidenced by rusty trim chains, original Grade 0 control rod ends, pre-2004 crack-prone hub bars, etc. For this reason, I must now discourage owners of such RAFs from adding merely the SC rotor/bar and not the entire SC upgrade.
On this point, I will recommend to Jim Vanek that in the future he not supply anything but the full SC rotor package to RAF owners unless he is personally confident that the customer has already carefully inspected/upgraded the OEM RAF trim/control system. I say this not to sell more parts from SC, but as a frank appraisal of the average RAF owner and his financial unwillingness to tackle the weaknesses inherent to his gyro.
Those who wish to reroute the RAF trim properly to the rotorhead might use the below idea of adding an arm to the rear of the torque tube:
Owners should inspect their torque tubes, and if not upgraded then at least replace them when in doubt of condition.
However, with the SC upgrade your RAF now has the very best rotor system of any other gyro. Sport Copter gyros can be flown vigorously, and even looped and rolled (if the pilot is qualified to do so). No other gyro rotor system can be flown so hard and hold up. Sport Copter constructs extremely robust machines. Yes, they do cost more, and although gyros are often thought of as "toys" any gyro can kill you, so it makes more sense to fly something not built like a toy.
IF ADDING SC ROTORS/BAR/HEAD/MAST PLATES, BUT STILL USING RAF TRIM SYSTEM:
EFFECT: With trim still set from the old RAF rotors, you will likely experience strong nose-UP forces, requiring strong forward stick pressure. (I saw this myself on a taxi-test prior to hooking up my SC air-trim, and still using the RAF cable/springs trim.)
CAUSE: Different pitch offsets of the rotorheads. The RAF trim system is now likely overly sprung, which applies unwanted nose-UP trim by pushing up the front of the torque tube.
SOLUTION: Gradually slacken out the RAF trim springs. The cable/springs might need to be slackened so much that they seem even loose at rest. You may need to even add an extra link in the chains. If you have an effective horizontal-stab (e.g., Martin, or Boyer), the you may also consider reducing by 1° its negative incidence (e.g., from -2° to -1°). With a negative angle-of-attack, the H-stab is designed to push up the nose, and not as much force is needed now.
NOTE: Since the SC rotorhead/blade combination hasn't the strong nose-DOWN forces of SC rotors on an RAF rotorhead, using RAF's trim system is not as remarkable. If something in the trim linkage broke in flight, you would likely be at/near zero trim and little stick correction would be required. I would nonetheless inspect and upgrade the RAF trim components as described above.
IF ADDING THE COMPLETE SC ROTORS/BAR/HEAD/MAST PLATES/AIR-TRIM:
CONGRATULATIONS! You've eliminated the previous trim forces from the non-robust RAF control system, greatly de-stressing those components. You're now safely "trimmed at the head", and the air-trim can be used as a secondary control system if something ever broke in the RAF primary controls.
You now enjoy a double roller bearing gimbal, and a stronger torque tube, gimbal arm, and mast plates.
The RAF torque tube, for example, has little margin of material strength.
Its spindle AN8-36 bolt is just "a half-penny away" from the AN6-44 pitch bolt.
That's a lot of stress within a very small bit of aluminum.
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