Kolibri's tips on adding Sport Copter rotors to the RAF2000

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:


Johns RAF1.jpg

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.


RAF broken torque tube-1.png
RAF torque tube-3.png
 
Last edited:

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+
Here are some tips, incorporating info from Sport Copter in one of their posts.



TIPS ON TRACKING YOUR NEW SPORT ROTORS

Make sure that Rotor A is installed on hub bar A side.
It matters, because that's how the rotors were balanced at the factory.

Confirm that you've little-no axial play in your teeter bearings.
In the SC rotorhead, axial play can/should be totally eliminated. First, torque the teeter bolt to only 160 in/lbs (should only have .001 - .002" play;
confirm that the teeter hats/bushings still rotate with the hub bar), then box up the towers with the handsnugged jack barrel/screw (and tighten the jam nut).


If you're still using RAF teeter towers, do realize that they typically have imprecise tolerances.
If you feel significant vibration, reversing the RAF teeter towers can sometimes reduce vibration.
Simply lift out the hub bar/rotors, turn the teeter towers 180° and drop in the hub bar. (Don't forget to again remove axial play and then "box" the towers.)


Another possible contributor to a 2-rev/shake in the RAF is an overtightened mast bushing bolt (it restricts the
cheek plates from easily sliding against the white nylon sheets). While the lower AN8 bolt is torqued to correct value
(~45-50 ft/lbs), the upper bolt should remain loose enough to barely see daylight between the cheek plates and nylon sheets.
If you suspect your upper bolt is too tight, just back off a flat at a time for your test flights.

When rotating hub bar during tracking adjustments, do not torque the pitch block 3/8-24 bolts more than 15 ft/lbs.

Attached at the bottom is my tracking pdf from 2016.





HOW TO INADVERTENTLY CREATE SPORT ROTOR BLADE IMBALANCE

If you experience a significant (and/or new) imbalance, the first thing you should have clear in your mind is that it is not weight balance between the Sport Rotors.
From the factory, they are within 1 gram of each other.


1) Incorrectly install Rotor A to hub bar B side, and vice versa.
Sport Copter balances, flies, and tracks your rotor set with the A-A and B-B. Reversing this to A-B and B-A will forfeit some-much of the precision of balancing and tracking.
The letters are clearly stamped in both blades and on each hub bar end.


2) After installation and tracking, remove the hub bar/rotors from the teeter tower and later reinstall them 180° opposite.

If you have committed either of the above, your new perceived imbalance will seem very confusing. You may be tempted to falsely suspect that the blades are actually out of weight balance. One owner apparently did just that, and eventually put 6" of lead solder in a blade, which only partially masked the new imbalance.





LUBING THE SPORT ROTOR PARTS
During installation, and then every 25 hours:

RING GEAR Mobil EM Polyrex (or any NGLI-1 grease, synthetic or oil-based)

BENDIX Mobil EM Polyrex (or any NGLI-1 grease, synthetic or oil-based) Do not over grease!

PREROTATOR FLEX SHAFT Molygraph (NAPA has it)

TEETER TOWER NEEDLE BEARINGS Aeroshell 14 grease (NOTHING ELSE!)
The old grease turns black and is pressed out as you relube. Every 25 hours, rotate the bearings a ¼ turn to avoid concentrating stress in any particular area.
 

Attachments

dunc

RAF/Sparrowhawk/SC 2.5 FI
Joined
Aug 1, 2016
Messages
158
Location
Crawford, CO
Aircraft
1967 Turbo/RSTOL/VG Cessna 185 Skywagon, 1946 Grumman TBM Avenger
Total Flight Time
5000
Thanks Kolibri, for the info. My new SC blades and trim system will arrive April 4 and am itching to get them installed.
 

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+
My pleasure, dunc, and I wish you great success on your installation.
Take it slowly, refer often to my tutorial post, and call Jim Vanek with any questions.
 

Supermotive

Newbie
Joined
Sep 13, 2019
Messages
97
Location
Greenville
Kolibri, I am looking to build a 2 place gyro, and was advised to use the Sport Copter super heavy duty rotor head and rotor blades. Do you have any literature on the system, such as what comes with it and associated cost? I think I will be around 29 foot rotor. I am currently looking at mounting the system on a 2x2 inch aluminum mast (1/8 wall of 6061 t6 aluminum). Thank you
 
Top