converting RAF2000 to the superior Sport Copter rotor system

[Kolibri]

LOL, eddie, it's been a close "race" with you but I've been flying lately. Will track the rotors soon, but stick shake hasn't been too bad meanwhile.

 

[eddie]

kolibri:
good to hear your flying,keep the reports a coming.It will be about a week before my

blades even ship.



Best regards,

 

[Kolibri]

tracking SC rotors

tracking SC rotors

I've completed my 5 hours of Phase 1, and began my rotor tracking adjustments. I hadn't the clampage necessary for the dial indicator, so I went Old School.

SC supplies small reflectors (red & white) to tape on the bottom of each rotor tip to view any disparity. (Watch SC's "Tracking" video. Don't place the reflectors inside their clear tape mount, but on the outside. If placed on the inside, it won't reflect well.) They recommend using a flashlight or mirror to illuminate them. I keep a 1,000,000 candlepower 12V light in my truck (yes, you read that correctly: one miillllllllliioon candlepower!), which plugs into the gyro's cigarette lighter outlet.

A bright sunny day bleaches out the reflections pretty effectively. I caught the white sometimes, but not the red. Noon wasn't the best time for this, but it was my flight window.

While the RAF hub bar/winglets allowed for individual blade adjustment (a neat feature, although with added system complexity and weakness), as you adjust a side of the SC pitch block it'll raise one tip in flight while concurrently lowering the other.

I believe I'm correct in saying that, for example, a ½ flat (30° -- .00347" at pitch block) will move each tip 0.35" from their respective previous positions -- i.e, either converging or diverging the tips (depending on adjustment direction), as both are concurrently affected.

Meaning, if the tips were 0.70" apart, they need move only 0.35" in convergence to even out (accomplished with a ½ flat pitch block adjustment), but if you tighten the wrong side then a ½ flat will further diverge the tips to a new relationship of 1.4" apart.

During adjustments I think it wise to always park the rotors with the same orientation (e.g., red in back) to avoid tripping yourself up on the pitch block. Also, make notes along the way, else you'll easily confuse yourself. So, I used eddie's idea of trying one way and then doubling back if wrong. If the reflectors aren't visible enough, one must guess at first which is higher. I guessed red, lowered it on the pitch block by ½ a flat, and took her up. (From stock position, I was now net change red-down ½ a flat -- do notate as you go both your adjustments and their respective incremental net change from where you began.) Tighten the desired side, then equally loosen the opposite side.

Stick shake had slightly (though noticeably) increased (I'd chosen wrong), so I landed for the next adjustment.

I moved up red by 1½ flats (i.e., from stock position I was now net red-up 1 flat). Even on spool-up I could see the unevenness, and in flight this gave me a very distinct 2-rev shake, which I'd never felt before. I'd gone too far (note: make only ½ flat net adjustments), and thus began to lower red incrementally. The 2 rev shake disappeared after the next adjustment.

Then, I decided not to further continue chasing the matter in the blind, and chocked the gyro where the rotor tips were in a hangar's shade. With stick locked forward (and the air trim also in full nose-down) I spooled up and used the spotlight to finally (but only sometimes) make out the red reflector. A ¼ flat adjustment from there has given me so far the smoothest result, but I will spotlight the tips in flight near dusk to confirm.

I think these rotor tip LEDs would have been a great help.

Moral: go ½ flat adjustments (30°) at a time, and once you know you're converging the tips, go ¼ flats (15°) from then on. Sneak up on it so that you don't go past it in the opposite direction. (Using your dial protractor to eyeball the wrench's movement is very helpful during these smaller adjustments.)

____
gain in cruise AS: I'm enjoying 10, if not 15mph increase. Will get some data across RPM ranges and recalculate my new greater endurance for x/c.

In all, I'm very glad (and relieved) to have made this upgrade!

Regards, Kolibri

 

[eddie]

kolibri I have also noticed that after adjusting the track its important to go back and

do the chordwise adjustment again,go 0.005 at a time one way or the other to find that

real smooth spot. With my RAF blades I have zero stick shake,but there is still a

underlying shake that really increases with weight or a increased G loading such as a

tight turn.



Best regards,

 

[Mike G]

Kolibri
I'm surprised to hear that changing rotor pitch (tracking) caused a 2/rev vibration. My experience is that when I change the pitch of the blades it increases or decreases the 1/rev vibration but not the 2/rev.
Did you actually measure the 2/rev vibration increase or was it just by feel?

For the tracking LEDs see this thread
https://www.rotaryforum.com/forum/showthread.php?t=45078
were we discuss the advantages and disadvantages of these LEDs.

I know I'm repeating myself but you'd be much better off doing the track and balance with a PB3, it takes all the guessing out of the equation and you can also balance your prop.

Mike G

 

[Kolibri]

My experience is that when I change the pitch of the blades it increases or decreases the 1/rev vibration but not the 2/rev.
Did you actually measure the 2/rev vibration increase or was it just by feel?

Mike G, now that you mention it, I'm sure you're correct about it being 1/rev, as I didn't measure it before my pronto landing. Thanks for setting me straight on this. I'll read through that rotor tracking thread, though I hope not to need my own PB3.

________

I have also noticed that after adjusting the track its important to go back and do the chordwise adjustment again,go 0.005 at a time one way or the other to find that real smooth spot.

Thanks, eddie, I hadn't considered that. I'll ask Jim about it as the only adjustment I yet know of is on the pitch block for tracking.

btw, since you'll probably be adding stronger trim springs for your SC blades, check out:
https://www.leespring.com/extension_spec.asp?springType=E&forWhat=Search

________
As I continue to accustom myself to the SC rotors and air-trim, I advise this upgrade only for non-newbie RAF owners due to increased "busyness" of acquiring proper pitch trim during the takeoff roll. The air-trim system has no indication of pitch attitude for when it's lost pressure overnight, and thus the pilot must deftly adjust as he adds power on the roll. I've found it preferable on back-taxi to add some nose-down trim, and then on the takeoff roll add whatever nose-up is necessary. (I've found backstick easier during the roll, vs. forward stick which requires increasing pressure as AS builds up. The OEM RAF landing gear with mains too far forward exacerbates the matter.)

Regarding pitch changes in the pattern, if you add sufficient nose-up to null out stick pressure on final, you will have waaaay too much if you do a go-around or stop-and-go. (For the same reason, in FW I generally do not add nose-up on final in case of a go-around. I also don't use full flaps unless I need the steepest descent to clear an obstacle.) So, with SC rotors I don't add any nose-up after downwind. This requires more backstick than I'm used to while turning base with reduced power, but I'm rewarded with approximately takeoff trim during landing.

____
Those flying SC rotors with RAF cable trim sometimes "reverse their trim" (according to Jim Vanek). One apparent example of this is somebody on RWF named John who (while using an anodized Wayne Hubb gimbal arm on the RAF rotorhead) utilized his old RAF gimbal arm on the rear of the torque tube for trim. Notice the much longer trim springs (which are internally secured in case of failure. (I assume it's cabin adjustable with the OEM trim wheels.)

___
Thinking aloud for the SC air trim on RAFs, I do wish it had a pitch trim cockpit LED index (as does the RAF Stabilator). Granted, an experienced pilot won't need it, but a <75 hour guy would. (I can't imagine a CFI wanting to train a total beginner without it, especially with RAF's OEM forward mounted mains. Dual occupant RAF takeoff roll procedure is to keep the nosewheel lightly on the ground, and a rank newbie would find that very challenging with SC rotors/air-trim.)

Thanks for y'all's comments along the way,
Kolibri

 

[eddie]

Kolibri my indicator for pitch trim is broke,what I do is adjust trim for level flight at the

speed I use most often and then leave it there even for landings, holding back stick for

the right airspeed isnt that hard to do.I have found that trim setting also works good

for takeoffs as well.



Best regards,

 

[Kolibri]

eddie, with the RAF rotors, I flew with about the same procedure as you do. However, I noticed a significant difference with the SC rotors. I'll be interested to hear your take on them regarding pitch trim.

_____
Went up today from grass for a quick flight near dusk. The red and white reflectors are veerry close to being even (within ½"), yet some stick shake persists. Hmmm.

Cheers, Kolibri

 

[Mike G]

Kolibri
I'm repeating myself, again, when I say that unless you're really out in the sticks on your own or are fascinated by vibrations, always try to buy a dynamic balancer in a group. Split between 2 or 3 owners it becomes very reasonable and saves a bunch of time. Also you can balance the FW guys props and make it pay for itself.

Regarding "persistent stick shake" try to understand if it is 1/rev or 2/rev. Again I'm repeating myself, if it's 1/rev you can do something about it (balance, tracking etc), if it's 2/rev you just have to live with it unless you're ready for some serious engineering and expense.

In this thread
https://www.rotaryforum.com/forum/showthread.php?t=42742
I wrote this
"The first thing you have to find out is at what frequency the stick is vibrating. This will then tell you what is exciting the vibration/resonance and what to attack first. There are two major exciting frequencies:

Rotor RPM, about 5 to 6 hz (300 to 360 rpm)
and
twice rotor RPM (2/rev), about 10 to 12 hz.

The simplest way to decide which it is, is to take a bottle of ketchup and shake it as fast as you can (make sure the top is screwed on). That is 5 to 6 hz. Most guys will find this motion quite natural, they don't even need a bottle of ketchup. So if the stick is shaking at a frequency that you can simulate by shaking a bottle of ketchup it's 1/rev and your excitation is due to imbalance, tracking or alignment.
From what you describe “after rotating to the usual orientation they were much better,” it seems you probably have a pretty fundamental imbalance problem anyway so try to find someone with a Vibrex, Dynavibe or equivalent it might help solve some of your setup problems.

If the stick vibrates at a faster speed than you can do it to yourself , it's probably 2/rev and that’s a discussion that we’ve had before on this forum and I welcome any corrections to the following.
2/rev is caused by :
-incorrect undersling
-rotating drag (difference in drag in the 12/6 o’clock position compared to 3/9 o’clock)
-inertia around the span axis between the CofG of each blade
-rotor in-plane flapping or free-free (depending on the mast stiffness) natural frequency at rotor rpm.
With the exception of perhaps undersling there’s almost nothing the average owner can do to change any of these causes.
Another simple and cheap way to find the major excitation frequency is with a portable telephone. Jukka Trevamaki suggested it with an i phone and I’ve used a free app (https://play.google.com/store/apps/d...ovalyzer&hl=en) on my Android phone. If you strap it to the stick you can quickly see the peak frequencies at which the stick vibrates.
Good luck."

I should add to the above that, after writing that, I am now pretty convinced that "incorrect undersling" and "inertia around the span axis between the C of G of each blade" are the same thing.

This might help you decide if you are as far as you can go or if there is still something to be gained by track and balance.

Mike G

 

[eddie]

kolibri, You are going to have your rotor setup issues resolved by the time I have my

SportCoptor rotors up and running.Sport coptor changed my shipping date from last

monday until around the end of next week the 19th. Any way I can read about your

answers to the various vibration problems and that should speed up my setup time.

Keep the answers coming my way.



Best regards,

 

[Kolibri]

Mike G, thanks for this very helpful info. The first increased vibration I wrote about was definitely 1/rev shake. The one I'm dealing with now may be 2/rev, as it's definitely much buzzier and seems faster than RRPM. I went up today again near dusk, and the red/white reflectors are in very good plane. I recorded a quick video of the stick shake (7megs, if anyone's interested; PM me your email address).

I'll check out your rec. app:
https://play.google.com/store/apps/details?id=de.bremen.btm.movalyzer&hl=en

___
btw, I've never seen such AS in my RAF, up to 85mph (90 mph GS with that slight tailwind). I'll be delighted to get rid of the stick shake to enjoy some higher cruising speeds.

Thanks, Kolibri

 

[Kolibri]

Had a chat with Jim Vanek about it, and since the stick shake increases with AS (classic 1-rev/shake symptoms) he's confident that there's still a bit of tracking adjustment still to go. He thinks I'm probably just a reflector's height off (¼"), that's how sensitive tracking can be.

Once I've got the tracking "dead nuts on", from there I can dampen any remaining shake by tightening the air-trim friction blocks (which are delivered pretty loose).

I installed Mike G's recommended vibration app to my Android tablet, and will analyze the shake frequency. (I'm continually astounded at the apps available.)

I'm repeating myself, again, when I say that unless you're really out in the sticks on your own or are fascinated by vibrations, always try to buy a dynamic balancer in a group. Split between 2 or 3 owners it becomes very reasonable and saves a bunch of time. Also you can balance the FW guys props and make it pay for itself.

Mike, I'm only fascinated with vibrations when they are fascinated with me! I am in the sticks/on my own, but using the PB3 for prop balancing may swing the purchase for me, thanks.

Regards, Kolibri

 

[Kolibri]

have greatly reduced stick shake, comments on p/r cable

have greatly reduced stick shake, comments on p/r cable

Flew even more near dusk today (landed 10 min. before civil twilight), and so I could really see the reflectors with the spotlight. The videos didn't quite catch it, but the tracking looked very, very good after a preflight 15° more tightening of pitch block bolts for red-down. I'd be surprised if I could further plane the tips.

The stick shake was reduced to about 70% of my previous setting.

Also, my Android vibration analysis app showed a solid 11hz, which is 2-rev/shake (not that I claim to have totally nulled out the 1-rev tracking issue).

So, I landed, tightened the air-trim friction blocks 2 turns, and went up again. That really helped; now the shake is about 40% of a few days ago. Aahhh. I'm not 100% there yet, but after tonight I'd take a day x/c trip with the results. It is smoother than after my installation with SC's settings, so I am pleased with the net progress. And, stick pressure didn't increase all that much.

I'll fly next time with 1 more turn on the friction blocks.

Oh, I saw 95mph AS and 106mph GS with a tailwind. (I never saw 95mph AS level flight with RAF rotors.)
Stick shake did not nearly as much increase with AS as before, so I've got the tracking very even by now.


_____________
The attached photo below describes the shorter prerotator cable length needed after the SC upgrade. (Diagram squares are ⅛". If you need a hi-res pdf, PM me your email address.) The stock RAF cable/sheath is 4" too long for the full SC upgrade.

Regards, Kolibri

 

[Kolibri]

some SC rotor tracking info in

some SC rotor tracking info in

The below are worth reading for better understanding rotor tracking:

Greg Gremminger on Magni smoothness
https://www.magnigyro.com/features/SMOOTH.pdf

Dynamic balancing autogyro rotors with the Smart Avionics PB3 rev for PSF.pdf
https://www.rotaryforum.com/forum/attachment.php?attachmentid=119779&d=1441009036

I've compiled what I've learned so far in a brief pdf. The two below jpgs are screenshots of it, and the pdf is higher res with embedded live links.

LMK please any revisions I need to apply,

Thanks, Kolibri

 

[Kolibri]

I cranked in one more turn on the air-trim friction dampeners (for a net change of 3 turns from delivery). I could feel a heavier stick as I preflighted, but it didn't seem objectionable so I taxied out. Crosswind was about 30° at 8kts. I began the takeoff roll, adjusting the air-trim on the way as needed. It all felt a bit odd, but nothing alarming. Lousy takeoff as I waddled up. Nose-up trim seemed sluggish but I got to pattern altitude and had planned to fly around a bit, but soon changed my mind. (Stick shake was slightly less than with 2 turns on the friction dampeners.)

I kept gradually losing nose-up trim, and the gyro just felt strange in the moderate gusts aloft. I wondered if I'd developed a leak in the pitch trim cylinder hose. I also suspected that the friction on the air-trim was now excessive, which made me feel that I'd lost about 30% of effective control. So, I decided to return for a straight in approach.

While descending on short final I felt that I couldn't quite outpace sink with increasing nose-up trim. Once over the deck I just used aft stick, and it needed a lot of that. She really wanted to sink, and it was a rather dicey last several seconds to gently get her down. It felt as though I'd very little nose-up trim authority.

I taxied to the run-up area, shut down, and loosened the friction dampeners to their previous setting of 2 turns. Then I looked her over very carefully as I regained my nerve to go back up.

The next flight hadn't the same vague wonkyness, although I was still having to frequently add nose-up trim (though not as much as the previous flight). There was some convection, and the most I've flown in with the SC upgrade so I wondered how much that was a factor. Also, being a near freezing day, it's possible that the air-trim hoses weren't sealing perfectly.

I recalled gyrogreg's comments on excessive friction in roll/pitch pivot points in his Magni pdf:

But, there will always be some minimal amount of rotor-induced shake. Magni uses one more trick to prevent the pilot and controls from seeing this remaining vibration as stick shake. Some amount of friction is applied in the roll and pitch pivots in the rotor head. This friction significantly prevents any rotor shake from transmitting through the controls to the stick, it prevents the rotor head from moving on its roll and pitch pivots with the vibration. [Kolibri note: The adjustable air-trim friction blocks serve as roll and pitch pivot points.]

By restricting movement of the rotor head itself, any rotor vibration is transmitted into the mast and airframe instead of through the control system. For the high airframe moment of inertia and very stiff mast and frame, the resultant body shake is hardly noticeable. What this is really doing somewhat, is to not allow the rotorhead spindle to completely move as the rotor centers remains stationary. Because of the high inertia of the airframe, some of the rotor out of-balance or shake is forced into the rotor disk and not all of it into the airframe body. At any rate, when this slight friction in the roll and pitch pivots is applied, increased body or airframe shake is not noticeable, but the "stick shake" transmitted through the controls is very noticeably reduced.

Ok, the more perceptive among you might argue that it is not a good thing to have friction in the controls! Without starting into the whole issue of pitch stability in gyroplanes, I'll agree that control friction is a thing to be avoided on unstable type gyroplane. If a gyroplane's airframe is unstable, that means it moves or pitches in the wrong direction in response to a vertical gust or g load transient. Because historically, most gyroplanes were negatively or neutrally stable in this regard, it has been very important to avoid friction in the controls or even a tight grip on the controls in those gyroplanes. Such friction or tight grip transmits the airframe wrong-pitch movements into the rotor, exacerbating the unstable situation into possible PIO or PPO.

I felt no tendency to PIO or PPO, just a frequent gradual loss of pitch. Some of it must have been related to the 3 turns on the friction blocks, as only 2 turns made the second flight acceptable (though not optimal). I think I'll back off to just 1½ turns and try that.

I'll also thoroughly check all the air hose connections. The pump cycled on/quit normally during preflight, and no system leaks were detected then.

In all, a very interesting experience. I'd recommend that any RAF owner with SC air-trim only gradually tighten the friction dampeners a ½ turn per test flight. And, do not layer in any other adjustment at the same time. You want to be able to isolate the cause of any new effect.

Stick shake still measured 10.50Hz, so it's 2-rev/shake (but with less energy). The more I flew this morning, the smoother it got as she warmed up. She still not as smooth as with the RAF rotors, but it's tolerable. I'm sure I've gone as far down the friction block dampening route as is feasible.

__________
THE NEXT NIGHT: First, I backed off the friction dampeners to 1½ turns.

Also, after reading gyrogreg's Magni report I got to wondering if I'd slightly overtorqued the teeter bolt during installation, causing pivot friction (a cause of 2-rev/shake). I had. Not by much, but it doesn't take much, as Jim explained what I needed to look for. So, I backed off the nut about a ½ flat. (eddie, make sure you get instructions on this, called "boxing the teeter tower".)

Went up right at sunset for best reflector visibility during a quick test flight. The darker, the better, and tonight's viewing was the best yet. Am still a skooch out of track, but it's very, very close. (Jim said that tips just ⅛" out of track can make a considerable difference.) Landed before civil twilight, my latest yet. Not used to that, but I did OK.

Best of all, slightly loosening up the teeter bolt reduced intensity of the 2-rev/shake by over half. Biggest single improvement I've seen so far. Am very nearly there.

I still think I've a small system leak in the air trim, which I'll locate this week.

Regards, Kolibri

 

[eddie]

Good report Kolibri,thanks for the good information,I have alway wondered about the

tightness of the teeter bolt and its effect , and how close the tracking really needed to be

it sounds like its a tighter tolerance than I expected. Good luck with your air trim.









Best regards,

 

[Kolibri]

You're welcome, eddie, glad to be of help.
I may go up again shortly after some more fine tuning, and will report back.

___
Have you plans to route the trim to a rear arm on the torque tube?
Many have done so after adding SC rotors to the RAF head.
I'd like to see some photos of how they routed the cables to the trim springs.

Regards, Kolibri

 

[eddie]

Kolibri I plan on using the trim system thats in place,my pitch trim is the RAF stabaliator,and

the roll is controled by the stock system.

My rotor blades shipped yesterday from Sport Coptor should be here friday or monday.



Best regards,

 

[Kolibri]

latest from the air

latest from the air

eddie, since your RAF Stabilator pitch trim LED indicator is broken, you'll probably want to fix it for your SC rotors (which fly very differently).

____
I've now 14 hours/27 landings in the SC upgrade. Landings are not an issue with me, although I won't be winning spot contests any time soon while I accustom myself to the new sink rate and float. I'm still not used to the increased back stick pressure needed after turning base (with a constant power setting, either idle or 3000rpm, depending on what I'm practicing).

Really, my only remaining trepidation (and this is steadily diminishing) is the takeoff roll with its concurrent pitch trim adjustment. My technique now is roll with a bit of nose-down trim and just accept the increased back stick pressure required to balance on the mains. (This technique assures that I will not prematurely lift off in ground effect and low AS.) Then once in the air I quickly add nose-up trim to attain 60mph Vy.

I've tried the reverse, where I'd a bit too much nose-up trim on the roll, and I didn't like the forward stick pressure and occasionally bouncing the NW (not a great idea in the noncastering/short-coupled RAF). I also saw a tendency to lift off more often in ground effect rather than at takeoff AS. I'm getting better at discerning during prerotation as I gradually pull back the stick where the nose-up trim is.

I continue to recommend that this SC upgrade be equipped with a cockpit pitch indicator (à la RAF Stabilator LED readout) due to no inherent trim settings or memory. This would be especially useful for changing takeoff trim with/without a passenger. I realize that with more experience the perceived need for such will slacken, but I still think I'd appreciate an indicator. Perhaps an AOA sensor would work for this, mounted on the torque tube?

Another idea would be to measure the pitch dampener rod at its takeoff extension. What I may do is experiment with pitch trim during a series of takeoffs, and once I'd nailed a good setting that allowed a nice balancing on the mains, land at once, taxi and park to measure how much pitch dampener rod protrudes below the friction block. Then during preflight I would adjust trim to that setting, before I even started the engine. (I'd also learn what setting is needed for a pax.)

Of course, once I move back the mains by 4-5" and add some suspension, all pitch trim takeoff settings will change. But for now . . .

___
I've not made any further friction dampener or pitch block adjustments since my previous post, but the system is certainly now smooth enough for interim pleasure flights. Last week I went for a 2.1 hour round trip to enjoy a "$100 Carne Asada plate" and "big city" shopping. It felt great to fly with mostly fun in mind rather than testing. I like to make cell calls Bluetoothed to my Bose A20 (still amazed how clear that is) and chat with friends and family.

My original purpose for buying the RAF was to own a fun 200 mile commuter, and bit by bit I'm acquiring what was advertised. (Also, I may have had a breakthrough on fixing the fuel tank seal, providing me some decent range.)

___
Today I went up for 1.6 hours to collect data on erpm, rrpm, gph, AS/GS. I am plotting a revised AS/consumption table for new range and endurance POH figures.

I also thought to confirm rrpm sensor accuracy by using the vibration app. What I saw was 10.75Hz at 340rrpm (should be 322rrpm, or 11.25Hz). I suspect that either my rrpm display is excessive by ~15rrpm, or the vibration analysis app by .50Hz (or a combination of the two). Meanwhile, the proper math works out to:

2-rev/shake frequencies and their calculated RRPMs

10.00Hz = 300rrpm
10.25Hz = 307rrpm
10.50Hz = 315rrpm
10.75Hz = 322rrpm
11.00Hz = 330rrpm
11.25Hz = 337rrpm
11.50Hz = 345rrpm
11.75Hz = 352rrpm
12.00Hz = 360rrpm

___
Going to dinner now, Happy Easter!

Kolibri

 

[eddie]

i got my rotors friday and installed them today,the wind got to 26 kts so tomorrow I will

fly them. I think that if you move your landing gear your takeoff problems will disapear

my nose stays on the ground until I raise it off just like flying a fixedwing.the only

problem you could encounter is if the trim is set for a really nose high takeoff. With the

gear moved back you can obtain a better angle of attack for the rotors to spin up faster,

My takeoff distance was reduced by at least 40%.Thamks for the good info.I also have

the Bose A20 headsets,I wont fly without them, simply amazing headsets.




Best regards,


.