HELP!! Need some advice on tracking my Mosquito

[floppywing]

I am have a real problem with getting my Mosquito XEL MR to track smoothly. I do not have access to any track and balance equipment so I am trying things the old way. I have the MR blade pitch links set up for the correct negative angle per the manual. I use a digital level with reading to 0.1 degree. Then I used reflective tape on the blade ends and hovered so a helper with a bright light could see the tip path. I also have flown it and adjusted the PCL until it was as smooth as I could get it. It is pretty smooth in hover but has a real vertical bounce in forward flight. The more collective the bigger the bounce. My blades do not have bendable trim tabs. I have set the sweep of each blade to 0 degrees, so both are neutral. I have not messed with adjusting the sweep angle. Any new ideas would be helpful.

 

[wolfy]

Without trim tabs it will be a compromise between hover and forward flight.
What speed does the hop come in, sounds like trim tabs would be your best bet.
Tabs at about 60-70% of radius work best for high speed, and further outboard is for slower airspeed tracking. Depending on the blades torsional stiffness, the blade manufacturer would advise on the best location for tabs.

wolfy

 

[GyroChuck]

I have the same problem tracking the blades on my XE285. I was told by one of the factory reps that tracking in hover is not the same as the tracking when in forward flight. So you have to also check the tracking in forward flight as it probably will change.

I have the original (Dragon wing) blades on mine. They have a screw on each blade tip. I was able to make 2 brackets that holds both a red and green led. At night I am able to see the tracking with the leds. I got the stick shake a lot better. But I still need to get out at night and do some more adjustments.

My original problem was stick shake. But along with that. When I lowered collective to lose altitude the whole cabin would start to shake.

I do have the trim tabs so I am able to adjust tracking with them.

 

[grevis]

I found mine had quite noticeable 2/rev vibration in forward flight. I swept the blades back (lagged) a fraction and it seemed to improve it a lot. The skids still wobbled a bit but it was good in the cabin and the stick had no shake. (video on youtube under XE285 in NZ)

I didn't find that the tracking of the blades made a lot of difference for me. With the adjustment of the links being half a turn at a time I went 1/2 then a full turn both ways from my hover tracking but the machine didn't change a lot.

 

[floppywing]

I found mine had quite noticeable 2/rev vibration in forward flight. I swept the blades back (lagged) a fraction and it seemed to improve it a lot. The skids still wobbled a bit but it was good in the cabin and the stick had no shake. (video on youtube under XE285 in NZ)

I didn't find that the tracking of the blades made a lot of difference for me. With the adjustment of the links being half a turn at a time I went 1/2 then a full turn both ways from my hover tracking but the machine didn't change a lot.

I am getting the same 2 per in forward flight with increase with more collective pull. I adjusted the PCL up and down until I had the least bounce. Very smooth in hover but not nice in forward flight. I guess I need to try sweeping the blades. Were you sweeping both blades equally or just one? How much sweep aft (lagging) did you go when adjusting the sweep adjusting screws/nuts? One flat on the nut or more? I don't have much of a house shake when bring the rotor up to speed on the ground. I heard sweep can affect that.

 

[bryancobb]

Guys, I'm getting the idea that your understanding about "sweeping the blades" is all wrong. Sweeping blades is done on a 2-blade rotor FOR THE PURPOSE OF CORRECTING CHORDWISE IMBALANCE OF THE WHOLE ROTOR SYSTEM. One blade get swept aft, ever-so-slightly. The other blade gets swept forward ever-so-slightly. Now the blades are only 179.99 degrees apart and that has moved the CG of the entire rotor system laterally along a move-line that is perpendicular to the rotor span. When the chordwise CG of the rotor system coincides with the rotational axis of the main mast on a helicopter, you have it as smooth as possible chordwise. On a gyro that has no main rotating mast, I have no idea what the usable reference axis is.

 

[floppywing]

Guys, I'm getting the idea that your understanding about "sweeping the blades" is all wrong. Sweeping blades is done on a 2-blade rotor FOR THE PURPOSE OF CORRECTING CHORDWISE IMBALANCE OF THE WHOLE ROTOR SYSTEM. One blade get swept aft, ever-so-slightly. The other blade gets swept forward ever-so-slightly. Now the blades are only 179.99 degrees apart and that has moved the CG of the entire rotor system laterally along a move-line that is perpendicular to the rotor span. When the chordwise CG of the rotor system coincides with the rotational axis of the main mast on a helicopter, you have it as smooth as possible chordwise. On a gyro that has no main rotating mast, I have no idea what the usable reference axis is.

Well I am open to being educated. You sound like you have a pretty good understanding of rotor systems. So can you offer any helpful ideas on how to address my issue? That is in the top post here. Can you give me your thoughts as to how I should correct this issue? So you don't think that sweeping will affect the bounce in any way? Suggestions please. No one here is talking about a gyro, we are addressing the rotor system of a powered helicopter. I am sorry if that was not clear.

 

[wolfy]

I have the same problem tracking the blades on my XE285. I was told by one of the factory reps that tracking in hover is not the same as the tracking when in forward flight. So you have to also check the tracking in forward flight as it probably will change.

I have the original (Dragon wing) blades on mine. They have a screw on each blade tip. I was able to make 2 brackets that holds both a red and green led. At night I am able to see the tracking with the leds. I got the stick shake a lot better. But I still need to get out at night and do some more adjustments.

My original problem was stick shake. But along with that. When I lowered collective to lose altitude the whole cabin would start to shake.

I do have the trim tabs so I am able to adjust tracking with them.

Be very carefull with tracking lights, really only want to use them at a hover unless you are 1000% sure they can't come off. The first helicycle that was built in Australia was lost because of one of the tracking lights coming off in flight, Herman said the vibration was so severe he could barely hold the cyclic, he could not fly the thing to the ground.

wolfy

 

[wolfy]

I found mine had quite noticeable 2/rev vibration in forward flight. I swept the blades back (lagged) a fraction and it seemed to improve it a lot. The skids still wobbled a bit but it was good in the cabin and the stick had no shake. (video on youtube under XE285 in NZ)

I didn't find that the tracking of the blades made a lot of difference for me. With the adjustment of the links being half a turn at a time I went 1/2 then a full turn both ways from my hover tracking but the machine didn't change a lot.

Pitch links are primarily for hover, trim tabs are for forward flight. And as I said the further inboard the tabs the higher the airspeed you are targeting fixing.
Without balancing equipment the human brain will have trouble picking up slight changes accurately. And sweeping the blades possibly tricked the brain into thinking you made improvements, but you have just changed the vibrations into something else.
Sweeping is not for tracking.

wolfy

 

[bryancobb]

Hey floppy, I'll be glad to help as much as I can. It's going to be tough without some kind of electronic balancer, but it can be done. Just be patient with me. I'm a little bit of a grouchy ol man these days. Let me go back and read exactly what's been posted before we attempt this. Good luck.

 

[floppywing]

Hey floppy, I'll be glad to help as much as I can. It's going to be tough without some kind of electronic balancer, but it can be done. Just be patient with me. I'm a little bit of a grouchy ol man these days. Let me go back and read exactly what's been posted before we attempt this. Good luck.

Thanks for everyone's input. I have heard that the Mosquito can be pretty smooth in flight and I am hoping that I can get mine that way. I agree that without proper track and balance tools I may be chasing my tail. I used to have a PB4 but sold it years ago and now really regret it. I am looking to buy something but most are coast prohibitive.

Pitch links are primarily for hover, trim tabs are for forward flight. And as I said the further inboard the tabs the higher the airspeed you are targeting fixing.
Without balancing equipment the human brain will have trouble picking up slight changes accurately. And sweeping the blades possibly tricked the brain into thinking you made improvements, but you have just changed the vibrations into something else.
Sweeping is not for tracking.

wolfy

No trim tabs on my blades. So sweeping is for lateral balance only? If it needed sweeping then that would show up as a lateral out of balance on the ground and hover, right? I really need to need to setup balancing accelerometers for both vertical and lateral to see what is really happening.

 

[bryancobb]

Are you ready to get started with questions/answers?
1) On your MXL, do you know much about its history?
a) Has it flown much?
b) Has if flown much recently?
c) When it was not flying and parked, was it inside or out in the rain?
d) Do you have any maintenance logbooks?
e) Do you have any idea what the feathering bearing condition is?
f) How about tetering-bearing condition?

If it has bearings that have not been cared for properly, and that have been flown a fair amount in ungreased or poor condition,
they probably have been brinelled and you will never get it balanced/smooth until the bearings are replaced. Warning: The feathering
bearings must be installed facing the right way. They are angular-contact ball bearings that can only carry centrifugal force in ONE WAY!

 

[bryancobb]

Thanks for everyone's input. I have heard that the Mosquito can be pretty smooth in flight and I am hoping that I can get mine that way. I agree that without proper track and balance tools I may be chasing my tail. I used to have a PB4 but sold it years ago and now really regret it. I am looking to buy something but most are coast prohibitive.

No trim tabs on my blades. So sweeping is for lateral balance only? If it needed sweeping then that would show up as a lateral out of balance on the ground and hover, right? I really need to need to setup balancing accelerometers for both vertical and lateral to see what is really happening.

No. No. No. Sweeping blades needs to be ignored and they need to be 180Deg apart to start the balancing process. Don't even think about sweeping right now. First step is to know WITH CERTAINTY that your bearings are in perfect or new condition.

 

[bryancobb]

Thanks for everyone's input. I have heard that the Mosquito can be pretty smooth in flight and I am hoping that I can get mine that way. I agree that without proper track and balance tools I may be chasing my tail. I used to have a PB4 but sold it years ago and now really regret it. I am looking to buy something but most are coast prohibitive.

No trim tabs on my blades. So sweeping is for lateral balance only? If it needed sweeping then that would show up as a lateral out of balance on the ground and hover, right? I really need to need to setup balancing accelerometers for both vertical and lateral to see what is really happening

Please just focus on bearings first. Don't worry about tracking or trim tabs. We are not even close to lateral balancing yet. We don't need accelerometers or electric equipment yet. Just investigate THE CONDITION OF YOUR HELICOPTER ROTOR HEAD, MECHANICALLY. You also really, really, need to sign up on RotorFX's Forum and get owners only access to the controlled section of the forum. You need your serial number from under your seat. The forum gives you polar balancing charts and other information you need.

 

[floppywing]

Are you ready to get started with questions/answers?
1) On your MXL, do you know much about its history?
a) Has it flown much?
b) Has if flown much recently?
c) When it was not flying and parked, was it inside or out in the rain?
d) Do you have any maintenance logbooks?
e) Do you have any idea what the feathering bearing condition is?
f) How about tetering-bearing condition?

If it has bearings that have not been cared for properly, and that have been flown a fair amount in ungreased or poor condition,
they probably have been brinelled and you will never get it balanced/smooth until the bearings are replaced. Warning: The feathering
bearings must be installed facing the right way. They are angular-contact ball bearings that can only carry centrifugal force in ONE WAY!

Yes
1 Yes I have talked to the original builder
a. 55 TTSN
b. 10 hours in the last 6 months
c. Inside my garage and protected
d. No
e. No other than the bearings feel good when the grips were off the MR head.
f. Bearings are like new, no signs of any wear or notchiness, bearing races like new

The entire drivetrain has been disassembled, cleaned and inspected. I did not disassemble the MR feathering bearings as the grips have always been attached to the blades. They rotated and felt smooth without any clickiness. The MR head assembly was disassembled and inspected prior to the static balance performed. Static balanced done using the assembled rotor system with the grease removed from the teetering bearings for less resistance.

I am and A&P/IA fixed and rotor wing mechanic and do have a bit of experience. I have maintained, repaired and overhauled Bell 206 and 47 helicopters. I just don't have a lot of experience with track and balance. When I did we used a Chadwick with Strobex. Not very doable in a Mosquito.

Dave Storey mentioned that I might have the old style blades and that some wouldn't track due to their twisting stiffness not being matched. If that is the case then I am chasing my tail.

 

[GyroChuck]

Does the end of your blade look like this. If so then it's the older (original) blade.

 

[floppywing]

Does the end of your blade look like this. If so then it's the older (original) blade.

Yes exactly. The kit date is 2011. So These blades might have a problem ever running smoothly in track due to their differences in how they twist in flight? A sad day for me if that is the case. Is there any way to fix this, other then replacing them? Can I install trim tabs?

 

[GyroChuck]

Do you have the builders manual for the adjustments.

 

[bryancobb]

OK Floppy! sorry for the fundamental junk, but I had no Idea of the person and the machine that was involved. Now I do.
g) As you probably know, all geometric BS must be checked and recorded to establish the start point.
h) If I were doing my own Mosquito, I'd start by confirming that some possum-eating Pennsyltuckian hasn't lifted upward or let their 14 year old grandchild hang from the blades and ruined them.
i) As a minimum, I'd remove the blades 1 at a time. Weigh them to the nearest gram. Then strap the root underside snug to a long flat table and see what the tip does. Check and record tip incidence/twist if any from root to tip. Then balance the blade spanwise on a row of utility-knife blades and determine and record the exact distance to the spanwise CG, FROM THE ROOT.
j) When both blades are done, compare the numbers. Worse case-this will tell you to saw the blades into and scrap them.
k) Before you can proceed, both blades must match. Serial no's are probably sequential or a & b etc.
l) Inspect with a bright, 36"+ fluorescent light, top & bottom looking for the ever-so-slight wrinkling/debond. Wrinkling between rivets on underside means the blade has been pulled down and ruined, Wrinkles on top mean a ham-fisted pilot was doing autos and had the collective up in his armpit during touchdown and forgot to put it down while rpm was still high. The blade turns to spaghetti when centrifugal force gets low and angle of attack is high.

NOTE: I would not be suggesting all this if you hadn't presented the case as being problematic. Truth seems to be...you just don't KNOW THE HELICOPTER ...yet Just be patient with me please. I'm really trying to help you. I can usually get vibes on a 2 blade helicopter below 0.03 IPS. To do that though, the machine and blades have to be real close to perfect. In my experience, 0.30 IPS will break things if you keep flying.
In the FAA's opinion 0.30 is safe. They make no claims about when your helicopter will crack or your pitch links will wear-out.

More Later.

 

[floppywing]

Do you have the builders manual for the adjustments.

Yes