Whatlimit
There are no short cuts to RTB on the 412 the key is making sure you are using the right program for your aircraft Landing gear (high or Lo gear) and pylon mount configuration.
The donkeywork is done on the ground and the hover using the initial flight plan before attempting the full flight.
The test condition FPOG means Collective FULLY DOWN and not lifted to ease the ground bounce.
Also pay attention to the MM AUM range stated for the procedure as the RADS response sensitivities are set for that AUM.
Here is a list of tips from Chuck Kemp who is the doyen of 412 RADS RTB and another list from Dave Burch from Bell, if these don't answer your questions then you will have to pick up the phone to Mirabel..
Cheers W
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Use the scripts on the following aircraft:
1. 412_41 (For those aircraft with soft pylon mounts (-105) and standard
landing gear low or high.
2. 412F (For those aircraft with soft pylon mounts (-105) and float style
landing gear.
3. 412_50 (For those aircraft with hard pylon mounts (-107) all landing gear
types.
Perform a visual inspection to determine which type of pylon mount
you have. Olive drab green are the soft mounts (-105) and Epoxy Polyamide
Yellow are hard mounts (-107). You also need to determine if you have dual swashplate drive links installed.
If you have single drive links this can give a problem where the ips level
will tend to bias around only one phase angle. Bell gave out dual drive links
for free when they introduced them but some AB412 customers still have
single drive links. If you don't have hard mounts or dual drive links then
you need to get them for a consistent rt&b solution.
If you go into flight with high vibration levels and a track split larger
than 45 mm's the machine is not ready for the forward flight flight plan.
The proper way to perform the initial is:
1. Determine which type of pylon mounts you have and use the appropriate script file
2. Obtain a perfect track of +20 m/m's on RED/BLU and -20 mm's on ORG/GRN +/- 1mm using p/c link at 62% idle. Turn off Tabs, Hub Weights & Product Balance at
this point using the diagnostic editor.
3. Run aircraft at idle and 100%FPG and 100TQ if high gear. Stop track change from idle to 100% using Outboard tabs. Turn off product Balance at this time using the diagnostic editor.
Don't make p/c links changes of less than two flats Don't proceed to Hover
until track change is less than 2 mm's and lateral balance is below 0.2ips (low
skid) or f/a is below 0.2 ips (high skid gear).
4. Now run idle, FPOG, 100TQ and Hover. Stop track change between FPOG and
HOVER using product balance. Hover lateral is not so important here instead we
are interested in stopping the track change. Keep performing this until the
track change is less than 4 mm's or you can't make a product balance move. All
test states should still be in limits. If all are good proceed to forward
flight.
Forward Flight (Soft Mounts using 412_41 or 412F scripts)
1. Perform forward flight taking data at all test states!
2. Set Auto-rotation on very first flight. Setting it last can cause 1 per
rev. and a couple more flights to fix.
3. Look at initial adjustments and predictions. On the first flight you will
probably do what the CADU comes up with.
4. On the second flight usually the verticals are down but you still have some
lateral. If vertical is down turn off Tabs leaving on P/C and Hub Weights.
P/C's will work you lateral in flight and hub weights will work your lateral on
the ground and let down.
Forward Flight (Hard Mounts using 412_50 script)
1. Perform forward flight taking data at all test states
2. Set Auto-rotation on very first flight. Setting it last can cause 1 per
rev. and a couple more flights to fix.
3. CADU will default down to a maximum of 6 adjustments. Usually these are
what you end up using.
4. Instead of playing with edit adjustables, use Max # and adjust that number
up or down to get you favored predictions. This will allow the CADU to pick
adjustments with the maximum effect and not what you think it will need thus
keeping track split close and vibe levels down.""""""""""
And here are extracts from a list of more tips from Bell CSR Dave Burch I hope he doesn't mind my posting it.
"""
412 MAIN ROTOR VIBRATION CHECKLIST
1. Insure that the tail rotor is in track and balance. An out of balance or track tail rotor is often felt as a roughness or a one per rev vibration in the cabin in forward flight and not as a medium (or high) frequency vibration. Feel the left hand elevator at 100% on the ground. Don't take the pilots word for it. Because of the hydraulics most pilots won't feel a tail rotor buzz until it is in the 0.6 IPS range.
2. Insure that the engine to transmission input drive shaft is balanced. The drive shaft will make a pulsating low frequency noise at about 1.25 second intervals in flight that will make the passengers and pilots feel very tired and uncomfortable in flight. This may be perceived as a one per rev vibration. Again many times this will not be noticeable to the pilots as a specific high frequency vibration in the airframe.
3. Wash and wax the blades. The 412 airfoil is very critical. It is not unusual to see 0.2/0.3 IPS vibration changes by just cleaning the blades. Be sure to use non-silicone wax per MIL-W-18723. Insure that the product balance weight pocket covers are sealed properly with no squeeze out above the surface of the blade while insuring that the gap around the pocket cover is filled evenly and smooth with the upper surface of the blade.
4. Inspect the skid gear cap assemblies for condition of the rubber. If the latest dash number elastomer (P/N: 412-030-437-103) are not installed; then they should be at the earliest possible date. Bad or old style (P/N: 412-030-437-101) elastomer/rubber will cause/feed vibrations and make it very difficult to work the rotor. Insure that any caps sent to Lord for rework are reworked to the -103 assembly.
5. Loose doors, cowlings, elevators or external equipment will amplify any vibrations and particularly the four per rev. Insure that they are tight. There are several Technical Bulletins to help reduce the noise and rattles from the doors that should be complied with on older aircraft. The latch pin rods in the hinge panels often rattle against the inside of the panel. These can be covered with plastic tubing which often decreases the cabin noise level considerably.
6. Check the elevators for looseness in the spar to horn and at the horn to fuselage mount bearings. It is necessary to disconnect the spring cartridge in order to check the preload. Be aware that the inspection criteria for axial play in the maintenance manual is currently incorrect.
7. Check that the pilot/co-pilot seats are tight on the rails and that the vertical lock pins or holes are not worn out. Many times the seats will be loose enough to increase the feeling of an acceptable vibration to an unacceptable one.
8. Insure that all the passenger seats and cabinets are tight. In particular, the high back seats used in the EMS sector give false visual clues by the tops moving excessively even though the vibration is not actually there.
9. Insure that there are not any pieces of equipment or cords in the cabin or cockpit area that are loose or can shake or move where they will give false visual clues to the pilots or passengers that there are excessive vibrations when there are none. Map light cords, windshield wipers and fire extinguishers are notorious for this.
10. Insure that all the equipment in the nose compartment is tight and in particular check for loose ballast or batteries. These make very uncomfortable vibrations and make it very difficult to work the rotor.
11. Insure that the hydraulic actuators are tight and aligned properly. Check that the universal bearings on the extension tubes are tight. This is difficult to check with the pitch links connected due to the loads of the elastomerics of the main rotor. Ensure that the pivot bearings on the input levers are tight. Check the lower mount for elongated bushings or worn bearings or bolts.
12. Insure that the minimum collective friction is adjusted correctly. A slight collective bounce will cause a lot of problems. On the 412SP and 412HP be sure that the droop compensator cable is not giving you a false friction.
13. Check the four pylon mounts for sheared rubber or obvious delamination or deterioration. Check the two friction dampers for proper operation and for loose bearings in the damper or the airframe mount. Loose bearings in the dampers or mount and/or bad or soft pylon mounts will increase the sensitivity of the airframe to the point that it may not be possible to get a good ride and really hurt laterals in the let down.
14. Check the lift link for loose bearings and for any damage to the mounts. Insure that the spacer washer is installed between the upper lift link bearing and the inside of the right side of the transmission mount. If this is not installed the link chaffs the mount and makes a thunk with power changes and adds to the four per rev vibration level.
15. Inspect the instrument panel mounting structure for security and tightness. Insure that all the mounting screws are installed and that the side braces are secure and have no cracks (particularly behind the plastic on the door post.) Insure that the glare shield is in good condition with no cracks or looseness. If the frahm damper is still installed on the instrument panel, insure that it is securely mounted and that the springs are in good condition or that it has been locked out.
16. Insure that the trailing edge expandable bolts on the main rotor hub are set for the proper tension and at the proper dimension from the yokes. This is a repetitive problem. If the customer wishes, PSE can authorize replacement of the expandable bolts with the normal bolt, washer and nut combination.
17. On aircraft with the elastomeric control system links, insure that the serrated rod ends and bushings engage properly and the bearings are set at zero preload at full down collective. Refer to the Maintenance Manual.
18. Insure that the collective levers to sleeve pivot bearings are tight and that pins to bearings are shimmed for the proper clamp up.
19. Insure that the collective lever and two swashplate horn universal bearings are tight.
20. Verify that the swashplate support, gimbal ring and inner ring mount bolts, bushings, and bearings are tight and the shims for the supports show no signs of deterioration or looseness of the mount screws.
21. Verify that the droop stops are rigged properly. Insure that the clevis arms are centered on the cams and do not contact the sides of the cams. If necessary, the thru bolts can be loosened and the lower support rotated to center the clevis to cam. Check the bushings for flat spots. Check the bearings for free movement and proper lubrication.
22. Inspect the elastomers carefully in the main rotor hub. Refer to the maintenance manual for inspection criteria. Insure that the spindle bearing to lead-lag damper joint is secure. Check for evidence of the lead-lag damper working in the damper bridge. Insure that the through bolts are tight and there is no evidence of the yokes moving on the center drive hub or upper or lower cone seats.
23. Insure that any cracks or erosion in the finish of the main rotor blade are filled properly. These can allow water intrusion into the core of the blade which will cause the blade to become unworkable. Check for cracks in the trim tabs or the tab mounting area. Check that the tabs have not lost their rigidity (become soft tabs) that will not hold their settings.
24. If the blades have been reworked, insure that the Bell Helicopter procedures were followed for sanding, repairs, rework, refinishing and re- balancing of the blades. Improperly reworked blades may not be able to behave properly in flight.
25. Insure that the simple pendulum absorbers are lubricated and that the bearings are free. Check by pulling outboard and aft on the weight arms and then check for roughness of the bearings or excessive fore and aft movement.
Hub Weights:
Maximum:
* 8 weights any location.
* 16 weights per yoke end.
Once you get to eight weights on trailing edge add to leading edge.
Product Balance:
Trailing edge weight adjustment does all the track change from ground to hover.
Leading edge balance pocket is just to offset the weight move to keep span wise balance equal.
* 1 weight move= 0.5 IPS hover lateral
* 1/2 weight move=4mm-5mm track change ground to hover
Standard Load:
Leading edge pocket: 135 grams (One thick flat and one thin flat washer)
Trailing edge pocket: 158 grams (One wedge and one thin flat washer)
Ratios:
Trailing edge to leading edge x 0.85
Leading edge to trailing edge x 1.17
It takes approximately nine (9) grams at the hub weight mount arm to offset a one (1) gram mistake at the trailing edge product balance pocket. It takes approximately ten and one half (10.5) grams at the hub weight arm to offset one (1) gram at the leading edge product balance pocket
412 Rotor Working Information
Try to work rotor at 800 to 1200 pounds of fuel, External Auxiliary Fuel Tanks empty and no more than three people on board. Make sure inboard tabs are set to zero before tracking.
On Initial:
1. Get maximum of 2mm track change between 62% FPG and 100% FPG.
If possible, get maximum of 4mm track change or less between 100% FPG and hover.
2. Try for total maximum change between 62% FPG and hover of 4mm if at all possible.
3. Initial does not work lateral in hover, only works track at 62%, 100% and hover and lateral at 100FPG on "412 F & 412_41" programs and fore/aft at 100TQ on the "412_50" program.
4. RADS phase angle is plus 62.5 degrees of the standard Chadwick to compare to charts. (2:00-2:15 on RADS is 12:00 on Chadwick charts, or 12:00 Chadwick = 62.5 degrees (RADS)
5. Concentrate on vertical on first flight before lateral.
6. Significant change in ride level with changes in gross weight indicate a product balance problem or bad rubber.
7. 412 normally indicates 19% to 21% torque at flat pitch on the ground if autorotation is correct. Check Auto rotation RPM on flight, first. Do not make rotor smoothing adjustments until auto revs are set.
8. When getting close to completing a rotor, turn tabs off (412F & 412_41). Concentrate on roll and hub weights.
9. Significant phase angle change from ground to hover indicates product balance needed. Watch phase angles for proper directions of move.
10. Excessive inboard tab may cause ground bounce.
11. Worn swashplate gimbal ring bearings or bores may show up as a lateral in let down.
12. Sudden severe lateral on pickup to a hover is probably a hung droop stop.
13. If you have shifting weight clock angle call out, then look at the opposite pair of blades lead lag dampers.
412_50 ver 5.3 or higher
This program differs in that it has a couple of states that are different than 412_41.
Listed below are the extra states:
1. 100TQ - This is 100% NR on the ground with 5% torque pulled in from the flat pitch reading. With the -107 mounts the aircraft may have more of a ground bounce than a standard aircraft. This will reduce ground bounce and allow you to balance the rotor.
2. 120/97 - This is 120 KIAS with the rotor beeped back to 97% Nr. This state can be skipped until your last flight. No rotor smoothing is accomplished with this reading. (Do not forget to beep back to 100% Nr upon completion!)
This program works diagnostics differently than 412F. It will automatically count down to the smallest amount of adjustments, usually about 6. You can do those adjustments or go into the "edit defaults" on the diagnostic menu.
Once there, turn the best number of adjustments to best 04 and "resolve to limits" off. Press DO, it will then give you the best 4 adjustments or less that will make the rotor smoother. Check the predictions if it is better than "default moves", do those. Try best 3 or 2 moves, they may be better. Just be careful and do not get caught up in trying to reduce the predictions that you are just dropping the vibrations .05 ips between the different adjustments. You are finished when the screen says you are below all set limits or you cannot obtain a smoother ride.
Installation: Install the RADS for 412F ver 1.40 the same as the Bell maintenance manual chapter 65, Install the RADS for 412_50 ver 5.3 the same as above but add a fore/aft accelerometer on the bottom of the instrument panel under the lateral accelerometer. The connector must point fwd. Attach it to channel 3. Reference Technical Bulletin 412-92-111 Rev. A.
412_41 ver 5.3
This program works the same as 412F ver 1.4 yet is to be used on soft mounted aircraft without external tanks and floats
Using The RADS At Night: Install the reflective tape supplied with the kit on the bottom of all four blades trailing edge. It must start at 9" inboard of the mid span tab and be 24" long. Turn the Day/Night test knob on the DAU to "Night."
Using a mini mag light ( something with a small focused beam ) align it with the UTD and adjust the angle of the UTD so that the beam of light hits the middle of the tape. (67 degrees from co-pilots seat rail) You are now ready to track at night!
Common Rotor Adjustment Mistakes: The RADS will only give hub weight adjustments for blue/org blades. If you have weight on red/green don't add to blue/org. Just remove from red/green. Mid span tabs move the blade about the same as outboard. You can use these to adjust track in lieu of outboard tab. Make sure you are not adjusting it opposite of the outboard tab and you are using the correct scale on the tab tool. Do not use inboard tabs. It may or may not work. It's not worth the gamble if you are getting the aircraft smooth without them.
If you have not made the aircraft significantly smoother in 4 or 5 flights, you have a problem. Start checking for loose drive link bearings, loose p/c link bearings, bad rubber, etc. All the bearings (hard) are .007 radial and .015 axial play. If all of these bearings are loose, they add up to a lot of play, which can make your job harder to accomplish.
On a freshly installed M/R head make sure that you retorque between each flight until bolts do not move.
To be certain which program you should use visually check to see which pylon mounts are installed. Hard mounts (-107's) are yellow and Soft mounts (-105's) are green.
You will be better prepared if you will watch the video tape titled "412 Rotor Inspection and Troubleshooting/Rotor Analysis and Diagnostic System", Chapter 65-03-00 through 65-05-00 of the Bell Maintenance Manual. and the Operators Manual supplied with each RADS. There is quite a bit of data that you could find useful in working 412 Rotors...