The following article concerns itself not only about DG gliders even if we give examples from our own gliders.
\nIn all types of aircraft, we hear unusual sounds from rumbling to whistling or vibration at specific speeds. The reasons for these things are hard to diagnose from a distance by telephone or even if they are brought to the factory and a test flight is made often the phenomenon doesn’t show itself at the factory!
\nIt is certainly helpful to list the different possible reasons because then the pilot can probably find the cause himself when he knows where he should look.
\nHere is the \u0093Funny Sound Checklist\u0094:<\/p>\n
Whistling sounds in the cockpit are the easiest to locate because one can put his hand on it during flight.<\/p>\n
By the way, if you put the seal on yourself, be careful that the surface to taped to is sparkling clean and free of oil. The best thing to clean it with is acetone and then be sure not to touch it with your fingers!<\/p><\/blockquote>\n
C. Undercarriage<\/h3>\n
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- Do the wheel doors close properly?
\nYou can check that in the hangar. Maybe the bungee in the wheel well is old and stretched? Or maybe the doors are crooked after a gear up landing?<\/li>\n- Does the steerable tail wheel vibrate?
\nIf it does, then something is wrong with the attachment. Push hard on both rudder pedals. Does the noise change? If so, it could be the rudder cable attachments and should be inspected by a certified mechanic.<\/li>\n- Is the tail wheel axle loose? That only happens with tail wheels that do not have ball bearings. Lift the tail onto the tail dolly and try to wiggle the tail wheel. Does it have play? Then it can spin in the air and vibrate.<\/li>\n
- Is there a vibration coming from the fixed tail wheel?
\nThe reason for vibration given above is the main reason for vibration. Check the axle bolt for looseness. There should be no axial play. The bolt should be just tight enough such that there is no axial friction on the wheel.
\nIf the tail wheel vertical axis is tilted, then the bearing must be replaced by a mechanic. Tail wheels that turn in the air are common causes for vibration. If the tail wheel bearings have no noticeable defect, try adding some friction to the system to prevent rotation in flight.
\nUnmount the wheel and attach some foam with double sticky tape to the wheel housing. Use a thickness that rubs slightly on the wheel. Does that cure the problem?<\/li>\n- Extract and retract the landing gear during flight.
\nWhen extracting the gear you of course will hear some wind noises. But does your strange noise change?<\/li>\n<\/ul>\nD. Rudder, Ailerons, Flaps<\/h3>\n
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- Is the mounting of the rudder loose?
\nDoes the noise change when you move the rudder or when you hold the pedals in position with both feet?<\/li>\n- Does your noise change if you move the aileron or flaps?<\/li>\n
- Probably the reason is the Mylar-Sealing.<\/li>\n<\/ul>\n
E. Engine doors<\/h3>\n
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- Do the engine compartment doors make a noise?
\nThis may be caused by a gap at the front edge of the doors. Stick some foam (e.g. draught excluder) under the front edge of the engine compartment doors. Did this get rid of the noise?<\/li>\n<\/ul>\nThese are the most likely causes of vibrations and odd noises known to us.
\nIf you have other experience from which other pilots might learn, please share them with us<\/p>\n