"Sucked out" is a weird concept on the bottom of the wing where one would expect hi pressure.  Perhaps airflow over a surface produces a local low pressure even though the pressure on the bottom is greater than that on the top?  However, if any air enters at the door leading edge, it is far easier to understand since the door is curved and could act like an inverted wing.  Then, when the rear is in the slip stream, the forward edge is forced closed and the "wing" stops flying, returning to the start state where air once again enters at the leading edge. Thus, the buzz.

 

Is the wheel well sealed to the cockpit, thus the door does not benefit from the low pressure in the cockpit trying to suck the door in. 

 

Interrrrrresting.........

 

Grayhawk

 

Just a thought:  would a couple of air vents in the doors solve the problem?   Start small and move larger until the noise stops or the doors stay shut.

 

Regards,

Harry League

 

 

---

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of marv@lancair.net
Sent: Saturday, December 06, 2008 21:46 PM
To: lml@lancaironline.net
Subject: [LML] Re: outback gear doors-vibration is back

 

Posted for mquinns@aol.com:

 Dom,
     AC-DC is not to my taste but listening to them would be far more musical
and pleasant than gear door rumblings. Attached is a close up picture of a
musical nocturne.
 
 Mark
 
 
 -----Original Message-----
From: Dominic V. Crain <domcrain@tpg.com.au>
 To: lml@lancaironline.net
 Sent: Fri, 5 Dec 2008 12:06 pm
 Subject: [LML] Re: outback gear doors-vibration is back
 
 
 
 
 I would think that the gear doors rumbling would be far more musical than
listening to AC-DC.
 
  
 
 Cheers
 
 Dom
 
 VH-CZJ
 
  
 
 
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of
mquinns@aol.com
 Sent: Friday, 5 December 2008 3:25 PM
 To: lml@lancaironline.net
 Subject: [LML] Re: outback gear doors-vibration is back
 
 
  
 
 Gerard,
    I had the same problem. Whenever the airspeed started moving past 210
knots a buzz would start and then turn into a rumble as the plane went faster.
If the aircraft was decelerated......to a speed around 205 knots, the rumbling
and buzzing would disappear but would reappear if the aircraft accelerated
back above 210 knots. I was certain it was the nose gear door (made from
fiberglass) so I took the advice in archive and fabricated a much stiffer
aluminum door. To my surprise the buzzing and rumbling problem was still there
over certain speeds.!!!!???!!!! Fortunately for me, I live at at a place where
we formation fly to breakfast every Saturday and I usually fly with the SX-300
guys. One of these friends volunteered to go up with me and formate under me
to
 see if the problem could be observed. Apparently, the main gear doors
trailing edges are being sucked out into the slipstream at certain airspeeds.
We repeated the speed runs (accelerate/decelerate) and proble! m was clear.
    My plane does have a difference with yours which is, even though I have
the outback gear, I decided to use the original cutout doors thinking they
would create less drag. Don't know whether they do or not but have been unable
after many different attempts to keep the doors closed at high speed. In
January I will be racing and afterwards plan on doing a major condition
inspection (demating wings, removing all control surfaces, etc) and at that
time will fit the original outback gear doors from the option kit. They do
appear to be stiffer (I hope they don't generate more drag). I hope that this
cures my problem. Some of the Reno racers have recommended stiffening gear
doors because this is a common problem for them while racing. If you find a
magic bullet to correct the problem, please post it. 
 
 Mark Quinn
 Lancair 360
 Spruce Creek Fly-in, Florida
 
 
 -----Original Message-----
From: gerardoconnell@optusnet.com.au
 To: lml@lancaironline.net
 Sent: Wed, 3 Dec 2008 9:15 pm
 Subject: [LML] outback gear doors-vibration is back
 
 
  
 
  
 
 Hi Ian and those whom have had gear door problems
 
  
 
 -Gerard from Down Under/Up Over has gremlins again
 
  
 
  
 
 Hope you're going well and enjoying you're flying. I'm just writing a quick
note
 
 both on and off
 list as we've been over this ground before.
 
  
 
 Do you recall discussing the buzzing noise I had some time back which I
resolved
 
 both by removing the nose gear door and overlapping the main and inboard gear
 
 doors to get better "purchase" and stop vibration.
 
  
 
 Well guess what?   Thhe noise is now starting to return-I initially thought I
 
 had the bass turned up too much whilst listening to AC -DC but even with the
 
 radio off I can appreciate the buzz from outside the aircraft.
 
  
 
 Perhaps I need to listen to Robbie Williams instead?
 
  
 
 I originally spent thousands of $ trying various solutions to this problem
and
 
 the final fix has worked for about 200 hours. I understand that some have
also
 
 extended the door hinge/bracket to address this problem.
 
  
 
 In short, my question is this-did you have this buzzing/vibration problem and
 
 what methods did you employ before removing the inner gear doors altogether?
Is
 
 this my best short cut to making the problem go away once and for all?
 
  
 
 Your thoughts would be appreciated including and issues you mar or may nopt
have
 
 experienced after removing the inner doors.
 
  
 
  
 
 Cheers,
 
  
 
 Gerard
 
  
 
  
 
  
 
  
 
  
 
 --
 
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
 
 
 
  
 
 
 
 Listen to 350+ music, sports, & news radio stations – including songs for the
holidays – FREE while you browse.
 Start Listening Now!