Jump to content

Ram Air Door Opens On Its Own At Cruise


Recommended Posts

Couldn't find this in my topic search so I thought I'd ask you all.  Sorry if this is a repeat.

When I had my alternator changed a few weeks ago, flight test afterwards revealed that the ram air door would open on its own when faster than 100mph roughly.  Had the shop open the cowl back up and they tightened something.  The cable wasn't slipping or anything like that.  The mechanic who initially worked on it then said that the mechanism was corroded during the alternator install and so he "cleaned it up."   I don't actually understand how the ram air door works.  What normally keeps it from opening when at cruise speed?  Is it just friction from a tight bolt or is there something more sophisticated than that?  Thanks for any ideas.  

This is what it looked like when the cowl was off and after the cleaning.  I don't have a photo of the before appearance.

image.thumb.png.a2a0b716372e7ac2e012fc75423def18.png

Link to comment
Share on other sites

I'm also interested in the cause of this, as mine will slowly creep open when the air pressure on it is high.  I have to be up closer to 140 mph airspeed before mine will open and then just a bit.  It's enough that if I cruise with it closed, the warning light comes on when the gear goes down, but not so much that you would notice by looking at the lever.  I think the push button locking mechanism just isn't holding well enough, but I'll see what others have to say.

Link to comment
Share on other sites

1 hour ago, apenney said:

Couldn't find this in my topic search so I thought I'd ask you all.  Sorry if this is a repeat.

When I had my alternator changed a few weeks ago, flight test afterwards revealed that the ram air door would open on its own when faster than 100mph roughly.  Had the shop open the cowl back up and they tightened something.  The cable wasn't slipping or anything like that.  The mechanic who initially worked on it then said that the mechanism was corroded during the alternator install and so he "cleaned it up."   I don't actually understand how the ram air door works.  What normally keeps it from opening when at cruise speed?  Is it just friction from a tight bolt or is there something more sophisticated than that?  Thanks for any ideas.  

This is what it looked like when the cowl was off and after the cleaning.  I don't have a photo of the before appearance.

image.thumb.png.a2a0b716372e7ac2e012fc75423def18.png

Your 76 may be very similar to my 75 F. What keeps the door closed is the latching mechanism on the knob. If your mechanic cleaned the cables up and the latch is not locked, I could see it being pushed open in flight.

Link to comment
Share on other sites

5 minutes ago, skydvrboy said:

I'm also interested in the cause of this, as mine will slowly creep open when the air pressure on it is high.  I have to be up closer to 140 mph airspeed before mine will open and then just a bit.  It's enough that if I cruise with it closed, the warning light comes on when the gear goes down, but not so much that you would notice by looking at the lever.  I think the push button locking mechanism just isn't holding well enough, but I'll see what others have to say.

The warning light is activated by cable position, not door position. I suspect that both of the aircraft in this thread need to have their Ram Air doors rerigged.

Link to comment
Share on other sites

Here is the picture of the locking mechanism. As Ross pointed out, the door itself doesn’t determine whether your annunciation panel will light up. The position of the cable does.

If I do not lock mine, the door does open a bit and the light will come on during flight.

5ece3ba2926309a884774e992724c230.jpg


Sent from my iPad using Tapatalk Pro

Link to comment
Share on other sites

We’re talking about two different birds in this thread. Both the 67 and the 76 M20F have RAM Air but the locking mechanism is different for each.  The 76 has a twist to lock cable in the 67 has a pushbutton lock mechanism. Also my ram air door does not have all of those linkages shown in the photo. I’m going to have a gander at the IPC to make sure mine is stock.

As for the two of you having problems with the door opening in flight. The first thing to do is to verify there’s no slop in the system. The second thing to do is to in sure the cable is properly secured at a point that gives adequate travel for the door to open and close. The last thing I would do is ensure that the cable locks. There’s little else to malfunction other than the door hinge itself.

Your mechanic needs to make sure the cable is secure (see red arrows). If the cable can slide within the clamps, your door will not operate correctly. 

BF6535A8-6369-44AE-A8C5-D8F208FD9AD5.thumb.jpeg.7b96e99397de39605f681159b473d728.jpeg

Edited by Shadrach
  • Like 1
Link to comment
Share on other sites

@Shadrach  You are spot on.  Here is a pic of mine.  I think that the push button that locks the cable slips when pressure is applied to the door itself.  It does open and close all the way when the lever is pushed/pulled.  I'll check that the cable ends are secured and don't slip next time I'm at the plane.  If the locking mechanism is slipping, is there any way to adjust that or does that mean it's time to replace?

  1994055250_RamAir.jpg.1623ea23aebfae895fec0e596e8daedd.jpg

Link to comment
Share on other sites

21 minutes ago, Shadrach said:

We’re talking about two different birds in this thread. Both the 67 and the 76 M20F both have RAM Air but blocking mechanism is different.  The 76 has a twist to lock cable in the 67 has a pushbutton lock mechanism.

Hmm... Our '76F has no twist lock, at least not as noted on the placard (I've never tried to twist it).  The ram air cable has always been very stiff to actuate, not sure if that's by design or due to lack of use.

Link to comment
Share on other sites

Hmm... Our '76F has no twist lock, at least not as noted on the placard (I've never tried to twist it).  The ram air cable has always been very stiff to actuate, not sure if that's by design or due to lack of use.


The “twist to lock” style has a little metal collar that a small knob locks into.


Sent from my iPad using Tapatalk Pro
Link to comment
Share on other sites

4 minutes ago, skydvrboy said:

@Shadrach  You are spot on.  Here is a pic of mine.  I think that the push button that locks the cable slips when pressure is applied to the door itself.  It does open and close all the way when the lever is pushed/pulled.  I'll check that the cable ends are secured and don't slip next time I'm at the plane.  If the locking mechanism is slipping, is there any way to adjust that or does that mean it's time to replace?

  1994055250_RamAir.jpg.1623ea23aebfae895fec0e596e8daedd.jpg

I have my doubts about your locking mechanism failing. A good way to verify the integrity of the locking cable would be to try and pull it open without the depressing the button.  If that checks out then I would verify that the annunciator light switch that attaches to the cable is tight  and properly adjusted to annunciate only in the open position. 

Link to comment
Share on other sites

21 minutes ago, Vance Harral said:

Our knob doesn't look like either of the photos above.  I realize this is a terrible photo, but for what it's worth...

ramair.jpg.6a659967a07a33a985c44fff276a73f2.jpg

The 76 F model is a bit of an odd duck.  The interior is in many ways more like a 77J than a 75F.

Yeah, lots of changes. The twist to lock is what preceded yours and I think began in 74 or 75. I thought it endured through the early Js but you learn something new every day.

Link to comment
Share on other sites

19 minutes ago, Vance Harral said:

Our knob doesn't look like either of the photos above.  I realize this is a terrible photo, but for what it's worth...

ramair.jpg.6a659967a07a33a985c44fff276a73f2.jpg

The 76 F model is a bit of an odd duck.  The interior is in many ways more like a 77J than a 75F.

Yeah, mine looks like yours.  I've never tried to twist it.  It has just been a little stiff in the past and there would be a point where a resistance changes could be appreciated when opening or closing it.

 

image.thumb.png.10c2c48ff1f69e24247cc93243d160ea.png

Link to comment
Share on other sites

41 minutes ago, skydvrboy said:

@Shadrach  You are spot on.  Here is a pic of mine.  I think that the push button that locks the cable slips when pressure is applied to the door itself.  It does open and close all the way when the lever is pushed/pulled.  I'll check that the cable ends are secured and don't slip next time I'm at the plane.  If the locking mechanism is slipping, is there any way to adjust that or does that mean it's time to replace?

  1994055250_RamAir.jpg.1623ea23aebfae895fec0e596e8daedd.jpg

I just looked through the ICP. The 67 model does not have the triangular frame or the linkage is associated with it. The rammer on my 67F is simply a cable with a naked conduit. The conduit is held in a fixed position near the ram air door. The cable connects directly to the Armature.

Link to comment
Share on other sites

2 minutes ago, apenney said:

Yeah, mine looks like yours.  I've never tried to twist it.  It has just been a little stiff in the past and there would be a point where a resistance changes could be appreciated when opening or closing it.

 

image.thumb.png.10c2c48ff1f69e24247cc93243d160ea.png

Yeah, that looks like an early J. Would be interesting to know what years the design changes took place.

Link to comment
Share on other sites

That picture really looks like the arm is designed to go over center, and that the current cable setting isn't pushing it  far enough.   I couldn't find a diagram in the M20J maint manual. 

Someone with a well adjusted ram air of that type should send a picture.   Or I would just loosen the cable and see if it can be pushed  shut by hand at the mechanism, and adjust from there. 

 

  • Like 1
Link to comment
Share on other sites

1 minute ago, PaulM said:

That picture really looks like the arm is designed to go over center, and that the current cable setting isn't pushing it  far enough.   I couldn't find a diagram in the M20J maint manual. 

Someone with a well adjusted ram air of that type should send a picture.   Or I would just loosen the cable and see if it can be pushed  shut by hand at the mechanism, and adjust from there. 

 

Good catch! That’s likely why there’s no lock on the cable. It’s clearle not overcenter in the posted pic.

Link to comment
Share on other sites

Our knob doesn't look like either of the photos above.  I realize this is a terrible photo, but for what it's worth...
ramair.jpg.6a659967a07a33a985c44fff276a73f2.jpg
The 76 F model is a bit of an odd duck.  The interior is in many ways more like a 77J than a 75F.


There are a lot of changes that the 74 through 77 F models went through (yeah, there were a few 77 F models). Quadrant carried through those years but yokes were changed out as well as a few other changes including flap deployment and cowl flaps.




Sent from my iPad using Tapatalk Pro
Link to comment
Share on other sites

14 minutes ago, apenney said:

Sorry but what does over center mean?  

9F3DE748-6635-4112-8A2C-DB02870E2085.thumb.jpeg.bf6b9e3f45f25063c98b0c1de14ec115.jpeg

It means that cable “A” should push Armature “B” forward and upward passed the straight position (center) so that the end of the armature ”C” locks against the stop bolt “D”. It would then be locked in the over center position.  In that position, airflow would simply push the Armature tighter against the lock. 

Edited by Shadrach
  • Like 3
Link to comment
Share on other sites

3 minutes ago, Shadrach said:

9F3DE748-6635-4112-8A2C-DB02870E2085.thumb.jpeg.bf6b9e3f45f25063c98b0c1de14ec115.jpeg

It means that cable “A” should push Armature “B” forward and upward passed the straight position (center) so that the end of the armature ”C” locks against the stop bolt “D”. It would then be locked in the over center position.  In that position, airflow would simply push the Armature tighter against the lock. 

I see.  So, with the knob pushed in the closed position, this setup should look like your description and not what is in the photo?  That would explain the change in resistance I used to feel...when it would go past center, if I'm understanding things correctly.

 

Link to comment
Share on other sites

Looking at your photo, it looks like the outer cable sleeve might be moving inside of the 2 clamps. I see a little polished metal there and the cable inside the cable guide isn’t far enough out if your  ram air door is closed. That outer cable guide should be further back with more cable showing when ram air is closed.

Have someone pull the ram air and see if it is sliding in the clamps.

David

Link to comment
Share on other sites

Geez, we all have different cables and knobs on the RAM.  Mine is a 68F, and has tge squeeze to open knob type.  I’m no mechanic, so not exactly sure how these go in there, but there a very small, like almost microscopic ball bearings that go into the locking mechanism somehow. Easy to lose...

E04D5E8D-1531-483A-A734-5835859A8922.jpeg

Link to comment
Share on other sites

44 minutes ago, Sabremech said:

Looking at your photo, it looks like the outer cable sleeve might be moving inside of the 2 clamps. I see a little polished metal there and the cable inside the cable guide isn’t far enough out if your  ram air door is closed. That outer cable guide should be further back with more cable showing when ram air is closed.

Have someone pull the ram air and see if it is sliding in the clamps.

David

 

Thanks for the ideas @Sabremech, labeling that photo and describing past center @Shadrach, and everyone else's input.  The collective knowledge, desire to help, and responsiveness of Mooneyspace really blows me away.  Thank you.

Link to comment
Share on other sites

Knobs and cables were used over a variety of planes in different ways.... over different years...

That silver knob with a push button also was used for cowl flaps in 1965...

The big vernier prop control in a 65C became a cowl flap control for the K, later on...

As intake design got improved, the ram air became less valuable...

As cowl design improved, cowl flaps got fixed (not moving), then eliminated....

I had difficulty with the silver knob, attached to my cowl flaps.... it’s last point of connection for the cable was on the engine mount... a place that got a drip of oil often enough to keep the cable mount lubricated and moving...

Bootom line... make sure the cable is firmly mounted at the end near the actuation point...

Owning an old Mooney should earn the owner a masters degree in mechanical engineering!

PP thoughts only, not a mechanic...

Best regards,

-a-

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.