Nose Gear Rubbing in Well on Retraction?

[1001001]

My '78 J is in for annual, and I'm told by the mechanics that the nose gear is rubbing the wheel well as it retracts.  I'm headed over to see it in a little while, but wanted to see if anyone here has thoughts on it.  The nose gear truss was replaced by the same shop last year during the pre-purchase inspection, and they did not see this kind of rubbing then.  They also re-rigged the gear and rudder systems during that inspection. 

I thought perhaps it might be related to holding right rudder during retraction, but they say that it does it when the gear is held straight as well.  Hopefully I'll get some pics this afternoon.  Any ideas on causes, and whether this might be a serious condition?  Where in the gear system can we look for any mis fit?

[1001001]

The tire is rubbing on the well and the hub is very close to touching.  The pin inthe castellated nut touches the wall of the well.  In addition, the retraction linkage pushrods appear to be bent.  I have had no hard landings or hits on the nosegear since i began flying the airplane.  No heavy side loads either.  They took a straight rod and checked alignment of the truss and found it was crooked a bit (pic attached). The frame on the airplane is straight and the bushings are concentric on both the frame and the truss.  They are recommending sending it to LASAR to check it.  Thoughts?

[1001001]

So, I am sending it out to Lasar to inspect, but still would love to hear from anyone who may have seen something similar in the past, and have any advice.

 

Thanks!

[N201MKTurbo]

Why is your retraction rod bent? Is the other one bent too?

The only way that can happen is if one of your limit switches failed or the gear was horribly mis rigged. It could also happen if you were using the manual extension system and didn't stop when the green light came on.

[takair]

12 minutes ago, 1001001 said:

So, I am sending it out to Lasar to inspect, but still would love to hear from anyone who may have seen something similar in the past, and have any advice.

 

Thanks!

I occasionally see rubbing Over the years and it seems to vary by my rigging and tire.  You will see pictures of variations in door position, main gear angles, etc.  Puck health, rudder rigging, etc.  While I expect trusses are welded in a fixture, I suspect over the years they can perhaps take on a slight bend with error stack up.

[1001001]

50 minutes ago, takair said:

I occasionally see rubbing Over the years and it seems to vary by my rigging and tire.  You will see pictures of variations in door position, main gear angles, etc.  Puck health, rudder rigging, etc.  While I expect trusses are welded in a fixture, I suspect over the years they can perhaps take on a slight bend with error stack up.

Thanks for replying.  It seems to me that the wheel has rubbed for a while (I don't remember a time that the paint wasn't rubbed there), but the shop guys say that during the retract cycle the tire was making a loud squeaking sound as it went up into the well, and that they hadn't heard that last year.  The truss is new from LASAR last year.  The axle mount and upper parts of the gear mount are not new, however, their paint is very good, and the logs show that this nose gear was replaced only a few years ago, when the prior owner had the LASAR modified nose gear installed via the STC.

Hopefully, LASAR will be able to see what's wrong, but what's really weird is that the gear doesn't bind at all other than with the tire rub.  It is moveable easily by hand and swings easily down by gravity, when it is disconnected from the actuation linkage.  If the gear structure or airframe were distorted, I'd expect it to bind, or the attachment bolts to be difficult to insert/remove due to misalignment, but there appears to be no such misalignment. 

The only thing we can think of yet is that the wheel appeared to always be slightly turned even if the rudder were centered, perhaps the truss came slightly out of whack from LASAR and we're just noticing it now?

The bent rod ends on the actuation pushrods are a head scratcher, though.

Edited August 27, 2020 by 1001001

[Marauder]

Just now, 1001001 said:

Thanks for replying.  It seems to me that the wheel has rubbed for a while (I don't remember a time that the paint wasn't rubbed there), but the shop guys say that during the retract cycle the tire was making a loud squeaking sound as it went up into the well, and that they hadn't heard that last year.  The truss is new from LASAR last year.  The axle mount and upper parts of the gear mount are not new, however, their paint is very good, and the logs show that this nose gear was replaced only a few years ago, when the prior owner had the LASAR modified nose gear installed via the STC.

Hopefully, LASAR will be able to see what's wrong, but what's really weird is that the gear doesn't bind at all other than with the tire rub.  It is moveable easily by hand and swings easily down by gravity, when it is disconnected from the actuation linkage.  If the gear structure or airframe were distorted, I'd expect it to bind, or the attachment bolts to be difficult to insert/remove due to misalignment, but there appears to be no such misalignment. 

The only thing we can think of yet is that the wheel appeared to always be slightly turned even if the rudder were centered, perhaps the truss came slightly out of whack from LASAR and we're just noticing it now?

The bent rod ends on the actuation pushrods are a head scratcher, though.

You haven't changed nose tires since the last annual? Anyone check the correct tire is on it?

[1001001]

The tire has not been changed, although they just repacked the bearings last week.  I *think* the tire is right--these guys are likely to have checked it--they are usually very thorough.

[1001001]

1 hour ago, N201MKTurbo said:

Why is your retraction rod bent? Is the other one bent too?

The only way that can happen is if one of your limit switches failed or the gear was horribly mis rigged. It could also happen if you were using the manual extension system and didn't stop when the green light came on.

Yes, both are bent, about to the same degree.  I have not used the manual extension system, and it looks as if they have been bent for a while, given that the paint is off the bent area, and the metal underneath looks fairly dull, not bright as migh be expected if it were recent.

It may be that the retraction rods were bent last year and we didn't catch it--there was damage to the nose gear assembly due to improper towing that was caught during the pre-purchase inspection, and the gear actuator motor and gearbox were trashed (unrelated).  Could the damaged gearbox have been related to a problem with over-extension?

Edited August 27, 2020 by 1001001

[takair]

Good catch on the bent rods.  That is probably worth correcting.  Lost of load on those rods and the bend certainly messes with the geometry.  As far as the rubbing, other things to look at are the spacers on the nose wheel bearings.  If a fat one ended up in there then the wheel will rub.  Tire brand and markings, inflation, etc will also eat into marking.  Worn steering links may not allow full centering as the gear retracts....allowing someone rotation of the assembly.  Note also that the sheet metal in the well seems to be bent out, like something caught it....near the rubbing.  This also eats into the margins.  Not sure what LASAR will find.  I have an old truss, will try to look at it later...for some reason I have a feeling that part of the geometry is ok.

[1001001]

Just now, takair said:

Good catch on the bent rods.  That is probably worth correcting.  Lost of load on those rods and the bend certainly messes with the geometry.  As far as the rubbing, other things to look at are the spacers on the nose wheel bearings.  If a fat one ended up in there then the wheel will rub.  Tire brand and markings, inflation, etc will also eat into marking.  Worn steering links may not allow full centering as the gear retracts....allowing someone rotation of the assembly.  Note also that the sheet metal in the well seems to be bent out, like something caught it....near the rubbing.  This also eats into the margins.  Not sure what LASAR will find.  I have an old truss, will try to look at it later...for some reason I have a feeling that part of the geometry is ok.

I asked the guys about spacers/shims and they said there only appears to be about 0.030" of play to adjust in the direction away from the wheel well wall (on the truss attach bolts).  I didn't ask about spacers on the axle.  I keep the tire inflated to the specified 49 psig.  I had not noticed the bend you saw in the wall, but do see it now, where the paint has rubbed (in my picture; I'm not at the shop at the moment).

[N201MKTurbo]

15 minutes ago, 1001001 said:

Yes, both are bent, about to the same degree.  I have not used the manual extension system, and it looks as if they have been bent for a while, given that the paint is off the bent area, and the metal underneath looks fairly dull, not bright as migh be expected if it were recent.

It may be that the retraction rods were bent last year and we didn't catch it--there was damage to the nose gear assembly due to improper towing that was caught during the pre-purchase inspection, and the gear actuator motor and gearbox were trashed (unrelated).  Could the damaged gearbox have been related to a problem with over-extension?

The limit switches are near the gear box, if something damaged the gearbox it could damage the limit switch. If the limit switch doesn't work, the actuator will run until it pops the circuit breaker. it is stronger than you think.

You are lucky your gear didn't collapse.

[PT20J]

Could the bend in the retraction rods shorten them enough to cause the tire to rub? There’s not much clearance. My nose wheel well is undercoated and had a rub mark. I applied more undercoat to see if it was still rubbing and it’s not, but the tire is about half worn.

Skip

[1001001]

1 hour ago, PT20J said:

Could the bend in the retraction rods shorten them enough to cause the tire to rub? There’s not much clearance. My nose wheel well is undercoated and had a rub mark. I applied more undercoat to see if it was still rubbing and it’s not, but the tire is about half worn.

Skip

Possibly, but the wheel rubs lightly when it's disconnected from the linkage...

[takair]

I just checked a truss that I have and it is fairly square, but not perfect.  That said, they are taking the measurement at a fairly extended moment arm, so the lack of squareness is exaggerated and I’m not sure if it would be all that substantial at the wheel.  These buildups are fairly crude, so I don’t know If any are perfectly square.  If it helps...if they give the lateral distance to where they are measuring I can double check mine, or have them check closer to the axle for squareness.  At that point mine was within about 1/16” Of square by a crude measurement of this truss.

[1001001]

Just now, takair said:

I just checked a truss that I have and it is fairly square, but not perfect.  That said, they are taking the measurement at a fairly extended moment arm, so the lack of squareness is exaggerated and I’m not sure if it would be all that substantial at the wheel.  These buildups are fairly crude, so I don’t know If any are perfectly square.  If it helps...if they give the lateral distance to where they are measuring I can double check mine, or have them check closer to the axle for squareness.  At that point mine was within about 1/16” Of square by a crude measurement of this truss.

Thanks, that's great information.  Just eyeballing it, I think they measured it about a foot outboard from either side, so you're right that it is exaggerated.  I'm not sure if they took that dimension from some resource or from talking with LASAR.  I know they did speak with LASAR about it before they talked to me.

[PT20J]

9 hours ago, 1001001 said:

Possibly, but the wheel rubs lightly when it's disconnected from the linkage...

Maybe I’m missing something, but aren’t the retract tubes what position the wheel in the up position?

[carusoam]

Are we talking this bend?

If yes... the clearance is only Millimeters and this bend seems to add a lot of unexpected change...

Bent retraction tubes are a common source of gear failures... and pretty easy to get bent when the gear isn’t set up to spec....

I didn't see any other bent rod ends like I had expected.... usually they bend on the threaded area and are easily swapped out...

PP thoughts only, not a mechanic...

Best regards,

-a-

[RLCarter]

When redoing the gear on my E there was a tell tell mark on the well just like yours. I seem to remember there are 2 eccentric bushings (1 on each side) changes how far up in the well that the wheel travels. 

[Guest]

As Robert points out above, there are 2 eccentrics where the nose gear push rods attach to the nose truss, these adjust the retracted height in the wheel well and may stop the tire from rubbing the top of the wheel well.
As to the marks on the side, the axle bushings may cause the wheel to be off centre in the wheel well, a mis rigged steering system may be allowing the wheel to retract while slightly turned or worn parts are not holding the wheel perfectly straight during retraction.

The nose push rods are under tension load during extension and compression load during retraction, so to bend as they are, it must have bent on retraction.

Clarence

Edited August 29, 2020 by M20Doc

[1001001]

Thanks for the additional replies, guys.  The bend in the push rod ends that carusoam highlights is the one in question.  As far as we can tell now, there are no other bent/damaged parts in the linkage.