Tapping brakes on gear retract?

[Schllc]

I know my formula was over simplistic.  I was trying to show the delta between the analogy of a the forces from a bike tire. 
but these forces if at all significant would have to be calculated in the design models right?
which also begs the questions, if it doesn’t exert significant force to damage anything, why the suggestion to do it?

btw, it was in the poh and my initial training in the Aerostar, but as I transition, it’s one of the things I have not been vigilant about doing…

[EricJ]

7 minutes ago, PT20J said:

Now that I've actually thought about it, I believe you are correct. The effect is to try to toe out the right wheel and toe in the left.

I think it toes both out.   The retraction force can be thought of as inward at the bottom of each wheel, so the precession force is inward at the rear of each wheel.

[EricJ]

4 minutes ago, Shadrach said:

Is that a fancy way of saying that all of the procession torque will be limited to the axle and bearings (90° to the wheel)?

It will be trying to twist each wheel to toe out along the axis of the gear leg.   So as the gear reaches the up position, it'll be trying to push the front of the wheel down.

[jetdriven]

7 hours ago, skykrawler said:

That's why we go through the annual ritual of removing wheels, clean/repack after 75 flight hours.

So all those planes getting the wheel bearings re-packed every year again the question is, has anybody found any wheel bearings that were damaged by hard landings or gyroscopic loads from retraction?  Probably 6000 of these planes in  Service still so that’s 6000 sets of wheel bearings repacked every year. I’m a big believer in changing my mind when the data supports that, but we haven’t seen anything….it’s like those leaking bladders and everything else.

[Shadrach]

1 minute ago, jetdriven said:

So all those planes getting the wheel bearings re-packed every year again the question is, has anybody found any wheel bearings that were damaged by hard landings or gyroscopic loads from retraction?  Probably 6000 of these planes in  Service still so that’s 6000 sets of wheel bearings repacked every year. I’m a big believer in changing my mind when the data supports that, but we haven’t seen anything….it’s like those leaking bladders and everything else.

I have never seen Bearings damaged from normal use. I have seen bearings that were improperly serviced that overheated. 
 

I’m used to being the board Heretic, so I will openly state that we no longer service the bearings every year. We check the wheels for play and resistance. We repacked the bearings with SHC 100 when we put new shock discs on in 2021. They have perhaps 150 hours since they were serviced. I will likely service them next year even though I bet dollars to donuts that they will show no evidence of needing it.

[PT20J]

19 minutes ago, EricJ said:

I think it toes both out.   The retraction force can be thought of as inward at the bottom of each wheel, so the precession force is inward at the rear of each wheel.

Both wheels are spinning in the same direction, but the rotation due to retraction is in opposite directions.

[jetdriven]

5 minutes ago, Shadrach said:

I have never seen Bearings damaged from normal use. I have seen bearings that were improperly serviced that overheated. 
 

I’m used to being the board Heretic, so I will openly state that we no longer service the bearings every year. We check the wheels for play and resistance. We repacked the bearings with SHC 100 when we put new shock discs on in 2021. They have perhaps 150 hours since they were serviced. I will likely service them next year even though I bet dollars to donuts that they will show no evidence of needing it.

The Cessna 172 service manual  says wheel brings every 400 hours. 

[PT20J]

2 minutes ago, Shadrach said:

I have never seen Bearings damaged from normal use. I have seen bearings that were improperly serviced that overheated. 
 

I’m used to being the board Heretic, so I will openly state that we no longer service the bearings every year. We check the wheels for play and resistance. We repacked the bearings with SHC 100 when we put new shock discs on in 2021. They have perhaps 150 hours since they were serviced. I will likely service them next year even though I bet dollars to donuts that they will show no evidence of needing it.

My 1978 M20J was tied down outside. I used to get very minor corrosion on the outer races due presumably to moisture getting past the felt seals. I could always dress it out with some Scotchbrite. Still on my 1994 M20J, even though it is hangared, I replaced the seals with the new rubber ones because I didn't want to bother taking things apart every year. We don't check the wheel bearings at annual -- my IA just checks the free play and spins the wheels listening for noisy bearings. I take a look at them if the wheels are off to change the tires but I don't usually repack them. 

[Shadrach]

I guess I’m not the heretic I thought I was…

[EricJ]

21 minutes ago, PT20J said:

Both wheels are spinning in the same direction, but the rotation due to retraction is in opposite directions.

Yes, hence the symmetry for toe-out on both sides.

[0TreeLemur]

2 hours ago, Schllc said:

yi.  
F = m × v² / r,  F is the centripetal force; m is the mass ; v is its velocity; and r is the radius

You forgot the parallel axis theorem, needed because the rotation of the gear is happening around a different axis than the wheel axis is rotating.   Just sayin'. 

[PT20J]

7 minutes ago, EricJ said:

Yes, hence the symmetry for toe-out on both sides.

Oh, man you made me go and draw vector diagrams. Getting signs right has always been my nemesis. But, I agree it is toe out on both sides. 

[LANCECASPER]

1 minute ago, PT20J said:

But, I agree it is toe out on both sides. 

I'm going to keep my toe in and not tap 

[0TreeLemur]

5 hours ago, LANCECASPER said:

I remember this same conversation going on shortly after I signed up for Mooneyspace back in 2011 (It starts on the second page of the post below). People who believed in tapping the brakes back then still believe in it today. People that didn't back then still don't today.

It's a pretty long play list, but all play lists repeat at some time.  I think this suggests that MS has "jumped the shark".  No wonder attendance is way down over the past few years. 

[PT20J]

So, here's what I've learned from all this:

1. The effect of raising the landing gear without tapping the brakes is a twisting force applied to the axels in a toe-out direction caused by gyroscopic precession.

2. The stress on the landing gear components must be negligible given that the same axels and other components must absorb landing forces which must be many times greater.

3. The precession reaction force should not affect the retraction force applied by the actuator or J-bar. The origin of the precession force is the retraction force.

4. Tapping the brakes won't hurt anything. It might keep the wheel wells cleaner if the tires are still spinning off water and dirt as they enter the wells.

 

 

[N201MKTurbo]

With regard to wheel bearings, An FAA inspector told me that there is no requirement to repack the wheel bearings every annual, but there is a requirement to inspect them. His opinion is that you cannot inspect them without cleaning them and after you clean them you must repack them.

[PT20J]

Part 43, Appendix D, (e) (7) just states

Wheels - for cracks, defects, and condition of bearings.

That is subject to a lot of interpretation 

 

[Fly Boomer]

5 hours ago, Hank said:

In RPN: 

    13enter 16<divide> 1+ 8{1/x} 7* - 2<divide> 3y^x 5* --- 19 buttons to press, counting "13" and "16" as two buttons each.

Show off!

[Bartman]

Tap and Retract

[EricJ]

3 hours ago, N201MKTurbo said:

With regard to wheel bearings, An FAA inspector told me that there is no requirement to repack the wheel bearings every annual, but there is a requirement to inspect them. His opinion is that you cannot inspect them without cleaning them and after you clean them you must repack them.

"Inspect" isn't well defined with the FAA.   The Siilats Legal Interpretation letter says "To examine in detail, esp. for flaws", for which they cite Webster's as the source.   We inspect an awful lot of things without disassembling them, since for some things doing so would make the inspection the major wear or risk or expense source.

I'm with Skip's IA, that the pertinent flaws in wheel bearings can be detected without disassembly.   I also agree that there's no requirement to repack them every year, just "inspect", which has an awful lot of room for interpretation, but should be done to a level to detect flaws, especially that would affect safety.

Just my 0.02.

[RoundTwo]

On 1/11/2024 at 3:23 PM, Hank said:

Nah. No alphanumeric display on that one. Running strong in daily use since 1984.

HP-41CX. Helped me with two college degrees.

Wow, that brings back some memories but you’re running the turbo version. I had the CV back in ‘82. It got to be a pain sending it home to Corvallis when the screen would start to bleed. No one ever made keys that felt as good as HP did. I also had a 15C, but that died a slow death when the button cell batteries died and leaked their juice. It was a sad day.

[201er]

8 hours ago, LANCECASPER said:

Well I guess it has. Scott Newpower from Beechtalk who doesn't tap his brakes shows how,  in 8 seconds after take-off, the brake drag and bearing drag stops the mains from spinning.

 

I posted a video of gear retract in 201. Gear retraction began 8 seconds after lift off and was completed 10 seconds after liftoff. The right main continued spinning well past 20 seconds after liftoff. Seeing this convinced me to tap brakes. 

Edited January 13, 2024 by 201er

[A64Pilot]

5 hours ago, Shadrach said:

I guess I’m not the heretic I thought I was…

I repack them whenever I change tires, mine doesn’t sit outside. I do check for pre-load and roughness when I do retract tests.

On the helicopter we repacked them whenever we changed tires, or when they were submerged in water, which wasn’t infrequent when it was muddy especially in Germany.

I’ve only seen bearings worn from dirt / sand due to the completely ridiculous seals we have.

Beringer wheels use sealed bearings. Sounds like another STC money maker to me because surely we could pop out the races and fit a spacer and sealed bearings in our wheels?

Sealed bearings I’d suspect would last decades perhaps longer, after all they last decades and 100’s of thousands of miles on cars.

https://www.aopa.org/news-and-media/all-news/2007/june/01/airframe-and-powerplant-(5)

Repacking the average GA airplane bearings ever year is sort of the definition of over maintain, I have no idea where it comes from

 

[Pinecone]

14 hours ago, RoundTwo said:

Wow, that brings back some memories but you’re running the turbo version. I had the CV back in ‘82. It got to be a pain sending it home to Corvallis when the screen would start to bleed. No one ever made keys that felt as good as HP did. I also had a 15C, but that died a slow death when the button cell batteries died and leaked their juice. It was a sad day.

I was working for HP when the 41 came out, so a bought one, with the card reader and printer at an employee discount.

A few years later a good friend wanted to buy mine, and I had another friend who worked for HP, so I sold the C and got a CV.

A number of years ago, I bought a CX from someone online.  It still sits on my desk.

I am pretty sure I have the Aviation Pack plug in module around somewhere.

And, as I mentioned, if you have a iPhone, go to the App Store and search for HP-41.  There is an emulator that looks exactly like a 41

[RoundTwo]

On 1/13/2024 at 11:10 AM, Pinecone said:

I was working for HP when the 41 came out, so a bought one, with the card reader and printer at an employee discount.

A few years later a good friend wanted to buy mine, and I had another friend who worked for HP, so I sold the C and got a CV.

A number of years ago, I bought a CX from someone online.  It still sits on my desk.

I am pretty sure I have the Aviation Pack plug in module around somewhere.

And, as I mentioned, if you have a iPhone, go to the App Store and search for HP-41.  There is an emulator that looks exactly like a 41

I geeked out with my 41 and had the card reader and printer as well. I’ll check out the emulator, but I’ll admit that my RPN skills are pretty much gone. If only they could emulate the way the keys felt.