Tapping brakes on gear retract?

[Pinecone]

15 hours ago, 0TreeLemur said:

We gave it up as our sales declined due to effective emulators on cell phones and retirement of folks who grew up with them.

My phone has an HP-41CV emulator that looks like a -41 keypad.

But it is better than an actual -41, in that there is a row of boxes at the top that show the contents of the stack.

[LANCECASPER]

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.

If you had a CFI that believed in it and drilled it into you then you stick with that. The first retractable I bought was a Cessna 172 RG in 1992 from man who had been a Cessna dealer in Iowa since 1947. He had flown and instructed in B-24s and Cessna 140s and everything in between. He was a DPE that had signed off on over 1000 new pilot's licenses and countless ratings. He had checked me out in a 172 that I bought from him in 1985 as a student pilot and the only check out in the RG was from him and he never mentioned tapping the brakes so, although I've heard about it, I've never done it.

A little over a year later I bought a 1983 Mooney 231, went up with an instructor for a check out after studying the POH overnight. Since neither mentioned tapping the brakes, my take-off habits didn't change. Three years later I bought a Bravo from Mooney and a Mooney test pilot did my check out, and you guessed it, never mentioned anything about tapping the brakes. A couple months later the 3 day Flight Safety course that came with the purchase didn't either. In 2000 I took the initial course at Vero Beach SimCom for the Piper PA46 (Mirage), no brake tapping. Three years later the initial course for the Meridian, never tapped a brake once. Every year in the recurrent PA46 training with different instructors every year, not one toe touched a brake after the airplane lifted off. I did the MAPA Safety course two years ago - not a single tap. I've done a Flight Review a couple times with a retired American Airlines check airman with 20,000 hours - never has the subject of tapping come up. No IA in doing my annuals has ever said "I can tell by your landing gear that you haven't been tapping lately".

There are things we each do that we hold sacred that someone else doesn't do. Sometimes we don't even know where they came from, sometimes we do and defend them vigorously. My only thought is that I'll continue doing what I do since that's my flow. Interrupting that is probably more harmful than whether the brakes get tapped or not. 

No doubt, 13 years from now we'll still be debating . . . and some will be tapping and others won't . . . lol

 

[kortopates]

I've always tapped the brakes on takeoff. It always made good sense to me to be gentler on the gear.

When I was first taught this, my CFI knew why and I could recall the angular momentum physics demonstration from first semester of physics. It was surprisingly damn hard to twist the spinning bicycle wheel against it plane of rotation - and that light wheel wasn't going anywhere near 60 mph.

Some of you may argue, why bother, your don't even have a brake for the nose wheel. But there is no angular momentum force introduced by raising the nose wheel, since its not rotated against its plane of rotation, only the main landing gears.

Here is two minute video on it. But what you really need to feel for yourself is how hard it is to twist the wheel when your feet are firmly planted on the ground so that your body can rotate - its hard to twist. So why wouldn't anyone paying the bills for their gear maintenance not want to be gentler on their main gear with a tap of the brakes? Is it going to be make a difference long term on your gear maintenance? Probably not as much as the pilot that never perfects his/her landings and touches down a couple times with every landing. But why put an extra unnecessary load on it?

 

 

 

[PT20J]

It would be really interesting if those with manual gear would try it both ways and report back on the difference in effort to raise the gear. Mooney’s present a unique opportunity to investigate this. 

[Bolter]

1 hour 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.

Such strong opinions on each side for so long.  After reviewing, I have decided to apply only one brake on each takeoff as a compromise.

[LANCECASPER]

No doubt someone will put a GoPro underneath their airplane and show us both methods. I would look forward to seeing that.

[MooneyMitch]

5 minutes ago, LANCECASPER said:

No doubt someone will put a GoPro underneath their airplane and show us both methods. I would look forward to seeing that.

I'm surprised this hasn't happened yet!

[LANCECASPER]

14 minutes ago, MooneyMitch said:

I'm surprised this hasn't happened yet!

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.

 

[Hank]

52 minutes ago, kortopates said:

I've always tapped the brakes on takeoff. It always made good sense to me to be gentler on the gear.

When I was first taught this, my CFI knew why and I could recall the angular momentum physics demonstration from first semester of physics. It was surprisingly damn hard to twist the spinning bicycle wheel against it plane of rotation - and that light wheel wasn't going anywhere near 60 mph.

Some of you may argue, why bother, your don't even have a brake for the nose wheel. But there is no angular momentum force introduced by raising the nose wheel, since its not rotated against its plane of rotation, only the main landing gears.

Here is two minute video on it. But what you really need to feel for yourself is how hard it is to twist the wheel when your feet are firmly planted on the ground so that your body can rotate - its hard to twist. So why wouldn't anyone paying the bills for their gear maintenance not want to be gentler on their main gear with a tap of the brakes? Is it going to be make a difference long term on your gear maintenance? Probably not as much as the pilot that never perfects his/her landings and touches down a couple times with every landing. But why put an extra unnecessary load on it?

 

Our Mooney tires are much smaller than this bicycle wheel [angular velocity varies with the square of the radius, so half the diameter is one quarter the speed], and our steel wheels are much, much heavier, resulting in a much lower portion of the energy being at the outside. So much less gyroscopic precessional force. I'm not worried.

[A64Pilot]

34 minutes ago, PT20J said:

It would be really interesting if those with manual gear would try it both ways and report back on the difference in effort to raise the gear. Mooney’s present a unique opportunity to investigate this. 

I think though that confirmation bias would rear it’s head. To do it properly you would need to instrument the aircraft, a fancy fish scale might help, some have markers that stop at the max weight.

I should have kept my force gauge but left it at work.

I’ve noticed that often, it’s just normal. It’s tough to not be affected.

I’ll throw out a for instance, some swear that flying without an AOA is just unsafe. I can’t see the need on a GA airplane myself, but see no harm in having one either, unless based on your trust of it you put yourself into situations you might not should. Not saying any do, just it’s the only way I could see how maybe an AOA could do harm.

Ag planes fly or at least turn right at the ragged edge of stall, the stall is what determines turning radius, if they could turn faster, it would increase profits. I’ve done an participated in testing of AOA sensors in Ag planes and came away with the opinion that sure why not, but that they didn’t increase safety

[Hank]

2 hours ago, Pinecone said:

My phone has an HP-41CV emulator that looks like a -41 keypad.

But it is better than an actual -41, in that there is a row of boxes at the top that show the contents of the stack.

I have two:  go41c [an actual HP-41C; I miss the advanced functions from my -CX], and RPN calculator [a generic RPN that is quite similar to my HP].

But I still prefer the original, because I can tell when I press a button,, and which button I press [no so on the smooth touchscreen on my phone . . . . ]

[Schllc]

46 minutes ago, kortopates said:

It was surprisingly damn hard to twist the spinning bicycle wheel against it plane of rotation

Wow, if you do the rough math based on a 20” bicycle wheel vs the 12” airplane wheel, assuming 3 lbs and 7 lbs respectively (approximate tire weight only)

The forces would be at least three times what you experienced with the bike wheel  

I had not considered these  forces and assumed the braking was to prevent he spinning wheel from damaging itself or anything in the well .

without knowing the calcs on the gear, although I’m assuming this is factored, it’s still a lot of stress .

 

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

[A64Pilot]

Back in 1978 I had an HP-33E, in College people would ask to borrow it, none ever figured it out.

HP used Reverse Polish notation?

[Hank]

3 minutes ago, A64Pilot said:

Back in 1978 I had an HP-33E, in College people would ask to borrow it, none ever figured it out.

HP used Reverse Polish notation?

You betcha! 2/Enter/2/+ yields 4.

The big saver is the elimination of ()s, and the floating stack. My generic simulator above apparently has an unlimited stack, but my trusty 41CX works well with only a 4-level stack.

Try this:  5((1-13/16 - 7/8)/2)^3  [an equation I just made up, and substituted numbers into]

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.

In Texas Instruments:

    5*(((1+(13/16) = -(7<divide>8)) = /2= ) y^x3) = --- 31 buttons, unless I confused myself with all of those parentheses!

Go RPN! HP Rocks!!!

[Pinecone]

1 hour ago, LANCECASPER said:

No doubt someone will put a GoPro underneath their airplane and show us both methods. I would look forward to seeing that.

This came up on BT.  And several showed videos with the wheels stopping in about 5 seconds after liftoff.

But there was the one posted here that showed the right wheel spinning for a long time.

As I stated, it was recommended by an A&P at my field based on what he felt was damaged caused by the spinning wheel being retracted.

[EricJ]

6 minutes ago, 1980Mooney said:

That is the "acid test".  If the J bar guys don't feel any difference in their arms testing it both ways in back to back takeoffs, then this just a lot of hand wringing over a minute issue.

It is a minute issue, and I don't think anybody is wringing their hands over it.

Plus, nobody is going to feel the precession in raising or lowering the gear, because the precession torque will make the tires want to turn to toe-out, not resist or aid the up-swing. 

I tap the brakes also to reduce vibrations from wheels that are a bit out of balance.    That can be particularly annoying on Cessnas with spring-steel gear when it hits the resonant frequency of the gear leg.

It certainly doesn't hurt to do it, and it might help a little.   

[Shadrach]

31 minutes ago, 1980Mooney said:

That is the "acid test".  If the J bar guys don't feel any difference in their arms testing it both ways in back to back takeoffs, then this just a lot of hand wringing over a minute issue.

BTW - over on Beechtalk same thing - doesn't seem like anyone worries about it - no issues in nearly 70 years of flying and swinging the gear in Bonanza's.

One pilot on BT expressed the same issue that I have - tapping the brakes as you rotate is just another distraction that you don't need at a critical time.  The video posted by @LANCECASPER noted that if you don't do it within a few seconds of liftoff the wheel is already slowing down and may have stopped before you "tap the brakes" and raise landing gear.   

Some on BT also noted that they adjust their wheel bearings on the tight side (with no deleterious effects over many years) so that the wheel slows down more quickly on its own.

That’s a tough one to test without equipment. I will give it a shot if I ever get this thing back in the never ending annual ever wraps up.

[EricJ]

9 minutes ago, Shadrach said:

That’s a tough one to test without equipment. I will give it a shot if I ever get this thing back in the never ending annual ever wraps up.

Precession torque is orthogonal to the applied force.   It will neither resist nor aid gear retraction, since the precession is caused by the gear retraction.

[47U]

On 1/11/2024 at 6:48 AM, r0ckst4r said:

Any of you guys tap the brakes on take-off?

Isn’t the pad (circled) in the top of the wheel well a rub strip?  Essentially, the up-stop for the gear when retracted?  If the tire sidewall engages the rub strip when the gear retracts, would it better to have the wheel spinning, or not spinning?  

Do all Mooneys have this rub strip, or did later models discontinue it? 

 

[N201MKTurbo]

Just now, 47U said:

Isn’t the pad (circled) in the top of the wheel well a rub strip?  Essentially, the up-stop for the gear when retracted?  If the tire sidewall engages the rub strip when the gear retracts, would it better to have the wheel spinning, or not spinning?  

Do all Mooneys have this rub strip, or did later models discontinue it? 

 

The rubber strip hits the gear leg, not the wheel.

[PT20J]

1 hour ago, Schllc said:

Wow, if you do the rough math based on a 20” bicycle wheel vs the 12” airplane wheel, assuming 3 lbs and 7 lbs respectively (approximate tire weight only)

The forces would be at least three times what you experienced with the bike wheel  

I had not considered these  forces and assumed the braking was to prevent he spinning wheel from damaging itself or anything in the well .

without knowing the calcs on the gear, although I’m assuming this is factored, it’s still a lot of stress .

 

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

Centripetal force would be the force on each increment of tire mass pulling it toward the axis of rotation and it would not change as the axis of rotation changes.

What we want is the torque due to gyroscopic precession. 

Torque is defined as a vector perpendicular to the plane of rotation in a direction that, by convention, follows the right hand rule (curl your right hand fingers in the direction of rotation and extend your thumb which represents the direction of the torque vector). Consider the right main wheel. When the gear is retracted, the gear motion is a clockwise rotation (viewed from the rear looking forward) and a translation toward the center of the airplane. Only the rotation creates a precession torque and so the translation can be ignored. The rotation of the spinning wheel causes a change in angular momentum which creates a torque which, by the right hand rule, is represented by a vector pointed toward the nose of the airplane. The effect of this torque is to apply a twisting force to the axel which would tend to toe the tire out. Calculating the torque requires knowing the angular velocity of the wheel/tire, the moment of inertial of the wheel/tire the gear geometry and the angular velocity of the gear as it retracts. I doubt it is all that much, especially since the drag of the brake pads and the friction of the bearings causes the wheel to be decelerating fairly rapidly.

[47U]

2 minutes ago, N201MKTurbo said:

The rubber strip hits the gear leg, not the wheel.

Ahhhh, never mind then…

And thank you!

[N201MKTurbo]

It seems like with a single wheel spinning, there would be a pitching moment when the gear retracts, but, with both wheels spinning in the same direction and one moving left to right and the other moving right to left, the pitching moments would cancel.

[PT20J]

14 minutes ago, EricJ said:

Precession torque is orthogonal to the applied force.   It will neither resist nor aid gear retraction, since the precession is caused by the gear retraction.

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.

[Shadrach]

17 minutes ago, EricJ said:

Precession torque is orthogonal to the applied force.   It will neither resist nor aid gear retraction, since the precession is caused by the gear retraction.

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)?