Braking After Landing

[Tom 4536]

I am new to this site and hope I am  doing this correctly. I have owned my 1979 M20K 231 for 3 weeks and love it, but after I land the braking is worse than any plane I have flown. Is this a characteristic of the M20's? The plane has about 20 hrs since the annual. It doesn't pull in any one direction when I apply the brakes so both brakes are acting the same, leading me to conclude the brakes are acting normal. Any input will be appreciated.

Thanks.

Tom

[neilpilot]

Can I assuming the brake pads are not worn beyond limits?  If the pads are OK it's likely old gummed up brake fluid.

Check theu log books and try to determine if your brake fluid has ever been flushed.  Brake fluid will thicken over time due to heat exposure, and you may need to flush at the individual cylinders. 

[Tom 4536]

There is no mention in the past 15 years that the brake fluid was flushed. I haven't figured out how to see the brake pads with all the hardware in the way but I will work on that.

Thank for your feedback.

Tom

[EricJ]

Just to be clear, though, don't get your hopes up.   The brakes just aren't very good compared to many other airplanes.   On touchdown I bring the flaps up right away in order to make the brakes available as early as possible.

I'm told the master cylinders are relatively small, which limits the effectiveness of the braking system compared to some others.

[jaylw314]

18 minutes ago, Tom 4536 said:

There is no mention in the past 15 years that the brake fluid was flushed. I haven't figured out how to see the brake pads with all the hardware in the way but I will work on that.

Thank for your feedback.

Tom

If the brakes and main gear are the same as the M20J (and I think they are), you need a flashlight shining at JUST the right angle to light up the edge of the brake pad.  There IS actually an angle, you have to shine the light from somewhere in the front, and stick your head somewhere above the wheels, but boy does it take a few tries to find those two spots.

[buddy]

The brake fluid should be flushed out every couple of years with new fluid as Neil says, for some reason you have to do this with Mooney brakes.

[EricJ]

52 minutes ago, Tom 4536 said:

There is no mention in the past 15 years that the brake fluid was flushed. I haven't figured out how to see the brake pads with all the hardware in the way but I will work on that.

Thank for your feedback.

Tom

 

30 minutes ago, jaylw314 said:

If the brakes and main gear are the same as the M20J (and I think they are), you need a flashlight shining at JUST the right angle to light up the edge of the brake pad.  There IS actually an angle, you have to shine the light from somewhere in the front, and stick your head somewhere above the wheels, but boy does it take a few tries to find those two spots.

Another way to do it is with a shop mirror (little articulating mirror on a stick) or a $15 endoscope from Amazon.   Even the cheapie endoscopes have a self-contained light source and make it easy to inspect the pads.

Edited June 19, 2018 by EricJ

[Bartman]

If you just bought it were the brakes serviced before you got it ?  I ask because of experience. First time I had the brakes serviced a few years ago they had to bleed old thickened brake fluid and had difficulty getting it out of the parking brake actuator, but finally got it working. Had to bleed the brakes with the pressure pot from the bottom up I was told.

This past annual I had new Flight Custom II installed on the mains and brakes pads installed just because they were both nearly 10 years old.  Yes that's right 10 years old and nearly 900 hours because I learned quickly the brakes are not very effective and have to land at the right speed and all. Anyway, after new pads this year I gave it a while for the pads to wear down and mate to the rotors but ended up having to flush the brakes again and then bleed from the bottom up with the pressure pot.  I was not there and don't know the specifics on the bleeding process but someone else can chime in.  Now they work fine just like before, but as said above they are still pretty weak. 

[jaylw314]

10 minutes ago, EricJ said:

Another way to do it is with a shop mirror (little articulating mirror on a stick) or a $15 endoscope from Amazon.   Even the cheapie endoscopes have a self-contained light source and make it easy to inspect the pads.

Before, I was actually taking a picture with my smartphone from above, and then looking at the pictures.  Now I'm too lazy to do that, so I probably won't go the endoscope route 

[Mooneymite]

I'm a C owner and was not aware there was a brake issue with the heavier Mooneys.

Give me some insight:  Are the brakes not capable of "locking up" the wheels, or do the wheels lock up too easily and skid rather than provide braking?

 

[DonMuncy]

When you say "the braking is worse", do you mean it doesn't slow down much? The brakes lock up and skid the tire? or what. 

If they lock and skid, it may be not all the weight is one the gear yet (still generating lift), or the fluid is gummed up. If the brakes feel good (not spongy), but doesn't slow down much, it may just be a Mooney.

[Mooneymite]

2 minutes ago, bluehighwayflyer said:

I also find the brakes on both our M20C and M20J to be rather weak, even after a fluid change and proper pressure bleeding, although that does help. 

Hmmmm.  On my C, the brakes work fine.  I can lock up both wheels under any condition and flat spot my tires anytime.  Keeping the wheels from locking up is another matter.  Dumping flaps, or modulating the brake pedals are possible mitigating techniques, but the brakes themselves are doing their job.

I'm not sure which is the issue for the OP.

[jlunseth]

I think you have a maintenance issue not a design issue.  The brakes on my 231 are good enough that I have to be careful about not braking too hard and flat spotting the tires.  When I was doing my commercial and lots of short field landing practice, I had to replace the tires although they were only about 6 months old.  I have plenty of braking power.

[skydvrboy]

Brakes?  Brakes for stop.  Plane not for stop, plane for GO!  Why you need brakes?

On a more serious note, though mine is an F model, I can lock up the brakes at just about any speed if I want to.  Typically though, I don't use the brakes until I am ready to stop at my parking spot.  Just slow down before you land.  I often find I need to add power just to make the 3000' turn off with nothing more than aerodynamic braking.

[EricJ]

Being able to lock up a wheel is a poor measure of the effectiveness of a brake.   e.g., Even really crappy brakes on cheap cars can lock up wheels.   The ability to generate braking torque while dissipating the generated heat makes a good brake.   The job of the brake is to turn kinetic energy into heat energy, and keep doing it until it isn't needed any more.   If the brake degrades with increasing temperature or can't dissipate heat effectively, it can overheat and become ineffective, aka "brake fade".

Locking up a wheel can be done with a short application of torque, and once the wheel is locked only holding torque is required (which is a lot less than what it takes to lock it up), as the tire interface with the runway surface then becomes the friction and heat surface.   The brake itself experiences no heating during a lock-up event.  This can be done with much less braking capability than is required to actually dissipate the energy of the moving vehicle.

On an airplane it is complicated by the variance in downforce on the tire as the airplane slows and lift is reduced.   Initial braking can easily lead to lock up when the wings are still generating lift and downforce is reduced.  Being able to modulate the brakes to get torque just shy of lockup (aka threshold braking) can be difficult because of this.   

[Mooneymite]

Just now, skydvrboy said:

Brakes?  Brakes for stop.  Plane not for stop, plane for GO!  Why you need brakes?

Or if you're like me, I operate off of grass most of the time, so I lock the brakes on landing and slide into the home hangar thus saving both tire tread and brakes!    

The grass grows back.

[jaylw314]

1 minute ago, EricJ said:

Being able to lock up a wheel is a poor measure of the effectiveness of a brake.   e.g., Even really crappy brakes on cheap cars can lock up wheels.   The ability to generate braking torque while dissipating the generated heat makes a good brake.   The job of the brake is to turn kinetic energy into heat energy, and keep doing it until it isn't needed any more.   If the brake degrades with increasing temperature or can't dissipate heat effectively, it can overheat and become ineffective, aka "brake fade".

By that same token, NOT being able to lock up a wheel would be a good measure of a really crappy brake!

[EricJ]

15 minutes ago, jaylw314 said:

By that same token, NOT being able to lock up a wheel would be a good measure of a really crappy brake!

Even worse, yeah. 

Unless, of course, you get all the torque you need without it locking up.   Race cars with sticky tires and lots of aero downforce require a LOT of pedal force to use the brakes efficiently...sometimes it's difficult to get to lock up.

 

 

Edited June 19, 2018 by EricJ

[wishboneash]

I try to not depend on the brakes. I only really need them for the runup.

[Bartman]

With light loading I can get my J off at the 1000 foot turn at my home airport. It requires braking of course but requires a fair amount of pressure. Kinda like the old 69 Rambler with Bartman powered brakes that I learned to drive in. Maybe we are all just used to the smart anti-lock power brakes in the new cars. 

[Mooneymite]

3 minutes ago, wishboneash said:

I try to not depend on the brakes. I only really need them for the runup.

And at 4 way stop signs....

[Andy95W]

My brakes were like the OPs when I first bought my current Mooney.  I found 4 things wrong-

-old o-rings

-incorrect brake discs (for the M20C they changed after 1965)

- old brake pads

- incorrect rigging (I had to push about 3 inches before I got any brake application)

By fixing all those things I also had to completely change out the brake fluid, so that probably helped, too.  Now my airplane stops like stink, normally less than 1000' rollout (I'm on a very short runway).

[Hank]

I don't use brakes until I've slowed to 50 mph or less. Then they work fine.

When I was based at an obstructed 3000' field with one exit at 1000', I would generally touch down on the 2nd or 3rd stripe (out of 13), and was usually turned around between 2000-2500' and back taxiing. 

Now I often visit a 5000' field with taxiway exits at both ends and the center. I rarely brake hard, and almost never go a long single stripe past midfield turnoff. 

• Fly the right speed on final.
• Cross the numbers at the correct (lower) speed.
• After nosewheel touches, raise flaps to put weight on the wheels. 
• Slow some more (I like 50 mph for my C)
• Then brake.

[carusoam]

Welcome aboard, Tom!

The K is a special M20...  It has a tendency to be nicely loaded with heavy devices.... 

summary...?

Welcome to MS’s Mooney Ownership 101....

1) Get the brake fluid changed... you get the flap fluid changed for free this way...

2) Check on the brake hardware... it should still be there...

3) In the first few months of Mooney flying, speed control is being developed...

4) Seek Don Kaye’s landing a Mooney video... for guidance. 5kias makes a lot of difference...

5) Flaps down, @ 60kias the plane is still flying while on the ground or not... brakes are pretty ineffective while still flying...

6) Pulling all the way back on the yoke helps the pilot know if you are still flying...  If the nose points to the sky, put it back immediately.

7) Raising Flaps is a great way to dump lift, or raise the gear... it’s best to not touch any switches or Jbars until off the runway... for some time...

8) there is a lot of information around on how to recognize various distractions... accidental gear raising, or forgetting to lower the gear are two of the crummy ones...

9) when the brakes lock and the plane is still moving... your flat spots grow deep incredibly fast...

10) Good speed control, braking is hardly used... aim for good speed control...

11) It helps to be able to see your ASI while while flying final.   Scan quickly/often if you can’t watch the ASI while looking out both windows...

A lot of assumptions are being made.  

• Did the OP get any transition training?
• Does the OP have any Mooney flight experience?

Note to the OP, tell us about your experience... it will help with the focus of the guidance you receive...

Best regards,

-a-

[320KPH]

Brake fluid is hygroscopic, it absorbs moisture fom the air and when the fluid is compressed the moisture can boil off, reducing pressure applied to the calipers. On motorcycles brake fluid is recommended to be changed annually.

Old brake fluid could therefore result in 'spongy" brakes and ineffective braking.

Flushing the system is recommended, rather than merely bleeding the brakes.

A vacuum pump system is available from auto supply shops for 'reveerse bleeding your brakes. with one of thes pumps bleeding or flushing brakes can be a one man operation.

If your brake fluid is discouloured, dark brown, your fluid is really old. Fresh brake fluid is clear in colour.