Directional control under hard braking

[AeroDog]

I'm doing the PAP taxi tests, including brake pad conditioning, which require max effort stops from 35 knots. I find the directional stability to be "darty" with small swerves left and right, rather than smooth straight-ahead stops. The brakes aren't grabbing and feel a bit weak. Anyone else see this?

Jerre

 

[N8DAV8R]

This is hard to assess based on typed out subjective descriptions, but I think what you are experiencing is normal or at least sounds familiar. Two things will happen as you continue to taxi and fly the airplane. First is that the brake pads will bed and break in and you will get a more consistent brake feel. You will also get more muscle memory and feel for how the brakes and steering on the airplane work.

I recently did new brake pads on a customer RV-12 as part of the annual. I took it out to taxi test and bed the pads a little bit, and even doing that I noticed it just felt a little off to me. In that case I would say that it took fairly heavy braking, which I think leads to the inconsistent directional control. The owner's CFI did a couple RTS and ferry flights and said they felt normal and working great by the time he dropped it off.

Hard to say from here but I wouldn't worry about this unless you're still fighting it as you work through phase 1.

 

[jabarr]

Neither Cleveland nor Matco require “max effort braking” during the brake pad conditioning procedure for non metallic pads.
I’m not familiar with the PAP tests- if that’s what they say, it’s contrary to the brake manufacturers recommendations.

 

[AeroDog]

Neither Cleveland nor Matco require “max effort braking” during the brake pad conditioning procedure for non metallic pads.
I’m not familiar with the PAP tests- if that’s what they say, it’s contrary to the brake manufacturers recommendations.

What the PAP actually says is "rapidly brought to a stop."

 

[jsalley]

What the PAP actually says is "rapidly brought to a stop."

Hi Jerre - I used the procedure recommended by Matco. They specifically say not to come to a full stop until you’ve done 2-3 runs. My brakes were a little squirrelly on the first run, but evened out after that and now (25 hours on the plane) are smooth and even. I agree with Nate that some of it is muscle memory once you accommodate to the way your plane steers and brakes.

 

[N8DAV8R]

You probably have things pretty well dialed in all around the airplane since you're at the inspection and PAP part of things, but there is one more detail to mention if you're thinking through an issue with the ground steering. The brakes themselves are pretty simple and once they will hold the airplane and you don't feel any spongy pedal it's unlikely the problem is there. If this persists after a couple more rounds of taxi or flying, double check the break-out force to move your nose wheel.

 

[Walt]

Avoid overheating the brakes, one 'firm' stop followed by full cool down, that is unless you enjoy blowing out brake caliper seals and getting to play fireman.

 

[Norman CYYJ]

Avoid overheating the brakes, one 'firm' stop followed by full cool down, that is unless you enjoy blowing out brake caliper seals and getting to play fireman.

Years ago I had a customer do his brakes after I thoroughly explained how. He thought faster and more power would be better. When he got back to the hangar, he had turned the pads mostly into powder and the disks were blue and destroyed. He was fortunate that he didn't have the wheel pants installed yet or he would have had some other major problems.

 

[wirejock]

I didn't enjoy the bedding either. One firm stop then cool completely. If you feel the need, one more. Cool. One more, cool. Like the man said, you don't want to blow fluid everywhere and torch the airplane. After 20 landings, I'm starting to get the feel.
What got me was the rudder pedals do nothing going slow so there's no need to move them. I kept pushing to the stop and the plane would keep going straight. Yea. Not the sharpest knife in the drawer!

 

[ravenstar]

Just for reference, the current RV-12iS PAP states:

Taxi at progressively higher speeds up to but not exceeding 25 knots. At each speed, verify
that aircraft can be accurately steered using only rudder and that the aircraft can be rapidly
brought to a stop while tracking in a straight line.

The following item then calls for performing the manufacturer's brake pad conditioning process and then letting the brakes cool for at least 5 minutes.

How this applies to the original question is I'm wondering if lower speed (25 vs 35 knots) might be related to brake behavior before conditioning?