Sigh...

[FlyingMonkey]

My idle is about 1500 RPM but I keep it above 1800 during tax, and all other times. A 1900-2000 RPM will give me a taxi above 12K if I let it. To keep it in the 10-12K range I don't ride the brakes but I give it continue short applications as required. I suspect much of my brake wear is due to my desire to make the 800 ft turn off.

 

But, I don't care. They are wear items and relatively cheap.

 

we have a long straight taxiway, and with my engine at 1700-1800 I will easily break 20kt on it if I don't brake.  Probably partially due to my tiny 4.00 x 6 tires.

 

I'm the same way, I will almost always add some brakes to make the first turn off.  Especially if somebody is on final behind me. 

[sandpiper]

I just got back from a flight and paid attention to taxi speed and RPM. At 2000 RPM it got to 15.4K and was still going up on the GPS before I slowed it down. With 1900 RPM it seemed to stabilize at 13.5K. Wind was cross at about 5K.

 

It seems smooth enough at 1800 so maybe I should taxi at 1850 or so instead of the 2000 I usually keep it at.

 

As I recall from flight school days we were taught to keep it at an apparent fast walk. Haven't done that for awhile.

[FlyingMonkey]

I just replaced the pads, no problems there.

 

However, I also noticed the same problem Ian described...the bolts used to index and set the pad distance were loose! Loose enough that I could turn them with my fingers. I don't know if the nordlock washers failed to lock or the bolts were never properly torqued.

 

I put a tiny amount of Loctite 242 on the bolt threads and tightened them up. I'm sure the Loctite won't do much once the brakes heat up, so I will re-check the bolts in 5 hours or so. They were loose on both sides, BTW!

 

Between my pads at the service limit and the loose bolts, the piston was coming out very far, probably 3-5mm or so. Now it barely pops out a millimeter or a tad more during braking. I taxied and glazed the pads per Matco instructions, but it was too windy for much else today.

 

On another note, while I was taking stuff apart I went ahead and re-shimmed the Matco axles. On both sides I put two washers (the max allowable) on each lower bolt hole. That should remove as much negative camber as possible, and hopefully let my tires wear better. I will have to see how this does and decide if more camber is needed and if toe-in is also an issue I need to address. The wheels sit noticeably more upright now, though not quite square.

[Roger Lee]

So while you did your taxi I take it they didn't lock up anymore? 

[FlyingMonkey]

So while you did your taxi I take it they didn't lock up anymore?

 

Correct. I want to taxi some more before flying to be sure, but it seems the problem is solved.

[FastEddieB]

Again, to make this seem more like a normal dialog, with normal responses to posts...

 

Prop rpm, which is what matters, is not that different from a typical Continental or Lycoming.

One needs to divide engine rpm by 2.43 to get an apples to apples comparison.

So 1,700 engine rpm = about 700 rpm at the prop. Maybe even less than a Continental or Lycoming direct-drive engine at idle.

Ed,

 

I actually knew we had a geared engine. Yet somehow when told the brakes wore so fast due to "high idle", I just thought that was logical, comparing 1,700 rpm to the much lower numbers I've seen on direct-drive engines. Somehow it did not "click" that the gearing had to be taken into effect.

 

Thanks for straightening me out, and I'm going back to the fellow that told me that and see what he says now.

[FastEddieB]

You're welcome!