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Surprise during taxi testing

airguy

airguy

Unrepentant fanboy
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I'm only days away from first flight (waiting on current strong west winds to drop for my north/south runway) so I'm doing some taxi testing. Life is good - so much so that a good friend of mine wanted to ride with me and kick the rudders a bit for grins himself. In doing so we discovered an issue - the right hand copilot brake pedal was sticking and would not return. After he kicked the pedals around a bit, the right brake was dragging and quickly got hot. This is not something I would have caught until who knows when...

This is why we test - because we don't know the things we don't know.
 
Good catch Greg. Remember there are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know. Keep testing. :D
 
Vlad said:
Good catch Greg. Remember there are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know. Keep testing. :D
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I think I know what you mean. ;)
 
I'm impressed

Vlad said:
Good catch Greg. Remember there are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know. Keep testing. :D
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The Vladster is writing in his third language, here. That he follows his own discourse here is accomplishment enough to have my respect. ;)

-Stormy
 
Been there done that

I immediately had to add the return springs using the parts in Daryl's post.

Taxiing with sticky brakes was no fun at all.

I think I confirmed the right side was just as bad, and ordered parts for both sides.

Filling the brake system from the bottom up is a lot easier when the masters are fully disengaged!
 
I was in a one mile long departure line at Oshkosh. There I am, third from departure and my left brakes sticks. I am sure the guy behind me thought I was nuts. I did a 360 and luckily got it unstuck. I need to install the spring kit. Oh how I dread the dive under the panel.
 
chipf said:
I immediately had to add the return springs using the parts in Daryl's post.

Taxiing with sticky brakes was no fun at all.

I think I confirmed the right side was just as bad, and ordered parts for both sides.

Filling the brake system from the bottom up is a lot easier when the masters are fully disengaged!
Click to expand...


I have some extra springs and nylon collars if you need them. Send me a PM
 
I built everything to Van's plans and had a dragging right brake on the initial testing. And even then, I've always had to reach back in to give the pedal a tug when getting out so that I could push it up the incline and back into the hangar.

During the most recent condition inspection, after changing brake pads (third set at 273 hours; the first set broke when they got frozen by packed snow after getting real hot, fun times in MN in the winter) and the O-rings on the disk, I spent a lot of time bleeding brakes.

I was positively anal about even the tiniest bubbles and while I created a murder-scene-lookalike in the hangar a few weeks ago, the difference now is un believable.

Yes, I did the whole "springs" thing etc, but in the end, I found the best way to get the brakes to work properly is to do a better job of bleeding the lines.
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If you haven't reached that point of the build yet (or even if you have), I highly recommend using a single long skinny bolt to hinge the brake pedals, instead of the stock Van's two-bolt setup. Eliminate any binding here and the stock internal springs of the master cylinders prove more than adequate. Also, a little filing on the rudder pedal weldment may be required.

My little surprise during the taxi test was that one of the tow bar bolts on the nose gear was lightly scraping against the tire's sidewall. As the first flights will be sans wheel pants, I removed the attach brackets for the nose wheel fairing....so missing that extra thickness of aluminum allowed the bolts to thread in too far. So I put a couple of washers under each bolt as a remedy.
 
You can also eliminate any chances of the brake pedal binding by installing a long AN3 bolt through the brackets in place of the two short AN3 bolts. I cant remember what size these bolts were when I ordered them but it is covered in an earlier post somewhere in the archives. Even after all of this, I still had some instances of brake dragging during the first 3 months of flying. This seemed to be relieved by tapping on the brakes with my feet.

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Please think carefully before carry out much taxi testing. Much more than walking pace to confirm the brakes work is probably too much.

Each taxi test should be briefed as a test flight, its very easy to use just too much power for a little too long and end up flying. Don't spend very much time taxiing a new airplane - if you need time on the airplane go use a friend's - or get your friend to fly the first flight. Taxi testing can be higher risk than the first flight.

Pete
 
I'm so tired of people saying that every little thing we do is dangerous that I could absolutely puke, except that is probably dangerous too. If I wanted to be absolutely safe I would stay in bed, except that would be risking a heart attack from lack of exercise.

If you find my taxi testing to be too dangerous for your liking, then I suggest you refrain from taxi testing. I felt comfortable doing what I did. YMMV.
 
I think he was just trying to be helpful to others. There have been many loss of control incidents doing taxi tests. Not everyone might be aware.
Each person needs to evaluate the risk/benefit against their own experience(s) and judgement.
 
Perhaps I just have my tail in a kink this evening. If that came across as too harsh I apologize.

I am just absolutely, terminally DONE with people being afraid of their own shadow and expecting others to do likewise.
 
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