REFLECTOR: how hot is too hot?

[davedent at comcast.net]

 Hay guys relate to brakes, don't take the heat lightly.  Last Saturday at 
the Livermore airport I was going to test fly a Standard Velocity for a 
short flight to trouble shoot a low power performance problem for a fellow 
that had just purchased it.  He said it just wasn't putting out the power he 
thought it should.  So after checking out a new cylinder that was just put 
on, it seemed that a bad lifter was the problem.  After the lifter was 
solved and getting good static RPM we cowled it up and I taxied it out for a 
short flight to see what it would do.

Now the two previous flights the wheel pants had been on but who knows how 
long they had been off before he bought the plane.  It looked like the 
Cleveland brakes were put on a while back. I didn't check the log to see 
when.  But remember the Cleveland brakes take up a lot of room inside the 
wheel pants, and generate a great deal of heat.  They have great stopping 
power but generate a lot more heat while they do so.  These pants only had 
two one inch holes at the front side of the inner panel of the pants. None 
in the top or out the back.

Well right after the roll got started with a little left brake and rudder 
because of a 20k quarter wind, I tapped the right brake because of a little 
over correction and it felt strange and then the plane seemed to start snow 
plowing.  So I aborted the flight and let it roll down to the next crossing 
taxi-way.  There I gave it a little more left brake to roll onto the 
taxi-way. Then when pressing on the right to straighten it out, the right 
brake went flat.  So with the cross wind now at my right the plane wanting 
to go left and out into the field that had high dry grass. Not a good thing 
to have with hot brakes.

The next thing I hear from the tower is you have a grass fire under your 
plane.  I said call the fire department while trying to bring it back up 
onto the taxi-way with one brake and tall grass.  This did not work at all. 
I shut everything down and jumped out of the plane.  Sure enough the right 
bake was catching the grass on fire and the wheel pant was starting to burn. 
So I pulled the plane around and into the wind and tried to pull it back up 
onto the taxi-way.  Even with all strength I had and the adrenaline pumping 
I couldn't get it back up on the pavement.  I ran back to the cockpit though 
the fire and turned the master and radio back on and yielded at the tower to 
call the fire department the plane was on fire.  Then I shut the power off 
and pulled the fuel shut off.  It was right next to the hatch and I could 
reach it easily.

The next minute or so I watch with horror while the plane turns into a 
blazing infernal.  No fire department on its way.  The fire barn is right on 
the airport.  The flames now are getting into the engine compartment area. 
One of the airport employees comes screaming up with his truck and he pulls 
out a big fire bottle.  I pull the pin and commence to cover the right gear 
and wheel pant area.  It slowed it down but not much.  He's yelling at me to 
get away because it's going to blow.  All of a sudden the tire blows and I 
thought it was all over. Boy a 68 year old guy can really move fast when he 
needs to.  I emptied the bottle on the fire but to no avail.  The fire 
trucks still haven't come into view.  The fire barn is right on the same 
side of the airport I'm on.  The new owner and at least two other people 
drive up and watch in dis-be-leaf.  With the turning the plane around the 
fire remained at the back of the right side of the plane and over the engine 
compartment.  If I hadn't turned the plane around the whole plane would have 
been engulfed. There are a lot of if here but let's just say I'm thankful 
God had let me get out of the plane and I didn't get hurt.

Now the crux of the story.  When we got it back to the hangar and the FAA 
and I were looking it over a number of things that should be addressed came 
to light when you are planning to put wheel pants on your plane.  The pants 
were a bolt on to the aluminum plates on the side of the gear, with the 
bolts that hold the axle on.  Just screws to hold them on to that.  When I 
took the left one off the caliper was still in contact with the side of the 
inner pant.  The gear did not have any heat shield between the strut and the 
brake disc.  No way for the heat to get out of the wheel pants without going 
out the bottom.  On the ground in dry grass, this is not good.

Now it may be the fact the more the brake pads wore the longer the stroke on 
the caliper was required. So the more landings that were made and more taxi 
work done the more room the caliper required.  So at the first it may have 
seemed Ok but in time it only got worse.  So if you don't have the room the 
brake can drag and build up heat real fast to a point that they can cause a 
big drag on the plane so doing causing a snowplow effect on the nose of the 
plane and mucho heat build up. I'm sure this is what happen.

Don't worry about streamlining to make them look better. Give yourself a lot 
of room for caliper movement. Even if you have to put a big bump on the 
side.

Good air scoops like NACA scoops on the the fwd inside and reverse NACA 
scoops out the top so it can get out. Heat rises remember.  It needs a way 
to get out.  On landing the disc can become almost white hot.

Give room for the caliper to move past the side of the gear strut while 
under heated conditions.  Cut it back a little more.

Install a good heat shield between the brake disc and the gear strut. This 
is normal for even the retract planes.

Change the hydraulic lines in the area to steel or copper, I'm sure the one 
on the right gear had failed because of the heat.  No NylaFlow type tubing.

The plane was a total loss.
Dave



----- Original Message ----- 
From: "Tom" <tomcat05 at comcast.net>
To: <reflector at tvbf.org>
Sent: Wednesday, June 24, 2009 7:35 AM
Subject: Re: REFLECTOR: how hot is too hot?


>I put my wheel pants back on to protect my prop from FOD, and now, of 
>course, the rotors are getting hotter after taxiing. I've got a NACA scoop 
>on the pants that blows air past the rotors, and I've got vents on the top 
>of the pants to let the hot air escape when the plane is parked. I also 
>loosened up my bellvile washer a little to make it easier to steer, and 
>that seems to have helped the rotor temperature.
>
> After the horror stories I've heard, since I started flying this Velocity 
> I've been worried about the rotors getting too hot and softening the gear 
> legs. I've got fiberfrax and foil tape around the left gear leg and just 
> foil tape around the right gear leg (because there wasn't room for the 
> fiberfrax.) I routinely touch the rotors soon after I park to see how hot 
> they're getting. They were normally never to hot too touch. With the wheel 
> pants they are hotter, but after loosening the Bellville washer I don't 
> burn my finger when I touch them. I think the threshold for heat pain on 
> your fingers is around 120 fahrenheit.
>
> My question is, "How hot have the rotors been for people who have had gear 
> leg problems?"  Didn't I read once where someone's rotors were actually 
> glowing red? If my rotors don't get over 150 F I don't think I've got 
> anything to worry about.
>
> Doug Holub
> -------------- next part --------------
>
>
> I wonder if anyone has dabbled with putting a small fan in the wheelpants 
> themselves. Nascar uses marine bilge blowers
> on rotors to help cool. If you cut the casing off of a small blower it 
> should fit. Of course wiring it might be difficult. Tom
>
> _______________________________________________
> To change your email address, visit 
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html