REFLECTOR: how hot is too hot?

Wed Jun 24 22:42:26 CDT 2009

Hi Dave, 

     Thank goodness you're OK. My condolences to the new owner. Thanks for an informative post.

Regards,
Jeff Barnes

--- On Wed, 6/24/09, davedent at comcast.net <davedent at comcast.net> wrote:

From: davedent at comcast.net <davedent at comcast.net>
Subject: Re: REFLECTOR: how hot is too hot?
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Date: Wednesday, June 24, 2009, 10:03 PM

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
> 
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