Tire pressure monitor

I once took off OK but the glider's main tire was totally flat when I landed. Surprise! Rollout was very short. Must have hit some sharp object in the air?

I've had problems with the tire leaking over months, 3 tubes & valves later it seems solved. Whew! With fixed gear and a wheel fairing covering the rim, checking the pressure is a chore. Of course I can look at the tire once the full glider weight is on it, even bounce the wingtips up and down, although with the stiff tire I used to have that was not sufficient to detect partial loss of tire pressure.

At 14:19 14 August 2019, Dan Marotta wrote:
I believe you are over complicating this.Â* My advice:Â* Just look at the

tires.Â* You can tell if they're too low to fly.Â* That's worked for me
for almost 50 years.

Not so easy to check by looking at the tire on the nose wheel of a two
seat glider such as a Grob Twin II or Duo. And main wheel tires often
look OK until you load them up with pilot and water ballast.

On Wed, 14 Aug 2019 08:19:20 -0600, Dan Marotta wrote:

I believe you are over complicating this.Â* My advice:Â* Just look at the
tires.Â* You can tell if they're too low to fly.Â* That's worked for me
for almost 50 years.

Dan, that's not often quite so easy on a grass field, especially as I
have a strong suspicion that grass on a UK glider field is somewhat
thicker and lusher than it might be in NM.

how I get on then I can post the results back here in a few weeks time.

Phil, I'd be interested to see what you find out.

I was thinking only yesterday that, after all the rain we've had
recently, it was getting hard to see if there was still a tyre on my main
wheel, let alone how much air was in it. There is very little space
between the bottom of the open wheelbox doors and the grass tops.


--
Martin | martin at
Gregorie | gregorie dot org

On Wednesday, August 14, 2019 at 8:30:05 AM UTC-7, Phil King wrote:
At 14:19 14 August 2019, Dan Marotta wrote:
I believe you are over complicating this.Â* My advice:Â* Just look at the

tires.Â* You can tell if they're too low to fly.Â* That's worked for me
for almost 50 years.

Not so easy to check by looking at the tire on the nose wheel of a two
seat glider such as a Grob Twin II or Duo. And main wheel tires often
look OK until you load them up with pilot and water ballast.

Agree with Dan, just look at them!
In my experience, the nose wheel on a Duo never touches the ground unless you have the CG wrong. Two pilots and chutes with no tail ballast will often do it.
Perhaps 99% of flats are on rigger, tail wheel, tail dolly and wing wheel.... all thin walled. Tost 400x4 and similar mains are pretty thin walled too.
Try Mr. Tuffy or similar material (an old cut up inner tube is better than nothing) on the other wheels.
Look for a high quality main wheel tire and tube. 500x5 seems the easiest to find these for. The beefiest example I've used:
Goodyear Flight Custom 3 with Michelin Airstop tube. Aircraft Spruce has them.
But check if the FC3 fits with the gear retracted!
Jim

On Wednesday, August 14, 2019 at 1:45:05 AM UTC-7, Phil King wrote:

This is a time consuming process - find pressure gauge...

Any sort of thing you add to the valve stem increases complexity and potential failure points and reduces reliability. In some situations that approach pays off. I think this is not one of them.

My advice: Fill the tire with an air chuck that has a gauge at the beginning of the season, while the glider is standing on it. When you do that, look at how much it bulges at the bottom. As long as the tire looks about like it did when you filled it, it probably is about right.

--Bob K.

Well, ya got me there... :-D

On 8/14/2019 10:23 AM, Martin Gregorie wrote:
Dan, that's not often quite so easy on a grass field, especially as I
have a strong suspicion that grass on a UK glider field is somewhat
thicker and lusher than it might be in NM.

--
Dan, 5J

On Wednesday, August 14, 2019 at 7:39:56 PM UTC+3, Bob Kuykendall wrote:

My advice: Fill the tire with an air chuck that has a gauge at the beginning of the season, while the glider is standing on it. When you do that, look at how much it bulges at the bottom. As long as the tire looks about like it did when you filled it, it probably is about right.

--Bob K.

This is what most probably would do (me included). However, it's impossible to see if you have pressure little bit on low side. Flight manual tire pressure is not maximum number, it is THE recommended pressure. Tube chafes with tire if pressure is short of this. Enough pressure and you really do not suffer from flat tires, at least that is my experience.

Lessons what I have learned: Never check the tyre pressure on the way to a
competition grid. Pump if obviously low and dangerous but otherwise leave
well alone.

In 2005 I did check the pressure at the 15s. Tyre went down and could not
be re-inflated as valve was jammed. Valve could not be replaced. Had to
replace the entire wheel. Got to the start, landed out in a penalty zone
took 500 point penalty. Altogether a bad day!

Jim

"If it ain't broke, fix it until it is."

As it turns out, I just recently addressed this issue for the JS3 tailwheel.. The retractable tailwheel is quite small. The air volume is such that any attempt to put a gauge on it will drop the pressure quit a lot. Also being so small, I found it hard to judge by eye.

The method I came up with uses a machinist outside caliper to measure tire bulge. It's easily understood with these pictures:

https://photos.app.goo.gl/uyt8BgJWRSKKHuj6A

There's a certain skill required to use the machinist caliper -- the key is zero spring pressure. Accuracy is about 5 PSI.

I was able to accomplish the calibration without any reference to dimensional measurements (inches or mm).

Since this was just devised a couple weeks before the OP came on with his question, it hasn't had much field testing. We'll see if this is a good solution after I've used it awhile.