Hello all, new to this forum, I have been lurking for a couple of years. I tried out an intersting idea this weekend and I thought I would share it with everyone. It is a way to measure takeoff and landing distances by measuring the distance your tire travels and counting the number of rotations by using a GoPro camera. I posted it on Supercub.org but I thought I would share it with the larger community.

That seems like it is very accurate. Most people are going to prefer the old three step method.
Estimate it in your mind, cut it in half, brag about it.

An accomplished fisherman probably "measures" take-off and landing distances as accurately as he measures his fish.

Cary

Hmmm my tires keep turning after leaving the ground

I guess I needed to be more specific - you start counting when the plane starts to move forward and you stop counting when the plane leaves the ground, don't count after the plane leaves the ground as you have already taken off.

The top of the tire (visible to the camera) will be further from the axke than the bottom of the tire, because of ther weight of the airplane. This may affect how far the tire actually rolls in one revolution on the top versus the bottom.

This would POSSIBLY affect the numerical distance, but it would not affect a comparison between one technique or one propeller and another.

I'll step back and let the degreed scientists here determine if, and how much, the low pressure tire squash affects the accuracy of such a measurement.

Alot less than the normal guy guestimating the TO or landing distances LOL.

a couple inches of tire squat, if that will only add up to a few feet in a normal TO roll.

Probably no difference at all--the length of the tread, i.e., the circumference, is the same, whether the tire is squishy or hard, unless the entire thing expands with pressure.

Wouldn't work with mine, anyway--I leave the skirts on year round, most years. Hard to see through them.

Cary

EZFlap wrote:The top of the tire (visible to the camera) will be further from the axke than the bottom of the tire, because of ther weight of the airplane. This may affect how far the tire actually rolls in one revolution on the top versus the bottom.

If ya measure mark strait down to strait down again... Your measuring the circumference, not the radius of the axle to ground vs axle to top side of the tire.

EZ, if you can get more inches of tire to travel past a given point, than a point on a circle 180* opposite, then you'll really have something to patent!!

Blu wrote:That seems like it is very accurate. Most people are going to prefer the old three step method.
Estimate it in your mind, cut it in half, brag about it.

Easy for you to say. Your CC get off the ground in about 2 plane lengths.

EZFlap wrote:The top of the tire (visible to the camera) will be further from the axke than the bottom of the tire, because of ther weight of the airplane. This may affect how far the tire actually rolls in one revolution on the top versus the bottom.

This would POSSIBLY affect the numerical distance, but it would not affect a comparison between one technique or one propeller and another.

I'll step back and let the degreed scientists here determine if, and how much, the low pressure tire squash affects the accuracy of such a measurement.

Probably not much. After the first couple of rotations, the centrifugal force will start to even out the squat. Aided by the lift of the wings the tires are nearly round shortly into your ground roll.

I take one of the flourescent orange fiberglass rods I use to mark my driveway in the winter (after a big storm it's easy for the Kubota to find it without getting into the rocks on the sides that play hell with the snowblower) and mark the 100 and 200' section of my runway. Plus I usually fly with a 100' tape, and a laser range finder thingie. Sometimes an angle finder (a Starrett adjustable bubble protractor, but I hear there "is an app for that" now for the smart phone), that way I know what the plane can do without too much guesswork. I like the wheel measurement thing though, especially as the bigger tires will be turning slower so easier to count.

Orange traffic cones --end and every 100-200 ft. along one side. Get and use Sparky's -"Mountain Flying Bible"

Always low tech in Africa, we used a very simple method. We would have one of the staff plant a pole adjacent to where we started. Then another staff member would wait down the runway, and see where the wheels left the ground. He would then plant another pole. We tied different colored streamers on the poles to denote the different pilots. We would use a similar process for landing distance.

I used this technique to train the pilots in the Caravans. It really isn't a STOL aircraft, so understanding exactly what it can do made them safer. I was the Check Airman for Zambia, quite an honor. So when I did checks, I made it interesting and made it into a bit of a contest. I would do the first takeoff and landing. If anybody beat my distances, I bought all the beer that night. We always had lots of staff to participate and get familiar with the aircraft at the same time. BTW, never had to buy the beer, all those FCLP's in the Navy goes a long way.

If you want to do rotational counts, there is a cheaper and simpler way. Get a cheap bike computer. They use stick on magnets and a sensor to do exactly that. You know when you lifted off, the speed jumps. You just need to enter your wheel circumference into the unit.

I use my GPS track to measure distance, WAAS makes it very accurate.

Simply measure the distance after importing to Google Earth.

And yes, the Wilga has a short roll.. calm winds I've achieved 310'

If you're on a paved runway, count the stripes. Taxi into the middle of the numbers with your tail even with the bottom of the numbers. From where you are in the cockpit to the end of the first stripe is 200 ft, to the end of the second stripe is 400 ft, etc. Just count 2,4,6,8 as you go past the end of each stripe. The stripes are longer than the distances between them, I think it's 120 ft for the stripe and 80 ft for the space between them. I use this on occasion to verify my calculated takeoff distances.

If you're on a paved runway, count the stripes.

Don't "count" on that to be accurate. While the FAA has suggested lengths for the stripes, they're not mandatory, so unless you've actually measured the stripes you're using, you could easily be misled into thinking that you have a shorter or longer roll than actual.

Cary