Compare Polars

For a better handicap scoring system I think this might be a good basis for scoring to see if pilots flew better than the polar of their glider.

Since you have 100% GPS scoring, analyze all the flight traces starting at the time when the gate opened, and stop it after 60-75% (arbitrary) of the contestants either finish or land out. Pull out the average McCready climb rate, and the average wind speed that the entire fleet saw. (you may not want to score to the slowest pilot since he may be motivated to circle longer in zero sink to game the system).

Now you can do proper "windicapping" handicap that takes into account the actual wind strength - this will really be important for the lower performance gliders to be compared properly - based on the polars. Also the climb rate tells you where on the polar we should be looking. We can fully vary to several decimal place between a strong and weak day and a calm and windy day.

I think this is worth investigating and discussing. The main downside is the fact that you score all happens in a opaque box score formula, but that is not far from where we are now. The score system could spit out all the data that it used in the formula, and could even graphically show where on the polar for each glider they would have to fly as a way to "audit" the scores.

I suggest for handicap we go full on with the computer simulation of what the pilot should achieve vs theoretical polar. Then for non-handicap flying the other extreme we go with grand-prix style head to head.

Chris

I suggest for handicap we go full on with the computer simulation of what the pilot should achieve vs theoretical polar.

Listening to this discussion, I have been thinking something similar.


If the computer looked at all the IGC files, created a model of the airspace, found the best path(s?) to fly, and then did a theoretical perfect flight for each plane's polar. The score would be the ratio of the speed of the actual flight against the perfect one in the computer. The scoring system would not be a black box. Each pilot could clearly see the 'perfect' flight and see where he gained and lost time.

It's not clear the computer could pick an ideal flight. The system would depend quite a bit on the published polar unless it could figure this out from the flight log.

It's not clear what competition strategies would evolve. Picking a plane that can be flown near it's published polar would be critical. Each pilot is effectively illuminating the sky for the computer for a specific region. If one pilot finds a nice energy line, then he is a bit like the one smart guy who busts the curve on the final exam. There might be bonus points for illuminating a good part of the sky first to help account for leaching. With flarm, it might be possible to run the s/w during the race. If you could account for leaching, a display in the cockpit would change racing quite a bit. A display on the ground might make things a bit more interesting for spectators.

It might be possible to test such a system by running it on existing contest data sets. Or one could score a contest two ways for a while.

I understand perfectly how the classic method is done. Johnson did it just as you describe. And got +/- 5% scatter (and criticism from the Germans). The other ways you describe are rife with potential errors (starting with the fact that still air does not exist). A much better method (from the point of view of errors) is two glider testing against a "golden" glider. Many of the common mode errors are reduced or eliminated. Very few individuals are going to put forth the effort required of either of these methods.

On Saturday, December 23, 2017 at 6:53:51 PM UTC-8, wrote:
Jfitch -- I think you don't understand how decent measurements are made. They are not made simply from ASI and VSI. Read any of the various documents on the topic.

The classic method involves calibrating the aircraft's pitot/static versus a trailing reference cone and then having done that making long straight glides in still air and using altitude differences ... with a lab-calibrated altimeter and altimetric corrections made from the hypsometric equation for the particular lapse rate.

There are other/augmented ways that are coming into vogue that allow good accuracy with "amateur" gear ... one of the better methods is to to use GPS and either circling or quadrants to establish tthe wind-aloft heading (at a good altitude where it will be stable over a good delta), and then fly out and back legs on the pure cross-wind heading. The GPS along-track data will give TAS very accurately if the legs are 2 km or longer e.g., small errors in the true cross-wind angle cancel by summing the out and back leg data due to sin(theta) ≈ theta for small angles.

And another way, used to some aircraft testing and apposite to sailplanes I believe, is towing with a tensionometer.


The biggest problems occur for the very highest performance sailplanes -- one tends to make these measurements in the still air of a high-pressure stagnation, and there is subsidence that may be as much as 10 cm/sec, and there are arguments about how to diagnose that, whether such corrections are right or not. Dick Johnson and the Germans battled over that one, I think that argument is still in play.

This all being said, it's easy to make mistakes or have bad data one way or another. If you want to see data that clearly looks like something is pretty wrong, look at the Discus A (L) data; that's clearly aphysical (for a ship with no flaps).

In Germany, the Idaflieg does exactly this: Comparing against the "golden" DG-300/17.
I wouldn't trust any of the Johnson measurements, for gliders 40:1 they include too much airmass movement to be meaningful.