Flight Attempt Friday: Power Numbers

After two weeks of video analysis, minor modifications and weight saving measures, we’re preparing for another AHS Sikorsky Prize Attempt this Friday, March 8th. Since last time out we’ve managed to cut off an impressive 4.2 pounds, which, in concert with a few other modifications should reduce the low-altitude power by about 40 Watts. In addition we’ve made modifications to the configuration of the bracing wires that should stiffen up the structure and allow us to input more power without throwing the blades out of balance.

Wish us luck! You’ll be able to follow the progress on our twitter and facebook pages.

Todd cutting off the top post after reconfiguring where the bracing lines attach.
Todd cutting off the top post after reconfiguring where the bracing lines attach.

With the collection of more flight data we’ve also been able to validate our theoretical models and power predictions for a AHS Sikorsky Prize attempt. Below is a graph of our predicted power (dashed green) and the in-flight power (solid green) measured with the on-board Look Keo Power Pedals. The data correlated surprising well except for the inertia of the helicopter which isn’t accounted for in the model (ie. it takes more power than predicted at the beginning as the helicopter accelerates upwards, but less power as it decelerates when cresting the peak of its climb).

Measured and predicted power from the last flight on February 22nd.
Measured and predicted power from the last flight on February 22nd.

The validated model was then used to predict the required power for an AHS Sikorsky Prize flight using several different climb profiles. The best climb profile is an all out sprint for the first 10 seconds, which takes advantage of the pilot’s short burst ATP/CP system and also minimizes the amount of time spent at altitude, where the helicopter draws more power. A more conservative climb is shown below, where a more moderate amount of power is applied (~900 Watts) for 20 seconds. The plot below shows the predicted power overlaid on top of one of Todd’s training sessions on a CompuTrainer. Evidently the difficult part is reaching the 3m goal at the beginning of the flight, after that, there seems to be at least a small amount of power to spare.

Measured power from pilot training session (solid green) with the best estimate of the power required (dashed green) and altitude (dashed blue) for a AHS Sikorsky Prize flight.
Measured power from pilot training session (solid green) with the best estimate of the power required (dashed green) and altitude (dashed blue) for a AHS Sikorsky Prize flight. The scale for power goes from 0 W to 1000 W. Altitude reaches a maximum of 3.2m.

 

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