Friday, November 20, 2015

Applying the Words of Charles Grant to My Model Flying

After building and making test flights of the Charles Grant designed Cloud Tramp rubber powered free flight airplane recently, I got out my copy of his book Gateway to Aero – Science Fundamentals of Aviation Demonstrated by Building and Flying Model Aircraft and started reading it.  Although the book is rather outdated I was struck by some of his insights at the time, so I copied a few things down.

Xplorer RC Sailplane Amazing Performance

Charles Grant Designed - Cloud Tramp

“The aerodynamic form and contour of the modern airplane are determined by the performance required of it.”  “Drag increases at the square of the speed” and “to further reduce drag all corners and angular contours were replaced with smooth curves”.   It had me thinking about what I had witnessed mainly in radio control sailplane flying this past year and how the performance differs so greatly with the aerodynamic form of the sailplane.

Shadow Left - Gentle Lady Right

Having participated in more thermal duration contests this year I was amazed at the performance of the top designs such as the Xplorer and Supra. In studying the form it is evident that angular contours had been replaced with smooth curves where possible. In flying in thermals the speed is normally not so great but zooming off the launch or flying out of sink reaching a higher speed is important. I realize there are many other factors why my box fuselage Gentle Lady sailplane was so much lower in performance than a Supra but extra drag is part of it. A couple of years ago I did a hand toss test between my Gentle Lady and a Shadow 2 meter sailplane which is very sleek but heavy.  The length of the glide of the Shadow was many times that of the Gentle Lady.

Curves in Fuselage of Dart Slope Glider
Low Pass

Foam Super Scooter Has Lots of  Drag

This past year I have done a lot of slope soaring from small slopes and the drag of the sailplane makes a huge difference there. It is the difference between not being able to fly for more than a few seconds or being able to slope soar for several minutes. On one slope I have been dynamic soaring and the sleek glider not only will stay up longer, it is also much easier to fly.

Bill Kuhl

Related Articles

Volare Cloud Tramp Review 

Dynamic Soaring One Year Progress

Slope Soaring Heavy 2 Meter RC Gliders

Comparing Two 2 Meter RC Gliders


1 comment:

  1. I have flown in a small glider contest for a few years. It is not only small by head count, normally a dozen. The gliders are small also, about one to one and a half meters. The first flight of the day is almost always flown in little to no lift. The first task from a hi start of three minutes was typically the most difficult of the day. I had built a Skeeter from Dynaflight, which is no longer in production. I had gone to great pains to make it as sleak and clean as possible. What I noticed was my plane flew fast and farther with a low sink rate. Yet I could not make time like some of the clunkier designs that just seemed to hang like a ballon. So in our design we must remember it is about duration not distance traveled. If you have a sleak plane you must find lift.