Calculating Speed to Fly
Some think speed to fly means looking at your flight computers up and down arrows. Others think it's installing a ring on your Winter vario. If you don't' have a speed ring, make sure your Winter vario has a beveled face plate, order the speed ring and 4 weeks later it arrives. Open the box from W&W, suck on your Jolly Rancher as you pop the speed ring on your vario. Bingo! Instant speed to fly indicator.
So how do you REALLY calculate speed to fly? Bob Wanderer has a great book that explains a speed to fly table step-by-step. In lower performance gliders all you really need is a speed to fly table. So that's what we will focus on.
Take the polar found in the flight manual. Then calculate the (most likely optimistic) sink rates at different speeds. Another option would be using the polar that was calculated by Dick Johnson. The write-ups are very good and I am sure there was controversy from some manufacturers with his tested numbers vs their calculated. Once you have the sink rate you can correlate the speed and its actual sink rate.
I remember one student landing out because as he sped up the sink rate kept increasing...all the way to VNE. The Johnson reports shows a 1200ft/min sink rate at that speed in an SGS 1-26. But with this table, you can tell what the achieved performance is at each speed and sink rate and understand if you are in rising or sinking air. Next, you will have to read Bob's book to get the following steps.
One thing that Bob points out in his book is that if you fly above or below best L/D speed you will achieve the same L/D. So if we fly a little faster you will achieve the same performance as flying a little slower. However, if you fly a little faster 2 important things will happen.
- You will get to the thermal before the guy flying a little slow, then you can start climbing sooner and get ahead of the other glider.
You are cruising faster which means when (not if) you encounter sink you will already be accelerated and will get through the sink fast. Spending less time in the sink means you will lose less altitude and be significantly better off then your slower friend who is trying to accelerate in the sink.
Cloth Tape is an adhesive tape resembles medical tape. It has good adhesion which holds up well to UV and moisture. Because of its good flexibility, it's great for gear and engine doors where mylar is impractical. Cloth Tape also works well as a control surface gap seal on older wood and metal gliders. It will shrink slightly so please take care not to stretch it when applying.
Bob Wander Speed to Fly Breaking the Apron Strings - Petmecky explains the fundamentals of flight preparation and in-flight decision-making for the cross-country pilot.
Safe Altitude profiles, Go-Ahead points, thermaling techniques, final glide considerations, height bands, speed-to-fly, landing considerations - it's all here in this book
Garret Willat holds a flight instructor rating with over 8000 hours in sailplanes. His parents have owned Sky Sailing Inc. since 1979. He started instructing the day after his 18th birthday. Since then, Garret has represented the US Junior team in 2003 and 2005. He graduated from Embry-Riddle with a bachelor's degree in Professional Aeronautics. Garret represented the US Open Class team in 2008 and 2010 and the Club Class team in 2014. Garret has won 3 US National Championships.
