Speed To FlySpeed To Fly

Jim CrowhurstJim Crowhurst

DefinitionsDefinitions

• Average speed:– Speed around the course.

• Speed to fly:– Speed you should fly at between thermals.

Speed Vs DistanceSpeed Vs Distance

• Speed to Fly is a Trade off:

– Fly slowly: Go further but arrive later

– Fly Fast: Get there faster but travel not as far.

– What speed should we fly at between climbs?

Cruise SpeedsCruise Speeds

MacCreadyMacCready

• World Gliding Champion 1956

• MacCready Theory:

There is an optimum speed to fly between thermals that combined with the thermal climb will result in the fastest average cross country speed. (reichman)

80 knots 80 knots

4 Knots 4 Knots 4 Knots

= 40 knots

av. speed

MacCready theoryMacCready theory

Cruise Speed vs. X-Country SpeedCruise Speed vs. X-Country Speed

4 40 knots

2

•20 40 60 80

• 2

• 4

3 knots

70

90

60

3 knots

Cruise Speed vs. X-Country SpeedCruise Speed vs. X-Country Speed

• Flying Faster

4 38 knots @ 90 knots cruise

2

•20 40 60 80

• 2

• 4

• 6

Cruise Speed vs. X-Country SpeedCruise Speed vs. X-Country Speed

4 40 knots @ 80 knots cruise - ideal

2

•20 40 60 80

• 2

• 4

• 6

Fly slow go slow

Fly fast go slow

Failure Of MacCreadyFailure Of MacCready

• Don’t know next thermal’s strength

• Not flying in still air between thermals

• The ground gets in the way!

MacCready Theory For DummiesMacCready Theory For Dummies

• Look ahead: If you determine that the next climb is stronger than that achieved, leave the climb.

• Cruise faster if the expected climb is very good.

• Cruise slower if the next predicted climb is weaker

MacCready flyingMacCready flying

• Next Climb.

• Performance of your glider.

Better the performance faster you go.

• What air you are currently flying through.

Stronger the sink…faster you go!

Speed RingSpeed Ring

• Your glider may have a vario with a speed ring.

• Simply put the arrow on the expected (average) climb rate and fly the speed that the needle points to.

• This is the most efficient speed to fly to the next thermal.

• Right?

Wrong!!Wrong!!

• If you leave a 3 knot climb, expecting another 3 knot climb, set a 3 knot ring setting….you will hit the weeds……soon!

• Why?

• We need to find the best climbs of the day, therefore sample as many thermals as possible.

MacCready ContinuedMacCready Continued

• Flying 10 knots too fast means you will get low and struggle for a while.

• Flying 10 knots too slow will mean you get there a minute later but 500ft/1000ft higher and centre a climb faster………or chose another!

• Conclusion: Flying slower is faster than flying faster…!?

How Fast then?How Fast then?

• Rule of thumb……take average climb rate and halve it. Set that as MacCready setting.

• Allows you to fly fast but also allows you to sample more thermals.

It’s all TheoryIt’s all Theory

• Pete Masson:2001 Club Class World Champion– Average speed Governed by 3 things:

Climb RateClimb Rate Climb Rate

Fly a little slower than MacCready says.

Cover more sky, sample more climbs, pick the best climb.

It’s all TheoryIt’s all Theory

• Jay Rebbeck:

2002 Junior World Champion:

“To achieve fast average speeds, it is far more important to climb in strong thermals than to stick to the perfect speed”.

MacCready MythsMacCready Myths

• “I can’t figure out why I went so much slower than you, maybe I set the wrong MacCready setting on my glide computer”.

• No, he was just using more thermals that were weaker and not centering them as effectively.

ConclusionsConclusions

• Above 4 knots it is important to have high speed.

• Below 4 knots it is important to search for thermals and go slower.

• Never fly faster but you can fly slower.

• Move around to stay in the lift.

• Stay in the lift and out of the sink!

Water-BallastWater-Ballast

• Will move polar curve forward

• Will increase speed to fly between thermals.

• Same LD will be achieved at higher speed

• Get to the same place faster

• Will climb slower

• Trade off between flying faster but climbing slower.

• Late in the day, climbs are slower and may need to dump earlier.

• Sometimes it can pay to be in the air longer to get the next climb (poor day).

• Keep ballast for into-wind final glide, keep it till the last moment.

Water-Ballast ConsiderationsWater-Ballast Considerations

Dolphin FlyingDolphin Flying

• Under a cloud street: Fly slowly in the lift and fast in the sink.

• In Strong conditions, pull up harder and steeper.

• Don’t pull up in every scrap of lift as you fly further.- With little difference in performance.

• Changing the AOA frequently affects the airflow over the wing and can affect performance.

ThermalingThermaling

• What speed?• Min Sink• Best L/D• ? Wing loading• ? Angle of bank• ? Handling at that Speed

• Whatever feels right……..

Other things to consider- Other things to consider- Height BandsHeight Bands

• George Lee:

Fly Fast when high and things are good: be picky with climb rates.

Fly a little slower at medium altitudes: cover more air so as to find a good climb.

Fly at zero MacCready when low: Maximise time in the air and maximise glide angle to find a climb.

Final GlidesFinal Glides

• The only certain time of knowing exactly what speed to fly at.

• Set computer to MacCready of the wings level to wings level Climb-rate of that Climb. Leave the climb when on glide,

• If Av. Is 3 knots, set it to 3 knots.

• Never set it higher than 3 knots!

Final GlideFinal Glide