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By Roadrunner71
#406284
I wonder if I had flown slower when I flew X-C. Maybe I would have ended up flying longer, farther X-C Miles when I was flying my Predator X-C? Did I fly muyself onto the ground by flying to fast. I mean I just love flying fast. I asked John Heiney last night on the phone. I asked John what speed was best glide in my Glider. John replied to my text question, by Saying 25 Mph.

Any thoughts on this subject of speed one should fly at in order to cover the most ground on a given Day.








User avatar
By sg
#406285
There are a lot of variables involved that go into speed to fly calculations.

Is there a tailwind? Headwind? No Wind?
Is there lift or sink?
Are you flying a spaghetti harness, or a top of the line racing harness?

Speed to fly on a glider, is gonna vary based on all of that and more.

Imagine there is SOME widespread lift and your effective sink rank is only 10 fpm.
Your best speed is gonna be MIN SINK. In a comp, that could change though. Depends on your goal.
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By red
#406286
Roadrunner71 wrote:
Mon Jan 21, 2019 12:59 pm
I wonder if I had flown slower when I flew X-C. Maybe I would have ended up flying longer, farther X-C Miles when I was flying my Predator X-C? Did I fly muyself onto the ground by flying to fast. I mean I just love flying fast. I asked John Heiney last night on the phone. I asked John what speed was best glide in my Glider. John replied to my text question, by Saying 25 Mph. Any thoughts on this subject of speed one should fly at in order to cover the most ground on a given Day.
Chris,

That Speed-To-Fly answer will change, from day to day. Paul MacCready has boiled down the answers into what is called the MacCready Speed Ring, if you want to see your answers. It is a Ring because it surrounds your round airspeed indicator, in a sailplane. The correct Speed-To-Fly depends on how strong (in vertical speed) the thermals will be along the way, on that day. There are HG varios on the market now which will compute the best Speed-To-Fly for you, if you want to be very precise in your XC flying for distance. I would not want to fly by the advice of a vario, but some pilots put their numbers ahead of their enjoyment. I have done that in the past, and it just sucks the joy out of flying; now I only fly for FUN.

John gave you a fairly good answer, for an average day on an average glider, but the conditions of the day will change the answer you will need. Sure, a speeding pilot can waste enough altitude to put themselves on the ground, if they start out too low from the last thermal, and/or the thermals are too far apart. I would rather stay up and stay flying, rather than trying to cover every possible mile. Miss the next thermal and just start walking? Not for me, thanks.
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By LoganR
#406290
Red,

You are awesome.

Chris,

If you want an *EXACT* answer to your question, go to https://www.willswing.com/polar-data-fo ... g-gliders/ (or get the polar for your wing, realizing that your conditions will be a touch different than factory configuration)

Put a point on the graph for your current wind conditions (down for sink, up for lift, left for tail wind and right for head wind) and draw a tangent line to meet your glider's polar curve. That will give you the speed you "should" fly.

As you can imagine, this does indeed suck all the fun out of flying. Some people decided to put this data into flight computers. That sounds GREAT! but your conditions are constantly changing (as you well know) so you compare the speed to fly with your measured wind speed...... and suddenly you are looking at gauges instead of flying your wing.

*MY* solution, find three points on the curve you like.

1) "I Love This Air" speed, that's the horizontal part of the polar. (about 25 mph for a U2) Get a feel for the bar pressure (or flap markings on a rigid) and learn it.
2) "Just cruising" speed, that's about the tangent line from your origin (30-35 on a U2).
3) "This sucks" speed..... take a tangent line from the worst-gust conditions you think you'd ever want to fly in. (45 and looking for a landing spot damn near straight down if it is a headwind).

Then I just have 3 basic options to build off of while still focusing on flying. That is *MY* balance between science and fun.

V/R

Logan
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By DMarley
#406292
Any polar for a flexy wing is merely an approximation based on much experience. The published WW polars are of the older models and older sails, but likely are good enough to begin your speed-to-fly quest. Same as any published data on other brands... no where near as 'exact' as compared to possibly a new, high-perf sailplane's polars. A pilot needs to adjust these polars to his/her weight and parasitic drag differences as per WW's and others' instructions, which I found comes out close enough to provide me my glider's best speeds-to-fly if I'm honest.... and as much as I can tell from very rough measurements in active air.

Davis has published some of his measured results as well as others, accumulated over many many test flights in stable conditions, but raw measured lift/drag points for a glider/pilot combo are hard to decipher due to them usually being scattered all over the place. It takes some good mathematics, guesstimations, and artistic license to draw a reasonable approximation of the polar curve for a flexy wing.

Some pilots enjoy simply flying by their experience without worrying about numbers. Others derive great enjoyment from squeezing every little bit of performance (or so they hope) out of their craft by "flying by the numbers." If you ask Johnny, Dustin, and any other hot XC pilot how they fly, it's probably some combination of the two, with the advantages of plenty of experience.

Chris, I'm guessing with your experience and many hours flying XC with John, you likely had a good intuitive feel for what speeds were best for you to fly with your glider/weight combination.
By Roadrunner71
#406294
You know Guys. Curently I am not flying: I am in a long drawn out process of recovering from injuries that I sustained when I pounded my Predator into the Ground. That being said when the Day comes, I hope that it does come when I fly my Predator again. The responses that you Guys have provided will certainly come into play. Thanks Guys for providing your great insights into Speeds to Fly By.
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By entelin
#406325
It's fairly easy to fly too fast.

There are two things that can be calculated, STF for maximal ground distance coverage which can be determined simply with your polar adjusting for wind. And best STF through the airmass. Ground distance is used for final glides, while the mccready formula is used for airmass.

One thing about the mccready formula is that wind is not part of the calculation. Mccready is the best airspeed through the airmass given a predicted strength of thermals assuming the thermals drift at exactly the same speed as the wind. In wind mccready will be wrong in cases of land locked lift sources, and of course normal flatlands thermals travel more slowly than the prevailing wind so it's not perfect in that respect either.

However despite that, spending some time exploring an estimated polar of your glider can be quite instructive. If only to give you some rules of thumb, or advise specifically what not to do. The basic formula will yield the same recommended speed to fly upwind, and downwind, and this would be correct if thermals did actually travel the same speed as the wind. However you might suggest, if you are flying into a strong headwind with a low MC you might not actually be going anywhere relative to the ground. This is true, yet flying with a higher MC would be inappropriate for the expected lift and increase your chances of landing. MC can be defined as the weakest thermal you would stop for at any given time and should be set accordingly.

All that said the reality is that unlike a sailplane it is very hard for us to fly one specific speed, we get bumped around a bit too much and you certainly don't want to be watching or messing with your instruments constantly. Instead, figuring out the big picture is important, generally being on target with STF, but not chasing the vario, or racing into the ground in a headwind.
By Roadrunner71
#406396
Thanks Guys for your responses to my Query regarding how fast I should fly my Predator between thermals. i have not even flown my Predator since March 28th 2010. i just hope that I will one Day fly it again. I just wonder if on X-c flights i tended to fly Fast. I really do wonder if I had Flown the proper Air-Speed for the Conditions at the time. If I might have flown farther?

Well it seems like I have some studying to do.
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