How to figure best glide speed?

[Scott]

I don't have a vario w/McCready function (e.g. 5030). I do have an airspeed indicator (one of the little Flytec impeller-type devices). I'd like to know what my best glide speed is, 'cause I have no idea.

WW publishes polar data on their gliders that they say isn't 100% accurate, but they say,

We have tried to state realistic data so that the data will be useful for speed to fly calculations.

Then they give figures on their assumptions for the polar data, which is a hook-in weight of 130% of minimum placarded hook-in weight. They also state how to adjust the polar data with varying hook-in weights.

So, doing the math (and assuming my Z5 harness weighs 15 lbs, which may be a bad assumption until I actually weigh it)...and using the WW polar data...I calculated that my best glide (for an Eagle 180) is 29.5mph.

I'm not naive enough to assume this is a perfect number...but does it even sound like it's in the ballpark?

Better yet, can anyone recommend an easier way to find best glide without having to do a dozen flights in calm air taking all sorts of notes and measurements? (And without buying a 5030?)

Thanks,
Scott

PS - I'm sure some of you think I'm an idiot for even caring what my best glide speed is when I'm a beginner pilot. Fine, indulge me! It's a fun way to pass the time on a quiet evening!

[XCanytime]

Got Pagen's Performance Flying book?? Read Chapter 7 Using Speeds-to-Fly.? All the info you will ever need.

????????????????????????????????????????????????????? Bacil

[Scott]

Yep---I've got that one, and I've read the whole chapter. Unfortunately, Pagen actually doesn't say a word about how to find best glide! He describes speeds-to-fly theory, then goes into elaborate detail on how to figure out all the speeds-to-fly after you have all your polar data (including best glide).

About the only thing he suggests (which---short of buying a 5030---may be the only way to do it) is to go fly at every airspeed and make a note of your sink rate at each airspeed.

I'm looking for an easier way! (I realize there may not be one...)

Scott

[XCanytime]

Scott,
???? There ain't no easier way.? Either you gather the raw data in still air on your setup (getting up with the birds at the crack of dawn), or check out the approximate polar that WW has for the Eagle.? Best glide in still air can be represented by a relative bar position, removing having to know the absolute airspeed.? Of course, when is the air still?? At the crack of dawn on rare occasions, or near sunset on rare occasions.? Do we fly at all during those rare occasions of still air?? Rarely, if at all.? So knowing your best glide in still air doesn't do much for you, because the air is almost always usually moving horizontally and vertically.? So Chapter 7 clues you in to what you really need to know in headwind/sink, tailwind/lift, xwind/sink/lift conditions, which are the conditions you will face on just about every flight you take.

??????????????????????????????????????????????????????? Bacil

[rs54263]

>> I'm looking for an easier way! (I realize there may not be one...)

There IS an easier way (don't led those experts fool you); Brian
Vant-Hull gave a great speeds-to-fly lecture a few years back, which he
followed up with a well-written 2-part article in our own Skyline
newsletter (January & February 2003).

The short version is this: when you're gliding, there is a point on
the ground that you would hit if you were to continue to fly in a
straight line while maintaining that glide slope. This is your "impact
point". Any points on the ground (such as the LZ) that is closer than
the impact point, will appear to move "down" as you get closer to them.
Any points on the ground that are farther away than the impact point,
will appear to move "up" as you get close to them. The best glide is
achieved when the impact point is as high as possible.

I've over-simplified here, and there's a little more to it, but this IS
the gist of it. I've used this technique several times in high
wind/heavy sink to determine whether I can still make the LZ or not.

~Ralph

[XCanytime]

Ralph,
???? There are two distinct things here.? Best glide speed is a speed that is defined in still air, air that is not moving horizontally or vertically.? Yes you could go to a training hill in the early morn when no air is moving, and try a few bar positions close to the best glide speed bar position and see which one gets you the furthest over the ground (to the round-out position).? That would give you your best glide speed for your setup (harness, pilot, instruments, glider).? The other thing, which you describe, is the "eyeball" method to get the best glide over the ground when facing a headwind or sink on the way to the LZ.? Whole different animal.? Which is where Chapter 7 comes into play.

?????????????????????????????????????????????????? Bacil
?

[Scott]

Thanks Bacil---I see your point. I understand the basics (speed up in sink, slow down in lift, speed up in a headwind, slow down in a tailwind). And yes Ralph, your point about parallax is good too.

I certainly recognize we don't have to know speeds-to-fly to get out there and fly. Plenty of other ways to become a better pilot! But it is a bit of a bummer that without a $1,000 instrument, a pilot is always at a disadvantage to one who has the $1,000 instrument (in terms of knowing the exact most efficient speed to fly in any given condition).

It would be interesting to hear Kevin or Paul say "I don't pay any attention to speeds-to-fly, I just fly," but I'd guess that isn't the case!

Scott

[rancerupp]

> Posted: Tue Sep 27, 2005 5:03 am

Scott, you sure are an early-bird.

Just think next week when you with your $400 inst. do as well as those with their $1000 inst. Then you'll be feelin great and none of this will matter at all.

Rance

[Danny Brotto]

... Do we fly at all during those rare occasions of still air?? Rarely, if at all.? So knowing your best glide in still air doesn't do much for you, because the air is almost always usually moving horizontally and vertically.? So Chapter 7 clues you in to what you really need to know in headwind/sink, tailwind/lift, xwind/sink/lift conditions, which are the conditions you will face on just about every flight you take.

??????????????????????????????????????????????????????? Bacil

Consider that the true speed to fly for maximizing XC speeds/distance includes the climb rate exected at the next thermal. If you see a glider climbing or a likely thermal source and you are likely able to intercept the glider/thermal, speeding up a bit (or more if a strong thermal is expected) will help overall performance.

Get used to visualizing via parallax experimenting with speed range to maximize that distant point. The technique is more effective for lower performance gliders where there is a marked polar (sink rate) difference at speed. The technique works unless at high altitude where it becomes practically difficult (at least for me) You should be flying the looks of clouds at altitude anyway. Stop focusing on the ASI. Trying to fly the ASI (in a hang glider) and correlating it to a polar will lead to confusion.

Danny Brotto

[heaviek]

STF.....I watch it. I watch it close

I also fly it by feel when I have obstacles or a goal
line to race too.

Kev C

--- Scott <sw@shadepine.com> wrote:

>
> Thanks Bacil---I see your point. I understand the
> basics (speed up in sink, slow down in lift, speed
> up in a headwind, slow down in a tailwind). And yes
> Ralph, your point about parallax is good too.
>
> I certainly recognize we don't have to know
> speeds-to-fly to get out there and fly. Plenty of
> other ways to become a better pilot! But it is a bit
> of a bummer that without a $1,000 instrument, a
> pilot is always at a disadvantage to one who has the
> $1,000 instrument (in terms of knowing the exact
> most efficient speed to fly in any given condition).
>
> It would be interesting to hear Kevin or Paul say "I
> don't pay any attention to speeds-to-fly, I just
> fly," but I'd guess that isn't the case!
>
> Scott
>

[XCanytime]

Scott,
???? Instruments have their place, but it is important to initially build up experience using your senses to judge conditions, launch in varying conditions at multiple sites, and judge approaches and landings in varying conditions at multiple sites (conditions appropriate for your rating at the time, of course).? Remember that the two most important parts of a flight are its start and its finish.? Aggressive, clean launches at the mountain and accurate, consistent approaches and landings are the mark of the skilled flyer.? Once a baseline store of experience in and knowledge of the launch and landing phases of flight has been accumulated , then you can concentrate on using whatever instruments suit your fancy to help you map the lift to get high and calculate the speeds to fly if you choose to try to go far.

?????????????????????????????????????????????????????????? Bacil

??

[brianvh]

To summarize what everyone's said:

1. It's way too early to worry about the exact polar of your glider. Maximize your fly by eye for now. The characteristic best glide for your glider applies to calm air and not to moving air unless you are ready to do some calculations. You ain't gonna calculate in flight unless you have a computer.

2. the Best fly-by-eye instrument is parallax. Since conditions change constantly numbers don't help unless you have a computer. If you can set various goals throughout flight, best glide is when that goal is falling as fast as possible in your view. If you can't adjust speed to get it to fall in your view, pick another goal, fast.

3. Parallax doesn't apply when you're thermalling. Listen to the vario and forget the speed-to-fly crap until you've lost the thermal.

4. Going XC for best time per distance requires a different calculation: is it worth your time to top out on a thermal before jumping to the next one? Will flying faster than best glide get you to the next thermal soon enough that you can regain the altitude you lost by not using best glide? This is far more complex. unless you are racing (and sometimes you're racing the sun) the best strategy is to top out, and go on best glide (your glider's characteristic) between thermals. You can use parallax on the clouds rather than the ground for this, because thermals move with the air, not the ground. This will maximize your chances to find the next thermal, though competition pilots will use the best cumulative speed strategy and quickly leave you behind. This is what Danny is talking about. NOTE: you are NOT a comp pilot yet. Trying to act like one too early will get you on the ground fast.

4. Folks with computers will outfly you. So what?

So we have 3 speeds to fly. In the order that you should worry about them:

A. Speed to fly relative to the ground - critical when keeping track of any possible LZ's, spot landings, or jumping gaps in ridges. use parallax on locations on the ground.

B. Glider's characteristic best glide - only used when jumping thermals and you're not worried about the ground. Use parallax on the clouds. Since they are above you, you want them to climb out of your field of view as slowly as possibly. If they are falling in your field of view, stop gliding and start circling, you numbskull!

C. Best cumulative speed, figuring in distance between thermals and the climb rate. Don't even go there yet.

[Scott]

Gosh Brian, I was just curious! (Kidding.) Thanks for the excellent summary---and of course, I realize there are a hundred ways to be a better pilot than by knowing best glide!

Scott

[brianvh]

Oops, one mistake I noticed.

I said when flying between thermals in situtations where the ground doesn't matter you can use the glider's characteristic glide speed. That's true so long as the air is only moving horizontally between thermals (i.e, prevailing wind). Of course, we all know we NEVER encounter sink between thermals

So unless you are programming your $1000 computer, there's basically never a reason to know the gliders characteristic best glide speed. Use parallax on ground or clouds. Since the few pilots I know who have flight computers seem thrilled with them, and they were excellent pilots before they got their computers, it seems parallax is just not sensitive enough to work perfectly. Since most of us who fly hang gliders are not interested in turning our flight over to the machine we just aren't bothered by the lack of perfection. Perfection = lack of freedom.

If you're curious what your best glide is, you'll probably have as much luck working out from the WW polars and hook-in weight (though note how they all have been adjusted so that the stall speeds match up...hmmm) as you would using a combination of parallax and air speed indicator in calm air. Do 'em both and see how they match up. Can we start a betting pool?

[padamez]

One of my most enjoyable and enlightening flights was during the Highland fly-in two years ago competing for longest flight without a vario. I was stunned by how well I did (over two hours - it was a one of those bullet proof days and I pimped alot and learned the advantage of getting high over other pilots). It was so enjoyable soaring in total silence without that constant vario noise! My senses became attuned to the texture of the air and I could tell when I was going in and out of thermals and my eyes on the ground became my altimeter so I knew if I was in sink or lift - although it took a little longer for me to notice the altitude change over time. What an experience it was to have such a flight with no instuments. I swore I was going to fly without them from then on, but alas I never did. Don't underestimate the joy of flight using only your senses, sometimes I think we would put a 747 instrument panel on our gliders if we could.

[XCanytime]

Paul,
???? You're onto something.? I've never used a vario in 12 years of mountain flying.

??????????????????????????????????????????????????? Bacil