final glide estimates

Newbie help required!
Lets suppose I am on a shallow final glide, 60k out in my 40:1 ship, cruising at 60 knots. Recent thermals have been at least 5 knots and I am coming into some big lift. For the discussion rough air Vne is 100 knots.
What strength thermal should I take to increase finishing speed to Vne and how much (if any) time will this save me?
How do I estimate this at the time? What is the latest point on track to take such a thermal?

Thanks, Bagmaker

Actually you want to glide back at the correct McCready
speed for the strength of the last thermal you use.
Climb just high enough to give yourself a reasonable
safety margin, for which you need a glide calculator
of some sort. If you are flying at 60 knots after using
5 knot thermals you are flying far too slowly for the
conditions (assuming that you are trying to race).
Did you mean that rough air Vne is 100 knots? This
sounds like a more reasonable inter thermal speed for
the conditions. I would suggest that you should take
any thermal that gives you at least a comfortable 5
knots climb rate.

Derek copeland


At 04:12 10 March 2006, Bagmaker wrote:

Newbie help required!
Lets suppose I am on a shallow final glide, 60k out
in my 40:1 ship
cruising at 60 knots. Recent thermals have been at
least 5 knots and
am coming into some big lift. For the discussion rough
air Vne is 10
knots.
What strength thermal should I take to increase finishing
speed to Vn
and how much (if any) time will this save me?
How do I estimate this at the time? What is the latest
point on trac
to take such a thermal?

Thanks, Bagmake


--
bagmaker

This begs the question: If recent thermals have been at least 5 knots,
why on earth are you cruising at 60 knots? Sounds more like you missed
the last one and are low, searching for the "get home" thermal. Been
there done that!

Then, while climbing, set computer to achieved climb, and start final
glide when proper altitude is reached (plus safety alt, and taking
winds into account - that's why you pay the big bucks for the
computer!).

Rarely will final glide be started at Vne - the high speed final glides
are usually the result of either running into a lot of extra lift
during the final glide (lots of fun, that), or caused by burning off
the safety altitude when the field is made. Of course, if you insist
on topping off that 7 knot thermal 10 miles out...

So if you want to finish at VNE, add 1000' to field elevation - that
should allow accelerating to VNE for that nice crowd pleasing low pass.

Cheers,

Kirk
66

wrote:

So if you want to finish at VNE, add 1000' to field elevation - that
should allow accelerating to VNE for that nice crowd pleasing low pass.

OH! OH! Bad, Bad, Bad! You can't do those! No! No!! NO!!!

Haven't had that flame war in a while.

HTH ;-)
Shawn

Hmm, anybody read the AIM carefully lately? Especially the part where
the FAA defines a "low pass"?

Looks like the FAA actually condones low passes - and tells you how to
do them!

Perfectly legal, if done correctly and safely, of course.

Regardless of what a bunch of jealous old twirlybird curmudgeons would
want you to believe...

Now, 500' finishes at 1 mile - THOSE are dangerous!

flame suit on ;)

Kirk
66

wrote:
Hmm, anybody read the AIM carefully lately? Especially the part where
the FAA defines a "low pass"?

Looks like the FAA actually condones low passes - and tells you how to
do them!

....as low approaches, in the context of go-arounds from practice
instrument procedures. [AIM 4-3-12]

If you think the FAA is defining/approving low passes by gliders at
uncontrolled airports, that is something we shouldn't wish for. It might
be hard to convince them that the 500' rule shouldn't apply.

I like low passes just fine -- those worms which are not used for bait
deserve a little warm-up -- but let's not stretch too far looking for
approval. You know what happens when you seek permission.


Jack

This came about doing sims, I realise things can get a little different in real life!
I found that if I estimated my glide distance at a slow speed, from the top of a distant thermal WITH MC AT 0 -even though thermals are mc 5- my overall finishing speed would usually be higher than stopping during that slow final glide to top up and finish faster.
How would I estimate it all?
Bagger

Jack, you are reading too much into the AIM - Instrument go-arounds are
given as an example only - not as the only authorized use.

Heck, a plain old go-around on short final for a cow on the runway fits
the example, too!

Or a flyby so the tower can see if the geardoors are flush.

The point is you don't have to land out of a approach.

If it isn't prohibited, it's OK, if done in compliance with the rules.

So yeah, don't buzz the ramp. But down the runway, back into the
pattern? Perfectly legal.

But I agree with not asking for permission - and it's just common sense
to pick the time and place carefully - not at the local part 141 flight
school airport on a busy Saturday afternoon, for example!

The problem is with people who should know better prohibiting
activities just because they think it is wrong, regardless of fact.

Kirk
66

bagmaker wrote:
Newbie help required!
Lets suppose I am on a shallow final glide, 60k out in my 40:1 ship,
cruising at 60 knots. Recent thermals have been at least 5 knots and I
am coming into some big lift. For the discussion rough air Vne is 100
knots.

Best not to confuse "rough air" speeds with Vne, which is the "never
exceed" speed. The "rough air" limit (I'm not sure this is used any more
- only my very old gliders had it) is quite a bit lower, and the newer
gliders don't have it, but do state "maneuvering speed", lower yet.

And, practically speaking, you certainly don't want to be going Vne when
there are thermals bigger than 5 knots in your way! If the glider hangs
together, it will be a very rough ride.

What strength thermal should I take to increase finishing speed to Vne

You need your gilder's polar to determine what strength thermal is
needed for any McCready speed determination - nothing else needed.

and how much (if any) time will this save me?

It will save you time, but without the polar, your altitude above the
finish, and the distance to the finish, we can't give you a number.

How do I estimate this at the time?

You don't have to estimate it. A chart of speed vs McCready settings is
made up ahead of time. The less thinking you have to do while flying,
the more time you can spend flying the glider.

What is the latest point on track
to take such a thermal?

I'm guessing, but I'd say about where you need to stay in the thermal at
least one full turn to get high enough to use the 100 knot speed. Any
closer, and you'd waste time getting unneeded altitude.


--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

Eric, regarding the rough air speed - I thought you
flew an ASH 26? If so the BGA datasheet (quoting the
'FAA Web') lists the rough air speed as 99 knots i.e
the same as the manoeuvring speed. For my 2005 Discus
2cT the speeds are both 103 knots. I think all gliders
have a rough air speed limit for conditions such as
'wave rotor, thunderclouds, visible whirlwinds or when
crossing mountain ridges' to quote my manual.

http://www.gliding.co.uk/bgainfo/tec...eets/ash26.pdf

Bagmaker - you seem analytically minded so have a look
at John Cochrane's excellent paper 'Just a Little Faster
Please'. The link won't post but if you Google +'john
cochrane' +soaring you will get his site.

John Galloway

At 06:36 11 March 2006, Eric Greenwell wrote:
bagmaker wrote:
Newbie help required!
Lets suppose I am on a shallow final glide, 60k out
in my 40:1 ship,
cruising at 60 knots. Recent thermals have been at
least 5 knots and I
am coming into some big lift. For the discussion rough
air Vne is 100
knots.

Best not to confuse 'rough air' speeds with Vne, which
is the 'never
exceed' speed. The 'rough air' limit (I'm not sure
this is used any more
- only my very old gliders had it) is quite a bit lower,
and the newer
gliders don't have it, but do state 'maneuvering speed',
lower yet.

And, practically speaking, you certainly don't want
to be going Vne when
there are thermals bigger than 5 knots in your way!
If the glider hangs
together, it will be a very rough ride.

What strength thermal should I take to increase finishing
speed to Vne

You need your gilder's polar to determine what strength
thermal is
needed for any McCready speed determination - nothing
else needed.

and how much (if any) time will this save me?

It will save you time, but without the polar, your
altitude above the
finish, and the distance to the finish, we can't give
you a number.

How do I estimate this at the time?

You don't have to estimate it. A chart of speed vs
McCready settings is
made up ahead of time. The less thinking you have to
do while flying,
the more time you can spend flying the glider.

What is the latest point on track
to take such a thermal?

I'm guessing, but I'd say about where you need to stay
in the thermal at
least one full turn to get high enough to use the 100
knot speed. Any
closer, and you'd waste time getting unneeded altitude.


--
Change 'netto' to 'net' to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download 'A Guide to Self-launching
Sailplane
Operation'