In wave, in blue hole at cloud level, hole closes, in IMC, then what?

FAR 23.335 use EAS in its definitions, but that's the regulation not the physics. If you can find any authoritative aerodynamic references regarding the relationship between flutter and EAS, rather than TAS, I would love to see it.


On Saturday, April 11, 2015 at 12:02:23 AM UTC-4, wrote:
"Its also worth mentioning that Vne is not based on load factor, like Va, but on flutter, which is why its True and not Indicated. "

Actually flutter is dependent on equivalent airspeed not true airspeed. There was an interesting article in Soaring magazine way back where Stan Hall brought in a NASA aerodynamic expert specializing in aeroelasticity and had his work peer reviewed by other experts to try and get a definitive answer on a flutter question arising from a flutter accident that led to several months of "argument by letter to the editor."

"In my glider, the placard VNE is 146 knots IAS but at 18,000 ft this is reduced to 122 knots IAS" Which brings up a question I've never been able to get a good answer to: what methodology do they use to determine reduced VNE with increasing altitude? Many gliders specify just IAS and the gliders I've dealt with which do specify lower VNE's with increasing altitude don't have those speeds match up with TAS at those altitudes. Calculate what TAS at 18,000 for an IAS of 122 knots actually is. It's higher than 146 knots.

As for the original question: where I fly the clouds are filled with granite up to 7000 feet or more, the valleys are narrow and the valley floors are not much above sea level. I don't have a turn and slip or AH and I have only had minimal training on those instruments over a decade ago in a Piper Cherokee. Being caught in cloud where I fly I would probably opt for the parachute pretty damn quick. That however is just the best of a bunch of bad options really.

On Saturday, April 11, 2015 at 12:02:23 AM UTC-4, wrote:
"Its also worth mentioning that Vne is not based on load factor, like Va, but on flutter, which is why its True and not Indicated. "

Actually flutter is dependent on equivalent airspeed not true airspeed.

VD is defined based on EAS (eg FAR 23.335), and Vne is defined based on VD (23.1505).

But EAS doesn't take into account air density, which is primarily a function of altitude (and a some temp thrown in). So Vne has to be corrected for air density, which is the TAS.

--bob

On Saturday, April 11, 2015 at 11:34:02 AM UTC-7, Bob Pasker wrote:
On Saturday, April 11, 2015 at 12:02:23 AM UTC-4, wrote:
"Its also worth mentioning that Vne is not based on load factor, like Va, but on flutter, which is why its True and not Indicated. "

Actually flutter is dependent on equivalent airspeed not true airspeed.

VD is defined based on EAS (eg FAR 23.335), and Vne is defined based on VD (23.1505).

But EAS doesn't take into account air density, which is primarily a function of altitude (and a some temp thrown in). So Vne has to be corrected for air density, which is the TAS.

--bob

A was mentioned previously, Vne is a flutter criteria, and flutter does not vary with density in the same way that TAS/IAS does. In other words, you cannot depend on flutter TAS being invariant with density altitude. There are some research papers on this you can find if you look.

On Sat, 11 Apr 2015 11:34:01 -0700, Bob Pasker wrote:

On Saturday, April 11, 2015 at 12:02:23 AM UTC-4,
wrote:
"Its also worth mentioning that Vne is not based on load factor, like
Va, but on flutter, which is why its True and not Indicated. "

Actually flutter is dependent on equivalent airspeed not true airspeed.

VD is defined based on EAS (eg FAR 23.335), and Vne is defined based on
VD (23.1505).

But EAS doesn't take into account air density, which is primarily a
function of altitude (and a some temp thrown in). So Vne has to be
corrected for air density, which is the TAS.

Are you sure about that?

This reference says that EAS is a measure of dynamic pressure and gives
several formulae for it that all use either air density or air pressu

https://en.wikipedia.org/wiki/Equivalent_airspeed

Yes, I know about Wikipedia's dodgy treatment some social facts, but IME
its pretty good on this sort of stuff.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Saturday, April 11, 2015 at 2:31:02 PM UTC-7, Martin Gregorie wrote:
On Sat, 11 Apr 2015 11:34:01 -0700, Bob Pasker wrote:

On Saturday, April 11, 2015 at 12:02:23 AM UTC-4,
wrote:
"Its also worth mentioning that Vne is not based on load factor, like
Va, but on flutter, which is why its True and not Indicated. "

Actually flutter is dependent on equivalent airspeed not true airspeed.

VD is defined based on EAS (eg FAR 23.335), and Vne is defined based on
VD (23.1505).

But EAS doesn't take into account air density, which is primarily a
function of altitude (and a some temp thrown in). So Vne has to be
corrected for air density, which is the TAS.

Are you sure about that?

This reference says that EAS is a measure of dynamic pressure and gives
several formulae for it that all use either air density or air pressu

https://en.wikipedia.org/wiki/Equivalent_airspeed

Yes, I know about Wikipedia's dodgy treatment some social facts, but IME
its pretty good on this sort of stuff.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

I always thought IAS (or EAS minus instrument error) was just an indication of dynamic pressure, in fact that is how the instruments are constructed: to measure dynamic pressure. It is proportional to rho, air density.

On Saturday, April 11, 2015 at 6:15:16 PM UTC-7, jfitch wrote:
On Saturday, April 11, 2015 at 2:31:02 PM UTC-7, Martin Gregorie wrote:
On Sat, 11 Apr 2015 11:34:01 -0700, Bob Pasker wrote:

On Saturday, April 11, 2015 at 12:02:23 AM UTC-4,
wrote:
"Its also worth mentioning that Vne is not based on load factor, like
Va, but on flutter, which is why its True and not Indicated. "

Actually flutter is dependent on equivalent airspeed not true airspeed.

VD is defined based on EAS (eg FAR 23.335), and Vne is defined based on
VD (23.1505).

But EAS doesn't take into account air density, which is primarily a
function of altitude (and a some temp thrown in). So Vne has to be
corrected for air density, which is the TAS.

Are you sure about that?

This reference says that EAS is a measure of dynamic pressure and gives
several formulae for it that all use either air density or air pressu

https://en.wikipedia.org/wiki/Equivalent_airspeed

Yes, I know about Wikipedia's dodgy treatment some social facts, but IME
its pretty good on this sort of stuff.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

I always thought IAS (or EAS minus instrument error) was just an indication of dynamic pressure, in fact that is how the instruments are constructed: to measure dynamic pressure. It is proportional to rho, air density.

Here is the reference I think I was remembering. Can't seem to access it now without money, but the abstract pretty much says it. I think Schleicher at least believes this, or they would not have bothered to put mention and tables in their manuals.

http://journals.sfu.ca/ts/index.php/ts/article/view/216

wrote on 4/10/2015 9:02 PM:
"Its also worth mentioning that Vne is not based on load factor, like
Va, but on flutter, which is why its True and not Indicated."

Actually flutter is dependent on equivalent airspeed not true
airspeed. There was an interesting article in Soaring magazine way
back where Stan Hall brought in a NASA aerodynamic expert
specializing in aeroelasticity and had his work peer reviewed by
other experts to try and get a definitive answer on a flutter
question arising from a flutter accident that led to several months
of "argument by letter to the editor."

"In my glider, the placard VNE is 146 knots IAS but at 18,000 ft this
is reduced to 122 knots IAS" Which brings up a question I've never
been able to get a good answer to: what methodology do they use to
determine reduced VNE with increasing altitude? Many gliders specify
just IAS and the gliders I've dealt with which do specify lower VNE's
with increasing altitude don't have those speeds match up with TAS at
those altitudes. Calculate what TAS at 18,000 for an IAS of 122 knots
actually is. It's higher than 146 knots.

As for the original question: where I fly the clouds are filled with
granite up to 7000 feet or more, the valleys are narrow and the
valley floors are not much above sea level. I don't have a turn and
slip or AH and I have only had minimal training on those instruments
over a decade ago in a Piper Cherokee. Being caught in cloud where I
fly I would probably opt for the parachute pretty damn quick. That
however is just the best of a bunch of bad options really.

According to the aerodynamicists I've talked, flutter at higher
altitudes is mostly dependent on TAS. The quirk is "at higher altitudes".

The "many gliders" you mention are likely older gliders, as Vne in TAS
is a "recent" change, where recent is about 25-30 years ago.

My 20 year old Schleicher ASH 26 E has a Vne of 146 knots from sea level
to 10,000 feet; there, the Vne = 146 knots IAS/175 knots TAS. That's why
the Vne in IAS at 18,000 calculates to higher than 146 knots - the Vne
is 175 TAS, not 146 TAS.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

VNE with altitude.

If your VNE changes with altitude, it will be listed in the glider's Manual, read it and quit trying to guess.

Todd Smith
3S

Interesting that you all talk about 'what to do' based on being caught in cloud on an unplanned basis. I fly with an A/H and am happy to thermal in cloud using that. However, I always worry about what to do if the A/H fails. My glider has no backup blind flying instrumentation (unlike most GA aircraft which have an electric turn coordinator as well as a vacuum horizon - and which are more speed stable than gliders).

My plan, tested in clear and admittedly smooth air, has been to open the air brakes and take hands and feet off if either the A/H shows obvious signs of failing or the airspeed increases over a certain level (I plan on 75 knots). A misleading A/H would be far worse than an obviously failed one, because you would be in worse shape before taking this action. However I recently talked to someone who had the A/H in his LX computer fail while in cloud.. He kept things steady while rebooting the LX and all was well. I think I would stick to the open the air brakes plan.

At 17:35 12 April 2015, waremark wrote:
Interesting that you all talk about 'what to do' based on being caught in
c=
loud on an unplanned basis. I fly with an A/H and am happy to thermal in
cl=
oud using that. However, I always worry about what to do if the A/H
fails.
=
My glider has no backup blind flying instrumentation (unlike most GA
aircra=
ft which have an electric turn coordinator as well as a vacuum horizon -
an=
d which are more speed stable than gliders).=20

My plan, tested in clear and admittedly smooth air, has been to open the
ai=
r brakes and take hands and feet off if either the A/H shows obvious
signs
=
of failing or the airspeed increases over a certain level (I plan on 75
kno=
ts). A misleading A/H would be far worse than an obviously failed one,
beca=
use you would be in worse shape before taking this action. However I
recent=
ly talked to someone who had the A/H in his LX computer fail while in
cloud=
.. He kept things steady while rebooting the LX and all was well. I think
I
=
would stick to the open the air brakes plan.



Sorry for the thread drift
One of my gliding club members in England was wave soaring over the
pennies when he lost lift ,and in to the cloud he went .
He switch his LX to horizon and made a safe decent ,but lost positional
awareness,he did not hit the hillside but at about 200ft it's fair to say
the
ground found him and a 6 month old asw31 would never be the same again .
He was not hurt but it took 3hours to walk off the hill and the retrieve is
was
a story all of its own and lasting over a week.
So the story is not over when you clear the bottom of cloud ,personally the

nearest I have been to a problem is descending through a closing hole only
to
find the canopy iced over ,but I managed to hang on until it melted and I
landed in a farmers field.As it was Christmas and my friends arrived with
the
trailer and bottles of wine he was very good with us and I put it down as I

learned from that and with the massive endorphin surge I had a great
Christmas.