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

"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 Friday, April 10, 2015 at 9:02:23 PM UTC-7, 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.

In a cloud, it would be best to observe the max maneuvering airspeed which reliably tracks IAS but is usually considerably below Vne.

As I understand it, the flutter dynamics do not change at the same rate as dynamic pressure which is proportional to air density and V^2 therefore TAS is proportional to delta density^0.5. The coefficient for flutter in somewhere between 0.5 and 1 so the flutter speed increases, but not as fast as TAS increases with falling density. A lot of flutter has to do with dampening, I suppose in thinner air there is less.

I don't think many modern gliders are actually tested to flutter, I believe you are allowed to use computed numbers now for cert.

On Friday, April 10, 2015 at 5:11:12 AM UTC-7, Martin Gregorie wrote:
On Thu, 09 Apr 2015 07:27:44 -0700, JayM wrote:

I have H201 SN 81 and it will do a beautiful benign spiral! I've had
"hands off" for 15-20 minutes when descending from altitude.
Love the Libelle!

Thanks for the info. I'll definitely check that out next time I fly.

Curiosity: my Libelle was one of two that the GSA (UK forces soaring
association) bought in early 1970. The other one went to the 1970 World
Champs at Marfa. Is that your Libelle? What trim setting do you prefer
for a benign spiral?


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

No, Mine was never in any National or higher competition according to the logbooks. I trim for 50kts, pull full dive brakes and take hands off the stick, feet off the rudders.
Jay

Using high-drag configurations or spins to escape IMC is a desperation move fraught with unpredictable and uncontrollable hazards. There's enough data in the accident record to say it often doesn't work.

If one planes to fly in wave close to lenticulars, there's a chance of becoming enveloped in IMC. To me that says having an attitude indicator and enough skill using it to keep the glider upright in turbulent air is an absolute necessity.

On Sat, 11 Apr 2015 08:01:45 -0700, JayM wrote:

No, Mine was never in any National or higher competition according to
the logbooks. I trim for 50kts, pull full dive brakes and take hands
off the stick, feet off the rudders.
Jay

OK, thanks.

Just now I looked up G-INFO, the UK database and found that S/N 83 is
also in the UK, so that's probably the other one the RAFGSA bought with
mine, but there's not enough detail to be sure.

You may be interested to know that S/N 3 is still registered and
presumably still flying.


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

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.

although the spin may not increase the load factor, after you recover from a fully developed spin, you will find yourself 30 degrees (or more) nose down. the pullout from the dive is a high-G maneuver. Pull out too quickly, and you risk an accelerated stall (or worse). Pull out too slowly, and you risk exceeding max dive.

On Thursday, April 9, 2015 at 11:42:03 AM UTC-4, wrote:
With the understanding that a spin is a 1-G maneuver, and responding to the original post, with sufficient clear air below and after slowing down, are there any comments about leaving the cloud using an intentional spin?

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 |