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Vario Comparison



 
 
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  #41  
Old September 7th 18, 03:31 PM posted to rec.aviation.soaring
Dan Marotta
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Me, too!* The maximum speed with the gear down in the Stemme is 76
knots.* I keep the speed very close to that number throughout the
pattern, slowing on final as the target point is made.* I also have very
effective dive brakes and so I keep the pattern in close.* I cringe when
I see a glider fly a half mile final at 50 kts or less. Sure, he's got
the glide ratio to make the runway easily, until that unexpected gust
comes along...

On 9/7/2018 7:08 AM, Nick Kennedy wrote:
I try to keep it over 70 knots the whole way to the deck, works for me.


--
Dan, 5J
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  #42  
Old September 7th 18, 03:44 PM posted to rec.aviation.soaring
Dan Marotta
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On 9/6/2018 7:21 PM, Mike Borgelt wrote:
if the aircraft is wanting to go a certain way and you are trying to force it to go another, just go with the aircraft as it is departing from controlled flight. Good advice IMO.

Exactly!* I had an incident two years ago while attempting to establish
in the wave in the lee of a mountain at about 2,500' AGL. The glider
suddenly rolled to the right and pitched down though I was well above
stall speed (and I understand AoA).* My response was to immediately
center the ailerons and add plenty of forward stick until the glider
flew out of the departure.* Of course I missed the wave that day...
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  #43  
Old September 8th 18, 06:49 PM posted to rec.aviation.soaring
[email protected]
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On Thursday, September 6, 2018 at 7:23:31 PM UTC-4, Andy Blackburn wrote:
Mike,

I understand that the short period response to a step function in vertical air motion would damp out after less than a second, but normally thermal entry would have a positive gradient in vertical air motion as the glider traverses from zero vertical motion to maximum vertical motion towards the center of the thermal. This ought to create a more prolonged nose-down pitch attitude in addition to upward acceleration, both of which ought to be detectable to accelerometers and gyros in a modern vario. This would be quite distinct from an ever-so-slow negative acceleration and nose up pitch rate from a horizontal gust on the nose. I expect having a sense for the distribution of strength and duration for horizontal gusts would also help a bit.

That’s what I tend to sense in moderate to strong thermals versus gusts. Is that that a correct interpretation?

Andy


I recently took a "refresher"course of four days with a truly outstanding professional mountain soaring pilot. Interestingly, he does not detect and select thermals by using the vario. He states that the vario gives old information that has long past. Intead, he trusts his "butt" and for a visual reference notices the nose of the glider pitching upwards. We seldom missed a true thermal. When a glider enters sink )as when leaving a strong thermal), the nose pitches upwards initially.
  #44  
Old September 8th 18, 08:03 PM posted to rec.aviation.soaring
kirk.stant
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On Thursday, September 6, 2018 at 8:21:39 PM UTC-5, Mike Borgelt wrote:

To digress from the vario topic slightly:
Which is why I said that flying attitude can kill you. I think this is what happened to an ASG-29 pilot at Waikerie about 2 and a half years ago, turning final with what seemed to be plenty of airspeed, into a strong thermal encounter and the next thing he was in the grapevines. Fortunately the wires and vines cushioned the stop enough and the spin wasn't fully established, that he survived. Encounter a fairly sharp 10 knot core at 60 KIAS and the AoA increases by 10 degrees. The AoA may be around 7 degrees before the encounter. What AoA do thin subsonic wings stall at?
This, I believe is one answer to the unexplained spin ins that occur from time to time.
Attitude is fine in equilibrium or very close to equilibrium situations. Doesn't work very well in other situations. How many have died in the winch launch failure scenario where you bury the nose well below the horizon, then roll and pull and the thing flicks in to a spin? Unfortunately all too many merely in practice.
A guy who was Chief Test Pilot for the Royal Australian Air Force during the 1950s and 1960s once told me if the aircraft is wanting to go a certain way and you are trying to force it to go another, just go with the aircraft as it is departing from controlled flight. Good advice IMO.


To continue this excellent digression from the original thread: This whole "pitchdown in the pattern due to a thermal" is the reason we should be using AOA in the pattern instead of Airspeed. An AOA gauge would immediately indicate the AOA changing due to a gust or thermal - before the ASI shows any change in airspeed. Couple the AOA system with a visual (or even better, an aural) indication, and you can fly the pattern safely without ever looking in the cockpit.

Caution, war story: The F-4 had a really nice AOA system with both visual (cockpit gauge and coaming AOA lights) and aural cues, that worked much like a vario audio, with different tones from fast down to on-speed and down to slow and dangerously slow. Very distinct tones which made it easy to fly the pattern at a nice safe speed (regardless of gross weight or bank angle) until on final, then slowing down to final on-speed for touch down - never looking at the airspeed indicator other than to cross check AOA vs airspeed at the start of the approach. Flying approaches from the back seat, you couldn't even see the airspeed indicator (due to having to lean way over and look around the pilot's seat - a crosswind or a bit of rudder helped ;^) so you relied entirely on the AOA tones to fly the approach - and it was the easiest, most natural thing to do, keeping the touchdown point in view the whole time.

Here is an idea for you smart guys: come up with a simple AOA sensor system consisting of small low drag bluetooth-enabled "pods" attached about mid-span on both wing leading edges, transmitting to the AOA system in the cockpit. When the gear is down (and/or spoilers open for fixed gear ships) the vario audio would be turned off and replaced by the AOA audio (which would be distinctive enough not to be confused with a vario), backed up with a set of FAST/ONSPEED/SLOW indexer lights on the top of the panel. To use, in the pattern drop gear or crack the spoilers, verify the AOA tone matches your approach speed on downwind (to check for stuck or failing AOA system), then fly the audio to touchdown, looking for a fast or slightly fast tone until short final when you slow to on-speed tone. If you hit a gust or thermal that bumps up your AOA dangerously, you would get an immediate SLOW or DANGEROUSLY SLOW tone and could react accordingly. Same if you have a PTT down low full of ballast and have to turn back to the field - the AOA tones would still be correct for your increased bank angle and wingloading.

Kirk
66

  #45  
Old September 8th 18, 09:13 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Mike Borgelt wrote on 9/5/2018 10:11 PM:
I had to derive this and I later found the derivation in a book called
"Airplane Response to Atmospheric Turbulence" by John C. Houbolt. Yep, that guy
- the one who pushed the Lunar Orbit Rendevous for Apollo.


Thank you for that reference. I had never heard of the struggle between three
methods of making it to the moon - and back. Fascinating!

--
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
  #46  
Old September 8th 18, 10:35 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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On Saturday, September 8, 2018 at 1:13:39 PM UTC-7, Eric Greenwell wrote:
Mike Borgelt wrote on 9/5/2018 10:11 PM:
I had to derive this and I later found the derivation in a book called
"Airplane Response to Atmospheric Turbulence" by John C. Houbolt. Yep, that guy
- the one who pushed the Lunar Orbit Rendevous for Apollo.


Thank you for that reference. I had never heard of the struggle between three
methods of making it to the moon - and back. Fascinating!

--
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


Watch "From the Earth to the Moon".
  #47  
Old September 9th 18, 01:14 AM posted to rec.aviation.soaring
SoaringXCellence
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AOA devices are becoming very common in the experimental/homebuilt airplane world. A recent publication from the FAA (!) recommended that pilots consider getting a AOA sensor installed in their airplane. The newer completed aircraft in the famous Vans Aircraft RV series are almost all equipped with a AOA device.

I have been investigating a AOA system to install in gliders for several years but keep running into challenges due to flaps and spoilers and their effect on the system. The whole device is very easy if the airflow and overall AOA doesn't change much with configuration changes.

One fix is to set the system primarily for landing and disable it for other flight regimes. Unfortunately that means you can't use the best L/D AOA, or other selected angles to correct for weight changes.

I also have a Raspberry Pi and considered just starting to log the data for my glider. This winter I'm doing a refinish; maybe that a good time to install the pressure sensors and start logging.

Mike
  #48  
Old September 9th 18, 01:31 AM posted to rec.aviation.soaring
SoaringXCellence
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Here is one that was published years ago, but it is NOT a AOA device but rather a pitch angle measurement. Close but not quite:

http://www.akaflieg.tugraz.at/wp-con...-sensor_v1.pdf

Here is a good discussion on the devices being used in the airplane world:

https://www.flyingmag.com/how-it-wor...tack-indicator

Another discussion particularly directed at gliders:

https://www.dg-flugzeugbau.de/en/library/side-string
This one shows some of the chanllenges for the glider version of an AOA indicator. The string method shown is still not a true AOA for the wing, and requires the pilot to be looking to the side to "read" the string.

Finally a former thread on RAS, this particular statement by Ian describes the challenges well:

https://groups.google.com/forum/#!ms...E/14QLGAt2_9UJ

Mike
  #49  
Old September 9th 18, 02:19 AM posted to rec.aviation.soaring
Tom BravoMike
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On Saturday, September 8, 2018 at 7:14:46 PM UTC-5, SoaringXCellence wrote:
AOA devices are becoming very common in the experimental/homebuilt airplane world. A recent publication from the FAA (!) recommended that pilots consider getting a AOA sensor installed in their airplane. The newer completed aircraft in the famous Vans Aircraft RV series are almost all equipped with a AOA device.

I have been investigating a AOA system to install in gliders for several years but keep running into challenges due to flaps and spoilers and their effect on the system. The whole device is very easy if the airflow and overall AOA doesn't change much with configuration changes.

One fix is to set the system primarily for landing and disable it for other flight regimes. Unfortunately that means you can't use the best L/D AOA, or other selected angles to correct for weight changes.

I also have a Raspberry Pi and considered just starting to log the data for my glider. This winter I'm doing a refinish; maybe that a good time to install the pressure sensors and start logging.

Mike


In the SZD55-1 Flight manual,

http://org.ntnu.no/nthf/dokument/fli...als/LN-GAZ.pdf

p. 12a, it says that "For airworthiness the JAR-22 require the sailplane to be equipped at least with: airspeed indicator, altimeter and STALL WARNING DEVICE." I can remember there was some kind of a buzzer on the SZD-55 I used to own for a short time, but I never heard it sound nor don't know how it was supposed to work.


Any other SZD-55 owners/pilots here?
  #50  
Old September 9th 18, 03:58 PM posted to rec.aviation.soaring
Dan Marotta
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Sounds like a great idea.* Maybe you could use a micro switch in the
landing flap position to change the mode of your AoA device.

On 9/8/2018 6:14 PM, SoaringXCellence wrote:
AOA devices are becoming very common in the experimental/homebuilt airplane world. A recent publication from the FAA (!) recommended that pilots consider getting a AOA sensor installed in their airplane. The newer completed aircraft in the famous Vans Aircraft RV series are almost all equipped with a AOA device.

I have been investigating a AOA system to install in gliders for several years but keep running into challenges due to flaps and spoilers and their effect on the system. The whole device is very easy if the airflow and overall AOA doesn't change much with configuration changes.

One fix is to set the system primarily for landing and disable it for other flight regimes. Unfortunately that means you can't use the best L/D AOA, or other selected angles to correct for weight changes.

I also have a Raspberry Pi and considered just starting to log the data for my glider. This winter I'm doing a refinish; maybe that a good time to install the pressure sensors and start logging.

Mike


--
Dan, 5J
 




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