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Minimum acceptable self-launch climb rate



 
 
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  #41  
Old April 30th 20, 04:56 PM posted to rec.aviation.soaring
jfitch
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Default Minimum acceptable self-launch climb rate

On Wednesday, April 29, 2020 at 5:07:37 PM UTC-7, Ron Gleason wrote:
On Wednesday, 29 April 2020 17:29:52 UTC-6, wrote:
I'm curious why motorglider pilots don't practice that at 200ft agl, as all student pilots do on aerotows as part of normal training.


FYI- the L/D of the Arcus M with mast extended and engine not running is approximately 13:1 with a sink rate in level flight of 495 fpm. Do you want to try a turn back to the runway with those numbers?


Come on Mark, 1980 vintage hang glider performance. Not an issue, could probably do a 360!


As one who has flown many vintage 1980 hang gliders, 13:1 was a dream that we could never achieve! 5 or 6:1 was more typical. 8:1 for the very high end.

The math is, a 50:1 glider at 1000 lbs has 20 lbs of drag. The dynamic pressure of 50 knots is about 8.5 lbs/ft^2. To get to 13:1 you need to add 57 lbs of drag or about 6.7 sq ft of flat plate area. A spinning 5 foot prop is 20 sq ft, not flat plate but pretty high drag coefficient. So it is plausible. On an ASH26 with a stopped prop at 20:1, it's just like landing a clean 2-33 or 1-26. Students do it all the time.
  #42  
Old April 30th 20, 09:43 PM posted to rec.aviation.soaring
Dave Nadler
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Default Minimum acceptable self-launch climb rate

On Thursday, April 30, 2020 at 12:34:24 AM UTC-4, Eric Greenwell wrote:
I'm astounded a 20M high performance, 50:1 glider can only manage 14:1
with the pylon out.


Why? Its only been explained here, like a thousand times?
In addition to open engine bay, the large radiator is a lot of drag.

The published min sink rate is at IIRC blue line.
Are you really going to attempt a turn-back at blue line?
No margin, and speed decays VERY rapidly with any inattention and all this drag.

Plummet mode in ArcusM is really not as bad as some older contraptions.
  #43  
Old April 30th 20, 09:44 PM posted to rec.aviation.soaring
Dave Nadler
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Default Minimum acceptable self-launch climb rate

On Wednesday, April 29, 2020 at 5:15:43 PM UTC-4, wrote:
On Wednesday, April 29, 2020 at 1:03:12 PM UTC-7, waremark wrote:
- climb for 200' or so, then set throttle to idle, and do a 180 degree turn,
lining up on the that road
- repeat the test, but this time, turn the ignition off, then turn as before"


I'm curious why motorglider pilots don't practice that at 200ft agl


Because we prefer not to die.
  #44  
Old April 30th 20, 09:45 PM posted to rec.aviation.soaring
Dave Nadler
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Default Minimum acceptable self-launch climb rate

On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St. Cloud wrote:
Someone please correct me if I am wrong but I believe
only 4 Arcus E's were sold and one of those was written off in an accident?


Those are correct numbers (at least as of a few months ago).
  #45  
Old April 30th 20, 10:41 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Default Minimum acceptable self-launch climb rate

Dave Nadler wrote on 4/30/2020 1:43 PM:
On Thursday, April 30, 2020 at 12:34:24 AM UTC-4, Eric Greenwell wrote:
I'm astounded a 20M high performance, 50:1 glider can only manage 14:1
with the pylon out.


Why? Its only been explained here, like a thousand times?


Well, probably because this is the first time I've seen it documented with numbers
from the flight manual. If I had a glider that sank at 500 fpm because the pylon
was extended, I'd sure mention it.

In addition to open engine bay, the large radiator is a lot of drag.
The published min sink rate is at IIRC blue line.
Are you really going to attempt a turn-back at blue line?


First, I would try it at altitude, as I have in my ASH26E. If that worked out, as
it did for my ASH26E, then I would be willing to turn back at the blue line in an
emergency. What do you think is the minimum safe altitude for a turn-back at blue
line in an Arcus M? What do other Arcus M pilots think is a safe altitude?

No margin, and speed decays VERY rapidly with any inattention and all this drag.

Plummet mode in ArcusM is really not as bad as some older contraptions.


--
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
  #46  
Old May 1st 20, 04:13 PM posted to rec.aviation.soaring
Dave Walsh[_2_]
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Default Minimum acceptable self-launch climb rate

At 20:45 30 April 2020, Dave Nadler wrote:
On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St.

Cloud wrote:
Someone please correct me if I am wrong but I believe
only 4 Arcus E's were sold and one of those was written off in an

accident?

Those are correct numbers (at least as of a few months ago).

The Arcus E has a pretty high wing loading; the one that crashed was
flying near Barcillonette in the southern French Alps, it appears to
have spun in. Neither pilot survived. It's not known whether the wing
loading was a significant factor.
Spinning any open class glider seems to be a hazardous. JM Clement,
who has very extensive gliding experience, is of the opinion that
none of them can be safely spun.

  #47  
Old May 1st 20, 04:27 PM posted to rec.aviation.soaring
Tango Whisky
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Default Minimum acceptable self-launch climb rate

Le vendredi 1 mai 2020 17:15:05 UTC+2, Dave Walsh a écritÂ*:
At 20:45 30 April 2020, Dave Nadler wrote:
On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St.

Cloud wrote:
Someone please correct me if I am wrong but I believe
only 4 Arcus E's were sold and one of those was written off in an

accident?

Those are correct numbers (at least as of a few months ago).

The Arcus E has a pretty high wing loading; the one that crashed was
flying near Barcillonette in the southern French Alps, it appears to
have spun in. Neither pilot survived. It's not known whether the wing
loading was a significant factor.
Spinning any open class glider seems to be a hazardous. JM Clement,
who has very extensive gliding experience, is of the opinion that
none of them can be safely spun.


The Arcus is not an Open Class glider.
Spinning an Open Class glider is suicidal. The moment of inertia of the wings is 3-4 times higher than that of a 15 m glider, but the rudder isn't. That makes that stopping the rotation takes significantly more time than in a small ship, and during this unstalling process the ship starts to accelerates. After the rotation has stopped, there are two choices: Exceeding v_ne, or exceeding max g-load above v_d.
Stupid enough to have been there and done that, lucky enough that the glider was stronger than the designer had expected.
  #48  
Old May 1st 20, 05:36 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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Posts: 1,463
Default Minimum acceptable self-launch climb rate

On Friday, May 1, 2020 at 8:27:07 AM UTC-7, Tango Whisky wrote:
Le vendredi 1 mai 2020 17:15:05 UTC+2, Dave Walsh a écritÂ*:
At 20:45 30 April 2020, Dave Nadler wrote:
On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St.

Cloud wrote:
Someone please correct me if I am wrong but I believe
only 4 Arcus E's were sold and one of those was written off in an
accident?

Those are correct numbers (at least as of a few months ago).

The Arcus E has a pretty high wing loading; the one that crashed was
flying near Barcillonette in the southern French Alps, it appears to
have spun in. Neither pilot survived. It's not known whether the wing
loading was a significant factor.
Spinning any open class glider seems to be a hazardous. JM Clement,
who has very extensive gliding experience, is of the opinion that
none of them can be safely spun.


The Arcus is not an Open Class glider.
Spinning an Open Class glider is suicidal. The moment of inertia of the wings is 3-4 times higher than that of a 15 m glider, but the rudder isn't. That makes that stopping the rotation takes significantly more time than in a small ship, and during this unstalling process the ship starts to accelerates. After the rotation has stopped, there are two choices: Exceeding v_ne, or exceeding max g-load above v_d.
Stupid enough to have been there and done that, lucky enough that the glider was stronger than the designer had expected.


I used fly a Nimbus 4 (best damn glider ever!) and one day while lowish over the local house thermal it started to rotate on me. I was slow on purpose (dry) as I wanted to see how slow it would thermal when I hit small bit turbulence and started to rotate. I smashed the stick to the instrument panel and stood on the opposite rudder. I had it flying in a quarter turn. Would not want to try that wet and perhaps not as keyed up for any problems. I only flew the nimbus without water a few times and frankly spinning anything full of water has all sorts of potential for heartache and hydraulic issues.
  #49  
Old May 1st 20, 07:38 PM posted to rec.aviation.soaring
Dave Walsh[_2_]
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Default Minimum acceptable self-launch climb rate

The Arcus is not an Open Class glider.

The Arcus E may not be strictly "Open Class" I don't know the strict
definition of "open". But the point I was trying (unsuccessfully) to
make is that the 20m wings are heavy maybe even heavier than
some true open class traditional gliders?
Anyone who has tried to pick up an Antares20E wing will understand.
Arcus E wings have 72 batteries plus associated mounting hardware,
each battery has a heating mantle, there are control electronics
boards every third battery plus the wiring & cooling hardware. As far
as I know it has exactly the same system as the Lange built Antares
20E. (Lange built the "E" bit of the Arcus).
Each battery weighs a little over a kilo so the whole lot possibly
weighs 80-85 kilos, add two pilots and you get high wing loading.
I understand the Arcus with full water ballast is pretty predictable;
maybe a pilot with Arcus E experience could comment on the
handling characteristics.

 




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