Minimum acceptable self-launch climb rate

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?

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!

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

Straight from the Schempp-Hirth Arcus M Flight Manual. Dave Nadler calls it "Plummet Mode."

When we converted four Arcus M gliders to jet power, we measured 38:1 with the engine extended but not running.

wrote on 4/29/2020 5:36 PM:

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

Straight from the Schempp-Hirth Arcus M Flight Manual. Dave Nadler calls it
"Plummet Mode."

When we converted four Arcus M gliders to jet power, we measured 38:1 with the
engine extended but not running.

38:1 -- is that with the jet engine extended, gear retracted?

I'm astounded a 20M high performance, 50:1 glider can only manage 14:1 with the
pylon out. Is that in landing configuration with the gear extended, also? My 18M
ASH26E is much better than that (about 20:1) with the pylon up and gear extended.
Do you have any idea what makes it so terrible? That's like a PIK 20E!

--
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

38:1 -- is that with the jet engine extended, gear retracted?

Yes- gear retracted, engine extended but not running.

The biggest cause of the terrible performance of the Arcus M with the prop and pylon up is the fact that the two huge 6 ft. long doors remain open and the big engine bay and the rest of the hole in the fuselage gives all those draggy little air molecules a place to run around before finally jumping out.

The ASH-26E appears to have smaller doors and a smaller engine bay, and possibly less drag because of this.

And for those of you who still don't believe, 495 fpm is 8.25 feet per second. 60 knots is 101.27 feet per second. 101.27/8.25 = 12.275.

At 13:17 30 April 2020, wrote:
38:1 -- is that with the jet engine extended, gear retracted?

Yes- gear retracted, engine extended but not running.

The biggest cause of the terrible performance of the Arcus M
with the prop
=
and pylon up is the fact that the two huge 6 ft. long doors
remain open
and=
the big engine bay and the rest of the hole in the fuselage gives
all
thos=
e draggy little air molecules a place to run around before finally
jumping
=
out.

The ASH-26E appears to have smaller doors and a smaller
engine bay, and
pos=
sibly less drag because of this.

And for those of you who still don't believe, 495 fpm is 8.25 feet
per
seco=
nd. 60 knots is 101.27 feet per second. 101.27/8.25 =3D
12.275.

Just out of interest the electric 20m Antares20E which has a
"book" L/D of 56:1 does 30:1, engine out and prop windmilling,
gear retracted. The main engine doors are closed when the engine
is erected. The prop is stopped by the "electronics", if it throws a
wobbly the pilot has no way to stop the prop. The prop is 2m
diameter, two blades. The engine is direct drive to the prop so the
engine would have had to seize up for the prop to be stopped &
erected. The circuit & landing are a bit of a non event, rather like a
K13.
I've never experienced "plummet mode" in an Arcus; the
DG400/800 plummet rather well.
Dave Walsh

On Thursday, April 30, 2020 at 7:15:04 AM UTC-7, Dave Walsh wrote:
At 13:17 30 April 2020, wrote:
38:1 -- is that with the jet engine extended, gear retracted?

Yes- gear retracted, engine extended but not running.

The biggest cause of the terrible performance of the Arcus M
with the prop
=
and pylon up is the fact that the two huge 6 ft. long doors
remain open
and=
the big engine bay and the rest of the hole in the fuselage gives
all
thos=
e draggy little air molecules a place to run around before finally
jumping
=
out.

The ASH-26E appears to have smaller doors and a smaller
engine bay, and
pos=
sibly less drag because of this.

And for those of you who still don't believe, 495 fpm is 8.25 feet
per
seco=
nd. 60 knots is 101.27 feet per second. 101.27/8.25 =3D
12.275.

Just out of interest the electric 20m Antares20E which has a
"book" L/D of 56:1 does 30:1, engine out and prop windmilling,
gear retracted. The main engine doors are closed when the engine
is erected. The prop is stopped by the "electronics", if it throws a
wobbly the pilot has no way to stop the prop. The prop is 2m
diameter, two blades. The engine is direct drive to the prop so the
engine would have had to seize up for the prop to be stopped &
erected. The circuit & landing are a bit of a non event, rather like a
K13.
I've never experienced "plummet mode" in an Arcus; the
DG400/800 plummet rather well.
Dave Walsh

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?

L/D with pylon out highly depends on IAS.
On a Ventus 2 CM with gear up, failed spindle drive, prop stopped, I was getting ~18 L/D at 50 kts. This was dropping fast below 15 L/D when accelerating above 55 kts.

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.

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