Minimum acceptable self-launch climb rate

waremark wrote on 4/29/2020 1:03 PM:
"You can simulate an engine failure during a launch at a safe altitude. I've done
at 2000'-3000':
- set your flight recorder to 1 second intervals, to get the best flight trace data
- at altitude, configure the glider for takeoff: gear down, flaps normally used
- line up on a long, straight road or similar
- establish a steady, full power climb at your normal climb speed
- 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"

You cannot do that last bit in an Arcus M - when you turn the engine off it commences the prop lowering process. In the ASH 26 I had before I did try this sort of stuff and would have been confident of a turn back from 200 foot. I think it would also be fine in the Arcus. However from my club's small grass field I am vulnerable to a potentially damaging off field arrival from about 50 foot to about 200 foot.

The only relevant power failure I have had was in the Arcus just after lift off, at 5 foot or less off the ground. There was a drive belt failure, and the glider plonked down rather heavily on the ground - instead of the lift component of the engine power I now had no power and a high drag prop mast.. Happily no damage done other than by the flailing drive belt(s). Since then I have tried to stay just above the ground until achieving say 55 knots.

In the Arcus while best climb rate is supposed to be about 52 knots, you can climb quite a lot faster without over-revving and without much sacrifice of climb rate - and there is a rev limiter which you could only hit in level flight, probably about 90 knots.

That 50' to 200' "window of discomfort" is disturbing, but would be still be there
when using a climb speed a few knots higher than the "speed for max climb rate"
that Steve M is looking for. It does sound like the Arcus M would be much more
suited to Steve's flying than the N3D, unfortunately at a much greater cost.

--
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

On Wednesday, April 29, 2020 at 1:03:12 PM UTC-7, waremark wrote:
"You can simulate an engine failure during a launch at a safe altitude. I've done
at 2000'-3000':
- set your flight recorder to 1 second intervals, to get the best flight trace data
- at altitude, configure the glider for takeoff: gear down, flaps normally used
- line up on a long, straight road or similar
- establish a steady, full power climb at your normal climb speed
- 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"

You cannot do that last bit in an Arcus M - when you turn the engine off it commences the prop lowering process. In the ASH 26 I had before I did try this sort of stuff and would have been confident of a turn back from 200 foot. I think it would also be fine in the Arcus. However from my club's small grass field I am vulnerable to a potentially damaging off field arrival from about 50 foot to about 200 foot.

The only relevant power failure I have had was in the Arcus just after lift off, at 5 foot or less off the ground. There was a drive belt failure, and the glider plonked down rather heavily on the ground - instead of the lift component of the engine power I now had no power and a high drag prop mast. Happily no damage done other than by the flailing drive belt(s). Since then I have tried to stay just above the ground until achieving say 55 knots.

In the Arcus while best climb rate is supposed to be about 52 knots, you can climb quite a lot faster without over-revving and without much sacrifice of climb rate - and there is a rev limiter which you could only hit in level flight, probably about 90 knots.


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.

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

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 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?