FES vs Gas Engine – Finding a Thermal?

While reading the FES article in June Soaring (yes, I’m behind in my reading), I noticed the author’s comment about searching for a thermal while FES was running, then shutting down FES as he started to climb. This is a topic I don’t recall seeing discussed in any FES vs gas comparisons.

In my Solo-powered Ventus 2cxT, my experience has been that the vibration (and possibly disturbed airflow) caused so much wild gyration in the vario readings that it seemed pointless to try to determine if I was flying into rising air, so I just climbed first, then shut down the engine and started a thermal search.

My question – do others have experience to share about their ability to find thermals while a sustainer or self-launcher (either gas or electric) was running? If electric has an advantage here, this could reduce the run-time needed and conserve “fuel�.

- Frank

On Thursday, August 24, 2017 at 11:29:01 PM UTC+3, V1 wrote:
While reading the FES article in June Soaring (yes, I’m behind in my reading), I noticed the author’s comment about searching for a thermal while FES was running, then shutting down FES as he started to climb. This is a topic I don’t recall seeing discussed in any FES vs gas comparisons.

In my Solo-powered Ventus 2cxT, my experience has been that the vibration (and possibly disturbed airflow) caused so much wild gyration in the vario readings that it seemed pointless to try to determine if I was flying into rising air, so I just climbed first, then shut down the engine and started a thermal search.

My question – do others have experience to share about their ability to find thermals while a sustainer or self-launcher (either gas or electric) was running? If electric has an advantage here, this could reduce the run-time needed and conserve “fuel�.

I've only had ten or so flights in a Grob 109, but on as far as I can recall every one of them we shut down the engine once established in lift ... in some cases in thermals, or often in ridge lift just after (barely) clearing the trees at the end of the strip (which was on a plateau).

On Thursday, August 24, 2017 at 4:29:01 PM UTC-4, V1 wrote:
My question – do others have experience to share about their ability to
find thermals while a sustainer or self-launcher (either gas or electric)
was running?

Sure, but it depends a lot on the glider and power plant.
In Antares I normally reduce power just after take-off down to 400-500fpm climb.
When I feel the first thermal, I make a circle to be sure.
If pretty sure, bring the power all the way back but do not shut down.
If I'm climbing one turn, I retract motor.
Typical altitude about 1000 ft, for example:
https://www.onlinecontest.org/olc-2....Id=-1855578239
or a bit lower, with a brief boost after initial shutdown:
https://www.onlinecontest.org/olc-2....Id=-1769203627
Try this in most motor-gliders and you'll kill yourself.

In ArcusM it is more difficult to feel the thermal, but in any case one
needs to go much higher for a safer shut-down (typically climb to 2500ft).
A thermal helps here but you still have to do the cool-down cycle and
plummet-mode during retraction (sometimes takes a couple tries).
And because of the plummet factor your search area is severely restricted
by the need to be close-in for an emergency return on failure.

In my prior motorglider was really hard to feel the thermals, and again
being gas powered with severe plummet mode, had to always go a lot higher.

If electric has an advantage here, this could reduce the run-time needed
and conserve “fuel�.

Absolutely, but ONLY if:
- there is lift near the launch point, and
- traffic permits low-level thermalling (while always maintaining
a safe emergency return plan).

Hope that helps!
Best Regards, Dave

It's pretty easy in the Stemme with the triple probe mounted to the
front of the nose cone, in front of the propeller.Â* All the soaring
instruments work as designed without interference from the prop. BTW,
the Stemme (used) costs less than the Arcus AND you can take a friend! :-D

On 8/24/2017 2:28 PM, V1 wrote:
While reading the FES article in June Soaring (yes, I’m behind in my reading), I noticed the author’s comment about searching for a thermal while FES was running, then shutting down FES as he started to climb. This is a topic I don’t recall seeing discussed in any FES vs gas comparisons.

In my Solo-powered Ventus 2cxT, my experience has been that the vibration (and possibly disturbed airflow) caused so much wild gyration in the vario readings that it seemed pointless to try to determine if I was flying into rising air, so I just climbed first, then shut down the engine and started a thermal search.

My question – do others have experience to share about their ability to find thermals while a sustainer or self-launcher (either gas or electric) was running? If electric has an advantage here, this could reduce the run-time needed and conserve “fuel�.

- Frank


--
Dan, 5J

Doesn't everyone with a SLSP do this every flight?
Worked fine in the ASH26E. CAI302 with electronic TE.
Seat of the pants input is useful too.
Vibration? That's for two-stroke users.
Jim

I fly an Alisport Silent 2 Electro (FES capable of self-launch).

I take off with full power, climb to a safe altitude, pull the gear up, reduce power to about 80%, and then cruise-climb looking for a thermal. When I find one, I start circling and continue to run the motor. This gets me up into the stronger part of the thermal more quickly.

When it is obvious the thermal is doing most of the lifting, I shut down the motor. With the FES, the shutdown is automatic after dialing the motor down below 1000 RPM (a couple counter-clockwise turns on the rheostat). The motor controller takes over, electronically brakes the motor/prop to a stop, and the blades fold back aerodynamically. The controller then positions the blades along side the fuselage by pulsing the motor.

I simply continue to work the thermal.

On any decent soaring day, I use about 20% of the battery capacity to launch and climb into a thermal, leaving 80% in reserve in case I do something stupid.

On more than one occasion, I have restarted the FES in flight when a thermal didn't pan out. One one flight, I had launched a little too early in the day and needed to restart/re-climb four times before the day started working. Fortunately, starting and stopping the FES is as simple as turning the volume up/down on a radio, minimizing pilot workload to near zero.

The pitot/TEC probe on the Silent 2 Electro is mounted high on the vertical stabilizer, clear of (above) the prop wash.

In my Solo 2350 powered 29E, I find it quite possible to recognize a thermal even though everything is vibrating and the vario readout is very nervous.. I try to circle with a constant speed and if the vario constantly is positive and I still have the impression (seat of the pants input) I'm in a thermal after 2 or 3 turns, I shut off the engine.

Of course only if situation (altitude, landout situation) permits.

Le vendredi 25 août 2017 08:37:15 UTC+2, a écritÂ*:
In my Solo 2350 powered 29E, I find it quite possible to recognize a thermal even though everything is vibrating and the vario readout is very nervous. I try to circle with a constant speed and if the vario constantly is positive and I still have the impression (seat of the pants input) I'm in a thermal after 2 or 3 turns, I shut off the engine.

Of course only if situation (altitude, landout situation) permits.

With my Ventus cM, I do exactly the same. I judge the quality of the thermal by the reading of the integrator value (and my seat pans); the TE probe sits in the propwash (haven't seen the necessity for a pneumatic switch during the last 10 years...) which makes the realtime vario reading fairly useless.

I'm with Dave Nadler on this; it's pretty easy to sense when
the Antares 20E is in a thermal even with the engine running.
Never flown a FES.
With a bit of practice sensing the thermal in the all-vibro-Solo
powered DG808 was possible too. I never bothered though,
just climb 5000+ feet, switch off and set off searching.

Dave N: Be interesting to know what on earth "plummet
mode" is in the Arcus M?

Dave Walsh

On Friday, August 25, 2017 at 10:15:06 AM UTC-4, Dave Walsh wrote:
Dave N: Be interesting to know what on earth "plummet
mode" is in the Arcus M?

Plummet-mode is when engine is extended and not running.
Not exciting in Antares or FES, a bit more so with turbos.
Exciting in gas-powered pylon self-launchers (engine/radiator drag).
ArcusM is not too bad - about 500fpm.
Some motorgliders are more like 800fpm which definitely focuses one's attention.

Planning for plummet-mode is especially important for safety during:
- departure route
- powered flight between landable areas
- shut-down activities
These engines have a very high failure rate and its truly exciting to have
a failure on departure - you better have your response planned in advance.
Power-plant retraction is also failure-prone, so advance planning about
when to give up and restart or land is advisable...

Hope that's clear!
Best Regards, Dave