fes ot jet (pros and cons)

Not in my Stemme.Â* It *does* have two heat sensors in the engine bay to
light up a big red light and sound a buzzer, but fire means get out.Â*
Period.

On 8/5/2019 9:15 PM, JS wrote:
With the well known outcome of a fire, every composite aircraft with an engine or motor of some sort has a built-in fire extinguisher.
All the manufacturers have that option.
Jim

--
Dan, 5J

On Tuesday, August 6, 2019 at 11:42:52 AM UTC-7, Dan Marotta wrote:
Not in my Stemme.Â* It *does* have two heat sensors in the engine bay to
light up a big red light and sound a buzzer, but fire means get out.Â*
Period.

On 8/5/2019 9:15 PM, JS wrote:
With the well known outcome of a fire, every composite aircraft with an engine or motor of some sort has a built-in fire extinguisher.
All the manufacturers have that option.
Jim

--
Dan, 5J

I have heard of far too many "failure to start" incidents with jets to consider them a viable self-retrieve option. Just consider it a bonus if they do start.

FES is far more reliable, assuming the battery fire incidents are a thing of the past (there have been design changes to the battery). Watched a mini-LAK FES self-launch at Ely, NV (6200') recently with a 200+ lb pilot on a warm day. Same glider did do a partial self-retrieve. Advantage of both FES and jet is they don't lose power with altitude (although the prop does lose thrust); not so with an ICE. By taking a tow, he had an hour of level cruise available, or about 90 miles at these altitudes. The batteries are removed from the glider for charging, which only takes a couple of hours using a 20 amp circuit. With a spare set of batteries the glider could be flown multiple times per day. Maintenance of an FES should be less than a jet.

While the fit and finish of the mini LAK was not up to German standards, it was still pretty good, and at about half the cost of a 31Mi (but with 2/3 of the wing span). It's not for me, but I can see where it would be a decent entry-level motorglider.

PS, one unexpected benefit of FES: he could match the glide performance of an ASH31Mi by simply running the motor at reduced RPM, allowing them to fly together.

Tom

Another thing to remember about possible "new" battery
technology is whether the glider manufacturers will have any
financial interest in updating their current systems. New &
better batteries may well appear but you can bet the glider
manufacturers will be fitting them in their latest creations. So
for anyone wanting to fly electric in the near future, or now,
your are back with Li-Ion etc.
Despite their many drawbacks it seems some of these (old) Li-
Ion cells (e.g. the SAFT cells used by Lange) will last ~20
years.
While the cost of an electric launch looks economic compared
to a tug the real costs are much higher......I seriously doubt
that overall the costs are lower; you pay for autonomy!
For FES/Jet sustainer systems (the original post) I'd say the
critical factor is start reliability; sitting in a field with an engine
that did not start must rank as bl**dy frustrating.

On 8/6/19 3:14 PM, Dave Walsh wrote:


For FES/Jet sustainer systems (the original post) I'd say the
critical factor is start reliability; sitting in a field with an engine
that did not start must rank as bl**dy frustrating.


Not nearly as bad as ending up crashing into an attic and making
international news. Still haven't seen an NTSB prelim for the guy from
Connecticut.

Tried to start his electric low over a high-density urban area, got
nothing but grinding sounds. Too low even to fire the ballistic chute.

Very poor flying technique, and I'm sure we'll see lots more of it as
FES becomes more prevalent. The OP's obsession with startup time is a
good indication of that.

On Tuesday, August 6, 2019 at 2:15:06 PM UTC-7, Dave Walsh wrote:
Another thing to remember about possible "new" battery
technology is whether the glider manufacturers will have any
financial interest in updating their current systems. New &
better batteries may well appear but you can bet the glider
manufacturers will be fitting them in their latest creations. So
for anyone wanting to fly electric in the near future, or now,
your are back with Li-Ion etc.
Despite their many drawbacks it seems some of these (old) Li-
Ion cells (e.g. the SAFT cells used by Lange) will last ~20
years.
While the cost of an electric launch looks economic compared
to a tug the real costs are much higher......I seriously doubt
that overall the costs are lower; you pay for autonomy!
For FES/Jet sustainer systems (the original post) I'd say the
critical factor is start reliability; sitting in a field with an engine
that did not start must rank as bl**dy frustrating.

I have never heard a fellow MG owner say that they bought the thing to save money on anything, let alone tows. That said, the more you can fly, the lower the flying costs, and motors allow you to fly more. Nothing worse than a great soaring day and no tow pilots; been there, done that.

Tom

On Tuesday, August 6, 2019 at 2:28:30 PM UTC-7, kinsell wrote:

Tried to start his electric low over a high-density urban area, got
nothing but grinding sounds. Too low even to fire the ballistic chute.

Better check your facts on that. As I understand it, it was absolutely not a case of FES not starting. Rather, he'd been running the FES motor for some time before it quit, likely because he ran out of juice.

Apparently the gauge said there was 20% capacity remaining. We all know how reliable aircraft fuel capacity gauges are...


But, yeah, beyond that the whole thing reflects very poorly on the pilot's planning and execution.

Startup interval is an important metric because it determines how soon you know which contingencies remain available. If it takes half a minute to deploy the engine and see if it's going to produce power, and you're coming down at 1000 fpm, your options are dwindling about as rapidly as your pulse rate is excalating. When you can flick one switch and twist a knob and know within a couple seconds that you can drive away from the hole you dug, it's a pretty strong motivator.


--Bob K.

OK. You need to re read my post. I said technology is changing, and by the time you need to replace your battery, something better MAY be out there. Just because it isn't being widely disseminated NOW does not mean that it isn't coming. Sure KOKAM cells (South Korea) are LiPo and SAFT (France HQ) use Lion cells, but this is not "State of the Art." They are about a generation behind the LiFePO4 technology, but widely available, tested and pretty reliable.

If you want to see what I consider to be "imaginary" power source technology, just pick up a copy of "Gliding International." John Roake will publish any press release about some new fuel cell, unicorn breath, unobtanium or imaginarium battery that is just about to change everything and make us ready to abolish the IGC.

At 20:30 06 August 2019, 2G wrote:

I have heard of far too many "failure to start" incidents
with jets to consider them a viable self-retrieve option. Just
consider it a bonus if they do start.

FES is far more reliable, assuming the battery fire
incidents are a thing of the past (there have been design
changes to the battery).

It's a bit more complicated than that.

Personally, I think it's a good idea to consider a start of any
engine a bonus, and to have a safe place to land if it
doesn't.

With the jets, if they are set up right they start very well.
Not all are set up right though, it seems. (It took a few
months to get mine set up correctly - it has been very
reliable ever since). Also, I know more FESs that have
ended up in fields than jets because they haven't had much
range after climbing.

With current battery technology the FESs have other
limitations too. My understanding is that full power is less
likely to be available on an even partially depleted battery.
So you can't perhaps do what you can do in a jet - climb
from low to a sensible height, then turn it off, and if
necessary do it all again a bit later. And again.

What was unexpected to me is that the FES owners I know
are using a higher decision height than I am with a jet. It
is the case that the jet takes ~40 seconds to get to full
power, but you know you have a start after 20 and having
the engine out adds little drag and workload. So in practice
you can start it at low key and go on with flying the rest of
a circuit - which puts my personal lowest start decision
height at about 500 ft AGL. (I've done it lower, but on
reflection think I was reducing my margins too much and
won't do it again). The FES owners seem to be using a lot
more than this due to lack of climb performance.

It's one of those interesting cases where there are several
different technologies to solve a problem - all have pros and
cons, but there's no clear winner. If you could double the
capacity of the batteries, then I think FES would win - but
as has been pointed out elsewhere, battery technology
moves slowly. So at the moment, it's a question of which
factors are important to you.

Paul

On Tue, 06 Aug 2019 18:38:45 -0700, markmocho53 wrote:

If you want to see what I consider to be "imaginary" power source
technology, just pick up a copy of "Gliding International." John Roake
will publish any press release about some new fuel cell, unicorn breath,
unobtanium or imaginarium battery that is just about to change
everything and make us ready to abolish the IGC.

I know exactly what you mean.

A year or three ago "New Scientist" would give 1/4 - 1/2 page to any test-
tube scale, proof-of-concept experiment for a new battery technology that
was going to change the world. Without exception these were never
mentioned again.

Thankfully, they've stopped doing that, and for good reason: the
theoretical capacity of say, Lithium-based batteries, was determined
decades ago and once cells were designed with capacities that were
reasonably close to the theoretical maximum, subsequent development has
been concerned with maximising charge/discharge rates, battery life,
operating safety, cost and weight. In short: we already know what energy
storage capacity is achievable with any practical cell chemistry and
further research isn't going to produce new, currently unknown super
capacity batteries.


--
Martin | martin at
Gregorie | gregorie dot org

On 8/6/19 4:33 PM, Bob Kuykendall wrote:
On Tuesday, August 6, 2019 at 2:28:30 PM UTC-7, kinsell wrote:

Tried to start his electric low over a high-density urban area, got
nothing but grinding sounds. Too low even to fire the ballistic chute.

Better check your facts on that. As I understand it, it was absolutely not a case of FES not starting. Rather, he'd been running the FES motor for some time before it quit, likely because he ran out of juice.

From the original discussion on this, the pilot who had been flying
with him that day said he had run his motor previously, but tried to
restart with the computer showing 18 minutes left. He got nothing but
grinding sounds. So maybe "as you understand it" isn't correct.




Apparently the gauge said there was 20% capacity remaining. We all know how reliable aircraft fuel capacity gauges are...


Actually, on electric systems they're quite good. You do understand the
difference between electricity and gasoline?




But, yeah, beyond that the whole thing reflects very poorly on the pilot's planning and execution.

Startup interval is an important metric because it determines how soon you know which contingencies remain available. If it takes half a minute to deploy the engine and see if it's going to produce power, and you're coming down at 1000 fpm, your options are dwindling about as rapidly as your pulse rate is excalating. When you can flick one switch and twist a knob and know within a couple seconds that you can drive away from the hole you dug, it's a pretty strong motivator.


--Bob K.


Are you serious about this? You're going down at 1000 fpm and you
really think an FES is going to save you? Wow.