fes ot jet (pros and cons)

El lunes, 5 de agosto de 2019, 19:10:09 (UTC-3), Steve Koerner escribió:
I'm sure there's a lot more pros and cons...

Another consideration would be fueling and defueling a jet. That's surely a bigger hassle than recharging an FES.

Also, one would need to examine cost and frequency of inspection, maintenance and overhaul requirements. I'm pretty sure the FES will win in that department as well even though the FES battery will be expensive to replace when that becomes necessary.

With an electric system, one would expect to experience gradual battery degradation. That's certainly a disadvantage compared to the jet which would be expected to sustain its initial performance over the years.

All-in-all, boom electric with self launch potency seems like the best idea to me. I hope that becomes a widely available option.

Batteries are expensive? Yes.
But you have to think about the retrieves cost and "time landed out" cost. Also the possibility to train a lot.
If you can self launch also, you will amortize the cost of the pack and maybe of the whole system.
Taking good care of the battery pack would extend the calendar life more than 10 years to the 80% of capacity.

Safety is a concern, of course. You will see a lot of news about electric vehicles catching fire, normal vehicles also catches fire but there no interest in that kind of news. In the past 100 years we get used to ride with a backpack full of explosive liquid and the inherent danger. Luckily we will do the same with batteries.

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

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

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 Wednesday, August 7, 2019 at 5:15:05 AM UTC-4, Paul Ruskin wrote:
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

My sense, from talking to a number of FES users, is that The major benefit is search for lift, not just climb out at high power for the save. This uses very low power to search around for the thermal that makes the save and conserves battery. Doing at a bit greater height adds margin but also makes the lift found more usable.
Re battery technology. It will remain an evolution, likely not revolution. High volume batteries have a very few common packages. Example- the 18650 cell that is used in everything from lap tops to Teslas. A new battery needs to fit into the user product architecture, as well as the established production system, to get a viable user base. New cells are coming now that add about 10% more capacity while still handling high current loads.
FWIW
UH

At 12:46 07 August 2019, wrote:

My sense, from talking to a number of FES users, is that The major
benefit is search for lift, not just climb out at high power for the save.


Yes, that's probably fair. But the result is a higher decision height than

with a jet. You probably don't want to be wandering around looking
for lift at 500ft.

And there are times when you're trying to get home under a dead sky
- there isn't lift. At that point, the FES has quite a lot less range than

the jet if you have to climb too.

One of the reasons I chose a jet in the first place was the low decision
height, having had a couple of 500 ft saves.

At the time, the FES wasn't available. But given the same choice
again, I think I'd take my jet over a FES.

Paul

Nor in my Shark FES



18:42 06 August 2019, 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