fes ot jet (pros and cons)

[[email protected]]

Any one with practical experience?
How do they compare?

SÅ‚awek

[Steve Koerner]

The beauty of the jet is good weight efficiency; at least for 100Km sort of range. Problems with the jet are slow startup; loudness and high RPM precision that necessitates a high degree of engineering perfection and production perfection to preclude start failure concerns.

The beauty of FES is fast startup and mechanical simplicity that should make it a very reliable alternative. The downside to FES is that batteries are expensive and heavy so range becomes a more difficult proposition. The other downside to FES is that drag in the folded prop position reduces glide performance.

A boom mounted electric is another alternative. Though a few seconds slower to get started compared to the FES and more complex in mechanization, the boom system eliminates stowed drag. A boom mounted electric also opens the possibility of self launch capability since the prop is not subject to nose over destruction nor FOD damage as would be the case for FES in self launch.

Both electrics and jets have safety concerns related to inflight fire that must be overcome with careful engineering and operational care by the user. Low production volumes make the safety issue harder than it would be if the engineering and testing efforts might be amortized over more units.

[Steve Koerner]

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.

[[email protected]]

Steve brings up a good point on the replacement cost of batteries, but one thing that needs to be considered is the rapid advance in battery technology. I am old enough to remember "D" cells with a carbon rod through the middle. Compared to Alkaline cells thirty years later, or NiCads, or Lithium cells, or the LiFePO4 units, the increase in performance is quite impressive. However, as with almost all new technologies, some hazards will always exist. Modern batteries are energy storage devices, and the amount of energy that can be released through misuse or damage can definitely rearrange your priorities. ("Run Away!")

When I was racing cars, a simple aluminum fuel tank was deemed sufficient. And then fuel cells with puncture resistant internal bladders became available. The were mandated (over protest, naturally), but I don't know of any drivers that would prefer to go back to the "BBQ Days."

It is conceivable that, by the time your batteries need replacement a newer, safer and more efficient solution may be available. Personally, I am holding out for the "Mr. Fusion" reactor seen in the "Back to the Future" movie..

[Emir Sherbi]

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.

[JS[_5_]]

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

[krasw]

On Tuesday, August 6, 2019 at 4:22:16 AM UTC+3, wrote:
> Steve brings up a good point on the replacement cost of batteries, but one thing that needs to be considered is the rapid advance in battery technology.

FES has used same Kokam cell for 10 years. Lange has used same SAFT cells for 20 years. There has been absolutely zero advance in electric glider battery technology. Just a reminder.

[[email protected]]

> FES has used same Kokam cell for 10 years. Lange has used same SAFT cells for 20 years. There has been absolutely zero advance in electric glider battery technology. Just a reminder.

Just because they are still using 10 and 20 year old cells doesn't mean the technology hasn't improved. It just means they aren't using it.

[Jonathan St. Cloud]

On Monday, August 5, 2019 at 3:10:09 PM UTC-7, Steve Koerner wrote:
> 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.

How long to a hot section with the jet and what does that cost?

[[email protected]]

On Tuesday, August 6, 2019 at 7:10:26 AM UTC-5, wrote:
> > FES has used same Kokam cell for 10 years. Lange has used same SAFT cells for 20 years. There has been absolutely zero advance in electric glider battery technology. Just a reminder.
>
> Just because they are still using 10 and 20 year old cells doesn't mean the technology hasn't improved. It just means they aren't using it.

Mark, it's an often repeated myth that battery technology has improved. In reality, all the e-vehicles from bikes to light trucks and FES or Pipistrel still use LiPo or LiFe chemistry, so do the solar storage systems. Yes, there are new chemistries that compete for future applications but none has even shown up in cutting edge systems such e-remote controlled planes - and those guys don't mind the occasional fiery crash. Please show me one commercially USED battery type that is substantially beyond the current 200 WH/kg..

[Dan Marotta]

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

[2G]

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

[Dave Walsh[_2_]]

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.

[kinsell]

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.

[2G]

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

[Bob Kuykendall]

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.

[[email protected]]

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.

[Paul Ruskin[_2_]]

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

[Martin Gregorie[_6_]]

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

[kinsell]

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.

[[email protected]]

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

[Paul Ruskin[_2_]]

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

[[email protected]]

Jet is lighter than FES. And a jet is cool in its own way.

[Bob Kuykendall]

On Wednesday, August 7, 2019 at 4:47:45 AM UTC-7, kinsell wrote:

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

With an old-school motorglider like a DG400, with the motor deployed and windmilling but not running, yes, you're going down at about 1000 FPM.

--Bob K.

[David Bingham]

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
>

[Dan Daly[_2_]]

On Wednesday, August 7, 2019 at 12:08:36 PM UTC-4, wrote:
> Jet is lighter than FES. And a jet is cool in its own way.

What is your fuel flow down low? I saw a video with 90 l/hr at max power... https://www.youtube.com/watch?v=B-EycC6OdIo . I think if I had to choose right now it would be FES.

[[email protected]]

On Wednesday, August 7, 2019 at 3:56:07 PM UTC-4, Dan Daly wrote:
> On Wednesday, August 7, 2019 at 12:08:36 PM UTC-4, wrote:
> > Jet is lighter than FES. And a jet is cool in its own way.
>
> What is your fuel flow down low? I saw a video with 90 l/hr at max power... https://www.youtube.com/watch?v=B-EycC6OdIo . I think if I had to choose right now it would be FES.

I don't have one. This stuff is way out of my league. Was just spitballing pro jet rationales. Both solutions are very nice.

[Dave Nadler]

On Wednesday, August 7, 2019 at 7:47:45 AM UTC-4, kinsell wrote:
> On 8/6/19 4:33 PM, Bob Kuykendall wrote:
> > 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.

That's a rather dangerous misconception.
With these cells, the actual amount of energy stored is not easy to estimate.
Quite unlike older cell technology where its easily estimated based on
cell voltage and monitoring of cell performance.
Now one has to know the exact cycle history...

> You do understand the difference between electricity and gasoline?

A bit ;-)

In the CT accident, my understanding is the pilot was showing
a sizeable percentage energy remaining when the motor quit.

My Antares drastically under-estimated remaining power with
the motor running, then the estimate came back to reality
sometime after shutdown. Better that than the alternative!
And of course as the battery discharges, the max power available
decreases. Not important in Antares but critical in FES which
has little excess power to start.

With any motor-glider, its foolhardy to ever get in a situation
where you don't have a safe landing option as PLAN A.
That includes during:
- take-off (no short fields departing over woods)
- in-air start (extra time, altitude, and field length needed vs. pure glider)
- in-air cruise (never where complete failure puts you in the trees)

When the motor fails, its easy to execute PLAN A.
Plan B is when the motor keeps running, cause for happiness if not surprise...

FES failures have included spontaneous shutdown due to electronics failure.
No electric system is even close to 100% reliable.
Of course you don't need to ask me how I know that...

Be safe out there,
Best Regards, Dave

[AS]

On Tuesday, August 6, 2019 at 9:38:47 PM UTC-4, wrote:
> 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.

To your point:
https://www.aopa.org/news-and-media/all-news/2019/august/06/bye-seeking-lithium-sulfur-power
This was posted in an AOPA newsletter recently.

Uli
'AS'

[Dave Nadler]

On Thursday, August 8, 2019 at 11:36:06 AM UTC-4, AS wrote:
> On Tuesday, August 6, 2019 at 9:38:47 PM UTC-4, 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.
>
> To your point:
> https://www.aopa.org/news-and-media/all-news/2019/august/06/bye-seeking-lithium-sulfur-power
> This was posted in an AOPA newsletter recently.

Very nice. Note only good for 60-100 cycles ;-)
https://45uevg34gwlltnbsf2plyua1-wpengine.netdna-ssl.com/wp-content/uploads/2019/07/OXIS-Li-S-Ultra-Light-Cell-spec-sheet-v4.2.pdf

[Tony[_5_]]

I hope you fly over very friendly terrain.

I have flown quite a bit (Nationals and two Worlds) in Silent 2 Electro with many self launches and many self-retrieves. Twice I have had to land at an intervening due to dwindling power. Both times I was then aero towed the rest of the way.

I was lucky enough this spring to do some flying in a JS-3 w/jet. I ran the jet twice. Once for practice over the home airport, another time to keep myself from landing at a grass runway in Oklahoma.

I did not find fueling/defueling the jet to be difficult. The JS-3 has a built in pump. You connect the line, select fuel or defuel, and turn on the pump. I understand the earlier JS-1's had a separate pump you had to carry around so maybe that setup is a little more kludgy.

In the JS-3's Jet Manual Supplement (111 pages) it says the certified operating temperature range is -15 to +40C. However only the -15C is listed on the limitations placard. Airspeed must between 54 and 65 knots when starting.. As has been discussed there have been several known failures to start. I think most all of these have ended with the glider in a field.

Loading/unloading FES batteries is also not too tricky.

One thing I'm not sure i've seen mentioned is that the FES with the Electro or Mini LAK will self launch.

I would choose FES if I was buying, which I am not. I will happily fly either and keep a landable field or two in range at all times.

[Sean Franke]

On Monday, August 5, 2019 at 11:13:30 AM UTC-6, Steve Koerner wrote:
> The beauty of the jet is good weight efficiency; at least for 100Km sort of range. Problems with the jet are slow startup; loudness and high RPM precision that necessitates a high degree of engineering perfection and production perfection to preclude start failure concerns.
>
> The beauty of FES is fast startup and mechanical simplicity that should make it a very reliable alternative. The downside to FES is that batteries are expensive and heavy so range becomes a more difficult proposition. The other downside to FES is that drag in the folded prop position reduces glide performance.
>
> A boom mounted electric is another alternative. Though a few seconds slower to get started compared to the FES and more complex in mechanization, the boom system eliminates stowed drag. A boom mounted electric also opens the possibility of self launch capability since the prop is not subject to nose over destruction nor FOD damage as would be the case for FES in self launch.
>
> Both electrics and jets have safety concerns related to inflight fire that must be overcome with careful engineering and operational care by the user. Low production volumes make the safety issue harder than it would be if the engineering and testing efforts might be amortized over more units.

Steve, jet loudness is music to some ears :) :) :) Start failure concerns are more specific to certain manufacturers.

Sean Franke

[[email protected]]

George Bye is a major promoter of bull****.

[Richard DalCanto]

On Thursday, August 8, 2019 at 1:55:56 PM UTC-6, Tony wrote:
As has been discussed there have been several known failures to start. I think most all of these have ended with the glider in a field.


Tony, did those involve JS3s? I ask because there have been improvements in the turbine and fuel delivery system for the JS3 that are supposed to improve reliability over the JS1.

[Tony[_5_]]

Richard,

The failures to start that I'm familiar with are all JS-1's

[JS[_5_]]

On Thursday, August 8, 2019 at 7:28:30 PM UTC-7, Tony wrote:
> Richard,
>
> The failures to start that I'm familiar with are all JS-1's

It was discovered that the M+D jets were being delivered within tolerances, but reliability could be improved by using more finely gratuated feeler guages.
Essentially: The tolerances were too wide. Keep the alignment as close to the specification as possible to achieve a more reliable start.
Jim

[[email protected]]

The manufacturing tolerances issue in M+D jets was what was related to surging after the start in South African conditions and before they reached the certification stage IIRC. My early pre- certification jet didn't have that problem. Over 135 starts during my time of ownership (mostly ground and air tests in both Scotland and South Africa) what I did find was that it didn't start reliably in cold UK conditions with diesel fuel but was fine with jet A1, whereas in SA it was very unreliable on jet A1. At the suggestion of the factory I started using premium synthetic/petrochemical diesel fuel (Shell V-Power Nitro) and with that it started 100% in both cold UK and hot/high SA. That stuff contains no biofuel btw.

The other thing I learned myself was to use an additive such as Biobor to prevent microbial overgrowth from clogging the fuel filters. 1 ml added to 10 litres was all that was required.

[RickH]

The manufacturing tolerances issue in M+D jets was what was related to surging after the start in South African conditions and before they reached the certification stage IIRC. My early pre- certification jet didn't have that problem. Over 135 starts during my time of ownership (mostly ground and air tests in both Scotland and South Africa) what I did find was that it didn't start reliably in cold UK conditions with diesel fuel but was fine with jet A1, whereas in SA it was very unreliable on jet A1. At the suggestion of the factory I started using premium synthetic/petrochemical diesel fuel (Shell V-Power Nitro) and with that it started 100% in both cold UK and hot/high SA. That stuff contains no biofuel btw.

The other thing I learned myself was to use an additive such as Biobor to prevent microbial overgrowth from clogging the fuel filters. 1 ml added to 10 litres was all that was required.

I have a JS-1C TJ as well. I had no issues with starts but rolling the throttle up through 45% produced a Flame Out. Turned out to be tolerance issues and was addressed by M&D very satisfactorily. They turned it around quickly and I haven’t had an issue since. Engine test in the start cylinder for every flight, and the occasional beat-up upon request, and not a failure since its return. I’ve used Jet-A and Diesel with good results but rely on Diesel due to availability around contest sites and M&D’s recommendation. 60-seconds to full power and the equivalent drag of your gear make it pretty attractive. 250-km saw-tooth range is a bonus as well. But yes, there is an airport, or good field within range on every start.

Rick
NR

[[email protected]]

Jet - we have heard opinions on reliability.

How many cases of Fes not performing?

Any experiences, anyone?

S