fes ot jet (pros and cons)

Any one with practical experience?
How do they compare?

SÅ‚awek

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.

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.

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..

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

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.

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.

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?

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..