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#21
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fes ot jet (pros and cons)
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 |
#22
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fes ot jet (pros and cons)
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#23
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fes ot jet (pros and cons)
Jet is lighter than FES. And a jet is cool in its own way.
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#24
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fes ot jet (pros and cons)
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. |
#25
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fes ot jet (pros and cons)
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 |
#26
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fes ot jet (pros and cons)
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. |
#27
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fes ot jet (pros and cons)
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. |
#28
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fes ot jet (pros and cons)
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 |
#29
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fes ot jet (pros and cons)
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/...m-sulfur-power This was posted in an AOPA newsletter recently. Uli 'AS' |
#30
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fes ot jet (pros and cons)
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/...m-sulfur-power This was posted in an AOPA newsletter recently. Very nice. Note only good for 60-100 cycles ;-) https://45uevg34gwlltnbsf2plyua1-wpe...sheet-v4.2.pdf |
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