fes ot jet (pros and cons)

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.

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

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

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.

Richard,

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

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

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.

Originally Posted by

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

Jet - we have heard opinions on reliability.

How many cases of Fes not performing?

Any experiences, anyone?

S