Which sustainer system would you chose for your sailplane?

About jet sustainers, it is not true to say that they are not cerified for aircraft use, the M+D (JS1) and PSR (Ventus) jets are EASA certified. As regards the need to be spun to high rpm to start - what is the issue there? Given that the turbines run at 75,000 to 100,000 rpm they have got to get up there somehow. The M+D jet is only spooled up to 8,000 rpm by the electric motor before the fuel system takes over (in two stages). 8000 rpm is nothing remarkable for an electric motor.

Lastly, we can't meaningfully judge the reliability of jets based on the experiences of pre-certification installations during the development stage - which includes all the JS1 installations prior to November 2015. My jet was installed under South African experimental type certificate. I think that the turbine and firmware are at or very close to the certification spec and so far I have had no failed starts out of 44 attempts.

In general I think that failures of all types of sustainer generally arise from ancillary components ( e.g. fuel pump, spark plugs, carburettor diaphragm etc) and electrical issues (e.g. relays, connections etc) and electric glider motors certainly have potential reliabilty vulnerabilities.

In general I think that failures of all types of sustainer generally arise from ancillary components ( e.g. fuel pump, spark plugs, carburettor diaphragm etc) and electrical issues (e.g. relays, connections etc) and electric glider motors certainly have potential reliabilty vulnerabilities.

I think the reliability of a FES would be more reliable than conventional motors due to less parts. However, over the long term a concern I would have about FES would be water/dirt/debrie in the motor and electrical components, assuming that not all are shielded and even then the deterioration over time. I would think that all gliders and motors that are 20-30 yrs old have had wiring, rubber tubing, and other non corrosive components replaced. A solid aluminum/metal engine can be rebuilt and wiring/tubbing replaced. But what about FES? I know the batteries are not an issue due to life expectancy and replacement. But what is the life expectancy of FES motor? How about the build up of dirt and debris from aero tow? Can the FES be air blown off or washed with water?

I really like and think the FES is great and the future but long term maintenance is key to resale ability and market.

On Thursday, 25 February 2016 13:38:56 UTC+2, Casey wrote:
I think the reliability of a FES would be more reliable than conventional motors due to less parts. However, over the long term a concern I would have about FES would be water/dirt/debrie in the motor and electrical components, assuming that not all are shielded and even then the deterioration over time.

It all depends on the design and materials but people are happy to drive EV's (like one's from Tesla) through mud, water and other harsh environments for years on end without trouble.
Or gliders see a bit of dust for a few seconds once or twice per weekend so I'd hardly worry about it.
I've seen brushless motors run for years in extremely harsh environments without any maintenance and servicing. If the design is right, a brushless electric motor should outlast a combustion engine many times over even with zero maintenance.

On Thursday, 25 February 2016 13:38:56 UTC+2, Casey wrote:
I think the reliability of a FES would be more reliable than conventional motors due to less parts. However, over the long term a concern I would have about FES would be water/dirt/debrie in the motor and electrical components, assuming that not all are shielded and even then the deterioration over time.

It all depends on the design and materials but people are happy to drive EV's (like one's from Tesla) through mud, water and other harsh environments for years on end without trouble.
Our gliders see a bit of dust for a few seconds once or twice per weekend so I'd hardly worry about it.
I've seen brushless motors run for years in extremely harsh environments without any maintenance and servicing. If the design is right, a brushless electric motor should outlast a combustion engine many times over even with zero maintenance.

On Thursday, February 25, 2016 at 2:26:37 AM UTC-8, wrote:
About jet sustainers, it is not true to say that they are not cerified for aircraft use, the M+D (JS1) and PSR (Ventus) jets are EASA certified. As regards the need to be spun to high rpm to start - what is the issue there? Given that the turbines run at 75,000 to 100,000 rpm they have got to get up there somehow. The M+D jet is only spooled up to 8,000 rpm by the electric motor before the fuel system takes over (in two stages). 8000 rpm is nothing remarkable for an electric motor.

Lastly, we can't meaningfully judge the reliability of jets based on the experiences of pre-certification installations during the development stage - which includes all the JS1 installations prior to November 2015. My jet was installed under South African experimental type certificate. I think that the turbine and firmware are at or very close to the certification spec and so far I have had no failed starts out of 44 attempts.

In general I think that failures of all types of sustainer generally arise from ancillary components ( e.g. fuel pump, spark plugs, carburettor diaphragm etc) and electrical issues (e.g. relays, connections etc) and electric glider motors certainly have potential reliabilty vulnerabilities.

Ok, so what you are saying is that jets installed in the last 3 months are reliable. My experience has been that engine installation problems may take years - not months - to reveal themselves. This might be ok if you exercise due caution, primarily having a landable field within easy reach. Jets do have the advantage that they are low vibration, an issue with a reciprocating piston engine (I really like my Wankel for this reason). On the down side, they consume a lot of fuel.

Tom

I am *not* saying that jets installed in the last 3 months are reliable.

I am saying that to judge the reliability of the jets in gliders it is only meaningful consider aircraft with the fully developed specification - just as we would do for any other product.

On Thursday, February 25, 2016 at 1:15:33 AM UTC-5, 2G wrote:

I personally won't have a sustainer. I fly a lot in Utah and Nevada, and the sustainer probably won't get me over the mountain ranges I have to cross, or even get me to a landable field that may be 50+ miles away.

But what about the use case where you plan to get home as a pure glider and use the FES to get you the last five miles to home or five miles to a decent landout field when you're a bit too optimistic? What about using FES for a few minutes when you have a PT3 or hit strong sink on final? What about using FES for a few minutes to find the next thermal before you descend below the 'lift band'?

From far off Vermont, there seem to be a lot of uses for FES in the SW that do not involve climbing above mountain ranges or sustaining flight at constant altitude for 50 miles.

On the other hand, I'm under the impression comparing SW and back east soaring, the SW has higher AGL cloudbase and stronger lift, so landouts are easier to avoid, so FES is less of a value proposition. Back east with lower AGL cloudbases and weaker lift, FES has more appeal, especially in areas with poorer landout options.


Questions about FES and Density Altitude:

I understand that High Density Altitude would reduce FES climb rate and that would reduce the value of FES out west (and electric self-launch would be impractical).

But how does Density Altitude affect FES range assuming level sustained flight? Sure, the prop would get less bite on thinner air and therefore the prop rpm would need to be higher to produce the same thrust, but battery charge rundown is proportional to thrust produced over time. I'm thinking that if the motor has the rpm for climbing at low density altitude, it would have the rpm for sustaining at high density altitude. Is the efficiency of FES lower at higher RPM?

I am no expert - but from the info at the convention:

Today there is no FESSL over 13.5m - it is a weight issue. the FES sustainer comes in 15m & 18m . There is one new Polish 13.5 with Electric motor on a boom, also self launching.

the 13.5m seem to have gained glide ratio - going from 37:1 to mid 40's:1 (if you believe the brochure.

I am also inclined to believe most people will opt to aero-tow with more reserve to get home - but having an option to fly on a weekday when no one is around to tow???? inviting, no.

WH1

On Thursday, February 25, 2016 at 4:09:07 PM UTC-5, wrote:

the 13.5m seem to have gained glide ratio - going from 37:1 to mid 40's:1

As a recreational pilot with small interest in contests, glide ratio seems much less important with FES. If I'm planning to land with the batteries half discharged, the FES will greatly extend my range for the day (and give me the same range as a higher L/D ship). If I'm flying XC with friends with better L/D ships, I can run the FES between thermals, compensate for my inferior polar, and keep up with the higher L/D ships.

If I ever compete it will be in handicapped club class, so 37:1 seems adequate.