FES&electric system batteries

On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?

Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

I think 20 years of good battery life might be bit optimistic. Antares has very expensive milspec batteries that should have long life, apparently that can be 10 years, but no one knows if that is 20 years. Other systems use cheaper (relatively) off-the-self batteries that might not last so well. Realistically, I would probably budget battery change every 5-10 years.

From the Lange website:
The life expectancy of the battery is decisively influenced by two factor the number of cycles and the natural aging process.

The battery capacity decreases with increasing number of charging and discharging processes. The life expectancy of the battery is based on the latest findings with more than 4500 SAE cycles. One SAE cycle stands for full charging of the battery and a discharge to 20% of the capacity. Partial discharge corresponds only to an equivalent portion of a full cycle. After 4500 of these SAE cycles, the capacity of the battery has decreased to 80% of the initial state. For the pilot, this means that the battery allows a minimum of 10,800,000 risers before it is replaced.

In practice, the natural aging of the batteries is more relevant. It is therefore recommended to change the batteries according to the latest findings at an average storage temperature of 20 ° C after approx. 20 years. Even then the battery capacity has decreased to 80% of the initial capacity.

On Thursday, December 8, 2016 at 7:26:05 AM UTC+1, Bruce Hoult wrote:
On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?

Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

To be certified as SLG according to JAR 22 do you need to meet specific performance in roll-out distans and climb. The 13,5m FES is only SLG in dry condition, if you load it with water is it only SSG. I guess that the LAK17 is to heavy to meet the performance requirements to be a SLG.

On Thursday, December 8, 2016 at 10:30:26 AM UTC+3, Per Carlin wrote:
On Thursday, December 8, 2016 at 7:26:05 AM UTC+1, Bruce Hoult wrote:
On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?

Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

To be certified as SLG according to JAR 22 do you need to meet specific performance in roll-out distans and climb. The 13,5m FES is only SLG in dry condition, if you load it with water is it only SSG. I guess that the LAK17 is to heavy to meet the performance requirements to be a SLG.

Yes I know. I wasn't talking about certification :-)

Of course there are lots of places that you'd be foolish to try it, but given an airfield large enough that you can circle within the boundary with less than 30 degrees of bank, the difference between a car tow with an aerotow rope and an aerotow to a release on downwind at 500 ft (which lots of people do) is probably ... about 300 ft by the time the motor starts.

Well, since you mention that, I did once launch in a friend's ASW-24E
out of Kelly Air Park (7,050' MSL, 3,500' paved runway) on July 6,
2000. It took two attempts to get airborne and then a little nap of the
earth flying to gain speed. Not for the faint of heart... The '24 is
labeled an "E" but I think "T" would be more reasonable.

On 12/7/2016 11:26 PM, Bruce Hoult wrote:
On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?
Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

--
Dan, 5J

Battery temperatures rise during use, it is part of what the pilot monitors during the launch. I've never seen or heard of battery temp being the limiting factor on power output. That is always motor temp in my experience.

What I've heard from Leo B-L is that the oldest highest use FES batteries are still charging to 99%. I'd love to hear more details on this 70% claim.

torstai 8. joulukuuta 2016 16.21.22 UTC+2 Tony kirjoitti:

What I've heard from Leo B-L is that the oldest highest use FES batteries are still charging to 99%. I'd love to hear more details on this 70% claim..

I'm a bit confused here. Are we talking about the voltage they charge to? You measure batter capacity by the amount of amperes you get. Obviously even older battery will have same voltage when charged full, but that does not say anything about capacity. If FES with 100% new battery gives you 60 minutes of level flight time (for example), 70% capacity battery would give you 42 minutes.

Tesla uses 18650 sized cylindrical cells, lots of them. This cell size was originally designed for laptops and was driven by the dimensions of the disk drives used at the time. As computers became smaller, so did the form factor for cells. For computers, 14650 cylindrical entered the picture for a while (as drives became flatter) and now flat pouches and prismatic. This left a large overcapacity with 18650 equipment which in turn drove pricing down.

The volumetric and gravimetric energy content of the Kokam cells used in the FES vs. typical 18650 is higher. In a battery configuration, cylindricals waste space. In a rolling platform, the weight/size disadvantage of the 1850 could be tolerated but not so much with an aerial platform.

Additionally with the small 18650 cells, you need a lot of them to get to a desired energy content for a car or airplane battery. That means more BMU (battery management) again increasing weight, size, complexity, and opportunities for failure.

The battery solution (and PC diagnostics) for the FES system is well thought out given the tradeoffs. I am eager to see the final design that the GP guys are going to employ for their gliders. I certainly hope they make their batteries easily removable for charging and storage outside the glider. The volume, mass, and energy content of the proposed GP battery is on par with the FES battery although the dimensions are more long and skinny too fit in the wings.

Danny Brotto

On Saturday, 25 February 2017 15:22:47 UTC+2, wrote:
Tesla uses 18650 sized cylindrical cells, lots of them. This cell size was originally designed for laptops and was driven by the dimensions of the disk drives used at the time. As computers became smaller, so did the form factor for cells. For computers, 14650 cylindrical entered the picture for a while (as drives became flatter) and now flat pouches and prismatic. This left a large overcapacity with 18650 equipment which in turn drove pricing down.

The volumetric and gravimetric energy content of the Kokam cells used in the FES vs. typical 18650 is higher. In a battery configuration, cylindricals waste space. In a rolling platform, the weight/size disadvantage of the 1850 could be tolerated but not so much with an aerial platform.

Additionally with the small 18650 cells, you need a lot of them to get to a desired energy content for a car or airplane battery. That means more BMU (battery management) again increasing weight, size, complexity, and opportunities for failure.

The battery solution (and PC diagnostics) for the FES system is well thought out given the tradeoffs. I am eager to see the final design that the GP guys are going to employ for their gliders. I certainly hope they make their batteries easily removable for charging and storage outside the glider. The volume, mass, and energy content of the proposed GP battery is on par with the FES battery although the dimensions are more long and skinny too fit in the wings.

Danny Brottoaw

I think glider batterys are not especially critical regarding dimensions. Antares uses large cylindrical cells without problems, as does Schleicher. More importantly, owners would probably be happy replace batteries with, say, one with 80% capacity and 20% of the price of the original.