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?