So Why?!

Why?

So this is a very unusual project... and it's probably important to take a step back and answer the most basic questions... Why?  You're spending all this money to make an airplane that's heavier, and won't fly as far?

Why the Silhouette?

For all the reasons I'll get to shorting, I wanted my next big aviation project to be an electric aircraft.  There are a few boxes which have to get checked.  First, it must be experimental certificated (preferably homebuilt) for ease of conversion/regulation.  The second it needed to be very efficient.  Those to criteria really drop the list considerably.  Candidate aircraft are;

• Europa
• Glassstar
• Sonex Xenos
• Pipstrel Virus or Sinus (homebuilt version)
• Whisper Motorglider
• Task Sillhoette

The Task Silhouette is a very unusual aircraft.   It's the only single place motorglider on that list.  That is a very big deal, it's a lot easier to convert a single place than a two.  Very few were ever built, only a very few are still airworthy and flying.   It's performance is good, but not exceptional.  24:1 with the wingtip extensions is good.

The reason so few where built was because they never had a good powerplant.  I think if they had had an electric option for this airframe, it may have faired quite a bit better in build numbers.

Cost

I personally believe that the expense in time and money are some of the biggest factors in keeping light aviation from becoming more attainable.  There are many costs in aviation, but the biggest single cost is fuel.  It's typically 90% of the operating costs and for my RV-4, which I fly 100hrs/yr, it's 60% of the total cost.  Electric aircraft can't fulfill most missions in aviation today, but they can do some and at a massively reduced operating cost.  I'll go into more detail in a moment, but as an example, the Electric Silhouette would cost $1 per flight hour.  Compare that to $15 for the 2-cycle gas-oil version and $31 for my RV-4.   In actuality, I intend to charge it with the off-grid hangar solar panel system I've already installed, so in actuality, it won't cost anything to fly. 

Simplicity

I have a passion for simple, efficient engineering.  I want an aircraft I can walk around, hop in, flip a switch and go.  That brutal simplicity intoxicates me.

Safety

Twin electric motors have exactly two moving parts, relatively low operating temperatures, and nothing trying to be ignited (hopefully).  This setup works very well for the Silhouette airframe.  The Rotax 447 has ver moving parts, but they are under extreme thermal and mechanical stress.  Failures are not uncommon and that's not acceptable.  The lack of suitable engine choices was one significant reason the Task Silhouette never gained three-digit build numbers.  It is a very small aircraft and that is a major factor as well.

Mission

So this is where it gets personal.  I'm building this for MY mission, and honestly, it's pretty simple.  99% of my flying has two profiles.  

Profile 1

I love to jump in a plane near the end of the day and just put the troubles of the day underneath me... To twist Jimmy Buffet; Changes in Altitude changes in Attitude!  These flights are always short, 20-30 minutes max. 

Profile 2

I'm blessed that I have an opportunity most good weather Saturdays and or Sundays to fly 45nm to my glider airport where I can soar, tow, and or instruct all day, then I fly home.  This is a pretty straightforward mission, fly 90nm round trip in a day, with a 4-6hr recharge opportunity in the middle.

I would argue there's a third profile, enabled by the right kind of aircraft which is not too dissimilar from profile 1, but I'll name it.

Bonus Profile 3

Get in the motorglider after work on the best days and find a few late-afternoon thermals or a cloud street and see how far I can get, hone my thermal skills, then motor home.

So those are my missions, and I need to choose my electric system to match all those missions.  I chose this specific mission profile.

2 Minutes at 100% full power, take-off

10 minutes at 66% climb power

90 minutes at 15% "best economy" OR 60 minutes at 25% "good speed cruise"

That mission meets all of those objectives.  I've also found that in electric vehicles (my experience is with cars) error on the side of having too much battery, it can't hurt and it makes everything simpler.