Bernard,

Precisely.

As for the rest, the choice isn't between the FES and a petrol engine motor. It is between the FES and the GP Gliders system or one like it. FES like operational simplicity and no performance penalty. For FES you need to cut off the nose, mount the engine, cut a hole in the turtle deck area, mount the 31 Kg of batteries on some reinforced area to take the loads. For the GP system cut a hole for the engine/prop assembly (could be in a bathtub like assembly) and mount the batteries in the wings or maybe behind the pilot under the wing and above/alongside the wheel box. If the wing root rib of the glider is designed to allow access to the volume in front of the spar, putting the batteries there is likely viable and better structurally. If better battery tech comes along the only thing you need worry about is form factor and you might need a new battery charger. I doubt you'll be faced with much improvement in electric motors and control electronics, nor in propellers. The motors are already 95% or so efficient.

The real problem with keeping motor gliders going is certification. There aren't many gliders anyway and adding a certification process that costs a lot of money and an unknown amount of time (which is also money) means developing and marketing a substitute system to support older motorgliders and selling a few a year as the older systems gradually die, isn't generally a viable business model although Walter Binder is doing this for the Nimbus 3DM etc to substitute a Solo engine for the original rotax. In Walter's case he already makes the power package which is certified. Treating gliders like certified aircraft which may be used to carry paying passengers always was a silly idea. No problem with the documents like CS22, CAR3, FAR 23 etc. Gives you something to aim for in the structural design but you should be able to build and test and then sell as long as you advertise the test results.

I am always amused at the ability of the soaring movement to glom onto bad ideas.

The history of total energy is another one.

First there was the old Irving TE probe. The venturi with the penny washer. This was around 1952. Worked great. Then in the late 1950's someone decided that the drag of the thing was too high (a small fraction of one % of total drag on the gliders of the day with the cruise speeds of the day) and the same effect could be achieved by the diaphragm compensator which worked from pitot and static. Sort of. At one altitude (it used IAS to compensate kinetic energy which is in TAS). So for the next ten years ago the literature of the 1960s is filled with "how to make your TE system work" articles along with "I didn't win/break a record etc because my TE system never worked properly". Finally around 1969-1970 Dr Althaus went back to the venturi type probe by essentially removing the penny washer. This made the thing more sensitive to yaw and pitch but TE started working again and it was regarded as an acceptable compromise between drag and TE performance.

Mike





At 08:04 AM 9/22/2016, you wrote:
Hi Mike

Please allow me to add to your concluding sentence.

While in Germany I spoke to an employee of a manufacturer who offers FES variants of his gliders. He said that customers complain about decals and rego letters not sanded absolutely flash but seriously considering an FES drive unit. Then he shook his head, turned around and walked away.

How any performance chasing glider pilot can willingly accept a turbulent airflow over the entire length of the fuselage will ever remain a mystery to me. Obviously some buyers are convinced by
such comments as "the performance degradation is not noticeable”.

It can be a truely strange world sometimes!

Kind regards to all

Bernard




On 22 Sep 2016, at 6:44 AM, Mike Borgelt <<mailto:mborg...@borgeltinstruments.com>mborg...@borgeltinstruments.com> wrote:

I guess you missed the bit below the video " Prototypeneinbau – die Rumpfspalten verschwinden in der Serie natürlich"

Means "single prototype, the gaps will naturally disappear in series production."

Google translate would have told you that too but you have to know you need to use it, I guess.

In any case on the contracting part of the fuselage like that the flow is turbulent and the boundary layer is fairly thick.

The boundary layer is defined as the distance from the surface where the flow attains 99% of the free stream velocity. The velocity profile isn't linear but about 40% of the thickness from the surface the flow will be at around 2/3rds the free stream velocity n turbulent flow.

A reference I found said the boundary layer grows about 16mm per meter from the leading edge assuming all turbulent flow so aft of around half way along the canopy the flow is turbulent and a couple of meters aft of that will be about 32 mm thick. Any small

discontinuities there are buried deep in the boundary layer and don't see anything like free stream velocity. Drag depends on velocity squared so very little drag.

Now the FES is on the nose and there might be a little laminar flow on the spinner in front of the prop so the boundary layer is very thin there when it encounters the folded prop which will cause it to turbulate and the folded prop will see most of the free stream velocity.

FES will certainly cause loss of significant amounts of the laminar flow that is otherwise present on the front of the fuselage.

Mike









At 10:53 PM 9/21/2016, you wrote:
Content-Type: multipart/alternative;
        boundary="----=_NextPart_000_011B_01D2145A.FCB61810"
Content-Language: en-au

You’re worried about the increased drag from a FES?
Looking at that video, I’d be more concerned about the increased drag from that appalling panel fit, never mind the huge gaps and the numerous screw heads. Look at the rear, where the pylon extends: that panel is sticking about 5mm above the fuse.
It looks like a dodgy home-built botch job.

Btw why not make the thing extend towards the fuse? I can’t recall if the motor was too wide, and life is too short to wait for it to load again…


From: Aus-soaring [ mailto:aus-soaring-boun...@lists.base64.com.au] On Behalf Of Mike Borgelt
Sent: Tuesday, 20 September 2016 7:26 PM
To: Discussion of issues relating to Soaring in Australia.
Subject: Re: [Aus-soaring] electric self launch

At 07:04 PM 9/20/2016, you wrote:

Any  good links?
I found a schematic diagram which indicates that the motor has a pusher folding prop. Not sure how it retracts and fits in the fuselage with the blades sticking up?


Here you go: <http://www.gpgliders.info/technik/>http://www.gpgliders.info/technik/ Scroll down to the videos. They took quite a while to load here. The link seems slow.
Sheer bloody genius I think.

Mike


Borgelt Instruments - design & manufacture of quality soaring instrumentation since 1978
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www.borgeltinstruments.com
tel:   07 4635 5784     overseas: int+61-7-4635 5784
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tel:   07 4635 5784     overseas: int+61-7-4635 5784
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