its not black and white. but grey is not a favourite color of some thinking 
styles.

all design is an art of compromise and tradeoff.

the upside of simplicity, reliability and ease and of use and speed of 
deployment and eliminating risk of paddock damage, vs small total flight (all 
phases) L/D differentials is an acceptable tradeoff to many.



 

> On 22 Sep 2016, at 8:04 AM, Future Aviation Pty. Ltd. 
> <ec...@internode.on.net> 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 <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/ 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
>>> www.borgeltinstruments.com
>>> tel:   07 4635 5784     overseas: int+61-7-4635 5784
>>> mob: 042835 5784                 :  int+61-42835 5784
>>> P O Box 4607, Toowoomba East, QLD 4350, Australia 
>>> _______________________________________________
>>> Aus-soaring mailing list
>>> Aus-soaring@lists.base64.com.au
>>> http://lists.base64.com.au/listinfo/aus-soaring
>> Borgelt Instruments - design & manufacture of quality soaring 
>> instrumentation since 1978
>> www.borgeltinstruments.com
>> tel:   07 4635 5784     overseas: int+61-7-4635 5784
>> mob: 042835 5784                 :  int+61-42835 5784
>> P O Box 4607, Toowoomba East, QLD 4350, Australia
>> 
>> _______________________________________________
>> Aus-soaring mailing list
>> Aus-soaring@lists.base64.com.au
>> http://lists.base64.com.au/listinfo/aus-soaring
> 
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