KR>Hershey Bar wing/ KRSport-Now KR1B

[Dana Overall]

>From: "Mark Langford" 
>The KR1B motorglider may not be such a bad idea after all.  Maybe not for
>Sport Pilot, but registered as a motorglider.



Here is a series of cut and pastes from the following website that addresses 
various gliders and motorgliders.  While it does not address the glide or 
wing loading requirements (if there are any) to be classified as a 
motorglider.  I'm sure it's out there somewhere to be found.

http://vansaircraft.com/public/rv-11int.htm

The term motorGLlDER implies that it is typically of lower performance, thus 
a GLIDER rather than a SAILPLANE. Later in this discussion the performance 
distinction will become more obvious

Sailplanes:  Simple; they just fly through air which is rising as fast or 
faster than their descent rate. If this parcel of rising air is of a size 
and shape that requires no turning (such as slope lift or wave lift), it is 
a simple process of comparing sailplane sink rates to the lift rate of the 
rising air. However, since the vast majority of lift used in soaring is 
thermal lift, sailplane circling performance must also be considered. 
Thermals are rising columns of warm air, and since columns are finite in 
diameter, one must circle in order to stay within them. More often than not, 
the diameters of thermals are so small that bank angles of 30-45° or greater 
are required to remain with their strong lift core areas. A sailplane which 
flies slower can circle tighter and thus remain in the stronger lift core of 
the thermals. In Figure 6 below, I have superimposed the sailplane sink rate 
drawing over a drawing showing relative lift rates within a thermal. From 
this it is easy to see that the low performance (slow) sailplane has a 
smaller turning diameter, and can more easily stay with the stronger lift. 
Often these slower sailplanes can climb as well or better than the higher 
performance ships with lower (level flight) sink rates. On the other extreme 
is the classic motorglider which has both a high sink rate and a high glide 
speed. It is relegated to the outer regions of the thermal where lift is 
less, yet it needs more lift than the other sailplanes charted here.

The result is that, in marginal lift, the classic motorglider cannot soar 
and thus must either land or start its engine and look around for stronger 
lift. On the other hand, the self-launch sailplane soars nearly as well as 
its unpowered counterpart. It has a slightly higher sink rate because of the 
weight of the engine it is carrying around, but its drag is essentially the 
same as its pure sailplane equivalent.
Statistics show that only 20 percent of the active glider/sailplane pilots 
in the US engage in cross-country flying. That means that 80% of them never 
venture farther than gliding distance of their home airport. There is 
nothing inherently wrong with that. Each pilot finds his rewards in 
different places. The pure joy of sustaining motorless flight is reward 
enough. For this majority, a sailplane of limited performance would suffice.
Back in the 1950s, the international soaring community chose a 15-meter 
(49.2 ft.) span as a practical size for competition and sport sailplanes. 
Thus, the majority of single seat sailplanes today are 15-meter ships, and 
they have become the standard of comparison. Recently, we have seen the 
establishment of an 18meter (59 ft) class, largely inhabited by self-launch 
sailplanes. The added span helps carry the weight of the retractable engine 
and still offer very good minimum sink rates.
Thus, let’s think in terms of a minimum 15-meter span as a basis for motor 
glider design concept. The best 15-meter fiberglass sailplanes achieve L/D 
ratios of 45 or slightly higher. The best of the 15 meter aluminum 
sailplanes can attain around 40:1 L/D. By rule of thumb, we might assume 
that the same basic wing used on a motor glider with a fixed tractor engine, 
a drag optimized cowl, and a feathering (or folding) prop, would achieve an 
L/D of 33-35. Sink rates of the better 15 meter ships come in at just under 
2 ft/sec. (120 fpm), so we can hope for as little 2.5 fps (150 fpm) for the 
motor glider equivalent. These are numbers which translate into what should 
be a very acceptable sport sailplane.


Dana Overall
1999 & 2000 National KR Gathering host
Richmond, KY i39
RV-7 slider, Imron black, "Black Magic"
Finish kit
13B Rotary. Hangar flying my Dynon.
http://rvflying.tripod.com/aero1.jpg
http://rvflying.tripod.com/aero3.jpg
http://rvflying.tripod.com/blackrudder.jpg
do not archive

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KR>Hershey Bar wing/ KRSport-Now KR1B

[Rick Human]

To add a little fuel to the fire here's a link to John Monnett's Xenos
Motorglider web page with the FAA and JAR definition and criteria of a
"Motorglider" - be aware that to legally operate a motorglider with a
private pilot's license you need a glider rating with a motorglider
endorsement. So unless you have those two additional pieces in your pocket
you can't build a KR1-B and thumb your nose at the FAA while flying with out
a medical (how every satisfying that might be).

http://www.sonex-ltd.com/motorglider_definition.html

Take it for what it's worth.

Rick Human
Houston, Texas
>

KR>Hershey Bar wing/ KRSport-Now KR1B

[Mark Langford]

Rick Human wrote:

>>(iii) The maximum weight to wing span squared (w/b2) does not exceed 3.0
kg/M2 (0.62 lb./ft.2).>>

Hm.  The KR1B Motorglider numbers that Virge cited of 484 empty weight
and 27' wing span yield .66, which is higher than .62.  I guess if you want
to build a KR1B and call it a legal motorglider, you've got to either make
it weigh less (doubtful!), or extend the wingtips another 6" on each end,
and you'd be at .62.

Sounds interesting...

Mark Langford, Huntsville, AL
N56ML "at"  hiwaay.net
see KR2S project at http://home.hiwaay.net/~langford

KR>Hershey Bar wing/ KRSport-Now KR1B

[Virgil Salisbury]

Wing Loading  8.7/1   Area 91sq ft. NUF SAID, Virg

On Sun, 15 Feb 2004 21:38:16 -0600 "Mark Langford" 
writes:
> Rick Human wrote:
> 
> >>(iii) The maximum weight to wing span squared (w/b2) does not 
> exceed 3.0
> kg/M2 (0.62 lb./ft.2).>>
> 
> Hm.  The KR1B Motorglider numbers that Virge cited of 484 empty 
> weight
> and 27' wing span yield .66, which is higher than .62.  I guess if 
> you want
> to build a KR1B and call it a legal motorglider, you've got to 
> either make
> it weigh less (doubtful!), or extend the wingtips another 6" on each 
> end,
> and you'd be at .62.
> 
> Sounds interesting...
> 
> Mark Langford, Huntsville, AL
> N56ML "at"  hiwaay.net
> see KR2S project at http://home.hiwaay.net/~langford
> 
> 
> 
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> 


Virgil N. Salisbury - AMSOIL
www.lubedealer.com/salisbury
Miami ,Fl