Apr 20, 2019, 12:22 PM
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Discussion

# Penetration

Can someone tell me if "penetration" is a real measurable thing like lift or drag or is it kind of a cover all word for how well a plane is performing on a particular day? I've been Googling all morning and have yet to find an actual definition.
Thanks
Don
 Apr 20, 2019, 12:52 PM Duane, LSF IV Peak lift-to-drag (L/D) is an indication of penetration, but normally that term refers to flying upwind where you usually have to fly faster than peak L/D. So, you'd have to look at the L/D polar to see how steeply it falls off on the high speed side of peak. Rule of thumb for full scale soaring is to fly peak L/D plus half wind speed, so use that to gauge how far to move right on the polar graph. Note that the L/D ratio is equal to no-wind glide slope (height lost per distance traveled).
 Apr 20, 2019, 01:28 PM Registered User As far as I can tell, "penetration" is a sloppy way to talk about speed, though of course it has to be at a reasonable L/D
 Apr 20, 2019, 02:48 PM Registered User In full size terms Best Speed to Fly. All flight modes have a theoretical best speed for achieving minimum sink and or best L/D . These are set by the Aircraft Design, weight, and surface and or seal considerations If the glider has wing camber control the position of the TE will also need to be considered. The next variable is wind. To penetrate or make headway against the wind to cover ground you need to increase speed or add weight. A full size glider pilot seldom flies at minimum sink in a straight line. They are normally nudging slightly forward pressure on the stick to cover more ground. L
 Apr 21, 2019, 07:43 AM Registered User Airfoil and construction technology sure has changed over the 30 years I’ve been flying (and crashing...). I remember when winch survivable wings with monokote covered flat bottom airfoils would fly backwards in the wind. Back then, “Penetration” meant the plane would get back to the field.
Apr 21, 2019, 08:19 AM
May the Wind Always be Good
That is why the Durex V was made and it was also known as the Minnesota Floater …. But took way over a pound of ballast to make it Penetration

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 Apr 21, 2019, 08:21 AM Red Merle ALES VII SJ This is a good read.... http://www.5c1.net/Glider%20Performance%20Airspeeds.htm
Apr 21, 2019, 11:35 AM
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Quote:
 Originally Posted by Curtis Suter This is a good read.... http://www.5c1.net/Glider%20Performance%20Airspeeds.htm
Thanks! This link has been posted to RCG before and it points out a big difference between RC and FS soaring. In FS the goal is to cover as much ground as possible in as short a time as possible for a given set of conditions. Even if the goal is max distance one still needs to fly fast because speed is distance when you consider there are only so many hours of lift in a day. OTOH, RC Soaring mainly involves duration (Although there is growing facet of XC style flying and contests). A big problem with the current format of RC contests is that modern RC gliders can boat around at min sink for the duration of a contest round without much skill involved (Except maybe skill in programing your radio to achieve the highest launch). To keep the scoring interesting the concept of Landing points was created where one crashes into the ground at a pre determined point when the time is up for a particular round. Here again contest landings are interesting (And sometimes amusing) to watch but it doesn't do much for a pilots skill set. Modern RC Thermal Duration Gliders are works of art in both form and function (Except maybe the broomstick fuselages) but they have exceeded the tasking system used at contests. I keep hoping that contest rules will be updated to reflect the current generation of RC gliders.
I know this post goes a bit beyond the scope of penetration but the subject of STF in full scale came up and I felt it would be good to point out how it is used differently.
 Apr 21, 2019, 12:08 PM B for Bruce I'm not so sure that there's that big of a difference between full and model sizes. Well, at least not once we hit a windy day. While that article is geared to full size we still fly like that even if we're not doing XC style flying. We thermal duration folks are faced with the speed to distance curves noted in that article each time we follow a thermal too far downwind and have to get back to the launch/landing point against a firm sort of headwind. And that's where the ability to push the nose down a few degrees and penetrate back upwind comes into play. Of course if it's a calm day with light fluffy thermals and the wind never gets above a jogging pace there's not much to test the new super gliders. And in such cases a well flown floater can easily beat out the modern "glass slippers". But give us a day where the wind is up and the advantage shifts clearly and strongly to the "glass slippers" and a few woody designs that were built to have a good speed range with minimal use of altitude to fly faster. And it's on those days that talk naturally turns to how well our models "penetrate". I'd also suggest that while the value for a given model of the best L/D speed is a good indicator of how the model will fly it's not the whole story. A model flown at the best L/D, if not ballasted might well still be losing ground. So we push in a trifle extra nose down trim to speed up past the best L/D speed in order to make distance over the ground against the wind speed. And that's shown in that article as well for both how best to minimize "damage" to our height by how to fly through sinking air and against headwinds to produce distance over the ground to get the models back to the launch point. So all in all I'd say that the article does have a lot to offer for those of us that regularly fly in blustery conditions. Latest blog entry: Sharpening carving knives for balsa or...
 Apr 21, 2019, 10:26 PM Registered User After a few hikes in the woods, I'm sure you'll find yourself putting in a bit of down elevator when returning from downwind. That's just the way it works. Let's say the wind is 12 mph and your floater flies 12mph. You'll make 0 headway. Now you put the nose down a bit and fly at, say, 16 mph. Now you're at least getting closer to the field, at 4 mph. Wind has everything to do with speed to fly if you're trying to get to a specific point on the ground. That's an extreme example, but if there's any wind at all, best speed to fly to make headway upwind will be at least slightly faster than best L/D.
Apr 21, 2019, 11:59 PM
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 Originally Posted by DougCorrigan A commonly held misconception in gliding is that you use a wind additive (Like half the wind speed added to your best glide). This is incorrect but I can see where it comes from. Here is a good way to look at it (As it relates to gliding not power), If the object is to get the best glide in a given piece of atmosphere then flying past the best glide speed doesn't help, It just gets you to the ground faster. Would you slow down in a tailwind (I hope not).
If you want to achieve the fastest speed through the airmass, then you would be correct. But STF is not constrained to just the speed through the airmass. If you want to want to fly the greatest distance over the ground, you would absolutely speed up with a headwind and slow down with a tailwind(but never slower than min sink). This is the shifting of the tangent on the drag polar left or right on the X axis by the magnitude of the wind. The context of STF depends on the objective.
 Apr 22, 2019, 03:58 PM Registered User I agree with Al and BMathews. I fly faster than max LD when trying to cover ground in a headwind. I fly too slow going downwind sometimes... but that is another story. I guess an important difference between RC soaring and FS soaring is that the RC pilot is standing on the ground and MUST keep the glider in visual range and within gliding range of the home field. Lincoln's extreme example probably doesn't sound very extreme to an oldtime RC glider pilot or even a hang glider or paraglider pilot. I'm sure all have experienced going backwards over the ground while flying at max maneuvering speed.
 Apr 22, 2019, 11:39 PM bayagliders.com In laymans term penetration is used to describe how a given model moves through a headwind. You increase the apparent windspeed and given the mass and drag of the model the model can even move backwards. Increase the mass or decrease drag and the penetration will increase. You can think of it exactly like a car that rolls down hill and reaches its terminal velocity, the only way it could exceed the speed without power is to increase weight or decrease drag.