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Nov 11, 2019, 02:33 PM
awesome sauce
Rich Erikson's Avatar
Thread OP

Still here


Quote:
Originally Posted by i_am_mark_evans

I think the OP may have left ages ago.
Iím still here.... reading all of this intently. I have zero experience so I donít have much to add so I am taking it all in.
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Nov 11, 2019, 03:23 PM
Come out swinging
sporter's Avatar
[QUOTE=Joe W;43145695] Strong wind without lift and I ballast so that best L/D airspeed is close to the wind speed. QUOTE]

How do you determine this? Wind usually is not sustained but rather comes in cycles and gusts. Do you just ballast so that you can fly forward with a little trim (without diving) in the prevailing wind?

If it's so windy that the glider is flying backwards relative to the ground, I should add ballast so that it flies forward?

Thanks
Sean
Nov 11, 2019, 03:57 PM
launch low, fly high
[QUOTE=sporter;43146531]
Quote:
Originally Posted by Joe W
Strong wind without lift and I ballast so that best L/D airspeed is close to the wind speed. QUOTE]

How do you determine this? Wind usually is not sustained but rather comes in cycles and gusts. Do you just ballast so that you can fly forward with a little trim (without diving) in the prevailing wind?

If it's so windy that the glider is flying backwards relative to the ground, I should add ballast so that it flies forward?

Thanks
Sean
If the wind is not smooth and consistent but instead is cycling with gusts, then there is mixing and lift/sink. The vertical movement may not be thermal driven... The magnitude of the changes in the wind speed gives one a hint about how much ballast to add. Usually it is best to ballast to match the strongest gust strength so that the plane still has good penetration capability

It has been noted that the best airspeed to penetrate upwind is faster than the best L/D speed. I think I will make some charts to illustrate this... will post with pics in a bit...
Nov 11, 2019, 04:28 PM
2.1.9 Forever
Miami Mike's Avatar
Quote:
Originally Posted by Rich Erikson
I am hoping this thread can be used to explain ballast in-depth...
Welcome to RCGroups! You might be interested in knowing whose attention you were lucky enough to attract.
Nov 11, 2019, 06:30 PM
launch low, fly high
Quote:
Originally Posted by Miami Mike
Welcome to RCGroups! You might be interested in knowing whose attention you were lucky enough to attract.

Blah, blah, blah...

The subject has come up in various forms in recent days, thought it was time to put forward some stuff that wasn't quite so subjective as some of the comments I've seen. Yes, I go by feel and intuition a lot of the time. I strongly suspect that my intuition has been solidly grounded in the analyses that I've made so many times in the past.

Attached is a generic DLG polar, plotting the airspeed vs sink rate. With this plot, one can evaluate the best speed to fly to get somewhere in calm conditions (maximize L/D), what speed to fly when flying in a headwind, as well as what speed to fly when in sink.

Rough rule of thumb, add about 90% of the wind speed to the max L/D speed to get the best penetration into the wind.

The best ballast to install for the conditions, that one is harder to define due to the other influences (amount of lift/sink, turbulence, pilot preference, airplane type, etc.). I like the idea of scaling from the amount of ballast required to do a minimum cruise speed stationary in the wind, with the scale increasing for the presence of lift/sink, turbulence, and even the task being flown.

BTW, I first presented an analysis similar to the attached pdf way back in the late '80s at the MARCS sailplane symposium. This is no great revelation here, just hoping to give people a refresher on what drives how we fly.
Nov 11, 2019, 06:48 PM
Time for me to Fly...
Mr. Wiz's Avatar
I’ll be honest, Joe. I don’t understand how to apply your graphs to my plane or any plane/ballast combination.
Latest blog entry: Something old is new again
Nov 11, 2019, 07:14 PM
Come out swinging
sporter's Avatar
I think the graphs are for illustration purposes, to demonstrate how adding ballast during a headwind results in very little penalty in sink rate but with the benefit of being able to fly faster (i.e., get where you need to go, particularly back home). I think you would want to experiment with different ballast combinations during different wind/lift conditions and determine what works best for your model, the conditions, and your flying style.

Sean
Nov 11, 2019, 07:25 PM
Time for me to Fly...
Mr. Wiz's Avatar
Quote:
Originally Posted by sporter
I think the graphs are for illustration purposes, to demonstrate how adding ballast during a headwind results in very little penalty in sink rate but with the benefit of being able to fly faster (i.e., get where you need to go, particularly back home). I think you would want to experiment with different ballast combinations during different wind/lift conditions and determine what works best for your model, the conditions, and your flying style.

Sean
Yep. Iím just going to play with the plane. All this discussion has done is muddy the water for me.
Latest blog entry: Something old is new again
Nov 11, 2019, 07:30 PM
launch low, fly high
Quote:
Originally Posted by Miami Mike
Welcome to RCGroups! You might be interested in knowing whose attention you were lucky enough to attract.
Okay Miami... you can teach me something! How... oh I see my answer in the quoted text above!!!

I was going to ask how you linked the url to the text in your message. Is there some way to do that without typing in the bracket and url stuff or do you have to just deal with remembering the url insertion formatting?
Nov 11, 2019, 08:25 PM
I'm not as bad as they say.
Quote:
Originally Posted by Joe W
Okay Miami... you can teach me something! How... oh I see my answer in the quoted text above!!!

I was going to ask how you linked the url to the text in your message. Is there some way to do that without typing in the bracket and url stuff or do you have to just deal with remembering the url insertion formatting?
Click insert link.
Paste link, hit enter.
Type words while in the highlighted block.
Latest blog entry: AIrcraft I've built.
Nov 11, 2019, 08:36 PM
I'm not as bad as they say.
So I think this follows from Joe:s pdf.
With a tailwind,the tangent approaches the min sink point. So raising the min sink point will increase the L/D wrt the ground. Therefore adding camber downwind decreases the loss of altitude running downwind.
Latest blog entry: AIrcraft I've built.
Nov 11, 2019, 08:39 PM
2.1.9 Forever
Miami Mike's Avatar
Quote:
Originally Posted by Joe W
I was going to ask how you linked the url to the text in your message. Is there some way to do that without typing in the bracket and url stuff or do you have to just deal with remembering the url insertion formatting?
I don't want to take the thread off topic so I'll just say that there are lots of RCGroups formatting secrets hidden away on this page.
Nov 11, 2019, 09:22 PM
launch low, fly high
Quote:
Originally Posted by mnowell129
Click insert link.
Paste link, hit enter.
Type words while in the highlighted block.
Thanks for that... I've never really transitioned to the icon paradigm, I'm still remembering fondly the older variants of excel.

I now have a far better understanding of how to interact and operate RCG and post stuff in a bit more user friendly fashion.
Nov 12, 2019, 10:28 AM
solastagia
kcaldwel's Avatar
Quote:
Originally Posted by mnowell129
So I think this follows from Joe:s pdf.
With a tailwind,the tangent approaches the min sink point. So raising the min sink point will increase the L/D wrt the ground. Therefore adding camber downwind decreases the loss of altitude running downwind.
It depends. In neutral air, gliding towards a fixed ground point, speed near min sink with camber will be optimum. But in most real cases, camber and min sink speed are not optimum flying down wind.

Case 1:
Flying downwind in sink towards a fixed ground point such as a tree line. I've butchered one of Joe's graphs quickly to show that camber and min sink speed are far from optimum when flying downwind in sink. While you should not fly quite as fast as upwind in the same sink, the optimum speed is still much faster than best L/D speed, and camber will not be optimum.

Case 2:
Flying downwind towards a thermal. Since the thermal is moving** with the air mass, you should ignore the wind direction and fly the glider through the air mass. This means flying at the same speed and glide ratio through the air mass regardless of whether the glider is flying up wind or down wind. The optimum speed could be as low as best L/D speed in neutral air, and much faster in any sink. Camber past "cruise" setting will not be optimum.


** The bottom of a thermal, where most DLG flying is done, is actually moving across the ground at the speed of the wind at about half the column height. This speed is often faster than the ground wind speed. Flying downwind, in order to catch up with the bottom of a thermal moving faster than the wind speed at the glider's altitude, you must fly even faster, as if the glider is flying into a headwind. The optimum speeds for best glide towards the thermal will be quite fast, and positive camber will not be appropriate.

Kevin
Last edited by kcaldwel; Nov 12, 2019 at 10:41 AM.
Nov 12, 2019, 11:09 AM
Time for me to Fly...
Mr. Wiz's Avatar
So in the wind we're suppose to fly nearly as fast (wind speed) down wind with our ballasted (faster) plane as we fly up wind. The ground speed at that point has to be pretty darn fast! So here is what goes thru my mind when flying in that condition. I damn well better know the lift is down there and reachable because I'm flying away from myself like a bat outta .... And, will I climb enough to make it home when I finally get there or will I be so far down wind that I can't see my plane?
Latest blog entry: Something old is new again


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