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Jan 03, 2018, 11:21 AM
Transplant Chey WY from Reno
Thermaln2's Avatar
OMG

While I agree that wide chords are a thing of the past, chord does matter to a major extent, if the design is right.

BUT to say that launch height matters most, I have to add that launch height matters only if you can use the potential energy. If you can't use it, a rock is a rock by any other name.

I think the XXlite was a prime example. It launched higher, ranged farther, but it still came down at the same time as other DLGs. Flapping the airfoil to 8 degrees as I suggested placed the airfoil in the region of LDA airfoils of Drela and improved the sink. (yes, go back and check the posted K, I did suggest that at the time). But the XXLite approach is an exceptionally approach that I am not sure was taken to the extent it needed to be.

So height does matter to all of us. For some of us we can only throw so high. So what we have to do is design for our height, and use that height. Obviously, if my plane cannot withstand the gorilla launches but excels and services my launches, then its design cannot be used by the top launchers. It soon will be incorporated as these things only last one contest.

I guess that is an axiom, significant advancements/advantages only last one contest.
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Jan 03, 2018, 11:23 AM
Transplant Chey WY from Reno
Thermaln2's Avatar
I wrote this before my last post, but had to post it after.

I always try to put reality into my thought patterns when trying to understand numbers that are quoted or published. I ask myself, are the numbers really telling me the right things, or are the numbers in the real ballpark, or perhaps even if the numbers are right am I seeing what is being proposed? As a scientist I then ask things like is my theory correct, am I missing a contribution, is there some assumption that is inappropriate, or did I shift a decimal point somewhere that alters the results. With aerodynamic issues I think we often try to equate, or relate, in some way the L/D and sink rate, all combined and relating to range. I am not claiming in any way that I am any sort of aerodynamic person, I just ask the questions for my own understanding, and if things don’t seem to add up, I ask why. Many people who have read my old posts might know, I am always asking about minima or maxima of calculation approaches, because I wonder if we have limited our designs.

So let me ask a few quite illogical questions.

1) If our planes have a sink rate of 0.89 ft/sec (0.27M/sec) and a competitive throw is 180+ ft, then why doesn’t every major competitor get over 3 minutes in the AM flights? (180 ft/sec /0.89 ft/sec = 202 ft)

2) If L/D is high, why do we fly backwards in the wind?

3) If L/D is high, then why do we bounce off the ground after 1 minute?

Yeah, all stupid questions, but I often think we don’t really know what we speak of. I once asked an EXTREMELY reputable designer if his calculations really matched reality when real measured numbers we not used to calibrate the computation values. He said that he saw the calculated results to be within 2-3% of measured values of the resultant airframe. So I ask, as I always do, are our results representative of what we see or are they representative of what we think we see?

So when I see all the quoted values in the previous posts, I ask myself is something getting in the way of what I really need to address.

Weird Huh?

Chris

PS: I LIKE Oleg’s comment!
Jan 03, 2018, 11:33 AM
Transplant Chey WY from Reno
Thermaln2's Avatar
I agree with Oleg's comments about 1.6-1.8M.

However, larger models get into other limitations that are really not aerodynamic in nature.

These are like required spin area wrt other closely positioned competitors. Also, landings for quick turn arounds. Of course there is the increased SAM threat as well as landing approaches. Just how many pilots could one get across the back , downwind end of the Poway field during a major ladder or turn around task? How fast can we maneuver the plane when landing in response to another pilot running in front of you.

Then...you have to ask the question no one really wants to address, "Did that competitor run in front of you while you were launching or landing to block your flight like they do in NASCAR?" think about it
Jan 03, 2018, 12:17 PM
In F3J size does matter!
roydor's Avatar
Chris,
You seem quite knowledgeable so I am a bit surprised at the questions...
1. I do get over 3 min out of 180 foot launch in dead air, as long as it isn’t turbulent air. As the turbulence grows I need to leave a bigger speed margin from stall speed so my time drops. Very early in the morning or late on a cold overcast day with no wind I get over 3 minutes consistently. A couple of weeks ago it was overcast, cold and low wind and I got 2:45-2:55 consistently on over 20 consecutive throws. It was with slightly higher turbulence as the wind was light but came from the direction of a nearby town and hills over some high vegetation.
2. Flying back against the wind has nothing to do with L/D. If the wind is higher than the airspeed you fly backwards. If you fly faster you advance. A model with higher L/D can usually give up a bit of performance and fly at a faster speed (where it losses a bit of L/D). If it started at higher L/D than another model it will loose less height on the return, as long as it has airspeed higher than the ground speed.
3. Sorry I don’t understand this question...
Jan 03, 2018, 12:24 PM
Registered User
Iím 6í5Ē and 250, Iím more limited on my ability to twirl quickly than the strength to throw a larger dlg. I throw my ballasted planes higher than the unballasted. Since Iíve never flown in a contest, meeting rules isnít a consideration. But I certainly understand rules are rules.
Jan 03, 2018, 12:38 PM
1 revolution and throw!
Quote:
Originally Posted by olgol
Kristof, maybe a larger span would allow you to make 5-6 turns (instead of 1-2 turns) in your windy conditions and still penetrate back to the field.

I for one am very curious to see what an unlimited HL class would evolve into
Even now, with the same launch techniques, for an average pilot, I think a slightly larger span would not reduce the launch height, and improve the glide. So 1.6m or even 1.7m could easily become the preferred span. With a double spin technique, we can probably launch 1.8-2.0m models to nearly the same height as we launch 1.5m models.
Just fun to think about it. It would be a very interesting design optimization challenge.
i'm not sure, i have to admit the first time i flew f5j i was amazed from how low the model could come back , put an f3k model at the same height and distance and it would never have returned to the field .
we oftenly have conditons where wind is stronger then thermal strenght , so following something wasn't worth it simply because you need to burn much more the you gain to comme back(if comming back is even possible)

Because i havent launched one myself i can only say what i saw and heard from others , it seems like launchheight drastically reduces when span grows , a local customer who bought an helios 1 from me several years ago also had a fireworks extended i think it's called , 2meter span .
he said the launchheight is excatly half for him compared to the 1.5m helios and i saw him launch and fly it .
you simply cannot rotate the way you do with a 1.5m gliders and i assume this effect happens quickly as span grows , lickely due to size and mass? then i would assume you need to build the larger span lighter to compensate but that's not possible .... and even it was possible returning from downwind would be worse .

the video's posted here about the gigantalus proves this , there even to a much larger extend, that's the current world champion f3k launching there but he comes to maybe 30% of his normal launchheight, i'm very sure i have very good chance beating him more often if he has to fly the gigantalus during f3k competition ;-)

someone should test out span and report , each time 5cm larger .......anyone ??
i would be very intrested to hear where the optimum span is for a descent launcher , i agree as long as launchheight and turnaround times doesn't suffer then larger span is better for this pilot but i reallly expect losses very quickly as span grows
Last edited by krikkens; Jan 03, 2018 at 12:44 PM.
Jan 03, 2018, 12:50 PM
1 revolution and throw!
Quote:
Originally Posted by Thermaln2
OMG



BUT to say that launch height matters most, I have to add that launch height matters only if you can use the potential energy. If you can't use it, a rock is a rock by any other name.


yes but i rock does longer time falling from higher distance

my launchheight offtenly saved me when taking the wrong decision , it gave me time to go elsewhere and pick something up from low altitude , with a lower launch i already land....

And i think the psychological disadvantage of launching lower is key in the popularity of high AR aswell , when the xxlite came people said sure it launches higher but my bigger wing floats better , then some other high ar models came and still the old bigger wings float better then these too yet nobody is flying these wings anymore .
it's so easy to blame launchheight when you land early it naturally forces people to chose a plane that launches high i think
Jan 03, 2018, 02:20 PM
wrong descision, wrong time
Being 6'8" tall, a 1.5m DLG feels so small. I wish they'd let longer wing spans in competition. I'd much rather have a DLG that fits me, rather than having one that is too small :P

#feelslikethrowinglittletoyairplanes
Jan 03, 2018, 04:56 PM
Team Spektrum FPV
aaronredbaron's Avatar
Quote:
Originally Posted by jeffmete
Iím 6í5Ē and 250, Iím more limited on my ability to twirl quickly than the strength to throw a larger dlg. I throw my ballasted planes higher than the unballasted. Since Iíve never flown in a contest, meeting rules isnít a consideration. But I certainly understand rules are rules.
Quote:
Originally Posted by dumb_thumbs
Being 6'8" tall, a 1.5m DLG feels so small. I wish they'd let longer wing spans in competition. I'd much rather have a DLG that fits me, rather than having one that is too small :P

#feelslikethrowinglittletoyairplanes
I knew I couldn't be the only one! You guys could come join me at Horizon, I'm an elite member of the floating heads club here (everyone sees my head floating above the cubicles as I walk the halls)

Seriously though, it would be so cool to have a bigger DLG option to really put some weight into!
Jan 03, 2018, 05:06 PM
hot air rises...
jfinch's Avatar
This is an interesting discussion. I think I could launch 1.7-2m (ish) size plane without changing launch style, but I've not done it so I could be wrong .

L/D...an important parameter that nobody actually measures
Jan 03, 2018, 05:38 PM
plays with toy planes
Quote:
Originally Posted by dumb_thumbs
I wish they'd let longer wing spans in competition.
I don't know, H...but until those spans are legal, maybe you extra tall guys should be penalized 1 second (that is, @ 0.89 ft/sec) on every flight.
Jan 03, 2018, 08:39 PM
Transplant Chey WY from Reno
Thermaln2's Avatar
Quote:
Originally Posted by krikkens
yes but i rock does longer time falling from higher distance

my launchheight offtenly saved me when taking the wrong decision , it gave me time to go elsewhere and pick something up from low altitude , with a lower launch i already land....

And i think the psychological disadvantage of launching lower is key in the popularity of high AR aswell , when the xxlite came people said sure it launches higher but my bigger wing floats better , then some other high ar models came and still the old bigger wings float better then these too yet nobody is flying these wings anymore .
it's so easy to blame launchheight when you land early it naturally forces people to chose a plane that launches high i think
You are correct that a rock thrown higher does spend more time in the air. Laughingly, we could say a flat rock might stay up a slight bit longer, but really the time might be indistinguishable from another rock, . What I am saying is what you do at the peak matters.

What we all know is that height gives you more options and permits you to recover from more mistakes in judgement as compared to a lower launcher. For those of us that don't (read can't) launch as high due to any sort of reason, we have only a 1 or 2 mistake height as compared to higher launchers. Higher launchers can realize their mistake and rapidly convert their height to distance and speed to get to the rabbits that have discovered the lift.

This then gets down to the planes again. If the plane can cover the ground, not loose a lot of height and reach the spotted thermal, then it really does not make any difference what height they stated at. For those planes that have a better sink rate, they can float a bit more to get to the lift, but they still get there. I used to fly a fast TD ship back in the floaters day, and I often got to my thermal before others and circled, got a lot of height, then dashed off again before the others could get the thermal I had located. Other pilots used to circle in zero sink or even down air to lure pilots to them, only for them to come down as fast as the circling pilot who wanted to come down. We all watch pre-task launchers do one circle before the window time but not do more so they do not call attention to any sort of lift that might be there?

But getting back to the span limitation, what can we do that is different than what we currently have optimized? We have reduced chord, but have we reduced it enough? Have we built or designed lighter? Is there a relation? If we need a 3.5 oz/ft2 for the current airfoils to work, will they work at a reduced chord? Do we have to re-optimize our airfoils for a more reduced chord? How do we handle launch flutter/stiffness? How is handling affected?

One of my current questions is when are we going to stop thinking that one airframe design is sufficient to be used for all contest conditions, and switch to planes more designed for specific conditions? I believe that we can have a better morning plane and a better mid-day wind plane. And they are not limited by span.

It would be nice if the span limit was removed as we originally conceived more than 35 years ago !
Jan 03, 2018, 08:42 PM
Transplant Chey WY from Reno
Thermaln2's Avatar
Quote:
Originally Posted by jfinch
This is an interesting discussion. I think I could launch 1.7-2m (ish) size plane without changing launch style, but I've not done it so I could be wrong .

L/D...an important parameter that nobody actually measures
Jon,

Actually there were actual L/D tests done nearly 35 years ago that correlated L/D to performance. The best correlation was that L/D best related to aspect ration, where L/D related to 1.9 times the AR.

I don't believe I have seen any really controlled condition measurements have been done since.

Chris
Jan 04, 2018, 01:29 PM
Closed Account
One of the corollaries of the comments I am seeing is that hand launch is more about launch height than flying skills. I see comments like, my launch height saved me, 2-3 mistakes high, low launching planes wont sell, a rock thrown higher will take longer to reach the ground...

I am pretty sure this was not intended to happen but the original question has also brought to light that launch height means everything in competition flying. This means we wont see much interest in planes under 1.5m or interest in planes much above 1.5m because a change in wing span in either direction would effect launch height negatively.
Jan 04, 2018, 01:42 PM
Registered User
clintc's Avatar
I don't think people think launch height is everything, but it definitely helps. It's just a reality that thermals are generally larger/stronger/easier to use the higher you are in the air. If the air is difficult to read, or thermals are moving fast or sparse, that extra height can make a difference in what thermals are reachable.

This discussion is focusing on launch height because it seems that is the thing most affected by wing span.


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