Some graphs. Угол атаки - aoa. К качество - glide ratio. Wing have 1m chord, 6.6 span.
Hi. It was Cyrylica, RussianWow. A bunch of work there. Your English is way better than my Lithuanian. Please help us with the plots:
Upper left appears to be whole wing lift coefficient vs angle of attack - Yes? If no please explain;
Upper right and lower lift are something vs angle of attack, but I can not tell what. Labeling of the abcissa makes no sense on either one, I suspect a column number got in as the Y axis labels;
The lower right appears to be Coefficient of Lift vs Coefficient of Drag - Yes? If no please explain.
Hi. It was Cyrylica, Russian
Cx = Cd Cy =Cl
K - glide ratio.
There is no title for the y axis on any of the plots, which makes reading and interpreting them reliant on assumptions that may or may not be correct. The slide titles are quite obscure to most of us... Please answer the following questions:
Now onto my look at your design study... The tips analyzed appear to come in four span-wise lengths, small (1-3, 6, 8), a little bigger (4-5), much larger (7), and tough to define (9). That brings up some immediate questions:
- I think the upper left slide is whole wing Cl vs angle of attack. Yes? If no, please explain what it is:
- I think that the upper right slide is L/D (glide ratio) vs angle of attack. Yes? If no please explain it;
- I think that the lower left slide is L/D (glide ratio) vs whole wing Cl. Yes? If no please explain it;
- I think that the lower right slide is whole wing Cl vs Cd. Yes? If no please explain.
In experimental design, we want to avoid confounded variables. According to wing theory, span loading has a strong effect upon induced drag. Wing taper as we go out the span also is attributed to having effects upon induced drag. The effects of tip span and total span are thus mingled with the effect of tip design, and your experimental design did nothing to allow you to distinguish or separate the effects the variables. That fits the very definition of confounded variables.
- With the tips varying in spanwise dimension, did you adjust the span of the straight section?
- Did you keep the straight section the same and allow the wing tips to add or subrtract from total span?
Confounded variable is common and has lead to a many design choices in directions away from the desired optimal choice. Let's detail and learn from what we do have. The existing designs can be grouped nicely:
It may be possible that section 3 (the best of the narrow ones) might be every bit as good as 7 if 3 and 7 had the same spanwise dimension and total span. Likewise, 4&5 might be substantially better if they also matched spanwise dimension and total span of 7. But we can not tell from current runs. And 9 might go from its current "bad" to really horrible by increasing its width...
- Narrow tips (they all appear to be the same addition to span) in runs 1-3, 6, & 8 and they seem to plot together. The L/D plots (if that is what they are) show #3 to be the best of this subset, and that is what I would expect from this subset;
- Wider tips 4 and 5. These two plot together with higher L/D, which we might expect with increased length and/or span;
- 7 has a much larger spanwise dimension, is the best performer of the bunch. Again, we might expect it to be so with its increased length and/or span;
- 9 is the oddball. How do we characterize it? Is the tip length the spanwise dimension from the leading edge to the trailing edge?
The designed experiment approach is to identify all of the variables, figure out which variables matter and then experiment in those variables in a controlled manner while fixing everything else as much as possible. Normally to explore a design space you run a factorial, which is all permutations of the available variables. If you have a bunch of variables, there are balanced fractions that can be run - you accept some confounding in exchange for brevity. I do not believe we need to do that here. I believe that we do need to control for spanwise length and total span.
If this were my experiment and knowing what I know about foils, I would make sure total span is controlled and then run narrow and wide tips of each type. That would add eleven tips to be modelled and run.
Is there anything we can do to narrow the search? Well, maybe you make sure that you run narrow and wide tips from the best of each group. This does have the risk of missing something significant in the ones skipped. You would need to model and run wide tips on 3 & 5 and narrow tips on 5 & 7, for only four more. Your knowledge base will still grow strongly. If the picture remains muddy when those are run, maybe you run the rest.
Other options are to only make narrow versions the best of each group. That means only modeling and running a narrow version of 5 and 7, but means skipping the effect of length on everything but 7.
Making sense so far? Oh, and please answer the questions I asked so I can help you.
Thank you moving this all to new topic.
Yes, it is 4 yes in graphs meaning. On span - it is with wing tips.
On aech drawing is a virtaul ruler with 1000mm scale. Two white strips.
Ok will move all of them to same drawing.
It is not my tests or my design Just a work of ony highly qualified aeri specialist.
Still - question here is - which one gives similar result with less area overall.
5 one was tested and it is used in be-200 aircraft.
I will put all of them on same image with same scale.Stanislavz,
Really tough to measure the white part with a ruler shorter than the white part and offset from it.
Wait a minute, all 9 samples, with wingtips, have the same span? This is a lot of difference for only tip geometry…
Oh, this is somebody else’s work who does not understand confounded variables and experimental design.
If the runs we have are it, the best tip is clearly 7. Who cares if it has more area, it is still the highest L/D over the range of climb and cruise Cl. This tip type or others of similar schemes have been widely used and work well.
I personally would love to see 3 proportioned like 7 modeled and run for comparison.
My airplane? Looks sort of like 3, with a span 0.375 of tip chord and an upswept outer edge. Look in post 39 here:
Do we see why I might be interested in 3 fattened up a bit?OK, got a picture of the rudder bellcrank and supports all together, they are not yet bonded into the airplane. The little truncated pyramid will be mounted to the floor, and the V will get those flat faces bonded to the back of the seatback bulkhead. All parts were previously pictured, but this...www.homebuiltairplanes.com
As for the tips with extensions of the trailing edge, they are trying to do the same work on the air with a lot less contact. That’s tough to achieve.
There is a lot of experience indicating that all other things being equal 3 is a pretty good base. Lots of later Mooneys and Lancairs and Glasairs have wing and tail tips treated this way. Lots of canard tips and racers this way too.
Maybe I'm missing something, but he is changing the tips while keeping the span constrained. This changes the area of the wing, both projected and wetted. But what is he using for calculating CL and CD, chord x span area or projected?
I know this probably seems pedantic but the other day I was reading an old Stan Hall article in SA that was all about wingtips. This is what he wind tunnel tested;
View attachment 126928
Which has slightly different spans and projected/wetted areas for each one, making direct comparisons hard.
I've tried testing out different wingtips in OpenVSP with the span constrained and keeping the wetted or projected areas constant but I don't trust the results I get from it.
Is that really a problem? The total span gives us our distributions of lift, shear, bending and torsion, so same overall span goes equivalent there. Any circular or elliptical tip loses 22% of the raw area, so they are pretty much equivalent on area.
Yes, 20% of span in 1/2 taper as per Strojnik wing. Which i a simplification of Schuemann which is used still today in most of gliders (two joined tapered sections)All in all...could one make a straight wing AC better ( better L/D ) than a tapered one....by using just a clever wing tip on a straight wing ?
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