stunthanger.com
Design => Stunt design => Topic started by: Will Moore on January 22, 2018, 01:48:41 PM
-
This has been discussed , briefly, but, which is better, unequal panels and less tip weight, or equal panels, with more tip weight. “World class”airplanes always seem to have inside panel half inch to one inch large. And I understand the reasons. However, can an airplane be as competitive with equal panels , and just add more tip weight?
-
Experienced winners have often said that wing asymmetry with the inner wing longer calls for less tip weight; so I believe them. However, roll moments aren't the only consideration. There are also yaw considerations that point to the need for more thrust offset or some tip weight to just keep the thrust line inside of the lateral c.g. on asymmetrical planes. This is probably one of those things that can't be accurately predicted just by theory, and require some practical experience. I don' think that my computations are the sole reason for those 1/2" - 3/4" differences in half-spans.
SK
-
Thanks Serge, appreciate the comment. So , it seems there are positive and negative aspects of each. And both have different effects on trim techniques. More ships have longer imboard wings, which should tell us something, namely, it is perhaps better of the two.
Thanks, again
-
Will,
Be interesting to have the wing measurements of the competition models guys are flying?
Some might put them up.
Charles
-
Will,
Be interesting to have the wing measurements of the competition models guys are flying?
Some might put them up.
Charles
There is a search function, this has been covered in exquisite detail for decades. Go search SSW, er, never mind...
Brett
-
This has been discussed , briefly, but, which is better, unequal panels and less tip weight, or equal panels, with more tip weight. “World class”airplanes always seem to have inside panel half inch to one inch large. And I understand the reasons. However, can an airplane be as competitive with equal panels , and just add more tip weight?
I think it's better to get the asymmetry correct, for the reasons previously discussed at length. Within reason, you can trim either a properly asymmetrical airplane or a "equal-span" wing to be equally good, at least to first approximation. Expect to have to put tabs on the outboard flap to get the equal-span to work, and the very large amount of tip-weight, and you should probably put the engine straight ahead.
Given all that, I certainly don't see any advantage to "equal-span" wings, when it's easy to cut 1/2" off the outboard wing.
Brett
-
Some observations—not opinions.
Randy Smith's SV 40 and Tempest 40 have 1/2" of asymmetry and the outboard flap is 1/8" wider at the tip—which on the SV 40, just happens to make the flap areas almost identical.
The Brodak Vector kit has the same 1/2" of asymmetry but the flap is not wider at the outboard tip—unless, as I have done with mine, you modify the flap blank.
The ARC/ARF Vector has symmetrical wings and flaps.
The Yatsenko Shark Ellipse has 24mm asymmetry but I don't know about the flaps. I will measure one if the weather is good at the weekend.
The Yatsenko Classic 2 has 30mm of asymmetry but again, I don't have any info on the flaps and we don't have one at our club so I will not see one for a couple of months.
-
Some observations—not opinions.
Randy Smith's SV 40 and Tempest 40 have 1/2" of asymmetry and the outboard flap is 1/8" wider at the tip—which on the SV 40, just happens to make the flap areas almost identical.
The Brodak Vector kit has the same 1/2" of asymmetry but the flap is not wider at the outboard tip—unless, as I have done with mine, you modify the flap blank.
The ARC/ARF Vector has symmetrical wings and flaps.
The Yatsenko Shark Ellipse has 24mm asymmetry but I don't know about the flaps. I will measure one if the weather is good at the weekend.
The Yatsenko Classic 2 has 30mm of asymmetry but again, I don't have any info on the flaps and we don't have one at our club so I will not see one for a couple of months.
There's no real question how this works or what the right answer might be, and that there is a range of asymmetry from 0 to around an inch that can be made to work. Statistical surveys on the topic on what various designers have done are vaguely interesting, but I am not sure what the point of it might be - its been documented in excruciating detail for around 50 years.
Additionally, people keep wanting to take a whole bunch of airplane "numbers", average them all together, and come up with the what is apparently the "correct" answer. The "correct" answer is not buried in statistical averages, and most of the airplanes designed aren't in any way optimized, nor is the performance, independent of the accuracy of construction, level of trim, powerplant used, evaluated well enough to give you much of an idea. The vast, vast majority of airplanes you see, including those finishing in high places at the NATs, are so "affected" by trim and power issues, that you really have no idea whether the underlying design is any good or not.
And in any case, just as an example, the optimal solution for a PA75 set up using Randy's instructions and the optimal solution for a PA75 using David's system aren't likely to be the same and certainly aren't optimal for a Saito 72, an ST60, or feedback electric system. So even if you use statistics to determine the "right numbers", you still haven't gotten anywhere.
People have known, to first and second approximation, what the "numbers" should be for a very long time now, and have a pretty good idea what things work with particular engine systems. But things that most people never even consider make a huge difference, and two extra swipes of sandpaper on the leading edge might make the difference between an airplane that stalls in round maneuvers at sea level air density, to a perfectly sound and reliably system that works at 105 degrees and 2200 feet.
Brett
-
I think it's better to get the asymmetry correct, for the reasons previously discussed at length. Within reason, you can trim either a properly asymmetrical airplane or a "equal-span" wing to be equally good, at least to first approximation. Expect to have to put tabs on the outboard flap to get the equal-span to work, and the very large amount of tip-weight, and you should probably put the engine straight ahead.
Given all that, I certainly don't see any advantage to "equal-span" wings, when it's easy to cut 1/2" off the outboard wing.
Brett
Would adding 1/2 inch to the inboard wing do the same thing, in approximation?
-
Would adding 1/2 inch to the inboard wing do the same thing, in approximation?
Build the wing and just place the fuselage off center.
Or if you really want to get to the bottom of it, build a model where the fuselage centerline is adjustable.
Offsetting the fuselage will get you your .5" or whatever?
Or, in my case of the ARGO 2, using a Thunder Bird wing already built, I centered the fuselage and both panels measure the same, did it just for looks. Flies OK for my limited abilities.
-
I have seen some gifted people make it seem that having an outboard wing at all is highly over rated. There have been flights I have witnessed where the model in question looses the entire outboard wing panel and they continued right on flying as if nothing happened.
-
There have been flights I have witnessed where the model in question looses the entire outboard wing panel and they continued right on flying as if nothing happened.
If this happens with a Flite Streak and you give an abrupt up elevator input flying level at about 75 degrees elevation, it will do a spin and chew up a set of lines. Try it. Works every time.
-
Would adding 1/2 inch to the inboard wing do the same thing, in approximation?
Yes, but I have a lot of "taking off" machines, and only a few "putting on" machines... Of course, adding also increases the wing area, and slightly alters the wing loading.
Brett
-
Thank you, everyone, for your comments.