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May 03, 2006, 07:46 AM
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May 03, 2006, 08:03 AM
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EdSoars's Avatar
Miniphase: the elevons are reflexed because the first sets of cores were cut with no twist, and the same airfoil, root to tip. Although this gives great inverted performance, I think it hurts the glide appreciably to have to reflex the elevons.

The kits will have one degree of twist in the cores.

Ed
May 03, 2006, 08:11 AM
antipodean recalcitrant
AntonL's Avatar
Nice flying; looks like a success! It will be interesting to find out what you thought about it from the pilot's perspective. It appeared as though the rolls became more axial in the later scenes, but I may have just imagined that. Shame about the 'bunting accident'* at the end!

[*You can thank/blame Tony AKA AntonSoarer for that phrase.]
May 03, 2006, 10:06 AM
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miniphase's Avatar
Quote:
Originally Posted by EdSoars
I think it hurts the glide appreciably to have to reflex the elevons.
Ed
I agree, my experience has shown it can realy narrow the wind speed range a wing can be flown in as aswell
great project, enjoying this thread
May 03, 2006, 10:35 AM
Registered User
EdSoars's Avatar
Greg: Nice flying and filming! Excellent first video! What were the conditions? Your launcher did what I did the first few times: underestimated the needed airspeed. That sucker moves faster than one expects. Still, your first flight was much longer than the sum of my first three!

What are your first impressions? With the extra few ounces, your Talus has great carry-through on the aerobatics.

And what was that you said at the end of the video? Something like, "... be a tape fix?"

Looked to me like a tip stall that did you in there. You had a very good roll rate, so it could have been a big elevon deflection at low speed. I'll bet a degree of washout will do some good.

ed
May 03, 2006, 11:13 AM
Registered User
Aio_1's Avatar
The video looks very promising. My turn to get one in the air!
Have you had the opportunity to do any experimenting with the CG yet or are you pleased with where it is? The CG position could have a big effect on the elevon deflection so it's definitely worth getting right before finalising the aerofoil and twist combination for the kit.

Aidan
May 03, 2006, 12:31 PM
Registered User
EdSoars's Avatar
Aidan: I've moved the CG back to 1/4" behind the TE at the root position. I haven't tried it further back, but will have to give it a try. At very rearward positions, would a swept wing show a tendency to tip stall, like a combat wing?

At the present position, it flies very nicely hands-off; no falling-off, goes where you point it, responds nicely. But maybe more can be gained! At this position, I think it's at the "3% static margin" as calculated by Norflugel.

Also, isn't the CG interdependent on the twist and airfoil, which in turn determine the static margin?

Ed
May 03, 2006, 01:25 PM
Registered User
Aio_1's Avatar
The static stability is usually given as the percentage of the mean chord that the CG lies ahead of the neutral point of the aircraft. The neutral point can be taken as 25% MAC (mean aerodynamic chord). For a constant chord flying wing the neutral point is 25% chord at mid-span. For 3% static stability you'd put the CG at 22% MAC. If you're already at 22% then I doubt you can go much if any further back. I would have guessed 20% as a good spot but if it's still flyable aft of that go for it!

Static stability in pitch depends on the position of the CG relative to the neutral point. The neutral point is not affected by wing twist or aerofoil selection. The CG position should really be decided based only on stability. Then arrange the twist and aerofoil Cm to balance that CG. Obviously the further forward the CG the more twist you require or the more nose-up pitching moment the aerofoil must have, or a combination of the two.

Aidan
May 03, 2006, 11:25 PM
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EdSoars's Avatar
I calculated the neutral point using your guidelines and a 24 deg. sweep. This puts the NP at 1.34" behind the root TE, and 3% static margin is at 1.126" behind the root TE.

5% static margin is behind the root TE is 1" behind the root TE.

Looks like I have some room to move the CG back, so will try it next weekend.

Ed
May 04, 2006, 01:30 AM
Throw Caution to the Wind
Lavawing's Avatar

Flight report/More video


Impressions from flying the Talus:

Slope where the flight took place is a curving ridgeline that faces mostly SW. Upwind terrain comes over low hills, then a stretch of very flat land just before abruptly lifting upward at a smooth, steep angle, maybe 60 degrees, perhaps 200 feet high. (Treat these estimates with caution.) In the past when I've flown there, lift has been smooth with a good vertical element.

Wind felt light at the edge, and I threw out my Bee combat wing first. Flew fine, and plenty of lift. Landed it and threw out my fairly heavy Moth, which didn't really feel like it would fly, but it flew reasonably well. (Though Glenn was embarrassing it with his Spinner XT, out-climbing it an zooming past it, which is ridiculous behavior by a DLG.)

The wind picked up somewhat as we flew and I began to have hope for the Talus. So I planted, er... landed the Moth and fired up the Talus. Glenn landed and we set up the video camera.

Wind was probably 12 mph or so, and I wasn't at all sure there would be enough lift to keep the Talus in the air. But, ah, what the heck, I thought. Nice soft dirt at the bottom anyway, and this was the third time I'd taken it to the slope, and didn't want to take it home without flying it.

My knees were knocking a little bit when Glenn threw it. It dove downward off his wimpy toss, but missed the dirt and as soon as it had enough speed, it was flying!

Throws were exactly as Neil recommended. Aileron, 20mm up, 14mm down. (60 aileron differential.) Elevator 7mm up and down. I'd leaned my CG back to about 1/16th inch behind the TE at the absolute root, and started with the short side of 1/16th of an inch upward elevator deflection. I immediately realized I needed more elevator, and gave it a couple clicks up, trying to fly gently but to keep the speed up. Kept things pretty flat at first. Added one click of right aileron, did some fine tuning/super-sub-trim of the elevator on the left stick. And it was flying fine!

Good speed, no flutter on any of the fast passes or dives. Great follow through! Ailerons were more sensitive than I'm used to, which kept me on my toes. (I'll think about adding some expo.) It made good use of what wasn't a huge amount of lift. Roll rate was pretty good -- for being the biggest, heaviest plane I've ever flown. My ability to keep the rolls axial got better as I flew. I may need another session to be able to pay attention to how much is attributed to my thumb learning to make adjustments, or if it was learning to NOT make adjustments.

At first there was a fair amount of "yawing" going on -- a slight waggle as it went -- that I was able to reduce by flying smoothly. And -- despite good rolls -- the plane did not want to stay inverted. Felt like it wanted to roll off to one side or the other -- almost like flying a high-dihedral plane inverted. Odd. Otherwise, it went pretty much were it was pointed.

With speed, I could yank pretty hard and get good results. I could fly it along more slowly, but had to keep it flat, or there was a definite tendency to drop a wing and start to spin in. I escaped a couple times, but didn't on the last one in the vid. By the time I got it back together (rear bolt had to be cut out) with a "tape fix", the wind had dropped back down, and I flew the Bee again.

Overall, it was great fun, and very interesting to see in the air! The carbon X seemed to take care of the flexing wing issues. (At least at the speeds I was flying it -- there was no holding back!) Once Ed gets the pod/joiner system refined, a little more sorting out of the CG and such, I think it's going to be a kick of a kit!

I'm wondering -- with some help from another local fly-guy -- if it's possible that it might actually benefit from a little more FORWARD CG? If it slows down at all, it gets pretty tippy. Will a swept wing like this show anything like a "hyper-stall" if the elevator rates are too high per the CG? I see that the calculations suggest it can go back, but -- for my flying skill -- it seemed like it was pretty close to the edge.

The LavaWing video shows the highlights. But Some Other Guy also happened to be there, and there's more video here:

www.bikeabout.net/SomeOtherGuy/index.html

This video shows over 7 minutes of the initial 10 minute flight. (Some camera technical issues edited out.)There's no music. Just the natural sound of the wind, our comments, the dog panting... And Glenn making airplane sounds as I fly. (He does that when HE flies. I didn't know he did it when I fly.) It's an annoyingly huge file, pretty long, and the plot tends to drag, but it does a much better job of showing the strengths as well as some limitations of this particular Talus. Comments and suggestions about its flying characteristics welcome.
May 04, 2006, 04:13 AM
Registered User
miniphase's Avatar
Great flight report

Haven’t looked at the vid yet, but my intial here are some initial comment

Cg sounds like it’s just about at its rear limit, that feeling that ‘its pretty close to the edge’
sums it up pretty well when outwardly theres no visible signs of instablity but you’re getting
that feedback that its ready to bite given half a chance. I wouldn’t add too much weight, just a few
coins taped to the nose shld be enough to keep it on the rails without killing performance.

You might want to dial down the control throws a bit, the dutch rolling or wagging might indicate too much aileron throw, something you’ve already alluded to. Lack of inverted stability could be a result of
fin/winglet height, you mention feels like a r/e high dihedral plane, well the winglets provide dihedral
(if you take a line from the root to a point ¼ of the way up the fin, you’ve effectively got that much dihedral) you could experiment with reducing their height, but I reckon they look pretty cool as they are!

Its gonna be interesting to see how the version with the washout compares!

Great stuff, can’t wait to view the vids
May 04, 2006, 07:39 AM
Registered User
Aio_1's Avatar
Quote:
Originally Posted by EdSoars
I calculated the neutral point using your guidelines and a 24 deg. sweep. This puts the NP at 1.34" behind the root TE, and 3% static margin is at 1.126" behind the root TE.

5% static margin is behind the root TE is 1" behind the root TE.

Looks like I have some room to move the CG back, so will try it next weekend.
Hmmm, that's interesting! If the tests don't agree with the calculations do go with the tests but I'm surprised it's feeling twitchy with the CG that far forward. I'd be tempted to move it a little further aft just to be sure but of course if it already feels twitchy that might be a risk. If you haven't already it would be worth checking the actual sweep angle as even a small building error could move the actual neutral point by a noticable amount. The best method is probably to measure half way out each wing panel and mark a point at 25% chord. Then put a straight edge or piece of string/thread between these points and see if it passes through the calculated 1.34" behind the root TE.
Perhaps my safety margin guesses are cutting it too close for this type of plane.

One thing worth mentioning is that a swept wing design has inherent roll and yaw stability due to the sweep that acts similarly to dihedral. Many swept wings have anhedral to compensate. However because this dihedral effect is due to the planform it will be the same either way up and anhedral will make things worse when you're inverted. For aerobatics the anhedral will probbably make things worse but swept wings aren't ideal for precise aerobatics anyway. For racing the anhedral might improve the handling. I think miniphase may be correct about the influence of the winglets but I'll have to have a think about it. If I remember correctly Martin Hepperle covers the calculations for amount of dihedral effect in the flying wings section of his MH-Aerotools site. If it's not there let me know and I'll see what I can dig up. Incidentally if you haven't already seen it that website is well worth a look.

Aidan
May 04, 2006, 08:36 AM
Registered User
EdSoars's Avatar
Aidan and Miniphase and Others: I really appreciate the knowledgable input on this design effort. The list of designers will be bigger than the box!

On the #2 Talus, I increased the tiplet area by a couple of square inches...no calculations, but kept the same shape. It improved the yaw waggle, and it is definitely stable enough inverted; no falloff.

Definitely check the sweep, because my CG is about 1/4" behind the root TE, which is still forward of the calculated 5% static margin position.

Talus #2 has a bit of anhedral due to my having the sealing iron a bit too hot during application of the bottom-surface mylar. I'm working on a CF cross-strip design to take the place of the mylar for torsional stiffening.

We'll be doing some flight testing, flying together at Montrose over the weekend. Greg, I'll be coming out with Will Phillips Friday morning. When will you get there? It would be good to be able to free-fly before the competitions start. With the rain we've been having around Colorado, that hillside will be treacherous!

Ed

Ed
May 04, 2006, 08:53 AM
Registered User

Ed, Another Great Project


Ed, as a fan of flying wings myself and owner of several classic designs I'm really excited to see this latest project. Everyone that has been in my basement or warehouse already knows that the last thing I need is another kit to build but this looks like one that I'll have to get.

Congratulations on another great concept.

Ed
May 04, 2006, 11:14 AM
Registered User
Daemon's Avatar
Before you mess with the CG too much, try reducing the control throws.
It is possible to fly swept wings with extremely rearward CGs.
By way of example, my latest Bee (with a Ming recommended CG of
7 1/2") is flying with the CG at 8 3/4". It was all over the place the
first time I flew it and I was tempted to move the CG forward, but instead
I've lowered the elevator rate to 15% and the aileron rates to 23% and
it's now quite responsive and loses almost no energy in turns.
And while it does waggle just a little bit when it's slowed down near
stall speed, otherwise it flies like it's on rails and I intend to combat
with it like this.

Ultimately I think for a wing or a plank, the CG is best determined with
the dive test. As long as it's not tucking in a dive, the CG is not
too far back. If it's twitchy or stalling, try reducing the throws until
that goes away.

ian


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