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Jan 25, 2012, 10:03 PM
TheyreComingToTakeMeAway!
derk's Avatar
using 6.05beta, and i followed one of the first videos that you posted. i didnt run any calcs on what the RN should be like so when i ran the airfoil, so i set it low 50k-100k as i want to build a lightweight floater.
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Jan 25, 2012, 10:05 PM
Just call me crash for short
Quick61's Avatar
Thread OP
Ah, good point there Eric, that had slipped my mind. (not that hard of a thing to do)

Mark
Jan 25, 2012, 10:08 PM
Registered User
ohmite's Avatar
Quote:
Originally Posted by derk
using 6.05beta, and i followed one of the first videos that you posted. i didnt run any calcs on what the RN should be like so when i ran the airfoil, so i set it low 50k-100k as i want to build a lightweight floater.
Low Re is not always a good thing and your sections (depending on which you choose) may not be able to keep the flow attached at the kind of angles of attack you need to fly at. Some airfoils are better at this and there are several that are optimized for low Re flight and can handle the more viscous air. The print was too small to read what section you are using.
Regards,
-Eric
Jan 25, 2012, 10:14 PM
Just call me crash for short
Quick61's Avatar
Thread OP
Also, when you ran your airfoil analysis, did you use the same numbers for the alpha that you are using in your wing analysis? Another thing you might want to do is expand your Re a bit. I run the batch analysis with an Re list that starts at 10,000 and ends at 500,000. That pretty much covers the range for the low Re airfoils and the speeds the wing might see, both ends of the extreme.
Jan 25, 2012, 10:21 PM
Just call me crash for short
Quick61's Avatar
Thread OP
I see by the last screenshot that your using the EH1590. I'v been looking real hard at that one my own self. Go back through and look at everything again, keeping in mind the tips here and see what you come up with. I'm still JUST learning this program too and have had several litle snags, all being fixed with making sure that the airfoil and wing analysis parameters match.
Jan 29, 2012, 02:58 AM
Just call me crash for short
Quick61's Avatar
Thread OP
I just upgraded to XFLR5 v6.04 Beta and it is different than the v5.x. Took me a couple of tries to get going. At this moment, I'm not quite sure that I know exactly what I did to get it to click over. It seems that the interface has changed some and there are more options now, most of which I'm not so sure of what they do. More learning, but at least that's fun for me.

While I was off poking around some foreign wing sites, I came across a nice little plank called Bleed on the http://ig-nurfluegel.ch/ site. Stretched the wings out to 2m and sticking with the jwl097 airfoil, started drawing up some plans. We'll see if this get's to a build thread. I figure a couple fins on the tips, single fin in the middle... what's the difference?

At any rate, here are a few snaps from the new XFLR5 running through with the jwl097 foil. It took a few searches to hunt down the .dat file for that one. The new program has an entire new area of analysis for stability. Got NO clue yet as to how that's suppose to work! Anyone have any pointers to on that?

Mark
Jan 30, 2012, 05:31 PM
Crazy Cessna Owner
Robbie d's Avatar
The trick is to have the fin to the rear of the CG, as I have learned here, if you have your vertical stabiliser infront of the CG, you introduce a destabilising element (Kind of like the feathers stabilising an arrow. It sounds like the shorter the moment arm between the CG and the fin, the less stabilising force produced. (someone jump in and correct my understanding if it isn't accurate).
Jan 30, 2012, 07:14 PM
internet gadfly
nmasters's Avatar
Quote:
Originally Posted by Quick61
I figure a couple fins on the tips, single fin in the middle... what's the difference?


Mark
Here's a video of the difference:
http://www.youtube.com/watch?v=W5HGHRz3bbI&t=35s
Jan 30, 2012, 07:45 PM
Just call me crash for short
Quick61's Avatar
Thread OP
Great video Norm. I was being a bit sarcastic with that comment, but I did not realize that there would be that much difference on a plank(ish) wing. Explains why we don't see many plank wings with big winglets.

On a side note, I've just about got the drawing done for a 2m plank based on the Bleed mentioned above. Hope to start a build thread in a few days, so we'll see how well a plank gets received in this forum. With all these excellent swept wing machines, I'm almost afraid...

Mark

And another side note, I mucked about with the stability analysis tools some more in XFLR v6 and got it to start computing "something" but it errors out and never gets to any output. I'm sure there is something I'm not telling it that it needs, but I don't know from where the info is missing. Or just what info is missing... More study needed.
Last edited by Quick61; Jan 30, 2012 at 07:53 PM. Reason: added another side note
Jan 31, 2012, 12:31 PM
Everything's A Composite
Knoll53's Avatar
Quote:
Originally Posted by Quick61
I've just about got the drawing done for a 2m plank based on the Bleed mentioned above. Hope to start a build thread in a few days, so we'll see how well a plank gets received in this forum.
I hope you DO post a build thread. I like build threads. We all learn from them. You don't have to be a NASA engineer to post here. We're just modelers.

Kent
Jan 31, 2012, 04:24 PM
Just call me crash for short
Quick61's Avatar
Thread OP
Thanks Kent, I will. You guys have set the bar up a few notches with your excellent designs and builds, hope I'm up to the task. I do have one little trick up my sleeve, so we'll see how that goes. Heck, I don't even have the plan 100% yet and I'v already started cutting out some ribs.

Mark
Feb 06, 2012, 08:15 PM
Registered User
ohmite's Avatar
I figured if I couldn't get to building, I could at least get some work done on some analysis. I have been evaluating Vern's Colibri 100 with XFLR5(6.05) and have some interesting results posted below. I have also attached the project if you are interested. I am working on getting control surfaces in to it right now.

Interesting plot of the lift distribution at various angles of attack. You can see how the distribution on this wing changes from a bell shape at lower angles to more of a parabola at higher angles. The program has problems computing data for the tips though as the Reynolds number is too low.

A little thing I've found is you must analyze the angle of attack range of the airfoils that exceed the angle of attack of the actual vehicle so when the twist is included the program has a chance to properly interpolate the information--If you have a -8 deg twist in your tip section, make sure you analyze angles down to at least -8 deg if you intend to compute the vehicle's characteristics at 0 angle of attack.

Comments and suggestions are welcomed.
Regards,
-Eric
Last edited by ohmite; Feb 07, 2012 at 09:40 PM.
Feb 07, 2012, 01:13 PM
yyz
yyz
Registered User
yyz's Avatar
Quote:
Originally Posted by Quick61
Anyone else have any work their doing with XFLR5? Post what you have and lets have a sneaky-peaky-lookie-see. Anyone else thinking about giving XFLR5 a try, go for it! It is a truly amazing program and I'v only just started to scratch the surface. Every time I work with it I find something new.

Mark
Mark,

I just noticed this thread and am subscribed. Interesting stuff. Not sure whether my work is applicable to a flying wing but there is some xfoil noodling here:

http://www.rcaerotowing.com/forum/sh...?120-Eta-Biter

Best of luck,

Mike
Feb 11, 2012, 05:17 PM
Balsa dust maker
plane_tech's Avatar
Quick,
I just came across this thread this morning otherwise I would have posted this earlier.
I started a similar thread a while back. It seems as if you are getting the hang of it, but in case you need some clarification, here is the link : Help with XFLR5
Feb 11, 2012, 08:03 PM
Registered User
ohmite's Avatar
In case anyone is still following this thread. I've been playing variations on Vern's Thermal wing from his earlier build log and flight posts. I have modeled it in XFLR5. I have tried several airfoils and settled on the RS004a (from the CO8 and one of Vern's designs-the Nemesis). The airfoils I tried including the SD7037, SD7003, MH45 and HM50t, I ended up picking the RS004a as it seemed to have a better L/D at higher speeds than the others for this configuration, it also seemed to have the widest peak L/D which should make it a little easier to stay near the max without worrying too much about speed variations. I also ended up applying a slight taper to the outer panel to improve the lift distribution get closer to the elliptic 'goal' I was shooting for.

Twist is 0deg at the first joint, -2.5deg at the 2nd, -4.5deg at the tip. Joints are at the 1/3, 2/3 span locations. Tip rudders are based on looks more than anything (looks about what Vern used ).

The lift distribution shot is approximately at the max L/D and at the Cl needed if it comes in at 1.5kg (my goal).

The polars show cg variations with control surface deflections (neutral, TED & TEU). I am thinking the cg might be best at somewhere between 250 and 275, it seems less sensitive to cg than the Colibri shown earlier.

I have attached some screen shots. I tried to include a copy of the project, but it is larger than rcgroup's max size. If anyone is interested in experimenting with this model and wants a copy, send me a PM with your email address and I'll email it to you (~3.6MB).

Comments and suggestions are welcome.

Regards,
-Eric


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