HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 29, 2009, 07:33 PM
agony sweetns the victory
atjurhs's Avatar
Any Flying Field Across America
Joined Jul 2005
3,513 Posts
Discussion
Characteristics of a good performing Cross Country XC Wing

Just for discussion it's getting near that "design/build time of year" again, and so my mind goes to asking the question, what characteristics comprise a good performing Cross Country XC Wing?

I would think that the two most obvious characteristics are wing chord and wing span. With larger wing chords comes higher Reynolds numbers and thicker airfoils, more visibility, but also lower Aspect Ratio


Acknowledging some of the great XC birds of yesteryear and their Airfoils:
SBXC SD2048
Astro Jeff ???
Sagitta XC E205
Sailaire Craft-Air 12% (Clark-Y with Phillips Entry)
CLOUD BOUND 4 Aquila airfoil
Thermal Queen E385


What are some other airfoils that should be particularly well suited for XC ?

E374
MH32
3014
AG4x Supra series
AG2x BubbleDancer XC series
7035/6/7/8

What are some other XC wing characteristics?
atjurhs is offline Find More Posts by atjurhs
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 29, 2009, 07:56 PM
Registered User
R.M. Gellart's Avatar
Joined Nov 2005
3,525 Posts
To give you another airfolil to work with, HQW3/13-15. These airfoils are on alot of scale ships but can fly very well with ships at that magical 11# max weight. I flew an Albatross with one of the HQW's on it and it was a great ship.

Marc
R.M. Gellart is offline Find More Posts by R.M. Gellart
Reply With Quote
Old Sep 29, 2009, 08:07 PM
agony sweetns the victory
atjurhs's Avatar
Any Flying Field Across America
Joined Jul 2005
3,513 Posts
Thanks Marc!!! I had forgotten about the HQW series.

And maybe I should not have included the wonderful AG4x Supra series. Perhaps it's too thin for XC ?
atjurhs is offline Find More Posts by atjurhs
Reply With Quote
Old Sep 29, 2009, 09:33 PM
Registered User
S. FL
Joined Jan 2007
840 Posts
atjurhs, XC isnt really about airfoils and leading technology. There seems to be a misconception between XC and "raceing"! XC can be any distance that you choose to go. If you think you "need" the latest airfoils or planforms to go XC you have been sadly misdirected. The latest airfoils and planforms may help you to go a longer distance and do it more quickly, ie better L/D speed, and at a huge cost, but regardless, you can still go XC even with a GL. It just depends on what you consider XC, 2 miles, 5 miles, 10 miles ect and the amount of sun lite in which you have to do it
Libelle201B is offline Find More Posts by Libelle201B
Reply With Quote
Old Sep 30, 2009, 09:16 AM
agony sweetns the victory
atjurhs's Avatar
Any Flying Field Across America
Joined Jul 2005
3,513 Posts
Quote:
Originally Posted by Libelle201B
atjurhs, XC isnt really about airfoils and leading technology. There seems to be a misconception between XC and "raceing"! XC can be any distance that you choose to go. If you think you "need" the latest airfoils or planforms to go XC you have been sadly misdirected. The latest airfoils and planforms may help you to go a longer distance and do it more quickly, ie better L/D speed, and at a huge cost, but regardless, you can still go XC even with a GL. It just depends on what you consider XC, 2 miles, 5 miles, 10 miles ect and the amount of sun lite in which you have to do it
Libelle201B, although I'm not fully understanding of the distinction you are making between XC and "raceing", in principle I guess I have to disagree with you. There seems to be plenty of posts in different XC threads that do indicate the newer technology (airfoils, planforms, etc.) will benefit XC.
atjurhs is offline Find More Posts by atjurhs
Reply With Quote
Old Sep 30, 2009, 09:57 AM
LSF V,LSF Secretary,AMA Lifer
Robglover's Avatar
Huntsville
Joined Oct 2003
2,077 Posts
Most of the XC competetions score distance and time, giving an advantage to a faster plane if the thermals are there to support it. The XC tasks for LSF goals have no points awarded for being fast. The wings designed specifically for each event might well look different. On a good thermal day the racing wing will be very capable of completing the LSF goals, but on a poor thermal day the fast wing might be at a disadvantage to a larger, lower wing loading, wing.

They could also look a lot alike, as the design goals are similar in many respects. Are you designing the wing to specialize for the LSF goals or XC contests? Or would you like something that will do both?

I've been involved with LSF V goal and return flights that lasted up to 4.5 hours, done in marginal conditions with an Aquila XL. Ask Nuevo for the blow by blow, it was a long hard road. I've also been involved in XC races done on a course that would qualify for an LSF V goal and return that were run in less than 45 minutes with an SBXC during very good conditions. Both planes were the right tool for the job at the time. Very different wings indeed.

As with most things soaring related, you comprimise for your own goals. Then you build it, learn how to fly it, and decide if it's worth trying again until you get it the way you think you really want it.
Robglover is offline Find More Posts by Robglover
Reply With Quote
Old Sep 30, 2009, 12:35 PM
Registered User
Tennessee
Joined Sep 2003
2,307 Posts
The requrements for a crosscountry model are
1. Stable
2. Big
3. Stable
4. Visible
5. Stable
6. Fast
7. Stable

As far as speed goes, just how fast do you want to ride bouncing around in the back of a pickup. I find that 45 is about my limit. I remember sneeking in a little flap to slow the model down because the road was so rough. Didn't tell the rest of the team I was dropping flaps. (Great race 1985) .
ChuckA is offline Find More Posts by ChuckA
Reply With Quote
Old Oct 01, 2009, 04:04 PM
Registered User
Seattle, Washington, United States, University of Washington
Joined Feb 2003
432 Posts
Is there any problem of having too much stability for a crosscountry model by adding dihedral? (Assuming that you do not run into dutch roll tendencies)

I think I would rather give up some L/D and speed performance in order to get more stability so the glider would be easier to thermal when it is hard to see.

-John Elliott

Quote:
Originally Posted by ChuckA
The requrements for a crosscountry model are
1. Stable
2. Big
3. Stable
4. Visible
5. Stable
6. Fast
7. Stable

As far as speed goes, just how fast do you want to ride bouncing around in the back of a pickup. I find that 45 is about my limit. I remember sneeking in a little flap to slow the model down because the road was so rough. Didn't tell the rest of the team I was dropping flaps. (Great race 1985) .
jbeanelliott is offline Find More Posts by jbeanelliott
Reply With Quote
Old Oct 02, 2009, 09:51 AM
agony sweetns the victory
atjurhs's Avatar
Any Flying Field Across America
Joined Jul 2005
3,513 Posts
I understand the need for having stability in the design, but I don't know that I'd want to give up too much ability to "penetrate and move" across the sky for added stability, ie. having a really forward CG will gain me stability but will also be more draggy. Not sure how much higher EDA values would degrade the model's ability to penetrate and move either. All good questions for this Grasshopper to ponder.....
atjurhs is offline Find More Posts by atjurhs
Reply With Quote
Old Oct 02, 2009, 10:36 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,151 Posts
After about 10 hours on the sticks I can say that this wing is pretty good. Thermals like a TD plane and fast enough to outrun any vehicle. Slightly noseheavy will still thermal well and not tuck at high speed. Carries 11 lbs easily and thermals like a hand launch at 8.5. Will tip stall slightly if pushed too hard but recovers very quickly. Take the dihedrals off the XCBD. Make shure it is strong enough not to come apart.
G Norsworthy is offline Find More Posts by G Norsworthy
Reply With Quote
Old Oct 02, 2009, 02:09 PM
agony sweetns the victory
atjurhs's Avatar
Any Flying Field Across America
Joined Jul 2005
3,513 Posts
Thanks G

A scaled version of the XC8 is VERY similar to the design I've been playing with. A scaled version of the XCBD is also VERY similar to the design I've been playing with. Amazing how the current set of wing design tools lead to VERY similar results

I'll be sure to take your advice about using the XCBD dihedrals, thanks again!
atjurhs is offline Find More Posts by atjurhs
Reply With Quote
Old Oct 02, 2009, 02:58 PM
Registered User
nuevo's Avatar
United States, AL, Madison
Joined May 2002
2,272 Posts
Greg,

your plane's aspect ratio at 14.9 seems a bit low for other planes of similar size. I know visibility (wing chord) is a big issue at the altitudes you fly. What other considerations influenced your choice of aspect ratio?

atjurhs, he gave you the dimensions. Built it!!
nuevo is offline Find More Posts by nuevo
Reply With Quote
Old Oct 02, 2009, 03:08 PM
Registered User
S. FL
Joined Jan 2007
840 Posts
Quote:
Originally Posted by atjurhs
Libelle201B, although I'm not fully understanding of the distinction you are making between XC and "raceing", in principle I guess I have to disagree with you. There seems to be plenty of posts in different XC threads that do indicate the newer technology (airfoils, planforms, etc.) will benefit XC.
atjurhs, sorry, I should have been more specific. You are correct in that "newer airfoils, planforms, ect will benefit XC". My post was intended to point out that newer airfoils, planforms, ect are not really needed to go XC. If I am not mistaken, alot of the hard core dedicated XC folks are flying a course or triangle and trying to do it in the least amount of time, also known as "raceing" in the full scale world. These planes as you suggest, are in fact designed to optimize speed and efficiency. That is what I meant by "raceing". On the other hand, a XC flight can be accomplished with ANY sailplane. You simply get some altitude, head down the road finding lift along the way, and go as far as you can. No $2000 dollar state of the art sailplane, filled with expensive equipment needed. Here is an example. In a 1 hour flight, if you were to take a GL that say had a cruising speed of 24 miles per hour and you spent half of that hour climbing, and the other half cruising, you would have been able to cover 12 MILES! And if you had a tailwind, maybe a whole lot farther. For a GL that is one heck of a XC.
Libelle201B is offline Find More Posts by Libelle201B
Reply With Quote
Old Oct 02, 2009, 03:47 PM
agony sweetns the victory
atjurhs's Avatar
Any Flying Field Across America
Joined Jul 2005
3,513 Posts
Anyone know of any real benefits of having both spoilers and flaps - RESF
atjurhs is offline Find More Posts by atjurhs
Reply With Quote
Old Oct 02, 2009, 03:51 PM
Registered User
nuevo's Avatar
United States, AL, Madison
Joined May 2002
2,272 Posts
complexity
nuevo is offline Find More Posts by nuevo
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion CROSS COUNTRY PROJECT... OR... EVERYTHING YOU WANTED TO KNOW ABOUT XC on the Cheap :) steelhead Cross Country Soaring 319 May 15, 2010 07:03 AM
Wanted XC Sailplane: Old floater type large cross country type metermatch Aircraft - Sailplanes (FS/W) 2 Jul 12, 2009 04:23 PM
Cross Country Flying MMangus Electric Plane Talk 3 Mar 07, 2002 06:29 PM
Anyone have a good performing aileroned Moth? Spaulding Parkflyers 2 Jan 01, 2002 01:18 AM