Airfoil suggestions for tailless FSW slope glider sought
Hello all, I'm in the pencil & paper stage on a tailless forward swept wing (FSW) slope glider design, and am seeking opinions regarding suitable airfoils.
This is the first plane I'm attempting to design completely from scratch, so it's a great learning experience for me. I do have a bit of experience flying tailless gliders (the Weasel to be precise) and have access to a very nice CNC foam cutter.
I plan to use a fiberglass fuse and balsa-sheeted EPS wings.
My current dimensions are as follows:
Root chord 10.5"
Tip chord 4.5"
Forward sweep at LE 1.5"
Fin length 12"
Fin height 6"
Apologies as I'm at work right now and don't have access to my pencil sketch of the proposed planform. I will post that later on today when I get back home. Hopefully the above information is adequate to give an idea of what I'm thinking about.
So, any airfoil suggestions?
Punta Gorda, FL
Joined Apr 2002
See Bill Evan's Saracen at:
The airfoil is tried and true for your application. There are many other possibilities. You will need low pitching moment coefficient airfoils and wash-in or, positive pitching moment coefficient airfoils with no twist in the wing. See:
A swept forward wing is unstable in yaw and needs a large vertical tail volume coefficient to stabilize it in yaw.
Aerodynamically, the sweep angle is defined by the 25% chord line , not the leading or trailing edge.
The CG, taper, sweep, twist and airfoil selection are interdependent in a flying wing design. All five factors must be harmonized to achieve pitch stability and pitch trim. Since four of the factors are usually built in and not very adjustable, successful flying wing design rests more heavily on theoretical calculations than does the design of a conventional, tailed configuration. By guess or by gosh seldom works for flying wings. Just so you know what you are letting yourself in for.
Scratch Design and airfoils
If your going to draw your own plans and need to
import your selected airfoil into the project you may
want to check out the Airfoil Design Workshop.
It's an easy-to-use piece of software that allows you to
display and interactively modify airfoil shapes. It can
import airfoil data files directly from a web site. You can
export the airfoils to either a DXF file or ASCII text.
If you don't have or need CAD software and just want
to view and print the airfoils you can use a free DXF
file viewer called CADView. (Link to this viewer
on the AFD web site.)
AFD Web Site - Free Demo
First up, thanks all for the advice. I'm aware of the special challenges associated with FSWs in general, and in specific when it comes to tailless designs. But I figure I get the most learning bang-for-my-buck this way!
Here's more detailed info, sorry for the introductory stuff, it was from memory while I was at work:
Wingspan 60.0" Root Chord 10.5" Tip Chord 4.5" Wing Area ~450 sq.in. Aspect Ratio 8.00 Taper Ratio 0.43 Sweep @ C/4 -5.62° Static Margin 3% / ~0.25" Neutral Point 1.30" C.G. 1.05"
I'm shooting for an AUW of around 20-22oz., and a wingloading of around 7oz./ft. A similar plane of about 51" span was built around this fuse, with FSWs and a V-tail. It came out to 16oz. balanced, so even with my rather noseweight-requiring large and rearward fin (to be from 1/8" competition balsa) I think I'll be OK with an estimated AUW of around 20-22oz.
I've been recommended to try to find an airfoil that is thin (~8% or so), with 1-1.5% camber, and an
average Cm of about +0.01. Apparently, EMX 07 might be a good candidate, although it might need a bit more reflex. In general, the recommendation has been to look at profiles for plank-type wings, as opposed to regular swept wings.
Thanks again for any feedback!
Any thoughts on HS 2.0/8.0 from the Flying Wing database mentioned above? Here's the link:
Here's the info:
Class: Schlagprofile (Reflexed)
Use: Plank, Slope
Punta Gorda, FL
Joined Apr 2002
I've decided to try it out with the HS 2.0/8.0...I've bounced that off my co-conspirator and we think it will work. Thanks all for your help, I'll be posting project progress reports to the Slope forum once it gets underway. Should be interesting, to say the least.
You, being an old slope hand, probably remember the Larry Renger Toucan, in a 1993 Model Airplane News construction article.
It was a very well done and attractive FS sloper. I ended up with a rather ratty DCU T60R (after buying someone out when they got out of the hobby), a developmental version of the Toucan kitted by DCU and Dreamcatcher.
Might be worth some research to see what airfoil Larry used.
There are some Toucan or T60R pics here on R/C groups, somewhere
The amount of forward sweep you're indicating is insignificant in terms of any possible forward sweep issues. Just treat the whole model as a plank style wing in terms of airfoil choice and CG location to the MAC.
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