I'd like to kitbash a new wing for a 4*40 fuse that I have. I would like to investigate the flight characteristics for a Selig 8036 airfoil. Has anyone used one of these? Any comments?

Thanks,

Bob

Be warned that the whole series of 80XX airfoils MUST be made to the finest tolerances to see any difference between them. Thie means a fully sheeted wing or better yet a vacumn bagged glass and foam type. And this assumes you can cut the cores or ribs so that the final shape is within probably 7 or 8 thousandths of an inch at any point and about 1/2 that for the first 1/4 of the chord.

For the usual 4-40 or 4-60 type open rib construction you are wasting your time using something this high tech.

Sorry for wasting the bandwidth if you already knew all this and planned on following through properley.

In any event I doubt that you will gain much by using such an airfoil on a power model where the performance gains over the usual "Florsheim 9%" will go largely unnoticed thanks to the engine on the front. These airfoils are really meant to shine on sailplanes where every last fraction of a percent counts.

If you're looking to experiment on a model of that type then I would suggest going for either a true Clark Y for slower flying or a true symettrical airfoil for better stunts. Or experiment with high lift devices like proper flaps and/or leading edge slats. Or how about a very high camber airfoil that isn't too critical to covering sag like a Gottingen 500? That would slow the model down. Perhaps add a camera and load bay for lifting things?

Wow Bruce....ya just punched me right in the stomach! I've been laboring along under the misconception that the S8036/8037's were the best things since canned beer. Been using them on all my semi-symmetrical winged designs (and on friends' projects where I was asked to do the wing design) for over 5 yrs. now. From the driver's seat, my perception has been that they were superior in terms of smooth flying, predictability and low drag. Most of them were D-Tube structures as well. Granted, they were all conservative designs with light wing loadings so maybe any old airfoil would fly great.

My latest project-in-planning has a triple-tapered fully sheeted foam wing with the 8036/8037 combo and 2 deg. washout. It should REALLY be nice with the accurate profile and all.

N1EDM, I'd love to hear your opinion of the 8036 if you build a new wing for your 4-40.

From what I've read about how critical these are this sentance pretty much sums it up I suspect.

Someone in another post was describing the shape of the 8035 and the "old" S7037 and how on a 10 inch chord the differences between the two are less than 30 thou or so and how important that 30 thou was if you expect to see the advantages in the new airfoil. Covering sag would account for much more difference than that so any advantages of one over the other just go down the flusher if you have any open bay style design at all.

D tube construction for such wings was also blasted by non other than Micheal Selig in Soartech 8. The transition at the rear edge of the D tube between the ribs wreaks havoc on the airflow in you're serious about your sailplane flying. Extending the sheeting on the upper surface back to about 60to 70% of the chord helps a lot to aid the airflow. But on shapes where the trailing edge cusp or local droop is pronounced, as in something like the S1223, the only way to get the advertised performance out of such airfoils is total sheeting or vac bagging.

Are we talking about the same airfoils? The ones I'm referring to are the S8036 & S8037, originally designed by the good Dr. S. & tested for the Top Flite P-47 R/C semi-scale model and subsequently used by lotsa folks on a plethora of other R/C power models with reportedly great performance.

The S7037 is kinda different, being a sailplane airfoil, yes? S8035 is 14% symmetrical aerobatic airfoil. [sm=confused.gif]

Well do I ever feel silly. I was thinking of the SA7036 which IS intended for sailplanes.

But the same rules apply to the D tube aerodynamics. It would be interesting to see how much better it does with the sheeting extended back to about the 60% point. Or make it sheeted foam.

Selig showed that regular D tube style wings developed little separation bubbles just behind the edge of the sheeting between each rib for even low to moderate lift coeffients. It also makes for a very draggy and mushy model at higher lift coefficients. Properley supporting the covering to guarantee the wing shape will make any decent airfoil perform better. Martin Hepperle has a good write up on his site on this as well.

With a honkin' great engine you may not notice the extra lift or care. In fact if the wing suddenly starts making LESS drag and doesn't stall as easily you may not like it. The snapping maneuvers would need to be entered more aggresively and the model may tend to float on landing more than you would like.

A lot of discussion is going on here...

In reading Seligs book on basic airfoil design, I got the impression that the 8xxx series was designed specifically for powered planes (which has that big fan in the front) while the 7xxx series was designed for silent flight.

If I recall correctly, the 8036/8037 combination is used in at least two (and probably more) of the Top Flite Gold Edition kits. The 8036 transitions to an 8036 at the tips to ease up on tip stall, if I remember correctly.

I want to kitbash the 4*40 as an experiment (it seems like all my planes are experiments in one way or another - whether I want them to be or not). If the wing works as well as I hope that it does, then I want to use that 8036 airfoil in a stand-off scale plane that I want to build.

For the record, I will be sheeting the LE right up to the high (and low) points on the foil, then go with capstrips for the rest of the way.

Dickeybird, I never thought of using D-Tube. Thanks for bringing that to my attention. I "used" to know what D-tube construction was when I followed R/C several years ago but haven't seen a recent example of it. I'm wondering what kinds of improvements have been made since then.

Can you suggest a web site that might show me some recent D-tube designs? I might like to try them out... The D-Tube stuff that I used to see was for CL, and that was only a vague memory.

I was concerned that C-tube of construction might be a little flimsy for R/C, but you say that you're using it with good results. Could you point me to an example of it? I'd appreciate it.

Does anyone else have any points for discussion about the 8036/8037?

Dickeybird, I may have answered my own question about D-tubes , but tell me if I have it right anyway... I did a search on YAHOO about D-Tube construction. What they call D-Tube appears to be (to me) ordinary construction.. i.e., a full rib with top and bottom main spar, sheeted, and with shear webs.

To explain, to me a D-Tube (waaaaay back when...) had a Leading Edge section that you almost built by itself, then added the aft portion of the rib later... that's why I said that I thought it was 'flimsy).

Let me know if this was your interpretation of a D-Tube.

Thanks,

Bob

Yup, either description you gave describes a D-Tube wing structure. The second example you mentioned is like the F/F'ers use with a carbon composite "C" that is molded on a form, removed, ribs placed and shear webs placed between the rear top & bottom edges of the "C" and in between the ribs.

Wigs built with D-Tubes and capstrips are very strong without the weight penalty of a fully sheeted wing. But, the covering droop between the ribs (as Bruce already said) creates additional drag and unpredictable results. Martin Hepperle even went so far as to make a computer model of a typical D-Tube wing showing the pressure gradients (I think that's how he described it....WAY above me!)

A multitude of models have been built with D-Tube wings with great results! I think the sailplane guys are the only ones that really sweat the extra drag from an open structure aft of the spars. That's my 2 cents anyway.

Guys, here is a quick drawing showing the extended leading edge sheeting that I'm suggesting. What this does is to maintain a better shape past the more critical high curved and forward portion of the wing. It's still a D tube but you just extend the sheeting a bit further back and then cap strip the rear portion of the wing. Very little extra weight but perhaps a whole lotta better aerodynamics. Note that the cap strips and open covering are now back at the portion of the curve where it won't sag anywhere near as much as if the sheeting ended right at the spar.

And I hope I got the right airfoil this time....

Thanks for the discussion... As for the construction, well, I guess I've been building my wings that way all along anyway, with a sheeted LE and capstrips to prevent the sag...

but in the end, my main question was about flight performance before we all took that left turn back there. And I think my question was pretty well answered... thanks...

Does anyone else have any comments on the performance of a S8036 airfoil? If this works out as planned, I will be making a tapered wing with a S8036 at the root, tapering to an S8037 at the tip.

Thanks again,

Bob

I'll just add that I think the S8036/37/38 airfoils are pretty bulletproof when it comes to tolerances. They were designed to be that way.

Yes, the sailplane airfoils are a different story.

Michael

Thanks, Michael. Any plans on an updated airfoil book coming out soon? I have Volume 3 (at least, I think it's volume 3. It's about 2-3 years old).

Thanks again for dropping by.

Bob

We finished Vol 4 this yr, and it's free online. Here's a link to what's in it:
http://www.ae.uiuc.edu/m-selig/uiuc_...ilsTested.html
It's small wind turbine airfoil related, but anything dealing with low Reynolds number aero can also apply to RC. The best part about Vol 4 (I think) is that it covers our methods for taking the data in great detail. We have NREL NWTC to thank for that because they funded it.

Vols 5 and 6 we hope to wrap up in the next 3 months. We have the data; we just need to write it up.

Michael

Thanks for that link!!

Bob

Bob,

I posted on another forum the good success I have had with a straight planform, S8036 wing with an aspect ratio of 6. I have never had an airplane with such broad performance envelope, from full out high speed power dives to really slow landings. This airplane has D-tube construction to 33%, 2.5" rib spacing and cap strips. Covered with silkspan (nitrate followed by butyrate), it has almost imperceptable sagging.

Now, the wing loading is low, (18 ozs) and I put in a fair bit of washout, but I really think the airfoil is, as the man says, bulletproof.

I am 3/4 finished my scratch-built Mossie, which has a severe taper (>2:1) and an AR slightly less than 6. I am using the 8036. This wing is fully sheeted. It is 54".

Lou

Lou,
I think I came across that plane in the other thread that you mentioned. I like the form of it... nice.

I'm going to try something bizarre. I have a Bridi Brown B-2 (aka "Miss Los Angeles" ) which was a Golden Age racer. It has a fiberglass fuse, so I'm locked into the airfoil shape, at least at the root where it fairs into the fuse. If I'm right, the upper camber is very similar to a Clark-Y.

I'm designing a built-up wing for the plane, and am going to try to go from this Clark-Y at the root to a S8036 at the tip (with washout). On another thread, I found out that the stock airfoil might be prone to tip stalling at slow speeds (as on landing).

Wish me luck...

Bob