Change the airfoil on a Sagitta 900 ? - RC Groups
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Sep 29, 2012, 12:58 PM
Planes > Time

Change the airfoil on a Sagitta 900 ?

I have always liked the shape and lines of the Sagitta 900; I finally was able to get a kit recently. I had been watching for about 25 years, for one I could afford.

Question; It has an Eppler 205 airfoil, is there a more modern airfoil, that would increase the performance enough to make the work pay off.

The Sagitta has a 99" wing with an 11.1 to 1 aspect ratio, 42-46 oz, and 6.7 - 7.4 oz/sq-ft.
These are off the box stats.

They seem to be a heavy glider, about 16 oz heavier than my Sky Sergio 09 and it has a motor and a full power system. Maybe they are better suited for slope use today.

I would like to get good performance from a hi start or winch, I donít know yet if I will try to motorize it. I am not a high level competitor, just ALES, and relaxing with a glider almost out of sight.

Any help will be greatly appreciated, I have a full wood shop, so I can make ribs to any airfoil shape.
Thank you
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Sep 29, 2012, 01:18 PM
Registered User
Larry Jolly's Avatar
As the product engineer for Airtronics during the Sagitta project, I would suggest that you leave the airfoil as is. The 205 is a great choice for this design, and gives good perfomance for the Sagitta. You would get more benefit by reworking the nose and tail moments, and getting rid of the counter ballanced rudder. But, then it would not be a Sagitta. Why not build it as designed and enjoy the glider that brings fear in to the hearts of other Nostalgia flyers !!
Sep 29, 2012, 01:20 PM
AMA 3959
alstrahm's Avatar
are you going E- power it? I have three, and stock they are a great TD plane, take a tap winch launch, or a full bungee. mine are all RES.

Sep 29, 2012, 01:24 PM
AMA 3959
alstrahm's Avatar
yeah, what LJ said
Sep 29, 2012, 01:44 PM
Planes > Time
Thank you Larry
That is what I figured I would do. The question came up because every time I mentioned the Sagitta, some one would say, O they have the wrong airfoil, or It should be this or that airfoil. I was about 95% certain I would build it as it is.

You did a terrific job on the Sagitta, I have a ridiculous number of gliders and glider kits, But The Sagitta, has always been the most beautiful glider (IMO) I have ever seen.

I am a little curious about exactly what you modify on the moments, would it change the look much?
Thank you for responding, you would know more about them than anyone else.
Sep 29, 2012, 03:23 PM
Registered User
Larry Jolly's Avatar
Many of Lees's designs could wobble with over zealous inputs to the counter balanced rudder. I was trained on the Hobie Hawk and never noticed the wobble or shimmy, I just flew the airplane. The Sagitta is a little short in tail moment as Lees's designs were designed to go in a 42" box. But if it were me, I wouldn't change a thing except...
Get rid of the pine wing joiner box and instead use a 1/16" plywood front web joining the spars at the wing root. Make sure you do a good job of getting a smooth radius on the cable elevator pushrod, or replace it with a bellcrank drive system. Other wise leave the Sagitta stock and enjoy it. LJ
Sep 29, 2012, 05:24 PM
Planes > Time
I like the idea of a bellcrank, instead of the cable. I try to eliminate all play or slop in control systems. Cables can give a lot of slop around corners. I will use the ply wood joiner for the spar.

I also flew a Hobie Hawk many many times, and am proud to say I have 2 of them, one is totally restored, mostly yellow with red trim, I call it Yellow Hawk. The other went straight into the ground, at probably around 100 mph, after I got distracted, then found my plane in a spiral dive, too late to pull out. But it is all fixed and ready to recover. It will be Blue Hawk. The wings ended up in 5 pieces instead of 2. I had do some research to fix them properly. I had the Hobie wobble when I first started fly it, but later changed to modern high quality radio and good servos, end of wobble.
Sep 29, 2012, 06:36 PM
Registered User
whacker's Avatar
I've built one with S 3021 ribs, I find it penetrates better on breezier days, my go to plane when the winds a little stronger, also lengthened the nose and Tail, and called it the Elio... AUW was 1415 grams , 50 ounces , lighter then my Sagitta
Want to build a S3021 wing?

Mind you the the Sagitta is really nice stock

Re wing joiner box,( box where wing tube fits thru fuselage ), I've used maple on my latest builds, wrapped with floss...

No problems yet.

Last edited by whacker; Oct 15, 2012 at 07:52 AM.
Sep 29, 2012, 08:31 PM
Registered User
On weight, you're comparing apples and oranges. If you pick the right wood and build carefully, you may get down to the weight range listed. If you do, it will be almost a floater. (A 42 ounce Oly 2 IS a floater, and has the same span.) A rough rule of thumb on weight is to compare weight to the square of the wing span. By this measure, a 44 ounce Sagitta 900 is equivalent to a 28 ounce two meter (or a 29 ounce Sky Sergio). That's fairly light for a two meter. Maybe 4 ounces heavier than a Gentle Lady done with old radio equipment. I used to fly a Sagitta 600 (two meter span) that weighed 42 or 43 ounces. If kept moving, it was fun to fly and I won many contests with it, even on days with little wind. I'll admit a mistake cost me more altitude than with some other gliders. I think a lot of that weight was because the tail was a bit heavy so the nose was full of lead. So if the 900 is anything like the 600, keep the tail light! Make sure the balsa in the tail is LIGHT balsa. I've also won some contest with my Cumic, which is the Sagitta 900's successor. I think mine is about 60 oz. I'd be happier if it was 50 oz. but it's usable as is.

The 600 fuselage can be weak right at the front of the fin. If I was making one, I'd make it a little wider there, or else reinforce. Maybe if the 900 looks very narrow there you could widen it as well. And the 600 could have used a longer tail, just as Larry said the 900 might. But then again, with the 205 it was a good idea to keep it moving, which would cut down on the wobble.
Sep 29, 2012, 08:34 PM
Registered User
P.S. If I WAS going to build one with a different airfoil, I'd probably go by this:
I'd pick one of the series recommended for heavier 2 to 3 meter planes. And I'd make every effort to keep it light. But as mentioned, it wouldn't be a Sagitta any more!
Oct 01, 2012, 12:43 AM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
I have found that you can easily modify the E205 airfoil to the S3014. I am considering this on my Sagitta 900 build.

Oct 01, 2012, 10:51 PM
Jackass of many Trades
MichaUT's Avatar
Oct 02, 2012, 10:56 AM
Registered User
As I remember, the Sagita airfoil was a 205 with the standard Lee modifications; flat bottom with increased leading edge radius. How much better could it have been if Lee had used a longer kit box.
Oct 02, 2012, 01:18 PM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
I matched up an E205 template to the plans and really didn't see much in the way of deviation so I'm not sure how much Lee modified the kit airfoil. I am torn as to just leave things alone or to move to a more efficient airfoil.

Anyone can post polars between the E205 & S3014 for me?

Oct 02, 2012, 10:07 PM
Registered User
If you poke around in here, you ought to find some polars of the two airfoils from wind tunnel data:
I think those two are probably in volume 1. I'd compare them for you, but my computer seems to be rejecting Profili these days.

If this is for the Sagitta 900, you should supply average chord and wing loading so the plots will be relevant.

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