Gentlemen,

     I was intrigued by a previous thread about the Google search for the Nemesis II, and also flooded with memories of that plane
from the late 70's.  If I recall, the Nemesis II was a mainstay of combat matches in those days.  Not only was it a great airplane,
but an eliptical winged version was flown, called the "Bosta."  Correct me if I'm wrong, but wasn't it by a guy named White who
was Howard's roomie at Purdue?  The Bosta seemed to be a lot more work to build, however.

     The Nemesis airfoil was also used, I believe, in the Mongoose I slow combat kit, and also in some of the M&P sport models.
such as the Cherokee.

     Now, this might be a stretch, but doesn't the Sig Skyray use an airfoil identical to the Nemesis?

     There are still Nemesis airfoiled planes flying at our field today, but I need to know:  Was there a Nemesis I?

     Many thanks,

     Richard Ferrell

That's right about the Nemesis II, Bosta, Neal White, and Mongoose.  I don't know about the Skyray.  Nemeses I and II were about the same, but the max thickness was squished forward to 20 % on the I, and 25% on the II.  I thought the II was a little faster, so I picked it to build more of.  I didn't do a very thorough experiment.  Gary James recently did a CFD analysis that said the I is actually better. I may build another Nemesis I.

The FAI version came later.  Steve Fauble (I think) did the 1/2A. 

Howard, I looked at the CD and CL plots that Gary provided. It looks to me that the difference between the two airfoils (Nemisis I and II) is insignificant until the AoA is very large, like well over 10 degrees. Do you or anybody have any idea what AoA a combat ship might see in a typical tight turn? Do they ever see AoA as large as 10 degrees?

IMWTK.

Regards,

Bill Lee

Bill, a rough calculation, an F2D plane going 132 fps can pull about 60g's in the first quarter of a loop.  Back calculating the lift needed(~60lb) I get a Cl of about 1 is needed.  Going by Gary's graphs that puts almost any airfoil well below the stall point.  I don't know of anybody who pushes a plane regularly anywhere near the stall.  Besides the risk of the plane actually stalling and going berserk, the drag starts to go up rapidly above 10 deg., making the plane wallow around.  Most guys seem to have more control than needed, but actively avoid going more than half way around a loop in order to avoid slowing down too much.  The planes can zoom into a corner and not lose too much as long as you avoid prolonged, high G turns.

Going from the sublime to the mundane here, the Skyray uses the Flite Streak airfoil.  I'm not sure how it compares with the other airfoils mentioned.

Both Phil Cartier and I saw the Wortmann paper on min-drag flaps bout 1976 and concluded they weren't worth the bother (you'd have to build them for about 1.2 oz. to break even), but the airfoil involved was thin at the back, which may have been most of the bother. 

Gary, did you test by adding a flap to the airfoil(longer chord), or shorten the airfoil and keep the chord the same?

Interesting,  pick 10deg on the plane airfoil and get x amount of lift.  The 10 deg. of flap doubles the lift, so look at the drag at 5 deg AOA.  The flapped version generates about 5-6% less drag.

From some similar test Igor Burger did(or was it Serge?) the Flight Streak airfoil(Naca section with a flat fixed flap) also picks up 5-6% better performance.

I predict the combat guys will be going back to the Flite Streak pretty soon.  It's the only reasonable way left to get any more performance out of the wing.

So the notion that gluing on a fixed flap improves performance does have merit?  I was wondering about that.

Gary, did you test by adding a flap to the airfoil(longer chord), or shorten the airfoil and keep the chord the same?

Interesting,  pick 10deg on the plane airfoil and get x amount of lift.  The 10 deg. of flap doubles the lift, so look at the drag at 5 deg AOA.  The flapped version generates about 5-6% less drag.

From some similar test Igor Burger did(or was it Serge?) the Flight Streak airfoil(Naca section with a flat fixed flap) also picks up 5-6% better performance.

I predict the combat guys will be going back to the Flite Streak pretty soon.  It's the only reasonable way left to get any more performance out of the wing.

Phil:

The chord remains the same.  That is the only technically accurate way to do it.  The flap is 20% of the length of the chord, so for a 10" chord, the flap would be 2"

Those Wortmann sailplane control surface airfoils always intrigued me, but ya gotta remember, Prof Wortmann designed those for much larger Rn's.  Howard sent me a link to a CFD study that Igor Burger did on them and he concluded that there was a non-linear pitching moment or something funny with them.  On the other hand, both Igor and Paul Walker use a similar technique on their stunt airfoils.  The whole point of the Wortmann sections was to eliminate the pressure peak that occurs at the hinge line when the flap is deflected.  If you look at the surface of the section with the flap deflected to the design position, you will see that it presents a smooth contour to the air.  On the other hand, when the flap is not deflected, the airfoil looks "pinched".

None of this airfoil foolishness has any importance anyway, I'm just goofing around with it because I'm bored.

and then:

 Am I misunderstanding Phil?

Did the test that was done with the Flite Streak airfoil non-dimensionalize the chord back to unity or was the 5% performance increase based on the original wing area or chord length?  If it was based on the original wing area/chord and not the increased area and chord due to the addition of the "fixed flap" (whatever THAT is, since a flap, by definition, is a movable surface) then the data is completely invalid.  You HAVE to compare "apples to apples" to have any meaningful information.

I just found this forum.  Wow people still talk about combat! 

Hi Steve!  Ya gotta come fly with us.  Lester has organized a WWII 70 mph event with monthly contests around Texas.  FUN.

Howard, What was the lightest Nemesis you built. My father seems to remember somewhere around 11oz. He said his were usually around 15-17oz.

Steve

Howard, What was the lightest Nemesis you built. My father seems to remember somewhere around 11oz. He said his were usually around 15-17oz.

16 1/2 oz. with engine, a plain-bearing Supertigre.  The best flying ones were about 20 oz.

I'm actually building some of these airplanes now.  They will be heavier, especially the ones with Nelsons.  

Howard,

     Are you making any structural changes in the latest Nemesis II's to handle the wild power you are going to get from the Nelson .36?  Are you increasing the wing area on these models to take care of the extra weight of the engine?........TDurrill      

I plan to add some black stuff to the Nelson-powered ones.  No size changes.  That wouldn't be authentic. 

3mm strips laminated to the top of the 1/4" sq spars just underneath the l.e. sheeting would give you the stiffness that you are looking for and would not spoil the authenticity.  Sounds fun.  I wanna see them the next time I get a layover in SEA.

Too late.  I haven't flown them yet, though.

I'm ashamed for anybody to see them until I strip off the Lustrekote.

I'm ashamed for anybody to see them until I strip off the Lustrekote.

Howard:

PolyFiber Light looks a lot like silk, but can be heat shrunk.  However, you must use their "polytack" to glue it down and their product line is specifically formulated to be compatible with each other.  Here is the link:  http://www.aircraftspruce.com/catalog/cspages/polyfiberuncertified.php

Is there a online copy of the Nemesis II construction article and bill of materials?