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It seems the GU in the rain thing is a non event, if you do this...

 

http://www.cozybuilders.org/newsletters/news_68.html#GU%20CANARD%20TRIM%20CHANGE

 

http://www.cozybuilders.org/newsletters/news_67.html#gu_canard

 

So other than the rain does the ronz beat the GU in any other way?

Might we consider the GU as a performance upgrade?

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It seems the GU in the rain thing is a non event, if you do this...

 

http://www.cozybuilders.org/newsletters/news_68.html#GU%20CANARD%20TRIM%20CHANGE

 

http://www.cozybuilders.org/newsletters/news_67.html#gu_canard

 

So other than the rain does the ronz beat the GU in any other way?

Might we consider the GU as a performance upgrade?

The RONCZ 1145 is higher lift so it can be smaller and lower drag. Also does not need any external tabs to balance control loads.

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The RONCZ 1145 is higher lift so it can be smaller and lower drag. Also does not need any external tabs to balance control loads.

This is incorrect. When clean, the GU has a higher maximum Cl than the Roncz, and also lower drag at higher Cl's. The GU (at least as implemented on the V.E., L.E., and COZY) did not have any external "tabs" for trimming the elevator loads, any more than the Roncz does.

 

Nat cut the canard length due to his interpretation of deep stall considerations, NOT because the Roncz airfoil allowed it. In fact, when clean, the GU would have had an even worse effect on the deep stall tendency, due to it's ability to operate at higher Cl's, and would also have required (in Nat's view) a canard shortening - possibly even larger than the existing shortening.

 

The Roncz has much better Cl and Cd characteristics when dirty (but neither airfoil likes to operate this way).

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This is incorrect. When clean, the GU has a higher maximum Cl than the Roncz, and also lower drag at higher Cl's. The GU (at least as implemented on the V.E., L.E., and COZY) did not have any external "tabs" for trimming the elevator loads, any more than the Roncz does.

 

Nat cut the canard length due to his interpretation of deep stall considerations, NOT because the Roncz airfoil allowed it. In fact, when clean, the GU would have had an even worse effect on the deep stall tendency, due to it's ability to operate at higher Cl's, and would also have required (in Nat's view) a canard shortening - possibly even larger than the existing shortening.

 

The Roncz has much better Cl and Cd characteristics when dirty (but neither airfoil likes to operate this way).

 

Here is a quote from CP-43 Jan. 1985. A reliable source:

"This completely new and never flown before airfoil is by far the best we have seen. It has a negligible rain trim and the rain only adds 2 knots to stall speed. Of course some more flight testing remains to be done, however, we are confident that we do indeed have what we have been looking for. The R1145MS produces considerably more lift than the original GU—5(11)8 airfoil, and in fact more than any we have tested so far. This enables us to reduce the span, reducing whetted area, and thus drag. The basic airfoil is also very low drag. Its trailing edge shape provides the correct stick forces without external devices."

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Here is a quote from CP-43 Jan. 1985. A reliable source:

No question, but.....

 

"... The R1145MS produces considerably more lift than the original GU—5(11)8 airfoil.....

This statement (in an aerodynamic sense) has no particular meaning - i.e., it could mean one of a number of things. To explain why, I'll need to get into aerodynamic theory.

 

In 2D aerodynamic theory (and verified by wind tunnel testing), the lift curve slope of ANY sharp trailing edge airfoil is:

 

Cl=2*PI*alpha

 

where alpha is the AOA measured from the zero lift line of that airfoil.

 

In 3D theory (and verified in wind tunnel testing) the lift curve slope is:

 

Cl=(2*PI*alpha)/(1+2*AR)

 

where AR is the aspect ratio of the airfoil (for the COZY canard, it's about 10-12). This, again, is completely independent of the airfoil shape, as long as the trailing edge is sharp.

 

Now the shape comes into play. Depending upon the shape, different "alphas" are achievable - some airfoils can obtain higher angles of attack than others, and thereby achieve higher maximum Cl's.

 

So the question is, what did they mean in the CP when they said the Roncz had "higher lift" than the GU? __ALL__ airfoils have the same Cl at the same relative AOA, so they couldn't have meant that the lift curve slope was different, and they couldn't have been referring to the _maximum_ Cl achievable, because the GU can achieve a higher maximum Cl than the Roncz can (Xfoil analyses of both airfoils show the Cl/Cd curves - I'll be presenting these results [from Todd Parker] at OSH).

 

The following statement gives a hint of what they PROBABLY meant (and we have to remember that the CP's are written for a lay crowd, NOT for aerodynamic engineers):

 

.... This enables us to reduce the span, reducing whetted area, and thus drag. The basic airfoil is also very low drag. Its trailing edge shape provides the correct stick forces without external devices."

When tying the DRAG into the issue, the Cl/Cd curves may explain what was meant. From Cl's of 0 to about 1.0, the Roncz canard has a lower Cd (about 30% lower) than the GU canard. Above a Cl of 1.0, the GU has substantially less drag than the Roncz (up to 75% less).

 

While both airfoils have maximum Cl/Cd ratios of about 120, the Roncz canard produces this at low Cl's, whereas the GU produces this at higher Cl's (closer to stall). This is not surprising, as the GU was developed as a laminar flow glider airfoil, and gliders spend most of their time at low speeds. For a cruising aircraft, however, the Roncz is more efficient at lower Cl's, and if you're willing to give up something near stall, then it's possible that operating the Roncz at a slightly higher Cl than you would the GU would allow the changes (and advantages) indicated above in the CP.

 

So, the statement "higher lift" doesn't mean anything in an engineering sense (which is how I was approaching it), but I can certainly see that from a layman's standpoint, the CP's wouldn't have gone into this kind of detailed explanation - for most folks it won't mean a hell of a lot unless they're interested in understanding the underlying aerodynamics of the aircraft.

 

PS - since there are no "external devices" on the V.E.'s or L.E.'s that I've seen with the GU canard, I'm not sure what the reference to them means in that CP statement with respect to the Roncz.....

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That makes sense. :) I mean tying drag and L/D into the question of "best" trade-off.

 

Operationally it wouldn't necessarily be a penelty to have higher drag at Cl max. Just like high drag/high lift flaps on a conventional airplane is not undesirable for the landing configuration. A good L/D in the climb configuration would be a good thing and low drag in cruise would be a good thing. What I don't understand yet is how (or what part of) the aircraft performance envelope would be improved by the GU airfoil... :confused:

 

Low drag at cruise is good - score one for the Roncz airfoil

Better L/D at climb Cl is good - score one more for the Roncz airfoil

Low drag at Cl max is not necessarily good - call it a draw

Higher Cl max may not be good if it is achieved at a higher AOA and cannot be utalized due to other limitations of the design (like main wing stall on a canard configuratiion). Usually a higher Cl max achieved by increased camber also moves the minimum drag AOA up. It does occur to me that this might be desirable if the canard airplane is nose heavy But that's not usually the case in practice. So, I'm gonna call this one "score one more for the Roncz airfoil for the Long eze/Cozy application. Other applications may reach different conclusions ;)

 

Also, I'm still a little bit dubious (I'm an old flight tester: math models are good, wind tunnels are better, but the proof of the pudding is in flight :cool: )about the comparisons at Cl max: Xfoil and other math models do work well at low to moderate angles of attack they do not always agree well with measured performance at high angles of attack. Also, Rutan specifically recommended against retrofitting the Roncz airfoil on the Veri Eze because of it's "higher lift". I'll have to go look for the specific CP news letter... So, the higher Cl max may not be "real" and if it is real it may not be "good" or usable.

 

And WRT the external trim tab: I'll go look at my Veri Eze plans tonight but I'm certain the original Veri Eze that I saw at Edwards AFB and got a brief ride in way back in the '70s had a small external airfoiled tab on the elevator to reduce the pitch control force

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So, I'm gonna call this one "score one more for the Roncz airfoil for the Long eze/Cozy application.

Agreed, for _this_ application - in a glider, the GU would be better (or in an aircraft that is trying to maximize range by flying at the max. L/D point, rather than a faster cruise speed). On the other hand, since the canard is such a small part of the overall flying surfaces of these aircraft, the small difference in drag is almost meaningless for us. The reason for the switch was 99% for bug/dirt/rain resistance, not anything else.

 

Also, Rutan specifically recommended against retrofitting the Roncz airfoil on the Veri Eze because of it's "higher lift". I'll have to go look for the specific CP news letter... So, the higher Cl max may not be "real" and if it is real it may not be "good" or usable.

Again, the "higher lift" is difficult to interpret in a laymans publication. It's hard to know what they meant, since "higher lift" doesn't have an engineering interpretation.

 

I'm certain the original Veri Eze that I saw at Edwards AFB and got a brief ride in way back in the '70s had a small external airfoiled tab on the elevator to reduce the pitch control force

Could be on the V.E., you maybe correct, although I don't remember seeing tabs on the V.E.'s I know - just on the VariViggen. I don't think there is one on the L.E., even with the GU canard, though. Maybe it's called for in the plans, and people just leave them off.....

 

The place to check with folks on the trim tab issue would be on the Canard Aviators mailing list - there are zillions of V.E./L.E. builders/flyers over there.

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