Wing area convention for canard aircraft

[Luka]

Hi to all,

I was wondering what is the convention for measuring reference wing area for canard-type aircraft?

I know that effectively it does not matter, but there must be a convention on whether you use the surface of the main wing only or the sum of both lifting surfaces?

Thanks!

Kind regards,

Luka

[Rob McDonald]

I see no reason to add them together.

I would just use the main wing's area.

If you switched from a canard to more of a tandem wing -- approaching a 50/50 lift split -- then I might have a different answer.

All you're trying to get out of choosing the 'right' value is to get numbers scaled appropriately so your intuition works.  Things like a magnitude for CLmax.  If Sref is off by 2x, then your CLmax intuition is way off...

If you're using an empirical model for induced drag (that depends on aspect ratio) then you need to make sure you're using a consistent definition with the empirical model.  However, if you're using computational models for all that, it really doesn't matter.  However, you might calculate Oswald e and get an unexpected answer...

If you're approaching a 50/50 lift split, then I would go back and look at old biplane stuff and see what they did there.

Rob

--
You received this message because you are subscribed to the Google Groups "OpenVSP" group.
To unsubscribe from this group and stop receiving emails from it, send an email to openvsp+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/de2ec2c7-1d17-4a1b-bd08-65ec8ef33ecan%40googlegroups.com.

[Luka]

Hi Rob,

thanks for the answer.

The reason I'm trying to find a convention answer is because I'm working on a glider design and gliders are mainly compared based on same wing loading.

Since the canard is carrying it's part of the weight, 15~25% of the glider mass, I am not sure if the wing loading of a glider that has it's wing 'relieved' of part of it's carrying weight can be compared to a wing of a glider which carries it's own weight + the downforce of the tail.

Again, I fully understand that it makes absolutely no difference when doing my calculations, as long as I keep it consistent, but I would still like to be able to compare two different types of aircraft configurations.

 I guess I am trying to compare apples to oranges.

This is why this may even be a question of a philosophical nature, in which case I am again interested in people's opinions.

Thanks and kind regards,

Luka

[cibinj...@gmail.com]

Luka,

From a purely convention perspective, most test cases for a canard-type aircraft (and not a biplane or tandem wing) in literature use just the wing area.

A popular paper cited in investigations of canard configurations is NASA Technical Publication 2382 which has experimental results for a Rutan VariEze aircraft.

Only the wing area is used for the full aircraft lift and pitching moment coefficients. For reporting canard lift and moments, both wing and canard areas are used as reference area.

- Cibin

[Neal Pfeiffer]

Yes, that is certainly one way to do the bookkeeping.  Having survived the Starship program, we used the entire wing area, including the fuel tanks in the leading-edge strake.  That added considerable area beyond the basic area the trapezoid shape of the main part of the wing.  While the VariEze does not have as large a strake, it still is sizeable and there is also an extension behind the trap wing.  When you use the full area as opposed to the trapezoid area, the aircraft lift coefficients are are reduced and do not compare well with other aircraft, or even the section coefficients on the airfoils of the outboard wing.

As long as you use a consistent reference area for all your aircraft coefficients, it will all work out.  But you may have issues when you try to compare with conventional aircraft, particularly for items like CLmax.

And as for a glider, there is a reason the only one Rutan Solitaire was built.  The canard configuration is not a very good solution for a glider.  The performance was poor and the ability to turn tight circles in small thermals was not on par with traditional designs.  Even a flying wing is better.

And for a powered aircraft, the fuel needs to be near the CG, and that is between the wings.  So it requires extra wetted area for strakes, unless the fuel is in the fuselage, where it displaces people or payload.  I stand by the comment I've made for years, the best place for a canard is on on your competitor's airplane.

..... Neal

https://groups.google.com/d/msgid/openvsp/42ccf8a7-7645-4823-87f4-c89c31dcca26n%40googlegroups.com

.

[Rob McDonald]

Neal,

I'm always amused when optimization studies of canard aircraft end up moving them to the aft end of the airplane.

Rob

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/689419375.633143.1646420710633%40mail.yahoo.com.

[Rob McDonald]

I do think it is a bit of apples and oranges.

One of the things you'd like is to maintain your intuition for CLmax -- and how it compares to sectional clmax across the wing.

However, in a proper design, the canard stalls first and your CLmax of the aircraft is not close to the CLmax of the wing alone -- or the sectional clmax for the wing.  So, your comparison intuition will be foiled before you even worry about Sref.

Wing loading in a sailplane is closely tied to stall speed (and for performance you'd rather have a higher wing loading).

Using Sref of just the main wing -- since you can't use all of the wing's CLmax capability, you will need a lower W/S for a canard sailplane to achieve the same Vstall.  If you include the area of the canard in Sref, it will only serve to make your W/S lower.  Since high wing loading is what you desire for performance, I'd say it pushes your comparison farther from what you want, not closer.

Neal Pfieffer is a great person to listen to on this thread -- not only was he at Beech in the Starship days, he is an experienced sailplane pilot who restores vintage wooden sailplanes.

Rob

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/3abde177-d484-4b95-9c07-d6b882febe06n%40googlegroups.com.

[Neal Pfeiffer]

Like there might be a reason?.?.


Sent from AT&T Yahoo Mail for iPhone

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/CAEppYpE3VXz5jGTEhbs-YvwVZv4qPRptNM0GwHp5WADAZmotBw%40mail.gmail.com.