Canard CGs

[Wing Zero]

Can anyone explain to me, how I would go abouts finding a C of G range for a canard type model? A fourmula would be helpful. Thank you. -James

[Antonsoarer]

A lot of dependencies, best to first make a small (scaled down) chuck balsa model and at least get a starting point for your design.

It will depend on aspect ratio and camber of both foils, distance between canard and wing, planforn (sweep, taper, etc).

I think the usual starting point is about 15-25% of the distance between the wing and the canard forward of the LE of the main wing

I am sure you will get plenty of responses with links and threads covering this one.

Tony.

[Wing Zero]

Thanks Tony. The chuck glider is a very good idea. Thanks for the tips and hints. -James

[Quacker]

You can get a fair approximate by first measuring the wing area of both wings. Then measure the distance between the ¼ chord points of the main and canard. Then the formula is:

canard area/main area/2 * distance between the ¼ chord points. This is the distance ahead of the ¼ chord point of the main where the approx. CG is located.

As a sanity check on this, imagine that both wings had the same area. It would seem rational that the CG would be exactly between the centers of lift of the wings.

Q

[omega blood]

Here ya go
http://www.palosrc.com/instructors/putte.pdf

[jhas]

In designing a canard, I understand that the forward wing is critical for lift, and essentially sets the stall speed. My question is regarding the design of the canard for pitch control. Initially, I have made the canard with a split in the center as a hinge line, but I am think that it may be very inefficient and may not fly well. The other design is to have the whole canard wing rotate avoiding the hinge line altogether. This would be technically be more difficult to build. Is the hinge line for pitch control going to be a problem? Do you think I will need to change the canard wing to a "full" surface area rotation design?
Thanks
Jason

[omega blood]

. Is the hinge line for pitch control going to be a problem? Do you think I will need to change the canard wing to a "full" surface area rotation design?
Thanks
Jason

No and no.

[chrisgood]

I took Ron Van Putte's equations and put them into an Excel spreadsheet a while back. It is here: http://www.chrisgood.com/rcplanes/fwiw/index.html at the bottom of the page. Just enter your values into the yellow areas on the spreadsheet and it will tell you the CG.

Chris Good

[adam_one]

I took Ron Van Putte's equations and put them into an Excel spreadsheet a while back. It is here: http://www.chrisgood.com/rcplanes/fwiw/index.html at the bottom of the page. Just enter your values into the yellow areas on the spreadsheet and it will tell you the CG.

Chris Good
Hi,
I've checked your Excel spreadsheet and notice an error at the canard P calculation.
You have entered (R*T) at far right of the formula as shown below:

The correct formula is:
P(canard) =(L x S(tail)) / S(wing)) + (1/15) ( (R^2 + RT + T^2) / (R+T) )

The formula you've entered in Excel is:
P(canard) =(L x S(tail)) / S(wing)) + (1/15) ( (R^2 + RT + T^2) / (R*T) )

You might wish to make an amendment. :)

[chrisgood]

Thank you. Good catch! I have made the correction to the Excel spreadsheet and reposted it to my website.

Now I need to go back and recalculate the CG for one of my canards.

Chris

[vinican]

In designing a canard, I understand that the forward wing is critical for lift, and essentially sets the stall speed. My question is regarding the design of the canard for pitch control. Initially, I have made the canard with a split in the center as a hinge line, but I am think that it may be very inefficient and may not fly well. The other design is to have the whole canard wing rotate avoiding the hinge line altogether. This would be technically be more difficult to build. Is the hinge line for pitch control going to be a problem? Do you think I will need to change the canard wing to a "full" surface area rotation design?
Thanks
Jason

One thing to keep in mind Jason, is surface deflection creates DRAG.
The more a control surface is deflected from centered, the more drag it creates. Especially on the pitch axis, this induced drag can cause a problem.
If the canard is only say 2 inches from the CG, but the TE of the main wing is say 6 inches from the CG, It might be better to use elevon mixing with the main wing, as the ratio of Pitch force to Drag force created by the elevons might be more desireable than using the canards for pitch. This is because the amount of force required to create a given pitch change using elevons would be 1/2 the force required to create the same pitch change using the canards, at least in the senario I mention. Less force = less induced drag, which is a good thing, usually anyway(exception explanation follows).
You still might want to use the canards as FLAPS, because in that case the drag induced would be desired, and the pitch movement is NOT desired, and is lessened vs elevons.

[kdwzagi]

hi

i came aross this post while looking for a canard c of g calculator

can you help me i must be doing something wrong

i have tried to work out a c of g for a canard with a nearly identical forplane to that of the wing

the answer i get must be wrong as its just in front of the ac on the canard yes the canard

thinking it was the way i entered it into my calculator i downloaded the excell version from the link in a previous post and i still get the same position

try putting some figures into the spread sheet with similar wing and canard sizes

i think the LS/S on the P calculation should be divided by 2

all the best

kev

[adam_one]

Hi,

I don't think your math is wrong.
The trouble is that your plane is more a tandem than a canard.
The formula used for the canard CG may only be valid to Foreplanes areas ranging from 15% to about 50% of the aft Wing area.

In your case, you may try using the following formula to find NP (Neutral Point) as % of the Wing's MAC forward of Wing's AC:

NP = Distance between ACs * Foreplane Area / ( .8 * Wing Area + Foreplane Area)
Then add about 10% Static Margin to the result in order to get a 'safe' CG location.
I think that will put you on the ballpark.

But if you're not so keen on formulas you may use the following calculator:
Canard CG Calculator (http://adamone.rchomepage.com/cg_canard.htm)

Good luck :)

[kdwzagi]

thanks

i thought i was going mad :D

kev

[vintage1]

hi

i came aross this post while looking for a canard c of g calculator

can you help me i must be doing something wrong

i have tried to work out a c of g for a canard with a nearly identical forplane to that of the wing

the answer i get must be wrong as its just in front of the ac on the canard yes the canard




What is the 'ac' - not the whole aircraft...? surely?

I woiuld say CG on a pair of almost equal planes would be somewhere around the TE of the foreplane.



thinking it was the way i entered it into my calculator i downloaded the excell version from the link in a previous post and i still get the same position

try putting some figures into the spread sheet with similar wing and canard sizes

i think the LS/S on the P calculation should be divided by 2

all the best

kev


Make up a chuck glider of depron and try...if you mistrust the calculations.

[peterangus]

A chuck glider is the quickest and most confidence-inspiring method.

Fuselage planform can have a significant effect. It can be incorporated in the chuck glider.

Also, look at...www.rcgroups.com/forums/showthread.php?t=415163 posts #7 and 19.

[adam_one]

A chuck glider is a good cheap approach while the calculator may give you the ballpark to start with, then you may fine tweak the balance point with help of the chuck glider.

However, you may still get into trouble despite the use of a chuck glider, especially if your canard is a tractor, see following post:
http://www.rcgroups.com/forums/showpost.php?p=3591801&postcount=20

Also, the canard’s airfoil should have a higher lift coefficient and stall at a lower geometric AoA than the main wing for a better longitudinal stability.

[Tony Oliver]

Vint - I think , by 'ac' he means Aerodynamic Centre. Got me wondering at first...