trying to find CG for burt rutan quickie - RC Groups
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May 06, 2003, 02:51 PM
Team Spektrum FPV
aaronredbaron's Avatar

trying to find CG for burt rutan quickie


it is sort of a canard/sort of a stagger wing bipe. I am hating myself right now for dropping out of aerospace engineering, AND selling my best AE book. what is the formula that relates the center of lift for both wings and then takes into acount the overall lift force since the area's are different? can I then simply average the distance??? any idea's?
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May 06, 2003, 10:38 PM
It wasn't me...
DanSavage's Avatar

Re: trying to find CG for burt rutan quickie


Quote:
Originally posted by aaronredbaron
it is sort of a canard/sort of a stagger wing bipe. I am hating myself right now for dropping out of aerospace engineering, AND selling my best AE book. what is the formula that relates the center of lift for both wings and then takes into acount the overall lift force since the area's are different? can I then simply average the distance??? any idea's?
I know what a Rutan Quickie is. My brother Daren is building a 1/4-scale model. This should help.

However, since the canard on a quickie is actually below the wing, I'm not sure whether the wing flys through the canard's downwash.

Are you building it from scratch or from a kit?

Dan
Last edited by DanSavage; May 06, 2003 at 10:42 PM.
May 07, 2003, 04:42 PM
Team Spektrum FPV
aaronredbaron's Avatar

my model is 1/4 scale and is already built


it currently is powered by a OS 40 FP w/ perry pump because the fuel tank is at the CG (I think) depending how well it flies I may do a brushless conversion. since your brother is building a 1/4 scale one too maybe you could measure the CG from a constant point (trailing edge of front wing/canard, or from the firewall or whatever) also if you could give me a constant length to go from (wingspan, fuse length.. anything) I should be able to account for any variences in size. from what I have heard the CG range should be pretty wide, so as long as I get it close and maybe a little nose heavy I should be OK
May 07, 2003, 04:49 PM
Team Spektrum FPV
aaronredbaron's Avatar

about the ineffectiveness of the wing....


I can't see how the image can apply to the quickie, because the front wingspane is nearly the same as the rear it would render to rear wing nearly useless. if you look at the plane from the front it has anahedral (speelled wrong) in the fron and it is at the bottom of the fuse, then the fuse extends upward and the rear wing is at the top of the fuse with dihedral. looking at it, for me, suggests that the reason the plane was designed the way it was, was to eliminate any airflow from the canard interfering with the airflow over the rear wings. I need to get a digital camera.....
May 08, 2003, 08:09 PM
It wasn't me...
DanSavage's Avatar

Re: about the ineffectiveness of the wing....


Quote:
Originally posted by aaronredbaron
I can't see how the image can apply to the quickie, because the front wingspane is nearly the same as the rear it would render to rear wing nearly useless. if you look at the plane from the front it has anahedral (speelled wrong) in the fron and it is at the bottom of the fuse, then the fuse extends upward and the rear wing is at the top of the fuse with dihedral. looking at it, for me, suggests that the reason the plane was designed the way it was, was to eliminate any airflow from the canard interfering with the airflow over the rear wings. I need to get a digital camera.....
I think you've got it wrong.

Find the canard area (A)
Find the wing area (B)
Find the Neutral Point for the main wing. (NPW)
Calculate the CG for the canard and the main wing at 1/4 chord (25% MAC)
Find the longitudinal separation distance between the two.

Multiply A times longitudinal separation.

Divide A + B by the result.

This gives the distance from the CG of the main wing to the neutral point. (NP)

Next, add the distance between the NPW of the main wing to its CG at 25% MAC to the result of the calculations above to find the starting CG of the model.

The configuration of the Quickie you describe is why I wrote what I did about the wing not flying through the canard's downwash. For the purposes of calculation, I could simply leave the rear wing effective area at 100%.

Dan
Last edited by DanSavage; May 08, 2003 at 08:11 PM.
May 09, 2003, 01:50 AM
Team Spektrum FPV
aaronredbaron's Avatar

thank you for your help


sorry about the confusion... there is only one way at this point to see if it is right!
May 09, 2003, 05:48 AM
Registered User
The downwash behind a wing extends several chord lengths above and below the wing. That's why some wind tunnels can measure the coefficient of lift by an array of manometers placed in the roof of the windtunnel. That's why biplanes are inherently less efficient than monoplanes and why the greater the gap between the top and bottom wing, the less the wings' efficiency is degraded.

The air flow over the aft wing is slowed by the influence of the forewing and fuselage. In calculating the neutral point, an allowance has to be made for the reduced effectiveness of the aft wing. This is usually done by using a smaller area of the aft wing in the neutral point calculation. It is very hard to accurately estimate the actual reduced effectiveness of the aft wing. To cover this uncertainty, it is best to start out with a static margin of 15 or 20%. That is with the CG 15 or 20% of the wing's mean aerodynamic chord ahead of the neutral point in a tandem wing design.

For a fuller discussion of tandem wing setup see R/C MODEL AIRPLANE DESIGN, Chapter 10 by A.G. (Andy) Lennon. The rules of thumb in Lennon's book have been verified experimentally and would apply well to the Quickie configuration.
May 09, 2003, 07:41 AM
Grand Poobah of Nothing
Trizza's Avatar
You could always build a small balsa model to figure the CG out with. Just to glide test in your living room or something.
May 12, 2003, 12:38 AM
Team Spektrum FPV
aaronredbaron's Avatar

I got ahold of the original plans and instructions!!


I feel very confident having the right info. they claim it is a very good flying plane and flies pretty fast...we'll see
Jun 02, 2003, 07:26 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
Hello guys!
I am very intersted in your Quickie, and I am in the proccess of designing a much, much smaller scale model of the quickie, and needed a few good pics or 3 view diagrams - well, the more views the better.

Do you still have those plans of the full scale Rutan Quickie? Do you know where I could get them or find pics? Or even less acurate drawings with just outlines? Can you scan in your plans?

If not, do you have any directly side view photos or directly top view (as for top, I see a good one on the link you gave in the first post, but it is small and a little hard to understand how/where everything goes/fits) or front or back?

Thank you very much!
-Michael
Jun 18, 2003, 02:51 AM
36 Russky jets
daisycutter's Avatar
does anyone have a pic?
Jun 18, 2003, 02:24 PM
Ascended Master
Sparky Paul's Avatar
Did a search on the 'net for "quickie".... !!!!! Amazing things you can find!!!! :
.
Got results with "quickie & Rutan"...
dimensions -can- be read with a little enlargement..
Jun 18, 2003, 02:25 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
guys, looks like somebody did ALL the math for ya......

and drew in formers, bulkwalls, fuse sides...an entire plan.

NO, two entire plans!!!!!!

https://www.rcgroups.com/forums/show...hlight=quickie

http://victorian.fortunecity.com/stoker/123/
Jun 18, 2003, 02:27 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
click on planos, then scroll down until you see "Quickie" under the canard section, then scroll down more until you see "Qac-Quickie" they are the two plans, both scale. The Qac-Quickie is harder to build from and much less complete, but it is far more scale. Elevator goes in front wing, aileron goes in the back wing, for three chnnels. For four, add the rudder..... rudder and elevator doesn't work...
-aeroP

P.S. SPARKY, that's noit the Rutan Quickie, I'm sorry to say. That's a dragonfly or something. The way you can tell is that the Q has straight fuselage sides, looking from a top view.
Last edited by aeropenguin; Jun 18, 2003 at 02:30 PM.
Jun 18, 2003, 03:42 PM
Ascended Master
Sparky Paul's Avatar
Quote:
Originally posted by aeropenguin


P.S. SPARKY, that's noit the Rutan Quickie, I'm sorry to say. That's a dragonfly or something. The way you can tell is that the Q has straight fuselage sides, looking from a top view.
.

magnify the title block.


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