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        Question Wing Loading on Micro and Small RC Planes

#1 chochmah Jan 12, 2013 11:19 AM

Wing Loading on Micro and Small RC Planes
 
Hi Forum,
Quick Question concerning wing loading and micro and small rc planes:
  • From what I read the wing loading has to be lower on a smaller RC Plane as compared to a larger one to get the same performance.
  • The Wing Loading Tables one finds on the Internet seem to be made form standard sized (around 2m wing span) airplanes and don't translate to smaller planes.
  • So from your experience what Wing loading correspondences to Trainer, Slow Flyer, Sport Plane in the micro and small rc plane world?

The specific question I have is: My Model has a wing loading of 20gr/cm^2 (6.5oz/ft^2) and is about 70cm (2f, 4inch) long and wide. Is the Wing loading to high and if not, will it fly like a Trainer or like Sport Plane judging solely by the Wing Loading? (I have taken the whole shadow of the plane to calculate the Area not just the wing, hope that's all right)

Thank you very much guys!

cheers chochmah

#2 pdawg Jan 12, 2013 11:48 AM

Yes I believe you have the right idea. A real P-51 weighs about 8,000 lbs and a 1/4 scale model flies nicely at 50 lbs....not 2,000 lbs. So if you follow that trend the smaller you go the lighter the relative wing loading must be to have similar flight qualities.

When calculating wingloading only calc the wing...not the other parts.

#3 chochmah Jan 12, 2013 12:09 PM

Quote:

Originally Posted by pdawg (Post 23791874)
Yes I believe you have the right idea. A real P-51 weighs about 8,000 lbs and a 1/4 scale model flies nicely at 50 lbs....not 2,000 lbs. So if you follow that trend the smaller you go the lighter the relative wing loading must be to have similar flight qualities.

When calculating wingloading only calc the wing...not the other parts.

Thank you for your reply. If the Fuselage is kind of shaped like a wing can't I use that as wingarea as well? How about canards? Here's the foodprint of the plane in question:

http://666kb.com/i/camvzsv9l1sh61ior.gif

cheers

#4 stegla Jan 12, 2013 12:49 PM

Hello Chochmah,

At 6.5 oz/sq ft your model will fly like a trainer.

Please recalculate for the wing only.

At 15oz/sq ft this size model will behave like a fast sport model but you will need say 200W to power it adequately.

Steve

#5 chochmah Jan 13, 2013 04:44 AM

Quote:

Originally Posted by stegla (Post 23792348)
At 6.5 oz/sq ft your model will fly like a trainer.
Please recalculate for the wing only.
At 15oz/sq ft this size model will behave like a fast sport model but you will need say 200W to power it adequately.
Steve

Thank you very much. Those where the Numbers I was trying to find.
I recalculated for the Wing only and I got 13.5oz/ft^2. Means I can go ahead with the project without the fear of ending up with an unflyable brick.

Cheers

#6 stegla Jan 13, 2013 11:25 AM

I'm sure that some of that fuselage will create lift as the fuselage is quite wide particularly at the leading-edge-extensions.

I believe that swept-forward wings are prone to tip-stalling? So a little washout if possible might help.

Good luck:)

Steve

#7 sloperjoe Jan 13, 2013 12:47 PM

Quote:

Originally Posted by stegla (Post 23800941)
I'm sure that some of that fuselage will create lift as the fuselage is quite wide particularly at the leading-edge-extensions.

I believe that swept-forward wings are prone to tip-stalling? So a little washout if possible might help.

Good luck:)

Steve


+1 on the washout, I built this one back in May last year http://www.rcgroups.com/forums/showthread.php?t=1655536 flew great, had a 64mm fan and 3s 1600mah pack, flew easily at just under half throttle nice and slow, but also could haul at WOT :D
I built in 3/16" washout each tip.

Joe

#8 Keenan smith Jan 13, 2013 01:46 PM

Washout is the Complete opposite of of what you want in an FSW, FSW's need Wash-in (negative washout, so the tips both stall at the same time dropping the nose and regaining airspeed Rather than wash out which would keep the tips flying and cause the plane to pitch up aggravating the Stall and causing an Eventual Splat! :eek: )
though FSW's Need to have a vey stiff wing (to go fast) due to aeroelasticty.. but im not sure that it comes into play at this scale..

Keenan

#9 Keenan smith Jan 13, 2013 01:53 PM

Quote:

Originally Posted by stegla (Post 23800941)
I'm sure that some of that fuselage will create lift as the fuselage is quite wide particularly at the leading-edge-extensions.

I believe that swept-forward wings are prone to tip-stalling? So a little washout if possible might help.

Good luck:)

Steve

FYI FSW's are know to be able to lock in to High alpha Flight and be very manouverable with a Relaxed CG ( With gyros ) but are know to be unstable in the yaw axis ...

P.s Chochmah plans to use an Caseless Orx 3 axis Flight Stabilizer For this plane
i have spoken to him on skype

Keenan

#10 stegla Jan 13, 2013 02:04 PM

Or is it the canards are set at a greater incidence to stall before the mainplane? A safer bet maybe?

Steve

#11 Keenan smith Jan 13, 2013 02:36 PM

Possible but that incurs extra drag and your tip stall worries are null due to the fact that chochmah will be using 3 axis flight stabiliser

#12 chochmah Jan 14, 2013 09:59 AM

1 Attachment(s)
Quote:

Originally Posted by stegla (Post 23800941)
I'm sure that some of that fuselage will create lift as the fuselage is quite wide particularly at the leading-edge-extensions.
I believe that swept-forward wings are prone to tip-stalling? So a little washout if possible might help.

Quote:

Originally Posted by sloperjoe (Post 23801623)
+1 on the washout, I built this one back in May last year http://www.rcgroups.com/forums/showthread.php?t=1655536 flew great, had a 64mm fan and 3s 1600mah pack, flew easily at just under half throttle nice and slow, but also could haul at WOT :D
I built in 3/16" washout each tip.

That's a beautiful model! If I can manage something half as good looking I'll be more then satisfied. Right now I have a build a profile foamy and I did some glide tests that where pretty successful. No need for Washout at the moment but that might change when I install the electrics and increase the weight. One thing though. No matter how far forward I place the CG, when the model flies below a certain speed the tail instead of the nose drops. Might be a characteristic of the forward swept wing.

Quote:

Originally Posted by Keenan smith (Post 23802555)
Possible but that incurs extra drag and your tip stall worries are null due to the fact that chochmah will be using 3 axis flight stabiliser

Hold your Horses! :) I want to build and trim a model that's stable without gyros and then play around with the CG and artificial stabilization. Besides, I don't think that a gyro will magically stabilize any plane no matter how unruly it is but I have never even seen one in real life so what do I know.

Cheers :)

#13 chochmah Jan 14, 2013 10:12 AM

Quote:

Originally Posted by Keenan smith (Post 23802116)
Washout is the Complete opposite of of what you want in an FSW, FSW's need Wash-in

Source Please.

Thank you

chochmah

#14 Keenan smith Jan 14, 2013 12:32 PM

cant find the page but i remember this ...

Quote:

forward swept wings stall from the most rearward part to the front, creating tip stalls, aka wing rock. The tips on a forward swept wing are in the front, almost completely eliminating the need for washout or wing tip extensions.
K :cool:

#15 indoor_fr Jan 14, 2013 12:59 PM

The scale speed is the clue of the problem.

Everything is explained here:

http://www.charlesriverrc.org/articl...scalespeed.htm

To summarize:

Rule 1 z2 = z1/r Wingloading, z, resulting from simple downscaling.
Rule 2 v2 = v1·sqrt(1/r) Velocity, v, resulting from simple downscaling.
Rule 2a v2 = v1/r True scale velocity.

Rule 3 w2 = w1/r4 Mass, w, required to fly at true scale speed.

Rule 4 svz = z1/r2 Scale velocity wing loading, svz, resulting from Rule 3

Plus:
If you want a plane to fly a the same scale speed than a plane that you take as a reference (mass w1, length L1, wing area S1), then the mass of your plane should be equal to:

Rule 5: w2 = w1 x (L2/L1)² x (S2/S1)

Note: If the plane is the plane of reference at the r scale reduction , then L2 = L1/r and S2 = S1/r², and we can verify that the mass is:

w2 = w1 x (L1/(L1 x r))² x (S1/S1 x r²)) = w1/r4 This is the Rule 3

Hope this helps.


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