As a starting point for a general discussion on aerodynamics, I thought I'd start a thread with a cool picture.

I've been doing a little research on fluid dynamics hoping to get some figures for Reynold numbers (Re) and drag coefficients (Cd) of classic pattern designs of different scales moving out at various speeds.

Here are my online starting points as I'm too lazy to go into the garage and dig out gas dynamics textbooks:

http://en.wikipedia.org/wiki/Aerodynamics

http://en.wikipedia.org/wiki/Reynolds_number

http://en.wikipedia.org/wiki/Drag_coefficient

I figured at least a few of us would chime in on this discussion starting with you, Cees!

Should be fun!

David.

Like they say ... a picture is worth more than 1000 words.
Will start learning more about aerodinamics with all your post's , I sure will not take a deep dive on it since i dont design planes at all, but is good to know about dinamics.

Do you remember why the learjet crashed in México city ? answer is in the pic you posted, pilot was to close to an airbus 300 turbulence.

Doxillia,

There is a lot of interesting stuff and important physical effects, but most people do not believe they exist and oyher does not find it interesting.

When you try to fly in "all" weather conditions or experimenting with “cruise control� as do, you find out it all yourself. Design a airplane, very interesting!

As example

The only moment I did use tip fortex solutions “winglets� was when I did design (+/-1980) canard models for contest flying with limited span (2m) and not the use of ailerons.

The extrem “backwards banked�, drag rudders (there is the first Contest Taurus of Ed again!!!!) did make flying like using frise ailerons possible (Orion!!!), look to the dihedral of this glider! But just as with frise ailerons no inverted flying!

So first goal (classic pattern?), then important facts (program to fly?) , then type, for the points to win (tricycle, taildragger), and then design (brakes, dimensions, airfoil, power, weight).

Think about this, Paul did tell us the Orion (taildragger with angled tail cone) he did fly, floated, just as Ed Kazmirski wrote, I have the same experience but also the Taurus does use the straight tailcone as a brake (of course the contra situation!) when try to get landing points.

I fly both Taurus and Orion. Orion does also use “Ground effect� that can be good or bad. (high weight Orion with retracts, so "GOOD")

So not trying to become a professor in the fluid dynamics, wasting of time.
Tell the important facts we all can use and try to explain. Downwash, wind gradient, groundeffect, propeller effects, etc.

But the first most important les to learn is:
The more you know, the more you know you don’t know!


Cees

Cees,

that was fast! I guess considering that it's coffee time over in Holland while I should be sleeping...

A quick comment. This thread is not intended to provide or seek lessons to or from anyone. Rather, I hope it to be a growing source of information related to the specific aerodynamics of classic pattern designs. I started it in the hopes of learning more about how things like Re and Cd change from one design to another - if significantly - and as a consequence, what type of power plants and prop dimensions might be best suited for given models and scales with an emphasis on electric power. E-power, by virtue of its nature, has considerably more latitude than glow power and therefore ideal power plant configurations are not always obvious.

In short, at some point it would be nice to have a little database of our models with descriptors and parameters that could serve as a reference for specifying appropriate e-power configurations.

The re-design of a classic is part of the motivation for the start of this thread.

As a comment to the end of your post:

"But the first most important les [sic] to learn is:
The more you know, the more you know you don’t know! "

That was fortunately the main outcome of an undergraduate degree and what gives me the psychological freedom to start a thread like this.

Cees, just so you know, we're not all out to get you despite the heated exchange on your Taurus thread. I suspect that much of that debate can actually be chalked up to language and cultural differences. At the end of the day, sometimes its good to "agree on disagreeing" as it leaves space for your quoted statement above to breathe again.

Enjoy your breakfast... actually it's almost time for ours [X(]

David.

Doxillia,

The content of my post was because you did start you thread in Classic Pattern Flying. and I thought you ask me to react.
When you want to know how I write posts about aerodynamics show in my history: Airplanes / aerodynamics.
When you want to know how I write posts about E-power, look for analog servo's, the only e-power I accept in a classic pattern plane.
I will follow your thread ofcourse, succes.

Cees

Well, Cees, good to see you have an open mind!

Like it or not, electric in classic pattern is going to continue to grow. Whether SPA or BPA recognizes or not, it's going to happen. A forward-looking body would take the initiative and help promote the use of electric power as a means of preserving flying sites. Large fields with (preferably) paved runways are few and far between, and being able to keep them in the growing suburbanization of the country is going to be difficult at best. If we can resolve the noise issue proactively it will prevent complaints from the NIMBY's.

Anybody who is serious about powering their classics with electric and obtaining equal-or-better performance from them needs to start with some good tools. I personally use Electricalc (from http://www.slkelectronics.com) and have pared down my motor and battery databases to only those items I use, or am considering. Until you've seen one of these databases you have no idea what is out there!

As for aircraft, David's post is related to an attempt to find an aircraft already in the database which could be considered typical for a Pattern plane. (Fortunately, he came up with the same model I did). What would be ideal, though, would be to add to the ecalc database appropriate data for our models.

So, who's game?

Andy

David,

Here is a link meant for full-scale pilots that is often referred to on RCU when people ask about the basics:

http://www.av8n.com/how/

I think a discussion of tail volume coefficients and cg placement for classic pattern models would be helpful. With an explanation of how to determine if for a given design, people could post the coefficients for different models with known handling qualities.

http://www.eaa62.org/technotes/tail.htm

This is something easy to control with a new design and the constraint to still look like a classic pattern ship.

Mitch

Since the thread is "Subsonic Aerodynamic Vortex", I'll start with that. One of the more interesting things I've discovered in studying aerodynamics of powered models is how small the vortex/induced drag component is compared to parasitic drag. Because we have so much power on tap, level flight requires very little angle of attack to generate sufficient lift to offset the weight of the plane.

Reynolds number is a dimensionless quantity derived from fluid velocity as well as the chord of an airfoil. Our planes fly much slower and have much, much smaller chords than big boy planes so our Reynolds numbers are much lower. The unfortunate result is that most published lift/drag data is at Re's 10 times what we need.

If you want a good book on the subject my favorite is Martin Simons "Model Aircraft Aerodynamics"[link=http://www.amazon.com/Model-Aircraft-Aerodynamics-Martin-Simons/dp/1854861905/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1238456643&sr= 8-1]here.[/link]

I think many of the classic pattern ships could be made even better with more advanced airfoils and planforms, but thats a BIG discussion.

Crate,

I like the idea of making them better, but I wonder if everyone agees on what "better" is. Many full-scale designers are focused on improving efficiency: lift versus drag, or specific fuel consumption. I don't think that these models are really in need of improved efficiency from that sense. A better airfoil for this aircraft type, in my view, would be one that produces the required lift inverted with the minimum of change in elevator deflection. And while doing that it produces the smallest amount of change in pitching moment (or required elevator deflection to maintain trim) with airspeed changes.

Sure, low drag is important for vertical performance, but I think we've got that one figured out. It seems to me that the "flys like it's on rails" and maybe the "lowest weight for a given size/shape" properties are the things to optimize.

Mitch

I recently assembled a pattern ARF called a Focus Sport for a friend with no time to build. The thing was based on a 2 meter design called the Focus. Anyway, this thing had very thin stubby wings with a long chord(thickness was 9% of chord I think) and I figured it would have to land pretty hot or stall. On the maiden the pilot slowed it down to almost a hover before it gently dropped its nose straight forward. Landings were slow, smooth and well controlled. He had a 4-stroker YS-110 in front.

Funny, I had always thought thin wings were great for speed but were snappy and hot to land. Now I'm not so sure. My old Kaos slows nicely for landings but it has a portly 18% thickness at the root and doesn't go very fast no matter how much engine I bolt to it.

I don't want to mess up the classic looks of the pattern planes of the 60's and 70's but if a minor shape change to the airfoil makes them fly better, heck, why not?

I see your point and agree that airfoil thickness would be a good thing to list against the various models along with some sort of description about high and low speed handling.

I'm not sure what the rules in SPA are about changing the airfoil. Many viewers of this forum are interested in keeping a model that is SPA (or BPA?) legal.

So David: are you going to start some sort of a Matrix? I volunteer to provide each of the parameters for the Deception and Calypso if you do. I could also provide Sig Mayhem which would be an example of extremely low wing loading and of large control surface size, however it is NOT a classic pattern ship (as you know).

After quickly re-reading the posts I think I may have hijacked your original intent. If so, please get us back on track.

Gents,

thanks for your interesting and illuminating contributions.

Mitch, that sounds like a good idea. I'd be happy to start a matrix. If you'd like to send me the parameters for the Deception and Calypso, I'll use those as a basis for the format of the table. I can make the table available in PDF format for download. In fact, perhaps we could send it to CAsniffer and ask that he post it on the classic pattern pages.

With some luck, it might grow quickly.

Thanks, David.

This is an interesting thread but it's hurting my ity bity brain. An intersting story involves the development of the P-38 Lightning. The prototype had a nasty tendency to develop flutter in the tail booms in a dive (among other probems). It was making Kelly Johnson and his crew at Lockheed nuts. The solution was faily simple. They wound up modifying the wing fillets where the main wing joined the cockpit pod and the tail flutter disappeared. You'll note the little teardrop shaped counter weights attached to the elevator of every P-38. That was the result of one failed attempt to resolve the tail flutter issue. It did nothing. The counter weights were to be eliminated on production aircraft. However, a U.S. Army Aircorps General felt they were absolutely essential so Kelly just shrugged and she went into production with the counter balance weights. They do kinda look cool.

Bill

David,

As a beginning, here are numbers for the Deception 60 from the plan:

Wing Area 750 sq. in.
Wing Span 63 in.
OAL 59.5 in.
Weight 8.5 to 9 lbs
Engine .60 cu. in. to 10 cc

These are "as designed" I'll post the "as built" numbers and other measured parameters soon.

Mitch

Kaos60 DirtyBirdy60
-
wingspan 59" 64"
wing area 644 688
wingload 22.7 26.0
aspct ratio 5.5 5.8
taper ratio 72% 66%
root chord 12.5" 13.25"
tip chord 9" 8.7"
avg. chord 10.75" 11"
sweep 0 deg 4 deg

airfoil type symetrical symetrical
thickness 18% (chord) 16% (chord)
l.e. radius 1/2" 3/8"
cg(%chord) 34% 50%
incidence 1/32" 1/64"

design weight 6.25# 7.75#

stab. area 108 155
elev. area 53 54
fin area 30 45
rudder area 39.5 27

fuse. lngth 47.5" 50"
prop to c.g. 15.5" 18"
c.g. to elev. 33" 32"
c.g. to rud. 33" 32"

right thrust 3 deg 0 deg
dwn thrust 3 deg 2 deg