Originally Posted by flieslikeabeagle

Chuck, a huge "Thank You!" for writing this up and helping out fellow RC pilots. I've written many threads and short tutorials on WebOCalc here on RCG over the years, but I never could find the time to keep doing it over and over - thank you so much for all the work you put into this write-up!

-Flieslikeabeagle

Welcome back, Beagle!!!

Geeze, quit making yourself so scarce, will ya?

I hope I'm doing justice to your excellent program, WebOCalc. There's so much more I wanted to ease the beginner's into like prop unloading, etc. But you know me... I like to get them into the ballpark first, before we find our seats.

Hey guys, Beagle is the guy who wrote WebOCalc, and my first (and still) mentor here on RC Groups...

Chuck

Just re-reading my post #89, I realize I may cause some confusion with the statement that I would not be surprised if the control-line wires cause more drag than the entire airframe of the model does. If that is the case, won't we need incredibly huge increases in thrust to fly? And how does that go with my other comment that, decades ago, inefficient little glow engines hauled these control line models around very handily?

Well, the answer is that for most RC flying, the drag of the model actually does not play very much of a role during powered flight. Most of the thrust in our overpowered models is used to fight gravity - weight - during climbs, or inertial forces during acceleration. Not to overcome aerodynamic drag, which is typically very small compared to these other forces. Adding draggy control lines may double the models drag, but that is still likely to be a small effect compared to the effect of gravity during, say, a 45-degree climb.

Only when flying at top speed or when gliding is the aerodynamic drag the dominant factor - the rest of the time, you can neglect it for typical sport or aerobatic RC flying, because it is so small compared to forces of acceleration (inertial forces) or gravitational forces.

Matter of fact, WebOCalc pretty much ignores the aerodynamic drag from the model - note that it really doesn't ask you if the model is sleek, draggy, or whatever - and as Chuck (NoFlyZone) and dozens of other people, myself included, can testify, that doesn't keep the program from coming up with perfectly acceptable power systems for RC planes. Every RC plane I have is powered with a combo WebOCalc came up with - that's another reason why I wrote the program, to help me pick power systems for my own planes.

I should add that for top-speed racing, hotliners, and distance record or duration record attempts, the models drag is very important indeed. But the typical RC model we use for fun, sport flying, aerbatics, and so on, is as primitive a beast as you can find, aerodynamically speaking. Slab-sided fuselages, fixed landing gear with big wheels hanging in the breeze, flat slab horizontal and vertical stabilizers, draggy cooling air intakes and exits, fixed-pitch propellers, no flaps or slots or slats - these are features that are still on most RC models, and these are all features that were mostly abandoned in full-size aviation almost a century ago, because they were inefficient and draggy. Our typical trainer or sport or aerobatic RC plane actually has more in common with a 1915 Fokker Eindekker than with most full-size aircraft built within in the last fifty years or so. Heck, a 1935 Douglas DC-3 has vastly better aerodynamics than most RC planes - and it dates from 75 years in the past!

Not to go on about this, but it is very instructive to compare a true master of aerodynamics - an albatross, say, or even a seagull - with the typical boxy balsa high-wing trainer or parkflyer. The albatross has a smooth streamlined fuselage, retractable landing gear (most birds always tuck their feet out of the airstream when they fly), extremely advanced low-speed high-lift wing devices (they reshape their entire wing, unlike our crude human flaps and slots and ailerons), and so on.

-Flieslikeabeagle

Originally Posted by NoFlyZone

Welcome back, Beagle!!!

Geeze, quit making yourself so scarce, will ya?

Chuck

Chuck, B.B. King described my current situation re RC flying very well:

he thrill is gone
The thrill is gone away
The thrill is gone baby
The thrill is gone away

So I'm not around much on this forum because I'm not enjoying this hobby any more, but fortunately that doesn't stop all of you fine folks from continuing to enjoy it.

Thanks again, Chuck, you're doing a fine job. And IMHO, you have laid out all the essentials superbly. Those hobbyists whose inner researcher wants to go on and dig deeper into theory have a starting point, and other hobbyists who just want to get out there and have fun flying are already all set - you've told them how to power their models.

And just so everybody knows, I'm fine, nothing bad has happened to me or my loved ones, and I'm actively enjoying another old hobby of mine: creating and playing music.

-Flieslikeabeagle

Awesome, entertaining and infomative stuff here guys. Thanks very much!

flieslikeabeagle, about drag...
I used to think " how bad could the drag from some skinny wire landing gear possibly be?"

The answer is "pretty bad".

Anyone that has Andy Lennon's book R/C Model Aircraft Design need only look at Chapter 12 - Reducing Drag.

For those that don't have the book here is a small quote....

Andy talking about drag....
....................
"This doesn't imply that the models don't fly well; they do!
In fact the high drag is benificial: it causes fairly steep glides-engines throttled-that make the landings of these relatively low-wing loading models easy to judge.
Their performance suffers in all other flight aspects, however."
...................

So drag can be benificial, depending on how you want your airplane to fly....

If you want a fast sleek model it is quite important to have as "clean" a airframe as possible.
Even a lowly rubber band that holds the wing on can introduce significant drag.

Sorry for the OT Chuck.

Back to our regular Web-O-Calc programming.....

Galaxiex, I remember being completely shocked by the drag figures in that chapter of Andy Lennon's book. It was a real eye-opener for me.

Along those lines, I have a little 48" Haikong Models Spitfire. With a beautifully streamlined fuselage and low-drag elliptical wing, it flies like a dream - and it is a bit of a nightmare to land. The dratted thing just floats on, and on, and on. Unless I make a final circuit of the field at about 6 feet of altitude, it will just glide the entire length of the runway without ever slowing down enough to land. If you've ever flown a little 48" model with a camouflage paint job six feet above the deck for an entire circuit of the field, you'll know why it's a bit of a nightmarish experience!

So drag can be good when landing, but it's bad the rest of the time. Which is why someone invented flaps, spoilers, and so on - lots of extra drag and/or lift, but only when you need it. Full-size aircraft have been using these devices for many, many decades...RC planes are still mostly stuck in 1915. It makes them easy to build, and it's "good enough" for the type of flying we usually do. The Spitty could really use flaps, but I don't want to add weight or cut into that beautiful elliptical wing.

Back on topic, the power system I chose for the little Haikong Spitfire is a 3S A123 lithium-ion pack driving a cheap $25 Turnigy outrunner. The low battery voltage lets the motor spin a big and therefore relatively efficient 11x8 APC E prop (a scale prop for a 48" Spitfire would be about 14" diameter, so even 11" is too small). Acceleration, take-off, and climb performance is much stronger than any full-size Spitfire was ever capable of. And, of course, WebOCalc came up with this power system.

-Flieslikeabeagle

Originally Posted by flieslikeabeagle

And, in the meantime - why not just slop on some extra thrust? With brushless motors and lipo packs, it's easy to add thrust these days. Also, we know that tiny and inefficient .049 and smaller glow engines were able to pull control line models around using tiny and inefficient propellers - so clearly there isn't all that much drag from the wires, no more than a few ounces at best.

-Flieslikeabeagle

It's funny you should mention the .049 because that's what the original motor was on this plane. Since I wanted to use some of the 2s lipos that I already had on hand, I found that I needed to go to a higher Kv motor to get what I needed.

Placed an order for the motor and speed control on Friday. Actual flight testing should occur within a couple of weeks to test my math.

Thanks for the well-explained reply.

Originally Posted by NoFlyZone

Let's take a typical park flyer type plane and examine it's wing. In the pic below, we can measure the wingspan from wingtip to wingtip and find that it's pretty close to 48", and the average width of the wing is about 7 3/16". By the way, the technical term for 'average wing width' is the word 'chord'. The weight of the plane below, as it sits on the runway, battery installed, and ready to take off is 25 ounces.

This is very interesting for me NoFlyZone, thanks for all your hard work.

How would you measure for the average wing width (MAC) if you have a weird wing shape, say a swept wing or a very tapered wing?

Thanks, Mike

Originally Posted by Patron

This is very interesting for me NoFlyZone, thanks for all your hard work.

How would you measure for the average wing width (MAC) if you have a weird wing shape, say a swept wing or a very tapered wing?

Thanks, Mike

Hi Mike,

There is a great online Wing Chord and Center of Gravity Calculator that many guys use. I've run across it many times and can't remember what the web site addy is, maybe a Google search will turn it up, unless someone chimes in with the addy.

And thanks for the kind words!

Chuck

EDIT: I found it for you...

http://adamone.rchomepage.com/cg_calc.htm

Beautiful, this really makes it easy

Thanks Chuck

Originally Posted by TheRocksKid

Chuck,
This is great stuff! I do have a question...
I've been wanting to convert some of my old control line stuff to electric. How would I modify the aircraft parameters to account for the drag produced by the lines?
Thanks,Rob

This is a great thread Chuck, thanks I can make a contribution on control line electric flight; I built one for fun a while back and posted my ideas on how to power it on this thread.
http://www.rcgroups.com/forums/showt...=750454&page=5

Sorry I used Wats per lb! I actually agree strongly with you & FB on this, on the other hand the Watts per lb approach is a sort of common currency to communicate with so I used it. On an earlier post you will see that I gave up trying to figure out the drag of the control lines & used an empirical approach to find a working solution.

Then we flew over long grass, which is a useful tip for this kind of aeroplane that never gets more than 30ft off the ground!

FB I understand your sentiments, stay in touch

Mark

Neat work.... I actually learned something!

Originally Posted by mrdarvin01

Neat work.... I actually learned something!

GREAT! That was the whole point of it... And it wasn't all that hard, was it.

absolutely the best article on RCG Chuck!

Too bad you hadn't had this written up last fall when I was badgering you and beagle to help me with my Nosen trainer! LOL!

John - even though you're off on another hobby (does it have anything to do with a certain fun little guitar amp?) I sure hope you will keep WebOCalc alive. That is the BEST little piece of software around!

Steve

Not sure if the right place here, but seems the closest thread to my question.
I was gifted with a quite strange prop: a foldable 13*10.
Tried a lot of setups with this calculator to find a proper usage for this prop, and nothing...
Anyone can suggest me what motor / plane can squeeze the best from this prop ?
Thank you.

i would say most likely a glider, especially because its a folding prop