Any R/C aviators? I need some info.

[onewhippedpuppy]

Tim, excellent suggestion on the arrow shaft for a stringer.

Bob, you certainly make an excellent point. We had hoped to avoid a bi-plane for the sake of simiplicity. We're very early in this, and are yet to start doing any calculation or design. With the use of flaps, would you forsee a single wing being sufficient?

[onewhippedpuppy]

Originally Posted by berettafan

Bob can you talk about the symmetrical wing and it's relationship to speed vs. a flat bottom wing?

While Bob can certainly give a better answer.....

Symmetric airfoils have zero lift coefficient at a zero angle of attack. Cambered airfoils have a lift coefficient at zero angle of attack, so even at level flight they are providing lift (assuming level flight = zero angle of attack, which is rarely true). Lift is partially based on velocity, so as your velocity increases, so does your lift. Induced drag is drag due to lift.

So, at a given AOA, the cambered airfoil is providing more lift, and more induced drag. This becomes a bigger issue as speed increases, because the drag and lift increases with it. So, the symmetric airfoil at a higher speed and trimmed to the proper AOA will provide the same necessary lift as the cambered airfoil at lower speeds.

[Tim Hancock]

Assuming standard small plastic partially filled water bottles, you should look at a hollow main spar capable of holding 7 bottles each (assuming biplane or triplane). The ability to mount the payload at the theoretical center of lift while minimizing the effects of the water shifting around front to back in the bottles will make it easier to fly the airplane with a proper cg irregardless of how the contest directors decide to assign a payload.

Picking theoretical airfoils in regard to maximizing speed is probably not important here. This contest is not going to decided by who has potentially the fastest airplane as clocked by radar, rather it will be decided by which airplane can be reasonably controlled in both heavy and light configurations.

IOW, don't sweat the airfoil, instead concentrate on light weight, ample wing area and minimizing cg change no matter what combination of payload is dictated.

just my two cents

[GO DAWG GO]

Flaps give you a pitch bias and allot of drag. I wouldn't suggest this, it also supports a propensity for wing stalls. I would design my wing to provide one major attribute "Lift" for this. The aircraft will never need to fly inverted or any other aerobatics. I will come up with a flat bottom high aspect ratio airfoil for you guys. Let me model it and provide some unknown parameters in the equation. This can be radio controlled right. So-Flaps are a possibility but better for landing.


http://www.standardcirrus.org/AirfoilCalculator.xls


Matt, have you ever flown a R/C airplane? Its not easy.

Design wise: I just don't see any options other than 2-3 wings to create enough lift to get you airborne in the 40 feet or so.. also: Lift is created by a Bernoulli effect of air molecules flowing over the top and bottom of the wing surface meeting at the trailing edge and creating a low pressure system above the airfoil. This can be provided by high velocity or distributing the effect over larger wings at a slower velocity (Make sense)? Thats why the trade study points toward multiple large wings to keep velocity to a minimum.

Remember if your not in the air by the designated V1 supporting the load, nothing else matters.


Do not worry about aesthetics. This thing will get beat to hell. if you don't have allot of radio time and if you crash, destroy it its purely academic.
I need to think this through and get back to you. The wing loading is high and you basically have a carrier takeoff. I have always jumped head first into these competitions and have done well. Lemme think...

I'm more worried about the initial acceleration required to get airborne in the distance allotted. Then the resultant airspeed after.

PM me if you want to talk.

Bob

[onewhippedpuppy]

Wayne, that is very true. After a year of being a full time AE student, 40 hrs/wk between two jobs, and my wife and two kids, I've gotten very good at juggling. The only problem, this is the first fun thing I've done in school.

Tim, interesting idea with the spar. Unfortunately, the bottles have to stand upright.

Bob, I don't care if we have the ugliest plane flying. Just so it wins. Our mantra is simple and lightweight. I won't actually be flying it, rules dictate that the pilot must be an AMA member pilot. They do not have to be a student. Transfer to Boeing Wichita, we'll let you fly. I'll shoot you a PM.

[berettafan]

strongly suggest you guys buy a radio and plane for practice. flying RC is one of the more difficult things i've done and requires practice. get your radio and go buy a couple planes for practice. recommend GWS Slowstick to start. $29 plane (+ servos, batts, rec'vr) and you'll be in the air right away.

completely missed the sloshing water issue! wow. suggest making your 'load bay' such that bottles hang down vertically or at least at opposing angles. something like / \ maybe. this carrying mechanism is going to have some weight to it as well.


Very interesting problem!

[berettafan]

damn OWP your prior post answered all my thoughts.

[GO DAWG GO]

Tim,

I agree in part but your wing area and foil will get what you requirements demand "Allot Of Lift" focus on limited weight and a high lift airfoil. I went back and read the initial thread and the takeoff distance is 75 feet...Thats better.

Matt; This going to sound goofy but start looking toward the tri-wing configuration. study the DR-1 and add dihedral and even poly to help you control it.

The airfoils have been cambered slightly and are semi symmetrical. This was for speed. You don't want speed. speed and this project wont mix and make it harder to control.

Good project

Bob

[onewhippedpuppy]

Triplane is certainly an interesting idea. Adds to the complexity for construction, as well as weight. What do you see as the advantages? 3 small light wings vs 2 larger heavy ones?

[Tim Hancock]

Originally Posted by onewhippedpuppy

Triplane is certainly an interesting idea. Adds to the complexity for construction, as well as weight. What do you see as the advantages? 3 small light wings vs 2 larger heavy ones?

More like 3 BIG LIGHT wings. If the bottles must be vertical, they could be double rowed vertically in a tall triplane (or biplane) configuration. Obviously the closer to the center of pressure of the wing and the centerline of the fuselage is best to optimize handling irregardless of payload. As you probably know, a BIG prop turning at somewhat of a slower speed is better than a small prop turning at high speed. Especially in regards to taking off in minimum distance with a heavy load.

[berettafan]

put enough dihedral in and you won't even need ailerons.


btw, i think you will end up making two or three of these for practice. keep an eye towards access hatches, etc. for the electronics (or even just mount them outside of the fuse.

[berettafan]

not to hijack but since there are some plane guys here anybody see the 'Dogfights' episode with von Richtoven and friends? best episode yet IMO.

[Overpaid Slacker]

As a Naval Architecture student in days past (fluid dynamics was a fave -- especially prop design) and an aviation and R/C buff, I was really enjoying the knowledge being dropped here.

That is, until this:

Originally Posted by Tim Hancock

... Obviously the closer to the center of pressure of the wing and the centerline of the fuselage is best to optimize handling irregardless of payload...

Dude, you did not just say "irregardless".

"Irrespective", perhaps?

Carry on.

JP

[GO DAWG GO]

Again....

You must realize that your wing loading is twice as high as a C-17 full loaded. So don't laugh about allot ot wing area. This absolutely has to be distributed over more area or the Turkey wont fly, Period.....Think wing area with a max span of 5 feet and don't go over a ~third of that in chord or you loose pitch control.

Lower- mid- upper wings with your bottles down the center directly balanced to the C/G of the wing profile. The symmetry of the wings will provide a bridge truss rigidity just like the old birds.

[berettafan]

Originally Posted by Overpaid Slacker

As a Naval Architecture student in days past (fluid dynamics was a fave -- especially prop design) and an aviation and R/C buff, I was really enjoying the knowledge being dropped here.

That is, until this:



Dude, you did not just say "irregardless".

"Irrespective", perhaps?

Carry on.

JP

Well somebody finally acknowledged the pink elephant in the corner

[onewhippedpuppy]

JP, in case you didn't get the memo, english and engineering don't mix. Or so says my thermo teacher, who took points away for anyone who didn't spell gauge "gage".

Bob, I get it now. 5x4 wing won't be ideal.

[Overpaid Slacker]

Originally Posted by onewhippedpuppy

JP, in case you didn't get the memo, english and engineering don't mix. Or so says my thermo teacher, who took points away for anyone who didn't spell gauge "gage". . . .

I struck from my first draft a line to the effect of "... which is one reason why I left engineering in my wake." For a career that requires such precision, to harbor so many of those undisciplined in their native language...!

How many times have you seen "guage" in technical journals? At least engineers don't tend to pepper their writing with superfluous (and erroneous) apostrophes. (or is it "apostrophe's"? j/k).

JP

[dhoward]

http://www.modefosheli.com/hurricane_550_ep
Start flying sim now...

[GO DAWG GO]

Well I've been noted as being the worst speller on Pelican...ask Nostatic...That was only by neglect not intellect. Sounds like Johnny Cochran... I'm usually too damn busy to check my work.... and really didn't want to compose a Shakespearian novel just a reckless thought....anyway- I forgive you...

Bob

[Tim Hancock]

Sorry for the sloppy grammar JP. I is a jest a dum asosiate decree micanical guy. I hope my ma dont reed this as she used two teech hy-scool englesh.

thare are peeple in life hoo build and create things an those whoo talk about bilding an creating stuf. me think me is latter. so sarry to disapoynt.