Any R/C aviators? I need some info.
 

As my AE senior project, a group of us are doing a design challenge. Essentially, we design an original aircraft to accomplish a specific goal, then compete in a series of challenges against other schools. Anyway, I have no desire to reinvent the wheel, and need some good sources for R/C airplane parts and materials. Production items will save us time, and also be of similar/greater quality than what we can build. We'll also need the over-the-shelf stuff like radios, receivers, servos, etc. Tower Hobbies is a big one, but anything you know of I will check out.

Before anyone suggests it, I'll add that I am also going to check out all of our local hobby stores. I just want to look at all options.

Also, we are now accepting sponsors!:cool:

Matt, as you probably know, when talking about small models, just about anything will fly if the cg is close. I have heard of guys mounting engines on record album disks and flying them. Don't get caught up in wasting alot of energy on airfoil designs. I have designed and flown a bunch of RC planes over the years and the most important thing is always to keep it VERY light. The other thing main thing to consider is that if you will be flying slow ONLY, you want big exagerated control surfaces/throws for maximum control at very low airspeeds. If however it will be flown at fast speeds also, big control surfaces/controls are not so good.

I can give you alot more info if you desire it. Just keep in mind that this small light stuff is much more forgiving than the real deal and a 1/2" foam slab wing will work just fine on a small light weight model.

http://www.towerhobbies.com/


great place to get anyting hobby related

goodluck!!


wait looks like u allready had it down......nvm then :)

www.rcgroups.com

many builders there. look for the foam builders forum. as Tim mentioned foam is the ticket. wing loading is key. you will want to use electric power if possible as it is very reliable. consider using things like carbon wing spars for stiffness. i believe the foam of choice is bluecor. it can be laminated and shaped just about any way you like.

i have had very good luck with Hi-Tec (sp?) O5S receivers (very small, light and cheap) and small Hi-Tec servos as well. your battery system can be an issue and will depend on the AUW of the plane. Lipo's are getting reasonable but handle them with the utmost care.

the lighter your plane the cheaper the power system will be. do not drop big bucks on AXI brand motors or similar. there are Chinese generics out there (www.gorillabobsshack.com is one example) that will do a fine job.

anticipated wind conditions will dictate your build, IMO. a 9oz plane will not like wind at all. a 6lb plane will have no problem with it (provided you are a semi experienced RC pilot).

what are the challenges btw? any payload capacity req'd?

oh, and www.hobbylobby.com carries a better quality lineup in general.

btw, using a computer radio will give you more flexibility in setting up control surface throws, etc.

what's your budget?

Off of the top of my head:

Aircraft must fit in a 4 ft x 5 ft square. NiMH or NiCAD batteries only. Max battery weight is 4lbs. Electric motors only, as many motors as you want. Must take off in 75 ft fully loaded. 40A max circuit. Challenge is to carry a random combination of 14 water bottles ballasted to 1/2 lb, and 4 4x4 brick things at 1.8 lbs. As I said, it is a RANDOM combination of the two, and they won't tell us until the challenge. Max payload is a bit over 7 lbs. First challenge is empty airplane, fly as many laps as you can in 5 minutes. Scoring is # of laps/battery weight. Second challenge is with random payload, must complete two laps (no time limit). Payload loading is timed, mission score is 1/(loading time x empty weight x battery weight). Payload flights are not timed.

SO, important stuff is a lightweight but powerful battery, plenty of lift, good motor/prop match, quick load/unload payload, quick unloaded flight. We have lots of ideas, and I plan on picking up the lightest and best of everything that goes on the airplane.

One word - SPAD. You build planes out of the corrogated plastic that they make signs out of and PVC rain gutter. There are literally thousands of designs. And they're cheap to build and they patch up pretty easily WHEN you crash.

Lots of websites out there with free plans, sources, forums - like this one:

http://www.spadtothebone.com/

Also should add, we can change props between the two challenges. Hopefully can find a speed prop and power prop and switch them out.

okay, tough but not impossible.

I fly a 6' wing telemaster with 14 Nimh's and the 3520-7 motor and it weighs in at approx. 6lbs unloaded. i also strap a 11oz camera under it and it actually flys better!

Consider the 3520-7 motor from Gorilla Bob and accompanying ESC. you will probably be pushing very close to 40amps carrying that kind of weight.

Batteries (Nimh) can be pch'd from www.cheapbatterypacks.com. They will custom up a pack for you.

I expect you will NEED carbon fiber spars to carry that kind of weight and you will use every bit of 5' for the wingspan.

check out 'motocalc' for planning your system. it is a freeware program that will be of great assistance in ballparking your setup.

also, 5 minutes is very short run time for a plane capable of lifting 7lbs with under 40amps so you have some battery room to play with. consider having multiple packs made up to wire in series (ie 2x7 or 3x5 or similar).

Thanks Berettafan, bookmarked both.

Are you suggesting it might be an advantage to change packs for each challenge? We are allowed to use different packs between the empty and loaded challenges. I think we stand a lot to gain/lose with optimizing battery & prop to work with our motor, as well as for each challenge.

well i'd defer to whatever Mike has to say about it (i am new to the hobby) but the idea of flexibility in pack size is simple to implement.

you'll need several packs charged and ready to go regardless. a 6lb plane with lots of lift (my telemaster is just that) would not be fun to fly at 1/2 the weight as you'd probably be putting in a lot of down elevator to maintain level flight. i believe (again, Mike may correct me) that your limitation in lifting 7lbs will be the amperage and your limitation in flying laps unladen will be wing design as a high lift wing (flat bottom, curved top) is not the fastest way around a circuit. perhaps some manner of flaps would be helpful. Mike?

if flaps become an option you will need at least a 6 channel radio with programming capabilities. I use a JR 6102 and am very pleased with it.

another thing to consider is gear or no gear.

I'm leaning towards simple gear, non-retract. Do they have wire gear that will support a plane with around 10 lb gross weight? As for the wing, my initial idea has been to utilize some form of flaps, possibly manually adjusted between challenges. You are right about the airfoil, anything with a lot of camber will have a lot of induced drag.

While the design must be original, you are allowed to use existing components for your original design. There is nothing that explicitly prohibits you from soliciting advice from others, you just cannot allow them to do your work or design for you. I'm simply gathering information.

Prohibiting advice from others seems like a very closed-minded way of doing the design. Might as well prohibit the use of any outside text sources as well.

Really, my primary goal with this thread was to gather info regarding sources for components and materials. Probably not the best idea to share our design on a well-travelled website anyway.

10 lbs is really heavy for an RC plane, you probably want to look into the aluminum gear rather than wire gear. The strength of wire gear is okay, but the load it palces on the airplane at hard landings is brutal. With a wide aluminum piece, that load is better distributed.

Matt, aluminum thin walled arrow shaft (archery stuff) is VERY light yet VERY strong/stiff and can be bought at most hunting supply stores. Carbon fiber arrow shafts are good also, but many are a heavier wall thickness compared to the aluminum. I have used the aluminum tubes as leading edges of large ailerons made from light weight competition Balsa to gain torsional stiffness in a very light structure.

Depending on how skilled the pilot will be (light balsa construction is not very tolerant of minor oop's), you may want to stick with durable foam as a main building material but reinforce it with arrow shaft type material and reinforced packing tape.

Aircraft must fit in a 4 ft x 5 ft square.

Matt,

Beneath it all. lets calculate wing loading first. All other variables will be designed to support this.

From your information the total weight/mass will be X for the airframe and 7 lbs of payload with a max of 4 lbs of batteries. (you will come now where near this weight in (Lipo) Lithium polymer.

Lets say for giggles you have a total gross aircraft weight of 11-12 pounds. mass will rise rapidly when you build a landing gear system to support that weight. Largest wingspan you can have is 5 feet and a cord of ~18 Inches.

Check Renolds and NACA airfoils you WILL need a A symmetrical High aspect ratio airfoil. wing loading is 1.5 lbs per sq ft. (Very high :eek:) with a mono wing

I would no doubt make a bi-plane then you increase weight a smidgen but decrease your wing loading by 50%. (Slower airspeed this will be necessary for the takeoff requirement).

Look for a digital brush less motor and speed controller that will create a minimum of ~7 pounds of static thrust to propel your craft and hit V1 before the mark. My calculations are approximate but very close. The more the better but with the weight issue being most important. This is a good engineering experiment. You will find yourself in stade studies for efficiency. adding motor weight for more power. wing area for lift.

Let me know if you want me to help. I am a aerospace engineer and have won the Boeings Engineering Machine Competition for 3 years in a row and a R/C Flyer.

Foam is very-very strong for its mass..Epoxy will not attack it and a great adhesive ....Go this route.:)

Bob

10lbs AUW holy ****! might need more motor than the 3520-7 then.

I suggest starting with the assumption that the plane will use a 5' wingspan and 4' long fuse. Go buy some foam and start playing around.

Carbon fiber gear is available (askman camera mount is what you're searching for).

I feel certain you will be changing props for the various challenges.

I wonder if a bi-plane is worth considering? 5' is just not very wide for that kind of weight.

As Tim mentioned earlier COG is everything so be sure to set it right when testing.

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

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?

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.

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

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

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.:D I'll shoot you a PM.

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!

damn OWP your prior post answered all my thoughts.

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

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.

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.

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.

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". :D

"Irrespective", perhaps?

Carry on.

JP

Think Wing Area
 

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.

Well somebody finally acknowledged the pink elephant in the corner:p

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.:D

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? :D At least engineers don't tend to pepper their writing with superfluous (and erroneous) apostrophes. (or is it "apostrophe's"? j/k). :D

JP

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

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

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.
:p:D