Matthewdupreez
Legendary member
if my cord is about 25 to 20 cm...
what angle of attack should i use?
and what thickness should i use
what angle of attack should i use?
and what thickness should i use
What Airfoil Should I Use?
- Thread starter Jackson T
- Start date
Matthewdupreez
Legendary member
i will measure my foam block so i know what the chord will/can be
Matthewdupreez
Legendary member
max cord is 270mm max wing height is 50mm.. max wingspan is 1.7m
clolsonus
Well-known member
I'm with Merv on a lot of this. People spend a ton of time thinking through airfoils, but at RC scales and RC speeds I don't think airfoil is the most critical design constraint. Maybe for specific competitions a specific airfoil could give your design a small percentage advantage, but one mistake on the transmitter sticks or one misjudgement about thermals and air-currents could give back all the advantage your airfoil bought you.
I could also comment that I was part of a project to design an ultra efficient long range/endurance uav, but the thing we learned the hard way is when you design to optimize the specs on the brochure, you end up with an airplane that is extremely difficult to launch, land, and can bite you any time you don't fly it perfectly. That's fine if you don't mind rebuilding your airplane 9 out of 10 launches or landings, or if you are really going for some specific behavior or constraint. But keep in mind there is a stress vs fun dimension, and each of us maybe come down in a different place on that scale, but it's easy to end up over optimized and over stressed (mentally) and miss out on the fun part.
So my best advice is spend 5-10 minutes picking your airfoil, and go with Clark Y if you don't have a really specific personal reason to do something else, and get your version 1.0 built and flying well. Then if you want to squeeze a bit more performance out of your wing, build a v2.0 wing (considering structures and materials and build difficulty and control surfaces and all the other real world constraints/challenges that can sneak up on you.)
Just my 2 cents for the little it's worth.
Piotrsko
Master member
Mostly the ^^^^^^^^, but I favor a semi symmetrical built by bending a clark Y nose up in front of the spar. Solves the incidence issue because it kind of makes its own incidence, promotes inverted flight and the 30% high point dissuades COP wander. Thinner is faster, to a point where structural failure rears it's ugly head. I'm a huge fan of the 12% laminar NACA SERIES 0012, but I crash a lot because of that choice since it does wierd things transitional which is where models fly. We also had tons of success tracing "old mans" shoe outline, aka shoe profile, since he had size 13 very narrow feet.
Last edited:
Matthewdupreez
Legendary member
80% of wing completed
Matthewdupreez
Legendary member
will post pics tomorrow
Matthewdupreez
Legendary member
can anyone tell me where the cg should be on this wing... see attached file.
i imagine it should be a the highest point of the wing?
i imagine it should be a the highest point of the wing?
Piotrsko
Master member
Well that appears a semi laminar with the highpoint around 30 ish percent kinda like the 0012 but thicker and a blunter entry. Arbitrarily, I would say 35 to 40 percent realizing that the more forward you go the less bad behavior it will have but at the expense of high speed performance. Stalls will be abrupt
For a rectangular wing, The CG shoud be at 25% of the cord. Example: If the cord is 10 inches the CG should be 2.5 inches from the leading edge.
Last edited:
If you are planning a swept wing, you need to find the MAC, mean average cord. The CG should be at 25% of the MAC
Matthewdupreez
Legendary member
it is not a swept wing. it is a straight wing...
so i will go for about 30% of cord... for the cg... the wing is done and now all i have to do is the fuse
.pics coming soon... after i've unpacked the dishwasher
I set the CG at 25% for the maiden flight, for improved stability. When the plane is trimmed out, I will start moving the CG aft until I get the amount of instability I prefer. The CG usually ends up being 27-30% of the cord.
Matthewdupreez
Legendary member
25% it is
Matthewdupreez
Legendary member
Matthewdupreez
Legendary member
oh yea and i'm not going to use the spar i was going to use
Matthewdupreez
Legendary member
oops please excuse the masking tape on the one wing... it was to prevent the wing sticking to the table
Matthewdupreez
Legendary member
hey guys i need some help.... i finished the glider and man i looked fantastic..... i balanced it perfectly on 25% cord..... and threw it that thing did not want to land... 25metre from a slow hand toss.... sadly i did not record any of this......
elated i picked it up turned around and threw it ... well i know it can do a figure of 9..........
turns out the weights in the nose had shifted.
but here is my problem... i am having to add 200grams of weight in the nose. which i desperately want to reduce...
so one problem i found was that the v-stab and h-stab weigh in total 50grams which means that i needed to add 100 grams of weight into the nose to counter that(the nose is half the length of the tail).
now how do i build an ultra light tail that is fairly rigid?
i can get balsa but that will only get here in a week and im kinda impatient.
Hot wire i chunk of foam.. that will be super light...
make a light frame from barbeque skewers and cover it in some laminating plastic
or use some fibre glass and make a fibre glass tail..
and advice would be much apreciated..
@Merv @clolsonus @Jackson T @Craftydan
elated i picked it up turned around and threw it ... well i know it can do a figure of 9..........
turns out the weights in the nose had shifted.
but here is my problem... i am having to add 200grams of weight in the nose. which i desperately want to reduce...
so one problem i found was that the v-stab and h-stab weigh in total 50grams which means that i needed to add 100 grams of weight into the nose to counter that(the nose is half the length of the tail).
now how do i build an ultra light tail that is fairly rigid?
i can get balsa but that will only get here in a week and im kinda impatient.
Hot wire i chunk of foam.. that will be super light...
make a light frame from barbeque skewers and cover it in some laminating plastic
or use some fibre glass and make a fibre glass tail..
and advice would be much apreciated..
@Merv @clolsonus @Jackson T @Craftydan
Matthewdupreez
Legendary member
wingloading at the moment is 11grams
clolsonus
Well-known member
I'm probably not thinking of all the ideas here, but if you are working on adjusting the CG location, here's what comes to mind:
Because the tail extends out further than the nose (usually) small weight changes at the tail require larger weight changes at the nose -- so it's a critical area to pay attention to.
Like you say: making the tail lighter could be a good idea, but you have to work with materials available and you also need to maintain enough structure. Sometimes lightening holes are used, but then you need to cover the structure with some sort of film or tape. In some cases it might help to pay attention to smaller details like how much glue you use.
I couldn't tell if this was an RC airplane or free flight? But if you have RC gear, then of course you could move your tail servos forward and use longer pushrods. You could push your battery as far forward as possible since that is usually the heaviest bit of avionics.
If you are rebuilding the fuselage along with the tail, then another thing people often do is design a longer nose, or push the wing mounting point aft so the airframe comes out closer to the desired balance point on it's own.
Sometimes it's fun to notice WW-II fighters or racers with giant engines and where the pilot is seated. Look at any 2-seater tandem open-cockpit airplane and usually the pilot flies in the back seat and an optional passenger is in the front seat close to the CG. The noses on WW-I fighters were often *very* short because the engines at the time were heavier. I find it interesting to look at how modern gliders are designed and where they put the pilot. I have an xuav talon with a pusher prop, and in this case the fuselage forward of the wing is very long to help offset the weight of the motor in the rear.
So all of this is fun. Figuring out how to balance a large network of design tradeoffs, come up with something that flies nice (performs well, handles well), and looks cool all at the same time.
Because the tail extends out further than the nose (usually) small weight changes at the tail require larger weight changes at the nose -- so it's a critical area to pay attention to.
Like you say: making the tail lighter could be a good idea, but you have to work with materials available and you also need to maintain enough structure. Sometimes lightening holes are used, but then you need to cover the structure with some sort of film or tape. In some cases it might help to pay attention to smaller details like how much glue you use.
I couldn't tell if this was an RC airplane or free flight? But if you have RC gear, then of course you could move your tail servos forward and use longer pushrods. You could push your battery as far forward as possible since that is usually the heaviest bit of avionics.
If you are rebuilding the fuselage along with the tail, then another thing people often do is design a longer nose, or push the wing mounting point aft so the airframe comes out closer to the desired balance point on it's own.
Sometimes it's fun to notice WW-II fighters or racers with giant engines and where the pilot is seated. Look at any 2-seater tandem open-cockpit airplane and usually the pilot flies in the back seat and an optional passenger is in the front seat close to the CG. The noses on WW-I fighters were often *very* short because the engines at the time were heavier. I find it interesting to look at how modern gliders are designed and where they put the pilot. I have an xuav talon with a pusher prop, and in this case the fuselage forward of the wing is very long to help offset the weight of the motor in the rear.
So all of this is fun.
Figuring out how to balance a large network of design tradeoffs, come up with something that flies nice (performs well, handles well), and looks cool all at the same time.
Last edited:
Similar threads
