atoine

Hi there!

I'm just about to finish this plane, and it would be really appreciated if some experienced people could tell me their opinion concerning technical aspects. It is my first design, so i'm not sure if everything make sense... (rib spacing, etc).

I'm gonna use monokote for covering.
Span : 50"
chord : 12"
airfoil : e475
Engine : OS 46fx

I'm just expecting the more obvious mistakes, dont bother to much!! And thanks a lot!

Tall Paul

Just for continuity of concept I'd put diagonals in the rudder and elevator.
THe wing trailing edge should be beefy... Built up with a spar down the middle, to give the hinges something to seat in.
A top and bottom spar in the wing instead of just the bottom spar. Makes for a better airfoild without too much sag between the ribs.
If the wing is one piece, have a sheeted center which is an inch or two wider than the fuselage to take the bending loads.
This is mandatory if it's a plug-in wing.
Other than these, the moments and area look fine.
It should fly OK however you make it.

SoCal GliderGuider

Looks like it will fly. What is your intended use? 3D?

A few observations:

Don't put holes in the ribs.

Don't mount the aileron servos through the ribs.

Think about sheeting the wing from the spar forward. Use a full depth spar if you do.

Think about cap strips on the ribs to improve their stiffness.

Depending on the servos being used you don't need counter balances on the rudder or the elevators.

If you are doing 3D then you need to make the rudder bigger. The V-Stab is ok. Ailerons reasonable.

allanflowers

I will concur with the comments on the wing structure. Since this plane has no dihedral, it is easy to run the structure right through the center, making it a one piece wing. This means the spars (top and bottom as T. Paul suggests), the leading edges and the trailing edges - of which you don't show any at all - should all join at the center. Skinning the front of the wing, from the spars forward is a good idea, as is skinning the center area a bit past the fuselage width.
The horizontal stab should also be one piece design and capable of a lot of strength.
Lastly, you have to consider how you will attach the covering and have wood where you need it. The aileron servos have to be "boxed" off, whether you put them in the rib or otherwise. The way you show them makes them very hard to replace if one goes bad.
The tailwheel is usually located at the rudder and turns with it.
Best thing is to study proven design models.
Good luck and nice start!
Allan

BMatthews

I see elements of a 3D model design coupled with elements of a basic sport model. The elevator is 3D sized but the aileorons and rudder are sized as per a general sport model.

The side keels of the fuselage could also use some help. You're trying to put the wood into that area but then you need to cut a notch in it for the wing spars and thus ruin the load carrying potential of these peices. An option would be to use smaller strips just above and just below the wing carry through and use a thin sheet and/or diagonal uprights to fill the area between these load bearing longerons.

And as mentioned the idea of upper and lower surface flat spars joined by vertical grain webbing would be both stronger and lighter. And you need the trailing edge strip at the ends of the ribs before the aileron.

But the basic proportions look OK other than the nose length may be a bit long depending on the overall size of the model and final weight of the airframe vs engine. I suspect you would need tail weight as it sits now.

onewasp

If I'm interpreting the plans correctly, you are placing the force of the landing gear entirely on the fuse sides. As the landing load is absorbed it will tend to 'twist' the fuse sides and attaching brackets.

I doubt that this will be strong enough. Try the conventional 'bent aluminum' gear so that the force will be distributed. Try not to rely on the torsional rigidity of the fuse side alone. There are a number of options which will give you durability without much (if any) weight increase.

Three inch rib spacing is about standard.

atoine

Thanks guys for all the inputs! I'll keep your advices in mind!

In fact, this model is suppose to be a sport plane, but I want to have real good control at low speed too to do some tricks... that explain why you cant really say what it is.

I was wondering if there is some charts or formulas somewhere regarding the torque needed VS control surface area and speed ? That would help a lot, because for example I'd like my rudder and ailerons bigger but I'm worried the servo won't be effective at high speed...

Also, if some of you have links showing some examples of aileron's servo installation (especially how to get the connector outside the surface of the wing) that would be great, I'm kind of undecided on this one !

Thanks again and see ya!

Tall Paul

Here's one... servo side mounted close to the wing surface, with the servo arm projecting outside the covering.
Another method is to mount the serve with just the arm outside the covering...
second image...

BMatthews

Low speed maneuvers will be fine with the sizes you have but it won't be a 3D style of response other than for the elevator. But bear in mind that wide control surfaces often lead to flutter problems unless the surfaces are very strongly built. And strongly built means heavy normally unless you get into some fancy options. So pick a speed range and flying style and be consistent within that envelope. And don't try to fly the model outside of that envelope once it's done. If it's a 3D'er then use the throttle of the often grossly overpowered engine to control the airspeed to keep it to only a fast cruise. If you go for the narrow surfaces and correct the elevator to match then you can go for faster airspeeds. The model will still slow down and be perfectly controlable but not in a 3D sense. But as long as you keep the model at or above the stall speed the narrower surfaces will be fine.

I've attached an image I did for someone else showing the upper and lower spar caps, some turbulator spars to add some light support to the covering material and how the trailing edge sub spar and aileron are added at the rear. Note in this drawing that the trailing edge sub spar is angled to stand square to the building board with the ribs sitting flat on the flat lower rear surface. Depending on how you make your wing some changes will be required to adapt but this is a pretty basic way of doing this. The trailing edge sub spar provides the rear support to line up the ribs, adds some vertical strength to the rear edge, provides a place to adhere the covering and also serves as the member to slot to revieve the hinges for the ailerons.

atoine

You're right on BMattews!

I now realize I was trying to do a "all in one" plane...! Before I read your post, I was working on enlarging all control surfaces, but I don't want a 3D plane. So i'm gonna adjust everything to get a sport plane, 3D is for later! And it make sense to make a sport plane since my airfoil is symmetrical and thin...

Whats next:

- Add some sticks (spanwise) to help support monokote (my ribs are 3.5 inches spaced...)
- Add a longeron at rear edge
- change landing gear
- change rear wheel

That's what it comes to mind for now...

I'll post pictures when changes are made, but I'm pretty busy at school for now so it could take a little!

Thanks all again!

Balsa Master

i have concerns about the twistability of the fuse. withouth top and bottom spars and or sheeting i see the fuse twisting horibly. i also agree with every thing said with the esception of lightening holes. though you do not need them unless your deisnging it to take a major load then theres no reason y you couldent use them. though its just extra wood to cut out for no reason. your engine mount also bothers me. i dont think it goes back quite far enough to aduaquatly transfrer load to the fuse. i think that you have the beginnings of a good flying modle. however theres defiantly room for improvement. (if you like i will make a scketch in autocad whowing the magor concerns and how to fix them, just PM me)

mwright

My Feedback: (5)

What are you anticipating for knife edge? Maybe a little bottom fin area (i.e. UCD 46) will be called for if you experience a lot of tucking. You have a lot of rudder area above the thrust line. Just stay focused on what you want your design to do then "rebuild it into submission". Good to see folks still hacking balsa.

atoine

Hey!

Got my stuff by mail... So there I am, I started building!

I'm gonna start with the wing.
First pic should be final design of wing (doesn't include some details to save time, will add a box for servos tho).

I know it isn't perfect, but I like to try stuff and then learn by my mistakes... Also consider it's my second plane (first one i built was in coro + aluminium = indestructible!), so I will accept a little more weight for solidity and simplicity. But I do take notes of your inputs, it will help me for sure for my next plane (and this one too).

So far I made the longeron, rear edge longeron and aileron (not finish).

mwright, sorry I should probably know what's a "knife edge" at this point, but I dont... As well as "fin area"... sorry I dont know much plane's vocabulary + I speak french...

Balsa master, about the fuse, I did'nt modelize yet spar between the fuse. It's to come! And for the engine mount, yeah it bothers me too!! look weak for now, I gotta work on it later....

OK, see ya later guys! I must say working balsa is much more rewarding than coro...

Kurt P

The counter balances on the elevators will eat the ground when you land.

But I think it wil fly ok.

mwright

My Feedback: (5)

atoine - Your english is much better than my french.

Knife edge flight put in simple terms is flying the plane on it's side with the wings pointing at 12 o'clock and 6 o'clock. The fuselage, fin and rudder provide lift when in knife edge. Lot's of people play with the rudder's hinge line, fin area, rudder area and stablizer position to minimize the tendency for the plane to deviate from the 12 and 6 o'clock position. Since this is a sport plane this should be way down on the list of importance to most peole but if you really like to knife edge then it moves up on list.

One other note on your design. Can you steer the tail wheel? It not then it may be difficult to control on the ground.

atoine

Here is half of ribs, not glued yet.

mwright, thanks its clear now. My first plane really sucked for knife edge... do you have examples of plane good at that? (pictures). I'd sure like my plane be able to do some, I think it's a cool-looking manoeuvre. About the tail wheel, its been fixed and now located on the rudder, thanks.

see ya

atoine

Lil' update:

Left side of the wing glued, ready to monokote (minus some sanding).
The stupid servo box took like 2hour to make, to realise after I won't be able to take the servo off... great... I wanted to save time without modelizing it...

txaggie08

was that done in inventor or CAD? i wish i was that good .....dont spend that much time doin stuff though

Tall Paul

Mount the servo to the cover, screw the cover to the wing structure..
But most of the time, the only time my servos come out is when the plane is being torn apart after a crash to get the servos for a new plane.
I build them in, mostly.

atoine

Wing is done, will do the covering at the end with the rest of the plane.

I configured the ailerons as flaperons; I tought as flaps the ailerons would only be deflected down, but they can go both up and down. As a result, I wont know where the are located when in flight... I guess you adjust it by the plane's response in flight?

Tsaggies08, the software I use is Catia. I'm a mechanical engineering student, so it's part of my formation and now part of my hobbies! Great software by the way...

Yeah, the servos will be built-in. I can't see why I should be able to remove them anyway (servo-failure is pretty rare I think).

My exams are done in 3 days, thanks god!! I want to flight this plane in 3 weeks, so I'll catch up after I'm done with school...

OK, more updates to come soon [8D]

atoine

I'm definitly building a plane...

atoine

Here is where i am,

I'm not very satisfied with monokote results, some wrinkles here and there, but it'll make it for this time.

[8D]

atoine

Almost there,

just mount the motor and landing gear, and a little monokote job, and it's done!

Thanks for those who helped me, I appreciate that!

Tall Paul

DON"T guess on the c.g.!!
Put it at 30%, no further back, on the root chord.
Tail heavy plane usually fly only once.
You don't want that!

atoine

That's the good thing about doing it on computer first... I did'nt determine the CG, CATIA did it for me [8D]. Of course there is a slight difference between the reality, but I can still change the batterie and receiver location, witch will be enough in my case.

Thanks, you could have save my ass there