Are you limited on wing span? Why such a small wing? Without doing any calculations I would increase span by at least 50% and cord by about 25% just as a rough target. Not enough wing area.

I would also modify the tail so that you return about 50% of the elevator back to the fixed h-stab. Too much elevator surface. It is not that you can't have all that elevator but you don't need it. You can have a full flying stab if you like.

Your issue isn't lateral stability. Your issue is tip stalling the wings in a turn. The plane will probably fly ok in a straight line, but as soon as you pull on the elevator to make a turn it's going to sideslip or tip stall (actually quite similar things) and go into a spin. It was hard to see what kind of airfoil you used, but if it's fairly thin and sharp up front that's going to aggravate the issue. Sharp leading edges stall suddenly with little chance of recovery, while blunt LE's ease into a stall more slowly giving the pilot time to react. This could be good experience for you though, since this flight shows you how a heavily loaded plane flies. You'll probably be up around 35 ounces/sq ft in the competition, so learning not to do those hard bank and yank turns will be vital to having successful flights. You need big smooth turns when you're loaded heavily to keep the wing flying.

Ed, I will pm more details about the wing selection details.

Jester, I would like to learn more about tip stalling. If you know of any articles, can you point me in the right direction?
As for the airfoil, it wasn't very sharp in the front but it was a high lift (wortmann FX60-100).

+1 you could very likely double the size of the wing, and 1/2 inch of dihedral wouldn't hurt either.
http://www.homebuiltairplanes.com/fo...cs-causes.html
a very small amount of washout would likely help lessen the tip stalling issues too.

Looking at the photo again, does the boom extend beyond the h-stab/VStab? Why? I have never seen an airplane design like that. Would seem to produce a very tail heavy type handling. Put the tail at the end of the boom or cut the boom.

perhaps it is just the photo.

AMA, thanks for the link will look into it. How does dihedral affect the plane's stability on the ground? Could it hurt the planes performance during the taxi mission?

Ed, the carbon fiber boom was used from last years plane. I was hoping to re-use it a few times before I start cutting. It is weird how it sticks out the back but besides a small effect on the c.g. I don't believe it hurts the planes flight characteristics too much.

By moving the empanage back to the end of the boom, you could reduce the size of the tail feathers as they will gain a mechanical advantage being farther out on the boom. Might save a bit of weight there. Also using a computer radio, you could add some expoential to your control surface throw so you get less throw at the middle and full throw at the ends. This will help with the over controlling of the plane. Good luck on the project.

Unable to access video of your first flight, but the wing in your last one (in addition to being small) looks very flat. Your stability might be improved with a little more dihedral in your new wing.

That airfoil is fairly sharp up front. Have a look at the clark Y airfoil to get an idea of what a gentle stalling wing looks like. I'm not much of an aerodynamics guy, but from practical experience that airfoil looks like it needs to go pretty fast to be efficient. You might consider switching to something that performs well at slower speeds given the parameters of your design.

All a tip stall is is when the tip of the wing stalls but the root does not. Some planforms are more prone to it than others, but all wings can do it. A tip stall results in the quick dropping of one wingtip (like in your video) and no response from the ailerons. Your pilot kept trying to correct the weird roll he was seeing but the plane either didn't respond at all or actually got worse, right? That's normal behavior for a tip stall.
Your tip stalls are happening because of a combination of conditions. First, you have too much wing loading to begin with, making the wing fly at a high angle of attack. So the wing is already close to its stall angle just in straight flight. Second, your pilot is doing those bank and yank turns which increases the wing loading even more and then encourages the wing to sideslip, which makes the inboard wing tip stall. The result is the beginning of a spin, which your pilot apparently doesn't know how to recover from.

For future use, the right way to recover from any stall is to point the nose toward the ground and gun the throttle. This is counter-intuitive since the plane is losing altitude, but it has to be done if there is to be any chance of saving the plane. Overpowered planes can just throttle out of a stall, but you don't have an overpowered plane. Tip stalls require a second bit of maneuvering and that is to rudder the plane in the opposite direction of the unwanted roll. DO NOT TRY TO ROLL OUT OF A TIP STALL OR A SPIN WITH THE AILERONS! It will just make the stall stronger and take away any chance of recovery as happened in the death spiral I saw at the end of your video.

If you want to win look up the theory on the spratt control wing flying boat. Properly executed this approach would be unbeatable in a lifting competition. And would be easy to fly though a bit different than most rc planes so use your own pilot...

I've thought for a day now about your question and I have one- how does a senior graduating with a degree in aeronautical design not know what a tip stall is? Does your school really think you're going to be ready to design airplanes for people to fly in if you don't even know basic aerodynamics and piloting concerns?

I graduated with a degree in mechanical engineering and a minor in aeronautical engineering and had never heard of the term "tip stall" until I got involved in R/C airplanes. In reality, a stall is just a stall, whether it occurs at the wingtip, the root, or anywhere in between will determine how it impacts the flight characteristics of the airfoil; however, it is still just a stall. I am sure that with your degree, you can design a wing that will give any stall characteristics that the customer desires (assuming they want any). Sometimes I think that in the world of R/C, the term "tip stall" is over used in cases where poor piloting techniques are more appropriate.

Thank you everyone for the suggestions. The team will make some improvements and try to get another test flight this weekend. We will use a bigger wing and hopefully have a third built by then. I will keep you guys updated.

Jester, I am glad you think about my questions away from here, I am honored

As for me, I am not a graduating with an aeronautical design, this is not offered from my school. I am aiming just to finish my mechanical degree and maybe go into concentration studies at a later time. The only classes on aero design I have taken are strictly for the this club and they are very limited with basic knowledge that only skims the surface of designing aircraft. My professor believes that this club is a great way to expand interest and create a demand for more aero classes and hopefully one day the school can offer aeronautical degrees. I certainly agree with him.

Some of the questions I ask are very basic but that does not mean I am totally clueless. Last year we designed a plane without any testing and with a very short and basic design class that performed decently at the competition. This year we are trying new things and testing them as we go. I believe it is a much better method of learning. Making mistakes raises questions, it makes the team look deeper into the problem and in the end we create a much better aircraft. Sure, we can look and copy an RC airplane that works well and slightly modify it to meet our requirements. Sure, this could be called engineering. Sure, it will fly. But, will it preform all the missions and score at the top? Chances seem low. On the flip side, I can take hundreds of aero design classes and learn all the formulas that aero students know and plug them in to build a plane that will fly because the math on the paper says it will it still does not guarantee first place.

So I guess to answer your question, more directly, no the school does not provide us with enough knowledge to be ready for designing airplanes for people to fly in but that is where the fun comes from.

i guess Charles also answers your question from another viewpoint.

My mistake. I thought everybody doing these contests were majoring in aero engineering. It makes sense that you need some of these basic things explained if you haven't focused on airplanes in your studies. I hope I didn't offend you with what I said.

I need some advice on servos and control horn attachment. Are there different locations that provide different flight characteristics or is there a set standard in RC construction?

there are several 'standards' for servo placement, example, one standard for elevator and rudder servos is to place them inside the fuselage... this means you'll have short servo wire leads going to the receiver but long pushrods.. the other standard is to mount the elevator and rudder servo's very close to the elevator and rudder... much shorter pushrods means less possibility of flexing, but much longer servo leads.. this method also places the weight of the servos much further aft, meaning a greater possibility of a tail heavy airplane.
(it's very common for 3D or other highly aerobatic airplanes) Similarly you can use one aileron servo to control both ailerons OR you can use one servo per aileron.
(using this method you can combine flaps and ailerons without actually having separate flap surfaces.. you can't do that with one aileron servo)
with that one exception (flaperons) the differences are mostly physical and won't make much difference in flight characteristics due specifically to the servo's location.

I'm sure you do realise that you can mechanically change the amount of surface travel by using different holes in the servo arm and the control horn...
(using the holes closer to the pivot at the servo will cause the surface to travel LESS distance than if you used the holes further away from the servo's pivot.
the reverse is true for the control horn holes... closer to the control surface will cause the surface to travel MORE distance, further away and the surface will travel less. (more surface travel = higher load on the servo, less travel = less load on the servo))

I should have mentioned... standard control horn placement is to have the horn placed as close to the hinge line as possible... if you'll notice how control horns are shaped, you'll see that the holes are actually set forward of the horn's mounting holes... the general idea is to get that control point at the hinge line.

Thanks AMA that was a big help.

It doesn't really matter where you put the servos. Designers usually place them in the location that helps get the CG right, but being easy to install usually trumps even that. The method of getting the power back to the control surface is another can of worms though. You can do a simple pushrod, pull/pull, or rod in a tube. Of the 3, I like the rod in a tube setup. Sullivan makes their "golden rod" product that gives you everything you need to set it up, or you can buy a simple antenna tube and some 2-56 metal rods that are threaded on one end to slide inside it. With either setup, you get a very positive slop free linkage with the added benefit that your control rod can go around gentle curves. As i recall, you need a lot of cargo space inside your fuselage, so the rod in a tube setup will let you route your control rod right up against the fuselage side keeping the middle clear. Aileron control rods are so short almost everybody does a straight pushrod setup. That also works well if you put your servos in the back of the plane with the control horns on the outside.

Thanks jester, I will keep this in mind. I might play around with the configuration to lean in favor of less weight. I will have to see see how much the push rods with covers weight vs wires leading the the servo and hopefully find a optimum configuration.

My next topic I would like some advice on is about creating a steerable landing gear for the taxi mission. I want to try tail wheel and then a tricycle set up in order to compare the two. Do you guys have any suggestions of what I can look at while designing the parts? Below is a video of a very basic taxi test. We used the smallest wheels we had. Will test others soon once we have some steering.
https://www.dropbox.com/sh/51ul7mra9qmz8jb/hapZ7LF7Eu

The pilot got another test flight in over the weekend. I was not there for this test either and I really cant tell much from the video but I will post the link below. I am not in charge of the the first prototype and I only have minimum influence on the decisions made but I would still want to ask what you guys think.
https://www.dropbox.com/s/pk53x0kk8a...Flight%203.AVI

Trike gear is easier to ground handle with. When the plane is slowing down (as it will be often on a bumpy surface) the weight transfers forward. So that puts more traction onto the wheel that is steering you with a trike. That's why cars are all built with the steering tires in the front. A taildragger will save you a little bit of weight and can make engineering the front end easier. Given the terrain you'll have to taxi on, you might consider using a servo saver for the front tire. A metal gear servo might not be a bad idea either.

On the test flight, it looks like you've moved the wing back some. The tail moment is so short on the plane that stability is going to suffer. If you guys will use the Cunningham specs for your overall plan, I think you'll be much happier with your results. If the tail moment has to be that short, have a look at the Sig Wonder to see what kind of horizontal stabilizer area is needed to keep the plane stable.

I agree.

I agree that tricycle landing gear will make the taxi mission easier but how does the weight compare vs conventional landing gear in terms of weight for the same sized aircraft?

This is true, and I was not happy with the reasoning behind the moving of the wing and also believe it affecting the plane. The esc was damaged so the wing could not be tested after being moved up. I have set up additional checks before further test flights to make sure the plane follows historical data.

There's not much difference in the weight. You're talking about maybe a foot of wire and a full size tire versus a tiny piece of wire and a tiny wheel in the back. So it's probably not over 3 ounces or so.