Feedback Request! Failed Test flight.

[Merv]

It looks to me like there was not nearly enough surface area aft of the CG to offset the massive surface area way forward of the CG.

In other words the nose acted like an anti rudder. Once the yaw started, the anti rudder nose took over, reducing the effectiveness of the elevator and drove the plane into the ground.

 

[Figure9]

Just another thought. From what I can see of the structure there is a lot ow weight there! The vertical fins obviously provided only small corrective forces and yet they are so strong in structure and weight. The real problem could be as simple as a severe weight problem or the weight could be making other problems even worse.

Have fun!

Hard to argue.

 

[spinnyboi10]

Although it might look nice, it's a poorly designed airplane 😂

 

[spinnyboi10]

I appreciate all of your input! Next year's design is in the works with all we learned from this past season.

 

[Hai-Lee]

I appreciate all of your input! Next year's design is in the works with all we learned from this past season.

Feel free to post your interim design for comment/ideas or ask for answers to any problems you encounter.

Just remember that whilst weight is what it must lift, weight is also the biggest enemy you face. Less weight means faster take off and better control.

Have fun!

 

[spinnyboi10]

Our design for the 2019 competition was super heavy! 43 pounds empty! This year our design came out to be 15 pounds so a big improvement from the previous year. We are going for something closer to 10 this year. We are probably going to be carrying only 1 soccer ball and a bunch of steel payload plates. The challenge is making the wingspan as small as possible while still offering the lift we need to carry our plane and get it off the ground quick enough.
We are currently working on figuring out our wing design first. We are running dozens of simulations on Solidworks to see what the best design is and then we will build the rest of the plane after we decide on the wing. There will definitely be a farther back tail that is also much bigger! CG issues will be taken care of as well and I'm thinking of incorporating some angle to the motor mount plate to account for torque and such.

 

[Hai-Lee]

Our design for the 2019 competition was super heavy! 43 pounds empty! This year our design came out to be 15 pounds so a big improvement from the previous year. We are going for something closer to 10 this year. We are probably going to be carrying only 1 soccer ball and a bunch of steel payload plates. The challenge is making the wingspan as small as possible while still offering the lift we need to carry our plane and get it off the ground quick enough.
We are currently working on figuring out our wing design first. We are running dozens of simulations on Solidworks to see what the best design is and then we will build the rest of the plane after we decide on the wing. There will definitely be a farther back tail that is also much bigger! CG issues will be taken care of as well and I'm thinking of incorporating some angle to the motor mount plate to account for torque and such.

In order to reduce the wing span you could consider a biplane type design, (stagger wing actually). In addition you need to increase the wing area to the max within reason. With short span wings designed for high lift I would consider flaps and slats as mandatory and I would strongly recommend the use of fences to reduce the air bleed from the wing tips towards to the centre of lift, (minimum pressure).

Forget worrying about ground effect as it is only applicable when very close to the ground and once you lift off the pressure under the wings rapidly decreases which can effectively help launch the plane into the air early, slow, and effectively hold you close to the ground at stall speed. You should also consider the use of the available motor thrust to augment the wing lift by blowing the flaps which will provide greater lift gains than ground effect ever could.

Keep the tail in clear air for best results even if you have to split the tail into 2. Finally you might consider the use of a cheap flight stabiliser so that the pilot inputs can be related to directions rather than to also respond to trim or similar issues. Done properly the bird should be able to take off almost by itself.

Just my thoughts!

Have fun!

 

[Ranger_107]

the rudder looked like it had an airfoil on it pointing to the left, giving it lift which made it yaw out.
and the feusalage is pretty large, considering the size of the wing.

View attachment 163338

 

[Hai-Lee]

the rudder looked like it had an airfoil on it pointing to the left, giving it lift which made it yaw out.
and the feusalage is pretty large, considering the size of the wing.

View attachment 163338

Yes I saw the original post of the plane at the take off issue.

You do realise that the fuselage does not need to be large enough to enclose the load unless that is a design stipulation. Outsized loads can be carried externally to the fuselage either in a specially designed pod or even using a harness arrangement.

Making the entire fuselage large in cross-sectional area because of a single outsized load requirement is just increasing the weight and complexity of the plane.

Better to design a plane with a long rigid beam type fuselage and then sling the load underneath, (in a streamlined pod if necessary), for a monoplane design and if going for a biplane then the lower wing is split either side of the load carrying area.

Just my thoughts!

Have fun!

 

[spinnyboi10]

Yes I saw the original post of the plane at the take off issue.

You do realise that the fuselage does not need to be large enough to enclose the load unless that is a design stipulation. Outsized loads can be carried externally to the fuselage either in a specially designed pod or even using a harness arrangement.

Making the entire fuselage large in cross-sectional area because of a single outsized load requirement is just increasing the weight and complexity of the plane.

Better to design a plane with a long rigid beam type fuselage and then sling the load underneath, (in a streamlined pod if necessary), for a monoplane design and if going for a biplane then the lower wing is split either side of the load carrying area.

Just my thoughts!

Have fun!

So the soccer balls did have to be fully enclosed and isolated from the airflow. A pod could have worked but would have been extreme for 7 soccer balls. This year we are definitely considering slats, but are a little hesitant on flaps as the airfoil we are using (s1223) is a high lift airfoil with a large camber which doesn't play too nicely with flaps. We are still looking into options though.
As for the flight stabilizer, we unfortunately are not allowed to have one on our plane. It's all up to the pilot and the design!

 

[L Edge]

If you evaluate it from the design of the Pregnant Guppy to the Beluga, oversize vehicles end up with the CG being moved vertical where it affects the directional stability of yaw and roll. In such cases, rudder is definetly needed to insure directional stability. If you design another, you should look at adding dihederal to the main wing or stab to improve performance as perhaps height to the rudders.

If you run the video at .25 speed and stop it about every foot or so, it tracks perfect on ground, but when you lift the nose wheel(OK), but when your main gear clears the ground, the plane starts its rotation in the yaw axis. I do not see any rudder action by the pilot, so it continues on rorating and when the plane is directly in front, there is still no right rudder added at all. Them it start with roll and......................!

At this point, the yaw problem is not addressed, so really don't know if it a design problem or pilot error.

 

[Hai-Lee]

Thanks for the additional info!

The main reason I suggest the high wing layout for the main wing is that you can make it lighter and stronger without resorting to dihedral and still have some inherent stability due to "Pendulum Stability".

Flaps do not need to be "barn door" type as they are to effectively provide an increase in wing profile incidence. If you have access to a wind tunnel it would be worth the effort to test various flap geometries purely because of the lift improvement.

Where flaps are definitely not to be considered you could consider the ability of changing the wing incidence for take off.

If fitting slats only, do not use any configuration that causes the effective LE to droop as this can actually decrease the wing effective incidence angle and hence the lift generated.

Finally I would look into mixing a little Aileron into the rudder to combat the chance of a loss of yaw control when attempting to control any roll tendency at take off. A high lift airfoil, near stall, can actually give what appears to be control reversal. This can occur when aileron is used to stop a yaw induced roll as the aileron on one wing which is deflected downwards in an attempt to increase the lift actually causes the wing to stall. The result is the wing that you are commanding to rise actually loses all lift and falls at the same time as the drag from the stalled wing increases causing the yaw induced roll to be exacerbated.

Just a few thoughts!

Have fun!

 

[quorneng]

spinneyboi10
It looks like the scoring equation does not have a time factor.
You have mentioned a take off within 100 ft but presumably to qualify the 'flight' has to met some criteria.
With no time limit there is advantage in flying slowly as fundamentally the power to fly is proportional to speed.
You do have a wing span factor but not on wing area or, as has been pointed out, on the number of wings.
This suggest a broad low aspect ratio (4:1?) wing or wings. Low aspect broad chord wings have 'depth' so are much easier to build strong, light and rigid.
You are building a 'payload' plane where structural weight is a key factor to maximise payload for a given amount of power (1000W).
As you are carrying at least one football, which suggest the fuselage has to have some depth, a biplane could make some sense.
If you are only going to carry one ball it could go in the nose ahead of the wing(s) with its weight countered by the much smaller but heavier steel plates behind.
Large wing area slow flight has the advantage of a low take off speed so avoiding the need for additional lift devices. Keep it simple and light.
Set yourself a power to weight target, say 80 W/lb (you could likely get away with quite a bit less), to get the 'target' all up weight = 12.5 lbs. Consider a 'slow flying' wing loading of 8 oz/sq ft. You would need a wing area of 25 sq ft. If it was a biplane each wing would need 12.5 sq ft. Say a span of 8 ft with a 1.5 ft (18") chord (aspect ratio 5:1). Even with a 'simple' wing section the wing is going to be over 2" thick.

With these sort of dimensions it should be possible to carry a 6.5 lbs payload in a plane that only weighs 6 lbs. It will fly at 8 to 10 mph and have power to spare. With such a target achieving the strength to weight of the air frame is likely to be bigger problem than the efficiency of its aerodynamics.

Just my ramblings at the problem but it is the sort of process I went through to build a plane that had to carry 50% of its weight as a payload but to do so using the lowest possible power.