Feedback Request! Failed Test flight.

[spinnyboi10]

How were the soccer balls secured & was it possible for them to contact any control rods or servos?

The soccer balls were pretty much held in tight by the side panels and top cover. All servos, arms and linkages were near their respective surfaces outside the fuselage so no chance of interference there. Also there were many checks beforehand to ensure the control surfaces moved in the correct directions.

 

[FDS]

Did you check for brownout in the control system? When you test each surface one after another you won’t approach peak load of the BEC, when flying you apply more than one control at a time and you have more servos than most 4ch set ups.

 

[Merv]

I looked at the video again, this time on a larger screen. I like @Tench745 observation, there is a lot of nose, very far in front of the CG. What is behind the CG, is too close to the CG to provide enough leverage.

It looks like the yaw starts form the moment the plane leaves the ground.

 

[Piotrsko]

I looked at the video again, this time on a larger screen. I like @Tench745 observation, there is a lot of nose, very far in front of the CG. What is behind the CG, is too close to the CG to provide enough leverage.

It looks like the yaw starts form the moment the plane leaves the ground.

On the big screen, do you see a stall,bobble or wobbles occur?

 

[perhapsleiana]

I had the same problem on my Origin 300i. Too much lateral drag area in front of the CG, not enough behind. It's like having your vertical stab in front of the CG, except it's the fuse.

On the big screen, do you see a stall,bobble or wobbles occur?

No stall occurs as far as I can tell.


Now, to solve this problem... If I'm right in assuming you can't extend the tail, there's still something you can do. you can have winglets that flare outwards, so that when the plane yaws left relative to the airstream, the right wingtip has more drag, and vice-versa. Keep your tail as it is- your thick airfoils were a good idea, as they help prevent stalling.

As for power, it seems like you didn't have too much of a problem, but usually a bigger prop with a lower kv motor/only two blades is more efficient at low speeds such as this.

 

[perhapsleiana]

So in short, flare your rudders outwards, and set them wide.

 

[Piotrsko]

Ok so no stalls, so what remains is lack of yaw cotrol force behind the COP/CG. Ditch the u tail and hang a massive fixed vertical surface on the end of an arrow shaft as far back as possible.

 

[perhapsleiana]

Ok so no stalls, so what remains is lack of yaw cotrol force behind the COP/CG. Ditch the u tail and hang a massive fixed vertical surface on the end of an arrow shaft as far back as possible.

I’m not sure they can make the plane any longer, which is why I recommended the flared winglets/rudders.

 

[Piotrsko]

Even if they made those surfaces into a V tail, it probably will lack enough authority to stop the yaw.

 

[perhapsleiana]

Even if they made those surfaces into a V tail, it probably will lack enough authority to stop the yaw.

Yes, which is why they will need to have a wider stance, hence recommending winglets the flare outwards about the vertical axis. The key to the method is the width between the flared surfaces. The main reason it's not a widely used method is how much drag it creates.

 

[Hai-Lee]

I question why the tail is actually mounted so low down at the rear of the fuselage. Heavy lift designs for bulky loads such as the Hercules and the like have a very large vertical fin which is effectively fitted on the line of the top of the fuselage, (getting it into clear air). Lifting body designs such as the Guppy have an enormous central vertical fin with a few extra vertical fins outboard on the horizontal stabiliser.

In addition the load could be carried in one or more pylons slung under or over the fuselage or the wings. This would allow the aerodynamics to be sorted out first and then the pylon used to position the load at the required CG.

There are a number of designs that allow for very long fuselages, that also get the wings and flight control surfaces into clear or undisturbed air. My personal favourite is a canard where the horizontal tail is mounted on the nose, the wings are connected atop the fuselage and the vertical fins are outboard on the wings. The aerodynamic effects caused by the fuselage and the load are minor. Sadly a steerable nose wheel would be considered as mandatory.

Just my thoughts!

Have fun!

 

[quorneng]

spinnyboi10
Clearly you plane was well constructed but how much freedom do you have on the planes configuration?
As has been pointed out on your plane the nose is long (and boxy) and the tail short.
The nose of a boxy fuselage not only contributes to side area degrading lateral stability but once at a positive angle of attack it also adds lift ahead of the CofG degrading longitudinal stability.
Does it have to have a single nose mounted motor?.
Was a low wing chosen so the balls could be loaded from the top?
With a necessarily bulky fuselage there are definite aerodynamic advantages in using a pair of wing mounted motors with a high wing layout. Such a layout might also allow the balls to be added through the front?

Of course without any knowledge of the competition rules these are just design ramblings but they might suggest alternatives if you choose to do the challenge again.

 

[spinnyboi10]

spinnyboi10
Clearly you plane was well constructed but how much freedom do you have on the planes configuration?
As has been pointed out on your plane the nose is long (and boxy) and the tail short.
The nose of a boxy fuselage not only contributes to side area degrading lateral stability but once at a positive angle of attack it also adds lift ahead of the CofG degrading longitudinal stability.
Does it have to have a single nose mounted motor?.
Was a low wing chosen so the balls could be loaded from the top?
With a necessarily bulky fuselage there are definite aerodynamic advantages in using a pair of wing mounted motors with a high wing layout. Such a layout might also allow the balls to be added through the front?

Of course without any knowledge of the competition rules these are just design ramblings but they might suggest alternatives if you choose to do the challenge again.

You asked a lot of good questions. So we had no length requirement, the main constraints were a max wingspan of 10 feet, single motor, and we had to optimize the cargo bay length to earn a higher flight score.
The low wing was chosen to allow top loading of the soccer balls and to possibly use ground effect to get us off the ground sooner as we had to takeoff within 100 feet.
Last year the competition objective was to carry tennis balls and we had a front loading design but it proved to be quite impractical especially since our front landing gear was mounted to the nose.
As for the motor/power we are only allowed a single motor and we need to have a 3000mAh 6s battery with a 1000W power limiter.

 

[spinnyboi10]

I’m not sure they can make the plane any longer, which is why I recommended the flared winglets/rudders.

There was no restriction on the length of the plane, only the wingspan. Definitely should have made it longer. There were winglets on each wing that only extended downward to increase the gains from ground effect. Although I do like your suggestion.

 

[spinnyboi10]

This year we are looking to carry a lot less soccer balls (1 or 2 compared to this year's 7). It doesn't make sense with the competition flight score equation which I attached here.

 

[Figure9]

So, no one has mentioned it yet as such, but you have a lot of fuselage out ahead of that wing, and the sides are very flat. Basically, the fuselage is acting like a big vertical stabilizer out in front of the plane. As soon as there was airspeed enough a little bit of yaw would build air pressure on the side of the fuselage and push it further off course. Some of those really long racers from the 30's like the Caudron, Goon and Firecracker had big slab sided cowlings way ahead of the wing and they could suffer "rudder lock." Basically, if they yawed far enough the rudder became ineffective and couldn't push the nose back straight ahead.
I surmise that when you couple that with the short tail of your aircraft which limits the effectiveness of the rudder, and the big flat fuselage blanking out the left v-stab.... you get the results seen above.

Edit: Also those are some unnecessarily thick control surfaces and that's a lot of plywood in the structure. Plywood add quite a bit of weight for little extra strength compared to balsa. I don't think it factored into this crash, but it for a competition aircraft I would think weight savings of any kind would generally be beneficial.

Prop thrust & wash is not symmetrical & flow is not straight back. The flow from prop thrust has a natural bend & rotation to it, thus the reason conventional twins have a critical & a non critical engine if the props both rotate the same direction.

It seems reasonable to me that the fuselage design might have generated the yaw by aerodynamic forces related to the propeller science even with a single engine.
Just saying.

 

[BS projects inc.]

To me it looks like a lot of it is due to the severe lack of leverage the rudders have on the plane. A tail that close will not have much effect on the plane. It's also important to make sure that the rudders are squared up and true with the rest of the plane. A lot of people mentioned it might be the P-Factor, but I thought that the p-factor resulted in a roll, not a yaw effect.

 

[Figure9]

To me it looks like a lot of it is due to the severe lack of leverage the rudders have on the plane. A tail that close will not have much effect on the plane. It's also important to make sure that the rudders are squared up and true with the rest of the plane. A lot of people mentioned it might be the P-Factor, but I thought that the p-factor resulted in a roll, not a yaw effect.

P factor generates yaw when the aircraft angle of attack produces a difference in the bite between the prop blade rotating upwards compared to the prop blade rotating downward. The upward rotating blade on the pilot’s right takes a bigger bite than the downward rotating blade to the pilot’s left & pulls the aircraft to the left at high angles of attack, low speed high power application. That’s most frequently the case when high power is applied to a tailwheel aircraft on the takeoff roll. P factor is reduced when the tail is raised to level the angle of attack & the bite of both blades are more equal. What you say about the empennage, as well as the P factor issue & the large fuselage surface are likely all valid considerations. There’s also the possibility of uncommanded rudder movement due to an electrical anomaly. The same design in a twin engine configuration might have been more stable. Not that that matters after the fact.

 

[Hai-Lee]

To me it looks like a lot of it is due to the severe lack of leverage the rudders have on the plane. A tail that close will not have much effect on the plane. It's also important to make sure that the rudders are squared up and true with the rest of the plane. A lot of people mentioned it might be the P-Factor, but I thought that the p-factor resulted in a roll, not a yaw effect.

P factor does result in a roll but the roll is due to the yaw effect slowing down one wing and speeding up the other hence the roll.
Unfortunately the yaw and roll happen at the time when the ailerons and rudder are least effective and so it becomes a serious issue and often results in a crash.

have fun!

 

[Figure9]

P factor does result in a roll but the roll is due to the yaw effect slowing down one wing and speeding up the other hence the roll.
Unfortunately the yaw and roll happen at the time when the ailerons and rudder are least effective and so it becomes a serious issue and often results in a crash.

have fun!

As usual, agree with @Hai-Lee The aircraft flight path reflect many or maybe even all of the theories described in this string.