RC-Captain

Today I was flying my extra 300 and notice the nose wanted to dive gradually. The plane would not track straight until I adjusted the elevator up about 3/16 of an inch. I balanced the plane with an empty tank, on its back, and it was perfect.

Can someone please explain to me what I may be doing wrong or what I can do to alleviate this nosing down problem . Thanks

Jim Messer

My Feedback: (2)

Sounds to me like you may have negative incidence in the wings. When the elevator is at zero degrees, the wing should be at zero also, or if you are like me, I set mine at 1/4 to 1/2 degree positive. I don't like everything zero-zero.

Flyboy Dave

My Feedback: (21)

Check the incedence of the wing, and the incedence of the horizontal stabilizer,
and their relation to one another. If you have positive incedence in the horiz stab,
it will push the nose down. Also, if you have a lot of fuel on board, and will be nose
heavy for much of the flight. If you have down thrust in the engine, it will also pull
the nose down.

FBD.

RC-Captain

maybe in the ailerons , I read some where the ailerons should be a tad bit down. I guess this is where flapperons would help instead of adjusting the rods.

Flyboy Dave

My Feedback: (21)

If the ailerons were a tad down, they would be creating lift....acting as flaps.
If that were the case, you would need down trim in the elevator.

I made this homemade incedence "stick" 30 years ago, It's the only one I
ever had....way before the laser was invented. This and a tee-square
are all you need to check out your alignments.

FBD.

majortom-RCU

My Feedback: (40)

If by "perfect" you mean right on the mfr's recommendation, then I would expect it to be noseheavy, since that's what mfr's consistently do, is recommend a noseheavy CG. After I eventually figured this out, I started ignoring their recommendations and started plotting Mean Aerodynamic Chord on all new models, and setting them up to start off balanced at 35% of MAC. On an aerobatic type (including 3D) model, this will give a reasonably flat glide, still require a little pull for straight & level upright and a little push for straight & level inverted. After I've flown it a bit, I may decide to nudge the CG a bit one way or the other, but often I leave it right at 35%. Mfrs assume that the RC pilot will adjust CG to suit his own preferences--but if you want their recommendation, they will give you something very conservative, which is noseheavy. On occasion I've known house reps to confide that they fly their own version with CG well aft of what the manual recommends.

Positive wing incidence can cure the dropping nose in upright flight, but shifts the problem around to dropping nose in inverted. For an Extra and other planes in its class, zero/zero is the best set-up for wing & tail, and vertical thrust offset is usually not necessary with such a set-up. Keep everything clean & simple.

RC-Captain

Actually the manual states 'there is a 1/4" margin forward and aft, but it is not recommended that the center of gravity be located any further back than 3-3/8" I have it at 3-1/8" which means maybe I should move it forward and rebalance the plane.

Flyboy Dave

My Feedback: (21)

No....move the c/g rearward....

FBD.

RC-Captain

Toward the trailing edge ? wouldn't that make it more nose heavy ? [X(]

majortom-RCU

My Feedback: (40)

We often confuse "actual CG", which is where the plane will actually balance, and "recommended CG", which is where someone says it ought to balance. If you shift weight back, you will move the actual CG and reduce the noseheavy flight behavior. You will be behind the recommended CG, which is more a legal concept in the mind of the manufacturer than anything reasonably connected to good flight behavior in the aerobatic domain.

The 1/4" margin is more of the same old baloney. Models are maneuverable and controllable over a much wider range of actual balance point than what the manual would suggest--assuming a pilot who is quick on the sticks. The manufacturer is happy when you have a nose-heavy model that is pitch-stable as long as you are pulling on the elevator stick and not trying to fly inverted or do anything other than fly an upright oval pattern. That is not why we buy aerobatic models.

Flyboy Dave

My Feedback: (21)

majortom-RCU has it right. The balance is set with an empty tank.
98% of the time....when you have fuel in the tank, you are nose heavy.
That's why pattern flyers put the tank over the c/g, and the c/g never
changes during the flight.

RC-FIEND....picture it this way....(pic #1 ) the c/g is at 4"....the balance
or "fulcrum point". If you move the balance ( or fulcrum point ) back....
like in pic #2, the plane gets real nose heavy. That's why in order to move
the balance point ( c/g ) rearward....weight has to be added to the rear of
the plane.

I know....without visualizing it, like I have done for you....it sounds backwards.
Don't worry, I used to think of it that way as well.

Dave.

Wing-Ding

Actually Flyboy Dave's incidence stick would work great along with this product- especially if you're trying to resolve a 1/4 degree accurately:

[link=http://www.aeroperfect.com]AeroPerfect[/link]

Check out the "incidence" link which also discusses making decalage measurements.

RC-Captain

When I say move the CG ,I was not talking about shifting the weight . I was talking about moving the actual point and then re-balancing the plane from the particular point, which now I realize this will only give me the same result. So to put it in plane* english all I have to do is shift the weight with the tank empty in order to make the plane less nose heavy when the tank is full.

RC-Captain

Thanks but no thanks, I can live with a little incidence problem , but I can live with spending $200 on something I can basically do with the naked eye

Wing-Ding

Wow, if you can see 1/4 of a degree, I'm very impressed.

Flyboy Dave

My Feedback: (21)

Get one of these at the hardware store for under 10 bucks. Use it with the
"stick" incidence finder....works like a champ. Use it on the firewall for down
thrust too....I use it for all kinds of things.

FBD.

Flyboy Dave

My Feedback: (21)

Wing-Ding....thank you for the input on the digital meter. [sm=thumbup.gif]

That is way beyond what I would ever need, but I'm sure the Pro's set everything
with those babies.

FBD.

RC-Captain

Nice Flyboy, does it work in any position ? I will look for one tomorrow in my travels. Probably could have got one today when I was in home depot.

Flyboy Dave

My Feedback: (21)

Yes, it works in any position....very handy, and you can eyeball 1/2 degree.

FBD.

RC-Captain

Thank You .

Flyboy Dave

My Feedback: (21)

...yer' welcome....

Bax

My Feedback: (11)

Just to give an insight on how the balance position of a model is determined..... The designer creates the model by using general formulae and techniques that are known to work. For any model, whether trainer, sport/aerobatic, scale, certain parameters, such as airfoil, moments, areas, and weights are chosen on the basis of experience. The good model designer knows what works fairly well.

When the model is drawn and then built, the designer knows that the model should balance at an approximate position on the wing's chord. The ready-to-fly prototype is balanced at that point. The model is then extensively flown. The model has the balance point moved forward and backward in small increments by relocating equipment inside and/or adding weight to the nose or tail. During the test flights with the different locations of the balance point, the model's handling is evaluated. At some point, when the balance is too far forward or too far aft, the designer will decide that the handing is starting to fall outside of the desired flight envelope. The forward and aft limits of the balance point are what you see on the plan. For some models, the designer will narrow that a bit to make sure the modeler stays within the range of balance points that give the desired handling.

The same goes for all-up weight. The model is ballasted until the takeoff, climb, g-load handling, and landing speeds are getting outside of the desired performance range. That determines the maximum weight.

One thing that must be realized is that a great many R/C fliers can fly a model that's balanced outside of the balance range specified in the plans or instructions. That's not the goal of a kit/ARF producer. They must put the model's parameters such that the vast majority of modelers in the target market can fly it. Those parameters tend to be conservative because there are a significant number of R/C fliers who could handle the plane well enough when balanced inside the range, but would quickly crash if the model was balanced outside of the range.

With a few exceptions, kits/ARF's will always have such limitations on their balance parameters.

RC-Captain

Bax, If the manufacturers go through such rigorous testing why not just include in the instruction where and and how they had the equipment installed when the found the perfect flying CG?

Flyboy look what I got
If I stay in your tracks I will be well on my way to being an official RC pilot [sm=idea.gif]

JoeAirPort

My Feedback: (41)

It's just the fuel in the nose that makes it nose heavy. Put your tank on the CG, re-balance the plane. The CG will not change anymore (not noticeable anyway).

I had the same problem and now put all my tanks on the CG.

RC-Captain

I could definitely move the tank back about 3 inches with out causing any problems , but how do you get around not disturbing the aileron servo when the tank is move to the CG ?