poor elevator response

[dusty IV]

I bought an ElectroStik ARF. Too heavy for me so I stripped the covering off and rebuilt it. Flys great but the elevator response is sluggish. Very slow to respond to inputs.

Got any ideas how to fix this?

[tmc_2]

its most likley a c.g. thing. move your batter back a little and try flying it, that should make it more responsive but move it back small amounts at a time until you find the setting you like. as you move it back you will have to retrim a little for level flight but thats fine.

[tmc_2]

Thats assuming your throws are correct of course

[dusty IV]

I've played around a lot with the CG. This plane is very touchy to its location. Back it flies like a glider and forward the plane is a screamer.But it's not the CG. The throw is a lot more then the instructions ask for for advanced pilots.

I was wondering if the stab's elevator is being blanked out by the wing. It looks ok in size but I could add a 1/4" or so to it by a bit of balsa and CA. This model as with most Stiks has a high wing and bottom mounted stab.

Never had this problem before in a plane.

[JetPlaneFlyer]

From the photo it appears that the elevator is very narrow in chord, make it much wider, like twice as wide minumum.

I'd also agree that too far forward CG could be part of it... how far back (as a % of chord) did you try the Cg at?

[bwalt822]

This plane is very touchy to its location.

What do you mean by this? The only way i can take it is that the plane doest trim well since the point of the thread is that the plane is sluggish.

There are four main things that effect elevator effectiveness.

CG, throw, elevator area, and elevator moment arm.

Since this kit is pretty tried and true, the latter two are probably not the problem. This isnt a 3D plane so the elevator doesnt need to be 50% of the stab chord. If you remember how far your thumbs move the sticks during a normal turn then see how far that moves the control surface on the ground you would be supprised at how little it takes. Even on full scale planes when the pilot banks the plane you can barely see the ailerons move.

You say the throw is more than recommended for advanced. How much more? This is a big might but, the elevator (not stab) might be stalled if the throw is way too much.

Could your servo be too weak to move the elevator in flight?

Like the others have said, its probably that your cg is too far forward. Try moving it back an eigth or quarter of an inch at a time.

[Texas Buzzard]

Have you made sure that the elevator pushrod (control rod) is stiff and NOT bending when control input is given?

Hold the elevator while you give up or down with radio.

A sloppy loose pushrod will do as you describe!!!!!!!!!!!!!!!

[bwalt822]

That elevator linkage looks beefy enough to me but i cant actually touch it so that could be the problem

[Cory]

Like the others have said, its probably that your cg is too far forward. Try moving it back an eigth or quarter of an inch at a time.

Along with this, you may find that you need to reduce control surface throws when you move the CG back. I regularly fly gliders with the CG at 35% MAC. They are not twitchy, but the control surface movement is not massive either.

[dusty IV]

Interesting answers. I may be expecting to much from the plane. This is the first ARF I've bought. I generally build and usually from my own or modified prints from some one else.

I think I will build a whole new stab. The present one doesn't have any diagonals,poor quality balsa and is warped. Can this plane benefit from a larger stab? It eyeballs ok. On the new stab what do you think of a 2/3-1/3 set up?

The plane has about 160 watts or so per pound and I think would make a good 3D plane with more control area.

[dusty IV]

Interesting answers. I may be expecting to much from the plane. This is the first ARF I've bought. I generally build and usually from my own or modified prints from some one else.

I think I will build a whole new stab. The present one doesn't have any diagonals,poor quality balsa and is warped. Can this plane benefit from a larger stab? It eyeballs ok. On the new stab what do you think of a 2/3-1/3 set up?

The plane has about 160 watts or so per pound and I think would make a decent 3D plane with more control area. I really enjoy bashing and have had some real successes in the past.

[bwalt822]

That elevator is plenty big, something else is wrong.

[Aphorism's Dream]

That elevator is plenty big, something else is wrong.

Decalage?
The effective elevator area may be blanked by turbulent airflow from the wing root and HUGE aileron area.
How does it perform inverted, or in outside manovers.
For in stance how is the pitch response to an outside loop?

Also the entire horiz. stab/elev. may be torsionally weak at higher manuvering loads (means warps at these flight loads/control inputs).

Just .25 cent worth.
Thank you

[bwalt822]

The plane is pretty basic looking, there are many planes similar to it so the elevator is most likely not being affected by the wing. Unless the wing is stalled it shouldnt matter anyway.

This plane is very touchy to its location. Back it flies like a glider and forward the plane is a screamer.But it's not the CG.

This statement needs further explanation because it seems that you have it backwards. Forward CG should make a plane more stable like a glider and aft CG should make a plane more "screamer" like. What does screamer mean in this case? Does it mean touchy? If so then your elevator works fine and you need to find the balance between glider and screamer.

You can build a new tail and this would probably solve the problem. However if no one else is having problems with this plane then its probably something that you are unknowingly doing.

Along with this, you may find that you need to reduce control surface throws when you move the CG back. I regularly fly gliders with the CG at 35% MAC. They are not twitchy, but the control surface movement is not massive either.

Gliders can get away with having a CG so far back because of their long tail moment. This causes the aerodynamic center to be much further aft than a "normal" airplane. As long as the CG is a little bit in front of the aerodynamic center then the plane is at least a little stable.

[Brandano]

AFAIK MAC takes into account also the tail area and moment arm, don't confuse MAC with mean wing chord.

[bwalt822]

MAC can stand for Mean Aerodynamic Chord or Mean Aerodynamic Center and isnt affected by the tail. MAC is determined by the planform of the wing and gives the "average chord" or the location of the aerodynamic center of a wing that isnt square. It is affected by things like taper and sweep.

http://www.grc.nasa.gov/WWW/K-12/airplane/ac.html

http://en.wikipedia.org/wiki/Chord_(aircraft)

Sailplanes get away with having the CG behind the aerodynamic center of the wing because the CG is still in front of the aerodynamic center of the entire airplane. Whenever you see a statment like 35% MAC they are talking about the mean aerodynamic chord.

I have never really heard the term mean aerodynamic center used at all before because usually when you refer to aerodynamic center you are talking about the entire airplane, not just the wing.

[Cory]

MAC is "mean aerodynamic chord". It takes nothing into consideration other than the dimensions of the wing. It is correct that a longer tail moment can make a diffence in the aerodynamic center. However, sometimes it's used to reduce the size of the tail. Not all gliders have that long tail moment. The sloper below was ballanced at about 33% MAC. It has a similar layout to the plane in question in this thread. It was quite responsive, but not twitchy.

In my experience it is very common for the powered pilots to make their planes nose heavy, and thus inefficient. It doesn't matter as much to them because they have a motor pulling them around.

Edit: I was slow getting my post written, and hadn't seen the above post.

[dusty IV]

The Jan issue of Fly RC has a review article on the ElectroStik. I should of read it but I'm not fond of reviews. So I sat down a few minutes ago and read it.

So the author says" "the elevator becomes very sensitive if you increase its throws beyond the throws suggested." The manual says 1/4" for high rate. Between the lines I think the author is saying the response is numb with the stock throw. Duh.

So I'll crank it up to 3/8" or more as needed. That is an easy fix.

As a comp the reviewed plane weighed 52 oz with one aileron servo and a 3s lipo battery. Mine after rebuilding weighs about the same except I use a 4cell 123 pack, two ail servos, a rebuilt tail wheel assy, a beefed up landing gear system and etc. The reviewed plane had a power of 396 watts and 122 W/lb. Mine has a power of 500 watts and 160w/lb. Battery cost me $40 vs $120 and since I can recharge in 10-15 minutes only one is needed.

[JetPlaneFlyer]

It is correct that a longer tail moment can make a diffence in the aerodynamic center.

Dont you mean 'Neutral Point' :rolleyes:

Aerodynamic Centre is something else altogether... it's the point on an airfoil about which the pitching moment is constant with change in AoA. This is 25% chord for subsonic airfoils.

[Cory]

:o oooops! :o

[bwalt822]

Neutral point is the aerodynamic center of the entire airplane so I will use that term from now on. Here is a link that shows everything.

http://www.geistware.com/rcmodeling/cg_super_calc.htm

[Brandano]

Right, then I was effectively confusing MAC with neutral point. I still think that considering an airplane as a sum of its part(wing, elevator, fuselage) rather than a whole aerodynamic device, is misleading. I think the formulae when used should apply equally whether the plane has a conventional configuration, canard, flying wing or other exotic layouts.

[bwalt822]

Depending on how detailed your equation is, they do apply no matter what the configuration is. Its just that some equations make assumptions to fit the most common scenarios.

In all but the most detailed analyses, its perfectly fine to treat an airplane as the sum of many parts.

[dusty IV]

If I get around to it I think I will work backwards with the theoretical material here to see where my ElectroStik fits. However years ago when designing a plane I tried to use some of this stuff without a great deal of success. The name Grant comes to mine I'm so old. So now I just use a seat of the pants empirical design and in most cases it works.

ie- In gliders I always make the fin a bit over sized and prepare to trim it down as needed to correct the spiral a too big fin causes and etc.

If I want a wind machine its designed a bit different then a fair weather plane but similar. Once I built a electric glider with a 1oz weight movable in flight by a sail servo. I could select CG while in flight. To achieve high speed wind penetration I pulled the weight forward. If I wanted an easy floater for thermal but no penetration I moved the weight back. I found you could do some what the same thing with a reflex wing. Flaps up for high speed and down for a floater.

Theory is fine for a starting place but if it really was spot on for models every thing would look identical, but they don't do they?.