shootnstarz

Our club members own a bunch of these gliders and we've noticed some fly much better than others. After checking them out we discovered each plane has a different degree of wing incidence. Mine was over 3 degrees positive and flew like a pig, or more like a porpoise. I cut the saddle down a little and now have less than 1 degree and it flies like a dream now.

What a great plane for the price, can't beat it !!!!


Rick,
Pensacola, FL

evan-RCU

More important is to have a little washout in the tips. Are you sure that you mean incidence and not washout?

shootnstarz

Yes, I meant incidence, the relation of the wing to the stab. We haven't even checked washout yet as the incidence made such a huge difference in the way the plane flies. The way the covering shrinks and expands in different weather I'm sure the washout changes with it. Whats the tagret, 2 degrees positive?

RH

evan-RCU

This is an ARF, you are telling me the fuselages are cut different between the ones at your club? Normally the incidence is not just wing to stab but also to fuse/ thrust line. Is it the wing saddle that is different between them of the way the stab is glued on?

shootnstarz

Yes this is an ARF and both saddles are supposed to be cut identical but for whatever reason the incidence has varied from 1 to over 3 degrees positive with the fuselage laying flat. There is no thrust line on a glider so only the stab/wing incidence are critical. You may doubt me all you like but I can only speak of my experience with the 8 or so Vistas I have checked. I wasn't there when they built the planes so I have no idea of their cutting/building process. For the price I'll do a little mod of the plane to make it fly better.

If your Vista stalls easily or porpoises a lot the check the incidence, what can it hurt?

RH

OzMo

My Feedback: (3)

HMMM ARF...Almost Reliable Facimile???
I have the tower "PRE Vista" or Tower 2 Meter EP ARF I will check the incidence closely when I assemble it.

glidagida

Had the same problem with one of my planes.

One a Chrysalis 2m was changed from rubber bands at the sides to bands fore and aft like the BOT. In the process I changed the incidence and it always flew like a dog except in heavy breezes and I noticed that the thing flew tail down and all draggy when coming into the spot in contests. It did not want to turn, it was impossible to do flat thermal turns and I just could not get the CofG right, if I put the CofG aft to where the controls were responsive it tip stalled whenever anyone sneezed. Altogether a nasty plane to fly and you had to fly it every inch of the way, and I [incorrectly] just put it down to a bad design.

Crashed my No.1 contest plane and had to revert to the Chrysalis and had to do some head scratching and figured out the incidence was wrong. Dug out the corroded old Du-Bro incidence meter from the shed and found -1 degree incidence. Changed that to +1 degree and what a difference! Handling changed completely and it will now turn nicely and it will turn flat and I can now relax on the sticks with the plane exhibiting normal behavior.

I could not believe the difference the incidence made!

All I can say is I wished I had twigged earlier to what was wrong.

Evan its not an issue of washout, the stalling may be caused somehow by the wing flying at the wrong Reynolds numbers perhaps, or flying with a rear CofG to try and 'tame' the beast.

The issue of ARF's with the wrong built in incidence is not unusual with some mouldies having a reputation for wrong incidence built in like the Gabby 2m. Correct the incidence and it flies very much better according to reports, you see I have done all sorts of research trying to solve my problem.

Cheers
GG

evan-RCU

I understand but usually if a plane has the wrong angles they are all wrong not some here some there. Mine flys good and I put washout in mine. The other people that have them and have complained needed washout and they flew better after I put some in for them.

OzMo

My Feedback: (3)

how much washout is good? [sm=72_72.gif]

glidagida

Hi Evan

While I know washout cures many stalling ills, it may in fact, be masking the real problem in some of these cases.

With a balsa kit the angle of the stab is critical, but depending on how manufacturers cut the stab seat, laser or die cut [die crunching] the angle can quite easily change.

I build from kits and from scratch, and depending on how the kit design at the rear of the fuselage is executed the stab seat can be almost self aligning where the kit may have a 1/64" ply doubler or ply sides, or the design may rely on only just the balsa sides for correct alignment. Generally these latter kits are the cheaper ones, and some poor die crunching in these models can affect the incidence, if the builder is not wary. In the manufacturing scene [sausage machine] the production costs may not allow the time to invest in checking/rejecting poorly cut fuselage sides.

With an ARF's from China some models lack the quality control of others, it is not surprising that some models vary. As you say that generally cheap ARF's will not be checked for washout and they can vary quite a bit. Some models may respond well to washout, and so you are right with what you say.

However you also need to check the incidence angle, as this can be masked by too much washout. I know I tried it!

The problem is that if a model has too much washout it tends to restrict the speed at which the model can travel [penetrate] or promote wing flutter. If you look at the tips of your plane with the wing level the washout the tips are sloping down compared to the rest of the wing. To put it simply, the tips are in effect 'diving' while rest of your wing is flying level. When the wing goes into dive during the end of your winch/bungee launch then the tips tend to start lifting downward at negative angles of attack[this is a simplified answer]. For a full explanation see Martin Symon's book "Model Aircraft Aerodynamics".

Compared to the rest of the wing the down lifting tips introduce a 'twist' to the structure which can lead to flutter. The Chrysalis I am talking about did just that on a windy day winch launch. In my case the washout had to some extent "cured" the stalling problem, it masked it, but it set up a potentially model destroying problem.

Also understand also that I am speaking from perfect 20/20 hindsight here, my answer only came together after long, hard thinking about the symptoms/causes.

So I suggest that your flying buddies get hold of an Incidence Meter and check their planes, you may be surprised at the further gain in flyability of your models. You will also be able to use the incidence meter to check your whole wing for '"propellor" wing where part of the wing is washed in and other parts washed out.

OzMo, generally around 6mm or 1/4" of washout from wing root to wing tip should be sufficient on a 2m model.

Cheers
GG

evan-RCU

Gee thanks, I guess....

da Rock

Each Vista had different incidence. As discovered by hands-on checking. And fixing the bad flyers turned them into good flyers.

Sounds like a significant couple of bits of information. Incidence actually is quite significant, isn't it. After all, it determines how efficiently the rest of the plane glides through the air, and what AOA the stab sees. Both those determine how efficient the plane flies. Amazing stuff.......

likeswindinhair

I noticed watching carbon art the used the aero perfect along with a incidence meter. Great planes makes one, meaning incidence meter, are there any others out there? Also do you need the aero perfect or will the meter with a bubble do the job?

Lnewqban

Aeroperfect is nice, but expensive.

There is the Robart incidence meter also:

http://www3.towerhobbies.com/cgi-bin...?&I=LXET66&P=7

Here is how to use it:

http://www.robart.com/how_to/incidence_meter.aspx

Regards!

likeswindinhair

thank you lnewban that ansewered alot of questions and i have a robort on the way

shootnstarz

Update after futher testing

We had a calm afternoon yesterday so with help from a modeler with some 60+ years of experience, much of which is with sailplanes, we did some flight testing on a couple of our Vistas. With little wind we could better determine what the planes were actually doing without outside interference. Both planes had been previously set at 1 degree positive wing incidence.

My Vista still had a tendency to stall very easily and the other was picking up speed quiclky and really zinging along through the flight.

We shimmed my wing even more with a popsicle stick which would have decreased the angle to 0 or slightly negative. Made a huge difference. I just thought it flew better before. Now it's basicly a hands off flyer, very little control input is needed to float along and the stall tendency is greatly diminished.

The other Vista had 2 sticks under the trailing edge for 1 degree positive. We removed one of the sticks which would have INCREASED the incidence to OVER 2 degrees positive. The plane flew much slower, floated along like it's supposed to and had a 10+ minute flight with almost no air on the cloudy day.

So, these futher test showed us that there is really no one correct angle for all Vistas, it seems to be a per plane situation that only flight testing can work out, at least with these two planes. We'll test some more Vistas when the members bring them out and I'll post the results afterward.

Rick

evan-RCU

The reason is that these are chinese made and shipped here in weather that can twist the wings before you assemble them. Because you have a certain incidence at the fuse does not mean that incidence is through out the wing. That's the reason for going over the wing with an iron to get it straight and then adding a little washout.