I'm having some problems and I just can't figure it out, hopefully someone else can.

The plane is a Sig Cap 231EX w/Saito 1.80 & MA 18x6. Ail & Ele servos are GWS ST03's, rudder is High-Torque Tower Hobbies (Futabas essentially) and throttle is an Airtronics 94102. Initial CG set to 4-1/2", ele at 1" low rates, ail at 3/4" and rudder at 3" for low rates.

First flight the plane took off and I flew it around. Trimmed it at WOT and it seemed to climb when I chopped the throttle. Thought it needed upthrust. On landing the plane seemed to be tail heavy. I add a start coming in and seems like it goes from 10° nose down to just a click on the stick and now it's balooning up 10'. Took it home and added a little up thrust last night and pulled out about 20% of the elevator.

Second flight was today, I took off and flew around for a few. Plane still twichy and it seemed like I couldn't get it to track straight (more on this later). I was nervous so I didn't do much other than an inverted spin (boy did if flatten out with a little aileron!). Anyhow decide to land it and on first attempt same thing, come in nice and I had to give some down elevator to get it to come in. Got it leveled and next thing it baloons up 10'. Well, scratch this attempt and go around and try again. Same thing. I'm only at 20% throttle or so and didn't make any changes to power during or before the balooning. Third try I run outta fuel on approach so I pretty much have to make it and even though it balooned (w/NO power) I managed to get it down on this attempt in one piece.

I talked to several others at the field looking for suggestions and maybe see if someone could fly it for me, no luck on the flying but I did get some advice. Everyone seemed to think it was tail heavy so I moved my battery from the back to the front which put the CG around 4" back from LE. Most were surpised by looking at the long chord thinking 4-1/2" wouldn't be too bad but we left it at 4".

Third flight I took off and the plane was squirely again. Coulnd't get it to track staright, stay level, etc. Maybe my nerves where shot as soon as I took off I started messing with trims trying to get it level and seemd trim it left (ail), make a turn and now I need right trim. Elevator was the same. I tell the fellas next to me training that I'm having trouble and bringing her in, they clear out and I prepare to ditch it near the runway. managed to bring it but tail porposies a tad but I mange to get it in one piece without nosing over.

Well I'm now stumped, Plane isn't tail heavy by the numbers. My next train of thought is that it's not an engine thrust situation, but these cheap GWS servos aren't holding center and have a poor resolution so that I can't get them dead center anyways. What are your thoughts? Is this something possible or should I move CG even further forward? Would it be bad to try some 94102's I have (65oz/in at 6.0v I think) just to see or is that not enough? I could keep throws to a minimum and use a mechanical advantage to keep their work load down. Any help is appreicated and if anyone lives near New Port Richey Florida with time to burn I'd love to let you take a stab at it.

- Joe

Sounds like you checked the upthrust and made an adjustment. Did you check it again the next day? Are you checking the CG inverted? How does the plane flew inverted? I it climbs that is bad and your CG is too aft. What CG does the manual call for? I live in Wesley Chapel off Route 54 by US 75.

Chris

It sounds like you might have negative incidence.

I only flew inverted a couple times. Although not 100% sure it seemed like it was a little down elevator to maintain flight but to be honest I'm not really sure. How do I check incidence? Is there an easy way to do this w/o special tools?

QSPILOT: Have you flown at the 'new' Bay City field off of SR 52, 3/4 mile east of Ehrin Cutoff? WOW. If you crash in the trees you will NOT be able to see your plane when it hits, there's that much room!

- Joe

From the sounds of you describing that the stick moves and then the the plane rolls the other way....never can get it trimmed out....

Couple things with this....I assume you have checked your linkages..#1 they are tight and slop free. They can't be flexing? Clevis' are not slop free connections....also 2-56 pushrods are not adequate no matter what the kit says.
Ball Links and 4-40 rods are the minimum you should be using in this type of setup. The best would be the Carbon Fiber Rods with Titanium ends sold by

www.centralhobbies.com

These rods are superb and super stiff...along with saving weight...lots of weight...Had a buddy save 3ozs on a pattern plane changing out to these rods and changing his ball links...
These are not needed but will also make a difference....What ever you use...turn the radio on and wiggle the control surfaces...find the slop and eliminate it!

Which brings us to the Servos.........

Now if all of the above are good to go.....Look at the quality of your servos. I does make a difference. You need some good quality servos. Prefer High performance maybe not digitals but something that is smooth and precise...JR 8101's 90oz for the wings and Elevator...then something with some muscle on the rudder a JR 4721 120oz. The Futaba Equivalents 60-90oz on the Ailerons and elevators and say 90+ for the rudder will work also....I used to know the Futaba Servos really well but not too much any longer...The 9202 is a good servo a little weak...but it centers well and is a coreless motor.

JR has some new high end Sport servos that are digital and under $50 each. These would be a good solution also. The precision of the servo makes a huge difference in the flight performance....I would look long and hard at these little gems. They would be a good choice. Budget priced and yet they have the power and performance of a digital servo...The main difference is the non-coreless motor. So they are not are smooth or last quite as long as the top end servos....My experience with them has been very good they will handle the loads and performance of the 1.20 sized planes...but that's about their limits....With the price and the performance they are a deal.....Now don't worry about running JR servos in Futaba radio gear. Its done all the time and works great. I ran JR servos for nearly 10 years while flying Futaba 9ZAPs before I switched the the JR 10X.


Your only link between you and the planes actions are the precision of the servos. You can't expect that an off brand budget servo is going to perform well under the type of loads you are inducing. The 1.20 size and above planes are kind of a threshold...you can't get by with a servo that merely makes the control surface move...That works on .40 size trainers and sport planes not when you get to 1/4 scale machines (Above 1.20 size).

You don't need to buy the top of the line servos...those are for the next level in performance or if you want them. They make a huge difference. Don't just look at torque numbers either. I know that the off brand servos show good numbers on day one...but lets see them after 25-50 flights...Or put them in an element beyond they performance and your dead.

As for the landing balloon issue that is a sign of TAIL HEAVY...This will also tend to make the Rudder and Elevator extremely touchy....If you have slop in the linkage...slop in the servo or both this will be amplified and make for a bad situation. Put the CG where they say on the plans....Doesn't matter where it is on the wing 4" 4-1/2"....I don't know what the instructions say...But start there....If the plane is floaty especially when coming into land and almost needs down elevator to hold the nose down...then it is tail heavy and move the CG...This can first be done with lead ballast to see where it needs to go and then move battery pack, RX and so on to achieve the desired balance point.

Don't be concerned yet with Incidence and such...ARFs today are pretty good and its probably either right on or darn close....The wing isn't moving in flight. The incidence is fixed if the wing is not moving and therefore is a baseline for now. ...Also variations in incidence are negligible until you start to really dial in the plane and trim it like a pattern plane. You can make huge changes incidence and it will have small effects on performance...I'm talking 1-2 degrees on incidence and only minor changes in the way the plane grooves....or the Elevator trim you have in the plane.

Look at the CG and your linkages-Servos....I would bet a Dollar this is where your issues lie.

Good Luck and let me know how things go.


Troy Newman
Team JR

Check your TX programming. If you have any expo programmed in on the TX, make sure it's not reversed. Futaba Radios require a negative number for exponential and JR's will have a positive number. If it's reversed it will make the control surfaces very sensitive around neutral stick.

Iflyrctoo

I would also tend to look at Expo, Slop (servo, push rods, and links), and incidence. The only plane that did this to me had a pushrod going to the elev that I found later had broken loose from the mid length support. With the radio on, try to move the surfaces by hand. Easy way to find a mistake. Good luck.

Joe,

I have this plane and give you a lil help, but first a few questions...

1...Did you build it? If so the stab is very tricky and you DO need an incidence meter to set the stab correctly.

2...The wing also needs to be put together correctly (it is easy to get a twist in it, and easy to get it out as well.

3...I have a Moki 135 on mine CG@ 4 1/4 and I have NO weight up front at all with NO up, down or right thrust, manual says not to add but some may need a little, depends on the engine combo.

As far as the hardware package that come with the kit (if used) It is all very good stuff. Depending on how you want to fly it the servos for 3d should be more than the manual suggest 60 OZ. is not really enough.
IMO you should not have the kind of problems you are having even if you were to use standard 40 OZ. servos just to fly around and trim it out. I wouldn't advise doing so, just making a point.

It sounds to me that you have your Stab off a little, thats the first thing to check.
If you are asking if there is a way to check it without having a meter then that tells me that (IF YOU BUILT IT) you guessed at the stab, and thats a BIG NO NO!
Make sure the wing has no twist as well.
I can tell you first hand that this plane is one of the best planes in the 120 size you will ever get your hands on.
When you get her all ironed out... your friends at the field will have to help you wipe the smile off your face...;>)

Cheers and good luck!

Robin

Wingspan99 had this same plane, and noticed that the horizontal stab came from SIG out of the box with -2 degrees incidence. Made for some really different and squirrelly handling at the opposite ends of the throttle. It handled the same as your plane did. He built a new stab for it, which seemed to help alot. This plane also has a very small landing envelope, too fast by a couple mph and it would float, a couple mph slower, and it would snap stall. Landings by far were the largest pucker factor of the entire flights on that plane. You can also try to mix in either spoilerons or flaperons to help with landings, after you get the balance, trimming, and incidence set correctly.

Shoot wingspan99 a message about the mods he made on his cap, I'm sure he wouldnt mind giving you the details.

Steve

Thanks for the tips. No, I didn't build the plane so I didn't set/check the incidence. The wing appears to be warp free from visual inspection though I don't have an incidence meter to check this with. My thought (maybe just a hope) is that these servos aren't as good. I knew they were cheap but they had high TQ numbers and low $$ numbers so I went with them. Is there a way to check incidence easily w/o the laser meter?

As far as slop goes, elevator has nil. I'm using dubro control horns and the 4/40 hardware that came withthe plane. The rudder and elevator are slop free but checking it there is slight slop in the aileron (1/16" up/down). I will ferret that out after work today and see what happens but if that is a problem, I suspect it's only part of the problem.

The balooning on landing isn't just a pilot error, though the planes pilot (me) isn't the greatest. It is like stevezero sais and there is a VERY small landing envelope. I will shoot wingspan99 a message when I get home tonight.

- Joe

Joe,

I would bet that you have an incidence problem in the stab.
This plane flairs out on landings better than any plane I have ever had or flown and I have had my hands on a lot of planes...you have yourself one of the best that the 120 size has to offer and when you get it figured out, your landings will be effortless, TRUST ME!

Do a search on the Sig Cap 231 in RCU and you will NOT find one pilot that has had any trouble with flying or landing that plane.
What ever you do...don't give up on this plane, you will love the way it flys.

I can land mine at a crawl and that is no exaggeration.
Get with someone at your flying field and see if you can use there incidence meter or better yet, hell bye one man, they are worth every penny.
As far as the stab being bad right out of the box, I don't get that because it sit on top of the turtle deck it does'nt slide into a slot like the H9 cap does, thats why it is easy to get it off and you DO need an incidence meter to set it up right.

I had to sand the front of the saddle where the leading edge of the stab sits to get mine @ 0 incidence.
I have put together about 8 or 9 arfs and I have had to fix everyone of them as far as the incidence.
They sit in a box coming from China, Asia or some other country that has a lot of moister in the air, then we get them and the wood starts to dry out and they will warp a little.
All you have to do is take an iron or a heat gun a take the twist/warp out, takes less than a minute.

Well just checked my incidence using the J-brone custom incidence meter (home made POS). Everything came out perfect with the main wing being dead nuts on with the stabalizer. There is perhaps 2° of slop in the ailerons, but I'm not sure how to minimize it any more. Elevator is minimal and rudder slop appears to be the worst but it's on pull pull and the slop appears to be just flex in the structure not play in the linkages.

Just as a test I played with the servos (GWS ST03's) and here's what I found. When moving to MAX deflection and releasing the sticks, they will swing slightly (5°-10° past center) and then return. However, they did not always return to center. For instance, if I gave it up elevator and return to neutral they would center perfectly, if I gave it down elevator and return to neutral they will not return all the way to center. If I give it up again this repeats itself. This appears to be in all servos and to make matters worse, with the elevator servos running in opposite direction (one is reversed so both move together) when I go up and release, one side remains a tad too high, the other centering fine. If I go down the other side will be a tad tot low and the other side fine. I also noticed the resolution appears to be poor, with each 'step' being much more pronounced than even these 94102's.

I now have the 94102's back in there, and the J-Brone incidence meter on the shelf. I printed out a trimming chart and will try my best to trim the plane this weekend.

On a side note because I didn't answer it earlier, my TX doesn't have expo It's a Radiant 6P, predecesor to RD6000.

R. Runyan....how does the moki 1.35 do for power? Can you hover, and do other 3d things? Do you think it would be better to get a 1.8?

Thanks,

torque_roll

torque_roll,

Yes the 1.35 will hover and 3d very well however if I had a chance to get a 1.8 I would go that way.
The 1.35 pulling out of a hover does not have the authority that I would like it to have.
My Cap comes in right at 10lbs 2oz. dry.

If you do put a 1.8 on it...I would NOT use all the power at one time...might blow the wings off...lol

I'm glad you found something not up to snuff....I bet with a better servo setup you will feel more in touch with the plane....

One thing on Incidences.....The elevator changes the incidence of the stab every time you move it.....Thats how it works....by changing the effective incidence of the stab it gives you pitch changes....So Incidence can be trimming issue...a good what to tell is if you are carrying elevator trim...meaning the elevator is not tracking with the stab.....This assumes that the CG is right and other things.....like wing incidence....Again there is a ton of latitude with incidences....

I agree having the plane straight is paramount...and you want the incidences to be right to fly right...

I fly pattern plane with fully adjustable wings and stabs....in the trimming process we move them all the time....Try a little of this and a little of that. Then we fly the heck out of them....literally I can move the wing on my pattern plane up to 1 deg each way and the only change I get is Elevator trim....physically...now yes the plane will fly different but not so much as to make it fly like crap....and the crappy characteristics are consitent all the time....now when you get to way off setting like then changes become unstable....but if you stick it close and I mean within a 1/16-1/8th of an inch LE of the stab up or down the elevators on that specific plane can compensate...ideally you want it where the plans call for it but in a pinch it will work and you may never see the ill effects.....Especially on an stab the elevator just compensates for it.

Stab incidence it has to be grossly off to really affect things badly....and where you will see it is with speed changes.....as the plane slows down the elevator trim is radically different than with full throttle...a prime example is up lines at the top when your slowing down...the airplane can pitch because the right amount of air is not moving over the elevator to counteract the stab AOA.

Same goes for wings.....Now thrust is also and issue here because the thrust line can change these things too....The wing start to stop flying or becomes less efficient and thus the forces change and the engine takes over and pulls one way or the other...this is because the wing and the thrust lines are too far apart....

All this stuff interacts with each other its quite an art to trim a plane....There are very very few people out there that can really trim out a plane well. Usually those guys are the top of the pattern-IMAC-TOC ranks....The reason being is that they have learned over time skills are needed but the plane has to help....Not even Quique, Chip or Jason, can win the TOC, the NATS or any other serious event without a plane working for them and not against them.


All things interact...radio...servos....linkages....and then you have the physicals of the plane. You can't get into the physicals of the plane if your radio gear is not up to snuff....and working properly....

You can't use a properly working servo setup if the linkage is poor.......

And you can't really determine the proper Incidences and flying characteristics of the plane if the CG is poor....

they all work together...and since you said it would not hold trim....looking at the linkages and servos is a good thing.....Since you found something...give it a shot....

As you will see in the trim chart from www.nsrca.org the incidences will cause things to happen with low and high speeds...rarely do they affect the plane squirmy and erratically....rather they are bad tendencies that go away with speed and crop up with slowing down....but they are almost never radical things they are usually consistent and predictable......
The best thing you can do is to make sure they are not radically off like 2+ degs.....Zero on the stab is relative...the incidence of the wing sets the angle the fuse will fly at in the air.....

Ever see a plane dragging its butt in the air...but the CG seems to be OK.....Well put some positive in the wing and the tail will raise up......negative in the wing and the tail will lower.....the elevator compensates the stabs incidence to make the plane fly level not climbing or diving.....but the the wing incidence changes the appearance of the fuse in flight....

Good luck with the new servos.....and then we will look at you other trim issues....like CG and Incidences...



Troy Newman
Team JR

Welcome to the world of CRAPS, I mean CAPS...
I have tried from a Hangar 9 1/4 scale to a 35% Carden, Lanier 28%, SIG and a few smaller sizes and have one word for them:
LOUSY !!!
They all had the same bad tendencies flying and landing; different attitudes with throttle, extreme pitch down with rudder, etc, etc...
Even for a simple hammerhead you have to be on top of it all the time correcting pitch problems. The way I see it, if an airplane needs that many mixes to do maneuvers, the design has to be bad.
They are good for some maneuvers only because of the fact that they are so unstable.
My advice; try an Edge 540, Extra or Lazer 200.

I love my cap thank you very much. I have been flying mine for almost two years and it is my favorite back up plane now. I had the same troubles you are descibing with the severe balooning on landing when I had HS 615's in the tail. I put HS 5625's in her and WOW what a difference. I am not sure what Sequimz is talking about on the down pitch with rudder as I don't have this trouble at all on the SIG CAP or the 33% hanger 9. I did have to mix 3% up to the rudder ONLY for knife edge cause I fly so tail heavy that I have a bit of down in it for normal flight. I like my EDGE but the CAP tumbles and spins much better. For IMAC I have to fake the stall on the edge by bobbling the elevator before a spin entry.

Well this is my second Cap, but first Sig Cap and my first one was a real *****cat. It would do what you wanted all day. Only real difference was the sensitive elevator, and I think this is more due to the shorter moment with the caps shorter fuselage and forward stabilizer. This is by design, and if allows for some tight moves once you realize it doesn't take much.

Welcome to the world of CRAPS, I mean CAPS...


Maybe its a pilot thing here because I have a Great Planes 1/4 scale Cap 21 that I was told from some older and experienced pilots that I would have my hands full if I were to try and fly it.

Well 4 years later I still love flying it and have had NO trouble at all.
I have the Sig Cap 231 as well that is like a trainer to land and I can do all the 3d you throw at me with no snap characteristics at all.
The 21 is an older model and is not as fun to fly as the 231 but thats due to the smaller surfaces...not much on 3d-ing.
The Cap received (years ago) a bad reputation and it has stuck with it, but I can tell you that I have 2 brothers that have H 9 Caps and same thing...they are great and NO snap at all.
I have flown Edge, Extra 300s, Extra 260s and Lasers they all snap if you stall the hell out of them...lol
Bottom line here is a love them all, and the Cap flys as good if not better IMO.

Just get that thing fixed and make up your own mind...I know you will agree with me that it will leave you with a big fat smile on your face ;>)

I LOVE MY CAP!

Cheers, Robin

Im surprised nobody said links sticking.but you did say that your servos would not center which is the same thing.put better servos in there and check that nothing is sticking and i bet your problems will go away.

If you woulda bet money you woulda won Today was a MUCH better day. The Airtronics servos seemed to hold up very well and the plane was flying good, or as good as I'm capable of flying it! Landings are still hairy but that's ME learning to land the bigger bird, not the bird giving me grief.

What I did was check the incidence of stab/wing and they were 0-0. Motor appeard to have a couple degrees of down-thrust (no device to measure but I 'made' a j-brone rig to do it). I now have it at 0, so all is 0-0-0. I put the new servo's in and they are centering fine and resolution appears to be much better. My only gripe now is that my Tx doesn't have exponential and it's hairy-scary even on low rates but I'm sure I'll grow into it. Thanks for all the help guys, 4 good flights today and 1 good landing (3 a little touchy but I'm going to fire my pilot and get a new one that can land!)

- Joe