RE: How to trim without subtrim
 

Ok with stab level, TE of wing root is 227mm LE is 229mm Chord is 283

The LE is quite thick, i measured it at it's widest point, i.e. with a square off the ground where the square touched the LE.


Stix

RE: How to trim without subtrim
 

Next to the fuse - looking at an online manual of your plane it appears that the wing structure is easily measured between the end of the aileron and the fuse side.

RE: How to trim without subtrim
 

Stix...With your report of slight positive wing incidence it would appear that you have ruled out an incidence issue as the cause of the necessity for gross up elevator trim. That doesn't leave many plausible explanations beyond a good Aussie sense of humor.... but I don't really think you are jerking our legs.

If it wasn't an ARF, I'd be wondering if asymmetrical wing ribs were inverted.

It really doesn't leave much...

You said you are using flapperons. Are the ailerons trimmed to conform to the wing foil when flapperons are off and have you been flying with them off?

Are the stab bolts firm so that the stab is not moving up or down on the mounting bolts?

Are the wing bolts securing the wing to the saddle?

RE: How to trim without subtrim
 

The incidence is measured near where the wing meets the side of the fuse.

The attached is an image of a SIGLT-40. Ihope that it conveys the idea. With the tail supported so that the stab is level, you can measure the LEand TEof the wing at the fuse. The aparatus shown on top of the wing in an incidence meter. It has a very accurate swing pointer and scale. There are digital meters that replace the swing pointer with a digital display.

RE: How to trim without subtrim
 

Sorry gus been away for a few days.


Indicators of being nose heavy. The first would be the requirement for excessive up trim. As stated by later posts, the OP states just a tad of positive wing incedence. This is the way I set up all my aerobatic models. I usually set up a model with a CG that requires no elevator trim. The 45 degree upline test is a good way to verify CG. If no elevator trim is required and it stays on an inverted 45 hands off or slightly pulls to level the CG is correct.

Pulling to the canopy in knife edge. Almost all the airplanes I have owned that are capable of knife edge will tuck towards the gear slightly when the CGis correct.

Fast landing, Nose heavy airplanes land fast.

The OP has stated that he verified the CG location as per instructions. This doesn't mean that it's 100% the correct CG. It usually mens the airplane will fly. Clearly the airplane is sending indicators that the CG is too far forward. I always get a chuckle when I read test flight results that ends with the model being in perfect trim when a few clicks of this and a few clicks of that are applied. My airplanes usually take about 50 flight to get into 95% trimmed. The last 5% is like chasing a Unicorn.

RE: How to trim without subtrim
 

Sorry about being slow. 2 mm rise over 283 mm run results in .4 degrees.

RE: How to trim without subtrim
 

I haven't been flying with flaperons, i find even a bit of flaperon reduces airspeed to much and makes the plane very unstable in the air.

All bolts and surfaces are tight and aligned.

I am reluctant to add more weight to the tail, as i said i did add up to 60gm of ;ead to the tail in 15gm increments but i went back to 45gm. I found the normal 3pt landing to be very very bouncy with the extra weight. In the air was quiet nice and very aerobatic feeling but it just wouldn't settle or flair for me even after 9-10 landings. I didn't measure the CG with 60gm on the tail.

Thanks for the help guys but i'm stumped as to why i still need so much up elevator? Maybe thrust line? How do i measure that? Does it sound like my CG is right?

Thanks in advance

Stix

RE: How to trim without subtrim
 

It sounds like your CG is nose heavy. It's usually not too hard to move your battery pack to get the CG where it needs to be. When I was initially trimming my Kaos I put lead in the tail just to figure out where the CG needed to be per the flying tests, then I found the spot where the battery needed to be to get it there lead free and made a hatch for it.

Thrust line is really the simplest thing to check. Go full power and trim for hands off level, the chop the throttle. If the plane keeps flying level for a few seconds before the loss of speed causes it to start going down, you're good. If the plane immediately noses down, you need more downthrust. If it immediately noses up, you need less.

RE: How to trim without subtrim
 

I think (from pics in manual) that the plane has an asymmetrical foil so KE issues are probably not typical to aerobatic planes. I do agree with you that there have been times that the published CG has proven to not be good.... but Hanger 9 is generally pretty good. I also agree with you that the symptoms fit a too forward CG... I wasn't arguing that they didn't... just that there wasn't enough information yet to conclude that... as at that time, there were no incidence numbers and there was a claim that the model was in proper balance on the manufacturer published number. I was also giving credit to the post by John Gilmore that outlined that the OP had used the smallest recommended engine and thus it should not have been grossly nose heavy, which gave some credence to the OP's claim that the plane was balanced properly.

Last... I'd never get involved in one upsmanship of experience. I respect the experiences of all others. Personally I've never seen a model that required more than one quarter inch of elevator trim that didn't have an incidence problem but I'd never argue that it couldn't happen.

To the OP

Two steps could be taken.

1. Go the Areodymanics forum and in the sticky thread, there are CG calculators. See if they verify the published point. I've used one of those and it nailed the CG for an original design and, though I can't guarantee the calculator will nail it every time... I know it did the one time I used it.

2. Start a thread in the ARF forum and list the model and catch the attention of other owners of the same plane and compare.

RE: How to trim without subtrim
 

Based on the manual for his plane his CG setting is toward the front of their recommended range. That's assuming of course that the measurement was done right and Hangar 9 did their calculations right (I don't doubt them). It could well be though that H9 is recommending a starting CG that is nose heavy to be safe, and expecting some fliers to like the stability and the wind handling.

RE: How to trim without subtrim
 

Who cares where it measures (as long as you are close). How does it fly? Sounds nose heavy. Saying the cg is right because the plans say so is like saying your needle valve is set correctly because the instructions say so. Put it where it needs to be.

Kurt

RE: How to trim without subtrim
 

If the CG is at 70mm, then it is in the middle of the range. The range is only 1/2" wide. He in fact did move the CG back... and liked the way the plane flew but doing so created landing problems of which there are two ways to read what he said. One way indicates that he was experiencing too great of elevator authority and thus was near the stability limit for moving the CG aft. The other is that the tail weight caused porpoising typical when having mains too far forward. I don't know which reading is correct. If the former... then he approached the stability point without curing the up trim problem.

Lacking was a report that the up trim was relieved when the CG was back.

RE: How to trim without subtrim
 

Hi!
Probably you have a nose heavy plane! Move battery and servos back! Do not put on lots of lead!
You said you had a wing cord of 283mm and C of G at 70mm from the leading edge. That is aprox a C of G 25%. Could be a littler too much forward.
Place it at 80 - 90mm instead.That will make the your CG around 30% Which is just fine for all sportplanes.

RE: How to trim without subtrim
 

Iagree. The C.Gfrom the plans or ARFmanual are what worked best (presumably) for the designer, or at least where he thought it should be placed initially. Your equipment installation is likely different. But it is a place to start and shound be placed there initially. The only way to judge best C.G.is in flight characteristics. No sense spending a lot of time static balancing a model - get close and get airborne. Unless your tank is at the C.G point it changes in flight, anyway. Even if the tank is there it changes from uplines and downlines as the fuel sloshes.

Us the time you save to laterally balance the model. It will make your loops more solid.