Half-A-Hec

Howdy all,

I tried flying my LLS today. Wind was breezier than yesterday. It was 12 mph. Probably too much for it. I had a really tough time controlling this little beast.

Flight two:

I removed .12 oz from the nose compared to yesterdays flight. I also reduced aileron throws and increased elevator throws. The plane took off and was still touchy with the ailerons. Man it was all I could do to keep it from crashing. It was all over the place. I lowered the throttle and walah a perfect landing.[8D]. Don't know how but it was.

Flight three: I took out the .12 oz. weight and added a full .24 oz. Just like Sundays flight. I reduced the ailerons even more. The plane took off. It seemed like any control input really upset the plane. This time it got behind me into the sun. she went in like a lawn dart. I ran out to the plane expecting to find a pile of sticks and all that happened was I broke the prop and the servo mounts broke loose. That's it! I mean the plane was probably 100 ft up when it winged over and went staight in.


What is the deal? Do I need more nose weight? What can I try? I need the help of all you gurus out there. Todays flights were really nutz compared to yesterday. Can I blame it on the wind?


Hec

BMatthews

I know this means flying it again but for CG location try trimming for hands off and then dive it and let the elevator go. If it pulls up smoothly but not too fast then it's good. If it keeps diving or tries to tuck then it's bad.

It may also be that you have a spiral instability issue. Will it fly in a straight line on it's own or does it try to fall off to either side and require constant correction? If so then your fin area may be too large. It was fine as a shoulder wing but by moving the wing to the belly you may well have upset the applecart.

Half-A-Hec

BMathews,


The plane flies level with hands off. The wings are level as is the pitch. As soon as I give it a tick of aileron, she banks and noses down. So I give up elevator and opposite aileron. Hmmm. Maybe I didn't put it enough dihedral?

Hec

ptulmer

My Feedback: (5)

The CG shouldn't make the ailerons sensitive. It affects the elevator fer sure! Too far forward and it's ineffective, too far back and it gets too sensitive. You say it banks and pitches down. Maybe you need/have differential in the throw? Ailerons can be more effective or cause more drag in one direction.

combatpigg

My Feedback: (3)

Dihedral on a low wing helps to lower the vertical CG, which adds stability. If your set up is too top heavy, either aerodynamcally or weight wise, then flying that plane could be like trying to balance a balloon on a stick. I think your first flight indicated that the CG was too far forward, and 25% checked with the model inverted should be easy enough to do with your pinkies. Decreasing the aileron throws to about 1/8" either way should give you enough control for testing.

I scratch built a bipe years ago that is impossible to fly inverted, even with a symetric airfoil, just because the vertical CG is real high when inverted. If you don't have control system issues like sloppy linkage, glitches, etc. and have a straight plane and wing to start with, I wonder if the fundamental problem here is a lack of dihedral? Over all, the plane looks pretty orthodox and looks like it should be able to fly just fine, kind of puzzling. I've scratch built small low wing planes [not this small] with no dihedral and they did just fine. The other thing to consider with a high thrust line is the motor could be trying to make the plane dive, hopefully you don'y have any down thrust built in?

Half-A-Hec

Guys, I have noticed that one aileron doesn't seem to center as well as the other one. So that may have something to do with. The plane doesn't want to dive in level hands of flight only when I try to turn. Yesterday the plane was more docile, even though my ailerons rates were set so high. I just flew with very little stick movements. I will check to see if it is top heavy. The plane does have about 2 degrees of down thrust built in. I noticed when I made a down wind turn and it really started scooting that it tracked very well. When she slowed down she really became a handfull, like when flying into the wind.


Hmm.

BMatthews

So you're saying that once it starts a turn it wants to keep tightening up the bank on it's own? So you need to hold "top" aileron to hold it?

If so then you've got a slightly milder case of that spiral instability I mentioned in the last post. To cure this you can either cut down the fin area a bit or add dihedral. At this point the easy solution would be to reduce the vertical stabilizer area by probably 15 to 20% and try it again.

When the spiral stability is in the "happy zone" the model should groove in a 30 to 40 degree banked turn with no need for aileron in either direction. But make it too small and you get the opposite effect where the model wants to fly in the turns with the tail sliding low and to the inside and you start to notice adverse yaw to aileron inputs and the model may wag it's tail back and forth in the old Dutch Roll syndrome. When the DR gets extreme it will often snap roll into a spin after a couple of cycles of the tail wag.

Half-A-Hec

Bmathews, CP


I just checked the balance and it is not top heavy. The plane wants to right itself. When I banked into a turn she banks hard but never goes inverted. I hold some up elevator to keep the nose up and then some opposite aileron to level it off again. If it had spiral tendencies would the plane hold level flight? I can do really big none agressive turns and she does fine. I did notice that I was probably over correcting with the up elevator. The plane would bank hard, then I give it up to much elevator and the nose pitches up to much and stalls. I have shortened the elevator throws back to what I had yesterday.

Hec

combatpigg

My Feedback: (3)

I would put some finger pressure against those ailerons and see if you are getting equal movement and centering then. Torque rod linkage that is built too light, long or loose can be a problem. Same goes with the elevator linkage. The servo output gear can be missing a tooth and cause a wandering center. Your plane from outward appearances just doesn't look like it would have any trouble[].

If you can cut the fin off cleanly and try a smaller test fin, you will know which direction you need to work, but first rule out all control issues. Once you get it all sorted out, it will be interesting to hear where the gremlins are hiding.

Half-A-Hec

CP,

I dunno, I think maybe it was the 12 MPH winds. Yesterday I had alot more control. Enough control where I could put it right over our heads for a picture. Today would of been impossible to take a picture! Unfortunately I won't be able to try it again till Sunday at the earliest. I am going to Texas for Thanksgiving and I leave tomorrow. I got it all together and ready for Sunday.

Hec

BMatthews

...and then again perhaps you're just trying to fly it in too much wind. In particular if there's any trees within a couple of hundred yards upwind there will be a LOT of turbulence off them and that may be what's kickin' you around.

Sounds like your turns are nice and groovy from the last post.

flyinrog

My Feedback: (1)

I'd say wind too,,but I built a LS and put a PWEE .020 and 1 day it flew great for 3 flights 2 days later without touching any thing other than removing the wing to charge it ,it launched straight into the ground,, after the 3rd time..well there was no point in launching it at that point,,hope you get a good day sunday to try again..and that the wind is the problem, I didnt think about the turbulence as Bruce stated but I have seen that happen too,,really pitch a plane up and down and the smaller the plane the more it just looks like its out of control as opposed to pitching, of course there may actually be gremlins in your applecart[X(] in which case you'll need a clove of garlic in the cockpit.....or was that wolfbane? ah..just put a pee wee on that thing...90 seconds of screaming fun....Rog

combatpigg

My Feedback: (3)

The wind will exacerbate designs flaws too. You could take the same plane, but turn it into a high winger, with the same dihedral, and bet that it would handle some wind just fine [as long as there was enough power to pentrate up wind]. Have you looked the wing over real good for trueness? It looks lightly built, and I wonder if it takes much effort to twist it? After reading some of the park flyer threads, it sounds like wind is the real enemy, even to those planes that have obvious attempts to design in lots of stability [high wing, low CG].

Half-A-Hec

Guys,

I think I have a game plan for the next flight. I have listened to all the great feedback you guys have given me. THANKS. Plus I have had a night to sleep on it. I am leaning toward the fact that the model may actually be a little top heavy. CP eluded to this earlier. I held the plane by the nose and the tail rotated it so that it had one wing pointed straight up then let it go. She kinda of wanted to self right itself. Tried again this morning and she rolled a bit the wrong way[X(]. I couldn't get it to flip over the right way with each test.

FACT:
My Servos are installed so that the bottom of the servos are about 1/16" off of the top of the fuselage. So therefore they hang upside down in the plane. Can't change that as it has the low wing. My battery is also mounted such that it is in contact with the top of the fuselage in the nose compartment. Essentially the Battery is touching the top of the fuselage, then the speed controller is stacked on top of it. The receiver is mounted to the top of the fuselage as well. Guess where the .24 Oz. weight was? You guessed it on the top of the nose compartment. So there is more mass located toward the top of the fuselage again. All that adds up to about 2.1 oz of weight in the upper half of the fuselage. The plane only weighs 6.5 oz. That only leaves the landing gear, wing and the lower half of the fuselage to counterbalance my flight pack. It aint going to happen! If I had my head screwed on right I would of built the access hatch so that it opened from the top instead of the bottom of the fuselage. This would allow me to easily install the battery so that it is located on the floor of the fuselage and not the top.

So for the next flight I will install the battery and weight so that it is located on the bottom of the fuselage, and possibly relocate the receiver from it current position above the wing to the nose compartement.

What do you guys think of this?
Hec

BMatthews

Sounds like a plan for sure. Lowering the radio parts as much as practical may be enough to make all the difference.

Consider for example if this design was enlarged directly to 48 inches. How big a cross section would the fuselage be then? The term "humoungous" springs to mind. Consider the effect of having the true CG placed high in such a fuselage.....

Half-A-Hec

Bmathews,

That's what I was thinking. The plane flew great level but as soon as turn was made, even the smallest turn, she would drop a wing fast. I hope this is it.

Keep ya posted

Hec

combatpigg

My Feedback: (3)

That kind of an experiment can do no harm, just some effort to relocate your radio gear. You could even try strapping the battery underneath the fuselage on the CG, near the LG. Try to fly a high wing [with dihedral] plane like this inverted, it is a real juggling act. You might notice how hard it is to check the CG on your fingers with the plane upright, then turn it over and try it that way, it should settle right in. This is why I think the long term fix is more dihedral, just build another wing for comparison. A finger tip CG check with enough dihedral will seem stable right there in your hands. For a plane this small and light, subtle changes can add up to a big difference. So far I have only struggled around with a weak running .020 on a 7 oz plane [flying wing]. It is a shame that the engine doesn't run better, but it might be a good plane to try electric power with. At least with E power, if you want to knife into the plane to make repairs or adjustments to a new design, you know that the patch job will hold like new. It's amazing how well these very light and compact planes take a hit when something goes wrong. It is helpful to tow a streamer if you fly stuff this small over tall grass, [when it comes time to find the plane].

Half-A-Hec

I did some calculations on my flight from Omaha to El Paso. My mind is always working, and here is what I have come up with.

The plane weighs 6.5 oz. All the radio gear located in the upper half of the plane weighs 2.11 oz. I wanted to find the weight of the plane without the motor and said radio gear to see how top heavy it is. So I subtracted the weight of the motor (.86 oz.), as it is centered on the fuse and contributes an equal amount of weight to the upper half and lower half of the fuselage, and the weight of the everything in the upper half of the fuselage (2 servos, battery, receiver, speed controller, .24 oz. weight) total 2.11 oz. This left me with 3.53 oz of weight for the plane without motor and said radio gear.
Assuming, and this is a big assumption, that the lower half of the plane has 60 % of the mass associated with it. Landing gear, wing, tail skid, and lower half of the actual fuselage, then the following numbers were found.
I took 3.53 oz x 60% = 2.12 oz. So 2.12 oz. is theoretically located in the lower half of the fuse. This leaves 1.41 oz. of weight to be found in the top half of the fuselage contributed by the rudder and actual upper half of the fuselage. If I add this 1.41 oz to the weight of the radio gear 2.11 oz. this gives me 3.52 oz of weight located in the upper half. A difference of 1.4 oz.![X(] over the weight found in the lower half of the fuselage. So I am out of balance theoretically 1.4oz. which must be moved the lower half of the fuse. I wish I was home so that I could weigh the wing and fuse separately instead of assuming that 60% of the mass of the plane is located in the lower half.


Hec

combatpigg

My Feedback: (3)

Sounds good, but you would some how factor in what dihedral there is now to arrive at the theoretical neutral point of the vertical CG. I don't know if you could just draw a line from wing tip to wing tip. Someone has already figured out what this sweet spot is[ for the vertical CG] and how to derive its location.

ptulmer

My Feedback: (5)

Hec, have you ever seen an Ace Pacer? (just to pick a VERY popular design) Your vertical CG just ain't far enough out to make a bit of difference. The Pacer had stuff much higher/heavier and zero dihedral. They flew like pattern planes! I think you guys are barking up the wrong tree.
It may be spiral instability, but I don't think so. None of the other problems associated with that were exhibited. As a matter-of-fact, the only complaint I see is that the wings tucks down and in when turning. Kinda like that panel is stalling or has more drag.

combatpigg

My Feedback: (3)

The PACER is a much bigger and heavier plane too. If the pacers' fuselage was in proportion to HECs', it would be twice as tall, wouldn't it? One thing that strikes me while lurking at those E forums is how often they complain that their 5- 6 oz planes become uncontrollable in very little wind. If so, then I think you need everything working for you, starting with a low CG and accurate [and positive] controls of the flight control surfaces. No flex, no slop, no gaps. Also, set the motor 0-0. His design also has a high mounted aerodynamic surface [the boxy fuselage and fin] that will tend to feed more spiral into a turn [when hit by the wind from a side slip angle] than the pilot might be expecting. Until he verifies that all controls are up to snuff, and the plane is balanced and straight, I agree that the other suggestions should be approached in the order of least difficulty. I'm tempted to build a scale duplicate of HECs' plane just to see what the deal is for myself. The difference would be easy to see if it was made to be convertible from high to low wing with just a couple of screws.

ptulmer

My Feedback: (5)

This is due to being designed for heavier and less powerful motors. With more modern equipment, the wingloading is too low and so is the aspect ratio. Makes for an unstable airplane.

Half-A-Hec

My plane came in at 6.5 oz. I think that is on the heavy side of what the Ace L.S. called for an AUW. So my wing loading is leaning toward the heavier side. The plane is very straight. There are no gaps in the surfaces as I used monokote hinges and the controls have no slop. The controls use .032 dia piano wire thru a plastic tube. Pretty stiff considering that the length of the pushrods is about 10 inches. I recall that on my first flight the .24 oz. weight was actually thrown in last and was located on the bottom of the fuselage. The other two flights I put the weight in first placing it against the top of the fuselage. Maybe this explains why my first flight has been the best?

Hec

combatpigg

My Feedback: (3)

Sounds like you have a fundamentally sound ship then. What is the square inch-age of the wing? Everything looks like it should fly anyway, judging from the photos, 6.5 ozs doesn't sound too extreme. You did say that the model practically jumped off the street. Do you have a beater plane that you could swap the electronic gear into, to see if your troubles are plane related or not? A faulty servo can produce a repeatable twitch that makes the plane look like it is at fault, especially a new plane that you don't trust yet.

Bipe Flyer

It sounds like it may be nose heavy. Bank - loses lift - nose drops - add weight to the nose - problem worsens. What is the chord of the wing and how far back from the LE is the CG?