Question trimming flapped ships...

I just about have my Brodak Zero trimmed out very nicely, but still am not quite happy with it's inability to snap turn. This is my second airplane that I have built that has flaps. Both of the flapped planes do not seem to turn as rapidly as my non-flapped, smaller models.

Before I went out flying earlier today, I added .5 ounces of tail weight to the Zero. I noticed that this greatly improved its ability to turn more tightly, but it would take a split second or so to change it's attitude going into the turn (sort of like a tight stock car trying to enter a turn)

This situation is similar to my last (now crashed) flapped airplane. It seems to me that if you want your plane to perform square manuvers, it needs to turn immediately as the command is given at the flight handle.

Is it correct to assume that flapped airplanes, correctly built and setup, turn very quickly, or is there suppose to be a split second pause before the airplane really enters the turn?

If so, what should one do to correct this slight pause? At this point I'm beginning to think non-flapped airplanes turn faster, and really don't see an advantage to them.

Some suggestions would be more then appreciated.

Thanks..

If you would make your flaps fixed without any other changes
to the airplane(same c.g, same elevator throw) it would turn
faster and easier. The reason is the fact that the flaps are
introducing a moment in the opposite direction of the elevator.
When elevator pushes down, the flaps push up.

You can wonder, why do we need flaps? The same question was asked by Ted Fancher in his 'DOCTOR' article is Stuntnews of a few years ago.

According to me (there are more opinions on this issue), flaps can be usefull for 2 reasons:
1. They make the airfoil more efficient on the moment you need it most: a sharp turn. Without flaps, the model might stall and fall out of the sky.
2. By adjusting the flap throw, compared to the elevatorthrow
you can actually trim the quality of turn. Without flaps the model (fuselage) needs a certain angle of attack to make a turn. It is kind of sliding trough the turn like a car in a turn on a dirttrack. With flaps you don't need your model to amke this angle of attack because the flaps are changing the angle of attack of the wing itself. So the fuselage can be made to follow exactly the flightpath.

What you are experiencing with your model is obviously too much flapthrow. The angle of attack becomes negative. It probably jumps into the corner instead of flying the corner.

Reducing the flapthrow can be accomplished in 2 ways:
1. change the flap/ elevator ratio by using another hole in the control horn
2. Changing the centre of gravity: Moving the c.g. backwards
will require less elevator throw to make a turn: Less elevator means less flap et voila!

Hope this helpfull

Paul, Belgium

A combat type plane will turn sharper and more violent, granted, but you have no stability, and that, plus the speed at which it flies will make it impossible to do anything with precision.

That said, a well designed and trimmed coupled flap ship will turn a beautiful "snap-tight" corner that a non-flapped ship flying the same speed will not be able to turn. Maybe a Canard, or another radical departure in design will change things in the future, but, for now, I don't see a lot of people flying precision stunt with non-flapped airplanes. And there is a reason for it. They out turn their non-flapped brothers designed for flying precision patterns.

I will respectfully disagree with Paul about a fixed flap version turning quicker and tighter. If it did, we would all be flying without flaps. Flaps do help and flaps are effective in improving the turn and the rate of turn.

That said, it is quite possible that what some have mentioned about having too much flap throw is a part of your problem. However, we really need more information.

1). What is the total weight of your plane? (If too heavy, it could be skidding/stalling in the turn).

2). What is your line length and lap speed? In other words, how many seconds per lap? Flapped airplanes are able to fly slower than non-flapped airplanes, and they generally turn better when they do. Those who have never flown one before may simply be flying too fast. However, you will need a certain minimum flight speed to maneuver properly. Dependinng on weight and area, a good "rule of thumb" would be 4.7 to 4.8 seconds per lap on 60 foot lines up to 5.3 to 5.5 going out to 70 foot.

3). Do you have the flaps and elevator set at a 1:1 ratio? You should never have more flap movement than elevator. Since this is a proven design, we can assume the amount of flap in proportion to wing and tail section is about correct, although I would suspect the tail surfaces could use a bit of enlargement by today's standards. However, light airplanes can sometimes use less flap (area or movement) compared to medium weight planes which will normally function well at that 1:1 ratio. I would suspect that you were not able to build this kit too light and this is not the real problem.

4) How much flap and elevator movement are you giving the plane? You should never have more than 30 degrees of flap movement. Never! Never ever! A good design will turn a snap corner with less than 20 degrees of total flap or elevator movement. If you are going over 30 degrees with flap movement, you are simply increasing drag and inducing stalling. This is another case where, if some is good, more is not, necessarily, better. (This is, also, one of the reasons why many have gone to 4 inch belcranks.) If you are going over the amount above, you can narrow the handle spacing to limit your control movement.

5). If you lock the leadouts, can you wiggle the flaps? If you lock the flaps, can you wiggle the elevator? If your horn/joiner wires are flexing or either pushrod is flexing, then you are losing the effectiveness of your controls and this needs to be corrected. This is why it is recomended on "full size" planes that you use at least 1/8 inch wire on the flap horn/joiner and 3/32 (some use 1/8) on the elevator, and, also, why many will use carbon fiber pushrods so there is no flex there as well.

6). While on the subject, does your stabilizer flex? If it does, you can lose some of the effectiveness of the elevator with a negative twist being induced in the stabilizer. On a non-flapped plane you may not notice this as you just give it more elevator. On a flapped plane when you give it more elevator you, also, give it more flap. This is why some people adamantly stick with the story that a non-flapped plane will fly better than one with flaps, and it is the design, not the flaps that are causing the problem.

7). Where is your CG? Planes with coupled flaps are able to fly with a CG much farther back (especially with a larger tail) than planes without flaps. If you keep your CG the same as with a non-flapped plane, well, you have lost some of your turn. (See the last statement under point number 6).

8). Do you have any gaps in the hingline? We work to try to get our hingelines as tight as possible, and Matt has worked out a procedure that generally seals things well engough, even when the controls are deflected, that he doesn't need tape on the hineline. However, it may be good practice to do this anyway. If one flap (or even elevator) has a slightly larger gap than the other, you will not only lose effectiveness, but give the airplane a tendency to roll. If the hingelines are sealed, you start out with everything equal and can save a lot of headaches down the line. If you have gaps in your elevator hingeline, they are not going to be effective (see point number 6).

Check the above and give us your results. You may already solve your problem. If not, we can help you from there. And remember, a heavy airplane is always a heavy airplane, whether it has flaps or not. (See point number 1)

I concur with your disagreement involving my comment about flapped models/non-flapped models turning capabilities. I understand perfectly well that all modern pattern airplanes are flapped. This has just been my experience thus far, and have only built two flapped airplanes to date.

I accurately cannot answer all of the questions you have posted except for a few.

As I mentioned, this is a Brodak Zero, with you're modified Tower .40 engine and tongue muffler Line length is approx. 66ft, and lap speeds average around 5 seconds. Prop is master/screw 12x6. Power is excellent, and line tension is great. I haven't weighed the airplane, but I don't believe it is overly heavy, and paid close attention to weight. I used lots of sandpaper, did not use silkspan on the fuse, and used monokote for the wing covering.

As I said, the airplane flies very nicely...very smooth and stable, and turns nicely ONCE I'm into the turn..it's just getting into it that concerns me. I will try a 1/8" pushrod to the elevator as the one I have now I believe is less.

I have flap ratio set in favor of the elevator to the extreme, i.e., bellcrank linkage connects to flap horn at it's outmost hole with respect to the wing, and with the elevator rod inserted right below it, going to the closest hole on the elevator with respect to the elevator.

As I said, I added a half-ounce weight to the tail last night, this seemed to help, maybe I should add more?

Some people want to make the plane nose heavy to start. I don't recommend it. If you do that, you are just fighting a dog from the word, "Go". Try to set it at the approximate CG that you think you need, and go from there.

And, if that means adding tail weight, do it. Have you ever seen a top stunt flyer with lead solder wrapped around his tail gear wire? Yup, it's been done many a time. (Matt builds a tail weight box into his planes these days. "Just in case.")

Okay, just got back from 3 flights with the Zero. Phewwwy is it hot out there! In between each flight I would have to guzzle down some water, and then re-apply bug spray because my skin would be covered in a glaze of sweat washing away the repellent! Grossssssss.....

I added .5 ounce more of tail weight before I went out. Nice improvement indeed. The airplane seemed to turn quicker then before. However, I still think it can be slighty better. I noticed the control rod to the elevator, definetly not 1/8", probably 3/32" at best. I'm going to the store to get some 1/8" rod and try that. I do believe it's bending under air pressure..it seems a bit flimsy.

Other then that the 3 flights were excellent! Smooth, precise manuvers with great line tension throughout the hemisphere. That Tower .40 engine you modified really is broken in nicely now. I get consistent, predictable engine runs every time. It pumps out great power, and can get a solid 10 minute flight out of 4oz. of fuel. I can only imagine the vast improvement in not only engine performance, but flight performance once the air cools and dries significantly.

This Zero is turning out to be a great flying airplane. And as I watch it cruise through the sky, the image of this plane flying over home territory makes me think of the last time we saw this; Pearl Harbor! Ahhhhhhh...

Thanks for the help.

But why are we guessing, Jim? Almost any design that you build should show the recommended CG on the plans. If it doesn't, or you want more input, ask someone who has built one before. Ask on this forum. Sure, if you build the plane with the CG an inch or two behind where it shoud be, it will get quite squirrely, but I am not recommending that at all. I am saying put it where it should be! the experienced flyer will do that automatically. The unexperienced flyer now has the ability to ask the experienced flyer how and where.

I think far more airplanes are wrecked by beginners who take a nose heavy pane out and try to loop it and find out too late that it won't than are wrecked because they got the CG too far back.

I have never wrecked a plane because I got the CG too far back. Never! I have wrecked planes in my younger years because they wouldn't loop but I tried.

I tried a 3-bladed Tornado prop. It seemed to lose line tension. I find that the 12x6 prop gives me the best line tension..

Maybe I will revisit the 3 blade guy again and mess with the leadout positions more. I also noticed that if you put the leadouts to far back, you lose line tension.