Tutorials on Knife edge flight
 

Hello are there any tutorials on knife edge flight how to ?

Also how to mix out coupling for plane pulling towads the canopy and towards the gear ?

Much thanks

RE: Tutorials on Knife edge flight
 

Hi,
I don't know of any documented tutorials here yet, so I will tell you how I go about it;)

Knife Edge Elevator Coupling

Knife edge is really a pretty easy flight attitude once you get the coupling issues corrected. The key is to get the airplanes really trimmed out for straight and level flight first and then work on knife edge.
Knife edge coupling issues are not only effecting the airplane when it is flying in knife edge, but any time the airplane is flying including when it is in a hover. Getting the plane trimmed out and then mixed out properly will make hovering easier.

1. Once you get the airplane trimmed out and you are ready to fly on knife edge, get up 3 mistakes high and get the plane flying level and parallel to the runway or even better straight into the wind. BTW, its best to trim for KE on a day when there is little or NO wind.

Lets start out flying left to right

2. At about 1/2 to 3/4 throttle, roll the plane on knife edge so that the canopy is facing you and immediately start to ease in just a little rudder.
*If you are rolling to knife edge from upright flight you will always input OPPOSITE rudder to the direction of aileron roll.
* If you are rolling to knife edge from inverted you will always input the SAME rudder as the direction of roll.
3. Do not correct with the elevator on the 1st try, just watch the airplane and see what it does and take a mental note for now.
4. Go back around and do it again, again just watch and makes sure it does the same thing again.
5. Now, go back around and have someone standing there so they can write down what you observe (unless you are sure you can remember) ie Say right knife edge, canopy facing me, the plane is pulling to the belly a little so that they can write it down for you.
Once you are ready, roll on knife edge and as the plane couples, begin correcting with the elevator to hold the plane in a straight line. Make a mental note of HOW MUCH elevator you correcting with and whether it was up or down elevator.

Now, lets fly right to left.

6. Repeat steps 2-5 but flying right to left and record your corrections, if there were any made with the elevator.

Mixing

Lets assume that on left knife edge it pulls to the wheels(belly) and on right knife edge it pulls to the canopy.

7. Now, go into the transmitters mixing menu and look for a Rudder to Elevator mix. If your radio only has the channel numbers then find a mix that uses the rudder channel (4 on Futaba) to the Elevator Channel (2 on Futaba) You might see a mix called !4 to 2. If there is no mix there, you will have to go into the programmable mix (pmix) menu and assign one of them to mix Rudder to elevator by selecting the rudder as the master channel and the elevator as the slave channel.
Master means just what it says, its in control of the slave channel. The Slave channel reacts to what the Master channel tells it to do according to how you set the mix.
7A. Once you find the mix, with your airplane on the ground (and the frequency pin in hand I hope) turn the airplane on and go to your mix.
7B. You should find a place where you can assign a +/- number from 0-100 for left rudder input and right rudder input. One will be for left rudder correction and one will be for right rudder correction.
*You will probably have to actually move the rudder stick to get it to toggle from the left rudder number to the right rudder number so pay attention to which is which. For instance, if flying left to right, when you input left rudder the plane happened to pull to the belly you want to add UP elevator.
* Move the rudder to the left and see which number the mix switches to. That is the one you will want to change to mix in elevator for left rudder .
8. Now that you have located the mix and know which one is for left rudder and which for right you can start programming.
8A. Move the rudder to the left and get on the correct adjustment number for left rudder mixing. Move that number to -5 to start.
8B. Move the rudder and watch the elevators direction of travel. Since on left rudder we said we needed down elevator the elevator should move down. If it went the other way, change the number to 5 or +5. Now, move the rudder again.
OK, so now you have it going the right direction.
9. Remember when you were making a mental note of how much elevator you needed to hold the plane in a straight line? Now we will correct according to that number and it is not an exact science. If you had to make a lot of correction ease the number up to about +/-8 to start. That is a lot is a lot of elevator correction, but it is possible that you could need more. Move the rudder and make sure the elevator is going the right way. If you only needed a small correction start on +/-3 and go from there.

10. Now starting with step 7 repeat the steps for right rudder correction (plane flying right to left)

11. Once you have the mix in and you are sure that the elevator is going the right way for whatever correction you need.
12. Fly the airplane and see if you can now hold a straight line without elevator correction.
12a. If it is still pulling in the same way it was before, add more mix by making the number more + o -, whatever is applicable. .
12b. If it is now pulling in the opposite direction, reduce the mix.
Continue to fly and adjust until the plane flies straight on knife edge.

You can also do this mix on a curve mix so that you can incrementally adjust the mix as you increase rudder input, but for now we will keep it simple.

Knife Edge Roll Coupling

Once you get the elevator mix done, you can now start on the roll coupling mix. That means that when the plane is on knife edge you are making subtle aileron corrections to keep the wings perpendicular to the ground.

1. Fly the plane left to right and do not make aileron corrections once it is on knife edge.
Try to fly all the way from one end of the field to the other and just watch and see what it does. If it continues to roll toward inverted you will need to add left aileron, if it wants to roll back upright you will need to add right aileron mix.
2. Once you have done this test from L to R and R to L, go back to the mix menu and look for or create a Rudder to aileron mix.
3. Just as before, with the airplane on and using the rudder stick setup the mix numbers so that the ailerons move the right direction for the mix you need. Same thing with +/- numbers. If it goes the wrong way go to a positive number. Again, start out small with the numbers I would not go more than 10 to start and adjust from there.
4. Fly the airplane and depending on what it does increase or decrease the mix until the plane flies straight down the field, without wanting to roll over.
Thats it!

Just be sure to remember to make SMALL moves, tiny changes can make a BIG difference, even though it does not look like the surface is moving much. A 1 degree change can make a big difference, all the difference in the way the plane flies.

Guys, feel free to correct me or add to this if you don't like.

RE: Tutorials on Knife edge flight
 

"You might see a mix called !4 to 2. If there is no mix there, you will have to go into the programmable mix (pmix) menu and assign one of them to mix Rudder to elevator by selecting the rudder as the master channel and the aileron as the slave channel.
"
Very good explanation Mike! You have a small typo here that you might want to correct to avoid any confusion. It should be elevator as slave channel since you're discussing the pitch coupling. ;)

"You can also do this mix on a curve mix so that you can incrementally adjust the mix as you increase rudder input, but for now we will keep it simple."

Also, a quick question. What is the benefit/advantage of doing this?
Thanks in advance! :D

RE: Tutorials on Knife edge flight
 

I mixing curve can be helpful because coupling can change with increased throw. Ever do a nice KE pass at speed and everything is fine, no coupling ('cause you mixed it out like Mike said) and then try a HAKE pass with the same plane and the airplane roll and pitches like crazy? That's because the greatly increased rudder input required for HAKE has caused a different coupling dynamic. So by using an exponetial, if you will, mix we can increase the ratio or correction to rudder input as throw is increased, such as when using 3D rates.

RE: Tutorials on Knife edge flight
 

Good catch and thanks!

Well, with rudder to elevator coupling, often as you increase the rudder throw,, say for high alpha knife edge or a knife edge loop you need proportionally more (or less) elevator correction. So from no rudder input to maximum rudder input the needed correction is not linear. What you can end up with is a plane that flies nice and true in high speed flat knife edge but as you increase the rudder throw to do a knife edge loop or a low speed high alpha knife edge the elevator correction just is not enough with increased rudder throw. So what you do is go to a pmix that allows a 5 point mix and you set the mix so that you get exactly the elevator deflection you want for a given increment of rudder input. On a 9C this is PMix 7. What you typically see is 5 points. The center, or #3 point is the neutral point where the rudder is at rest. Points 2 and 4 are where you set the mix at lower deflections, 2 is for left rudder and 4 is for right rudder. 1 and 5 is where you set the mix for higher rudder deflection, 1 being left and 4 right. This allows you to set a non linear R-E mix that works just like a throttle or pitch curve on a helicopter. That way whether you are flying a nice flat normal knife edge, or digging in with the rudder the plane will track straight(er). Its almost impossible to get it perfect but it sure makes things easier.

The mix may look something like this
1. -10
2. -4
3. 0
4. -3 (because left and right coupling may or may not be the same)
5. -8

Again, this further improves the planes general flight characteristics, even moreso in high alpha flight where you really use full deflection rudder.

RE: Tutorials on Knife edge flight
 

Thanks AeroDave and Mike. That makes a lot of sense; never really thought about that! ;)

RE: Tutorials on Knife edge flight
 

Oh man nice write up. It will indeed do me well and take a while to digest. But hopefully i will get it all downpat

I have a 9c radio and currently flying foamies only. I sold all my glow models and focused on foamies to become a better pilot.



Learning knife edge flight will make me complete in basic aerobatics i belive.

All manuevers are based on loop roll knife edge and inverted right ?

Having that foundation will do me good i hope

I got tired of flying round aimlessly in the sky and wanted to look a little like a pro :)

RE: Tutorials on Knife edge flight
 

Well, yes and no. Its all about learning to fly REALLY straight lines and putting the airplane exactly where you want it when you want it.

There are several keys to flying precisely.
A. A good flight setup. You need to learn to setup your plane to fly neutral. Neutral basically means that it only does what you ask it to do and nothing more other than what gravity obviously effects. That is,
1. when you want to fly straight and level it flies straight and level.
2. When you pull vertical and the wings are level, it goes straight up!
3. When you roll inverted it takes a SLIGHT amount of down elevator to fly level.
4. When you fly knife edge it goes straight.
5. When you do a stall turn(hammerhead) and the plane is falling straight down it should go straight, not tuck to the wheels or more commonly pull towards the canopy with power off.

B. Good mechanical setup of your servos to the control surfaces. You need to get the maximum resolution and mechanical advantage for the type of flying you want to do. This can be a trade off, so you have to decide which you can afford to compromise and go from there.

C. Practicing the basics until you can do them in your sleep.
1. Flying a stright line is probably the most ignored skill there is. You should be able to fly a straight line at a continuous altitide and a continuous distance out. Regardless of crosswind, headwind or whatever. If you cannot fly a straight line you cannot fly precise.
2. Flying a constant speed. Learning throttle management is another key to precise flight. You need to be able to make the plane appear to be traveling at the same speed all the time. Only use throttle, when you need it and learn to only use what you need! Too much os not a good thing.
3. Yes, learn to make round loops. Learn what a round loop should look like, not what YOU think it should look like.
4. RUDDER CORRECTION- This is CRITICAL to flying with precision and real control. Learn to use the rudder man. Flying straight lines is one of the biggest helps for this there is.
4* Exercise- Fly a straight line upright from one end of the field to the other start into the wind. At the end of the straight line, Pull and do a 1/2 loop. Make the 1/2 loop a specific size, do it with purpose. Gently correct with the rudder as you pull through the loop and exit inverted. MAINTAIN THAT ALTITUDE and HEADING but inverted!. Fly right back down the field, inverted and at the altitude and distance out that you exited the 1/2 loop. Correct with the rudder so that you fly STRAIGHT back down the field. At the end of the inverted line, get off the throttle, pull through a nice gentle 1/2 loop the same exact size as the one on the other end of the field and exit at the exact same alitiude the exact same SPOT as you started the exercise.
Wen you are done, this should create a giant upright oval in the sky that is flat on the top and bottom. The 2 half loops the same size, the two straight lines parallel and at the exact same distance out.

Do this until you can do it perfectly, from one end of the field to the other. Lines parallel, exit the 1/2 loops flat no climbing or diving on the entry to, or flight through, the straight lines. Sounds boring, but until you take the time to learn these simple drills you will not be able to really control the airplane.

Whenever you go the the field have a plan. It does not have to be complicated, just pick a few maneuvers that you can link together to form a looping sequence and that way you can just go through several simple maneuvers, ending up right where you started so that you can practice whatever it is you want to work on that day.

I alway try to save about 2 minutes at the end of the flight to relax and punch holes though. Helps me to relax, and often my last flight is nothing but 3D, or just goofing around to keep it fun.


There is a lot more to tell so ask questions,. We are all learning, just sharing what we learn with each other as we go along.[8D]

RE: Tutorials on Knife edge flight
 

Hi Mike,

Great stuff, keep it coming.

RE: Tutorials on Knife edge flight
 

Nice thread, this is often assumed knowledge but its good to see it gone through in such detail. I use Futaba and find fliht conditions very useful for the expo typ emixes needed for low, med and high rates. I find most aircraft as you say are markedly different in their coupling dependent on both airspeed and angle of attack. With flight conditions I can change the whole feel of the airplane at 3D rates to make it easier to fly and put in the groundwork to mix out some of its vices at low speed, high alpha. Without it affecting the much smaller coupling tendencies it has with IMAC style flying.

RE: Tutorials on Knife edge flight
 

i treied the above mentioned and whoooo it worked on my beat up foamy its awsome !!

i tried rudder to elevator mix and rudder to aileron mix
Nice



I did a knife edge circle and it was awsome oh man i am so grateful.


Thank you.


Any more tips ?


I am going to by that bobcat pusher (GLOW) hopefully it has aenough power to knife edge :)

RE: Tutorials on Knife edge flight
 

Here is a thought.

Learn to fly knife edge WITHOUT the necessary corrections mixed in. Why, well it is impossible to deal with every flight condition. I fly knife edge a lot and the corrections for slow high alpha knife edge are quite different from the corrections for high speed knife edge loops.

Learn how to compensate for the problems, educate those digits, THEN mix out as much as you can. IMHO this will make you a beter 3D pilot as you can fly around the problems.

RE: Tutorials on Knife edge flight
 

I agree in principle, but you cant mix it out correctly without having the skill in the first place.

RE: Tutorials on Knife edge flight
 

[8D]Respectfully, IMO, "learning to compensate" I don't think will do anything to make you a better pilot at this level. But I do think that becoming aware that problems exist and then working through them is essential to becoming a better pilot. I say that because once you become aware that there "is" a problem and you know "what it is you want the plane to do" then the learning really begins. At that point the pilot can shift gears from setting up the planes physical characteristics to simply get the plane to fly to analyzing the planes flight characteristics and setting up the plane to fly neutral. THAT is what will make you a better pilot.

If compensating for problems makes us better, then why do we adjust the thrust of the engine, wing incidence and trim the plane out? Lets just bolt the engine straight on and take the trims off the transmitter and deal with it.

Its no different than what you want your car to do. You want your car to go straight down the road, hands off right? I have used this analogy before, learning to drive your car down the road with the front end knocked out of alignment, crabbing sideways down the road does not make you a better driver. It simply teaches you to compensate. Now, for a beginner pilot maybe, MAYBE this drill has some value. However, if you are at the point that you can fly 3D or precision, these issues are nothing more than a distracting nuisance. Can you learn to do it without mixes, SURE! and I am sure that a lot of pilots at all levels do for that simple reason. But why?? Just so you can say "I fly without mixing"or "I fly without expo"?

I say spend WHOLE lot of time flying, analyzing how the plane flies and mechanically correcting flight deficiencies. Once you have exhausted all efforts to get the plane to fly neutral, mix it out.

RE: Tutorials on Knife edge flight
 

I totally agree Mike. There are more interesting things to do with your aircraft than compensate for the fact it doesnt fly straight! I learnt this with the first F3A pattern ship i flew...and it helped me learn to fly a hell of alot better because any flying 'faults' were mine NOT the airplanes.

RE: Tutorials on Knife edge flight
 

I think a lot of this comes from the impacts advancing technology has had on our hobby. So many active modelers (I'm one of them) were flying before we had servo reversing. I hear lots of grumbling at my field about how mixing and computer radios are a crutch and fly the plane for you. My take is they don't really understand the intent of these features and simply equate them with the snap roll buttons of years gone by. What we're talking about is similar to the difference between a straight and a warped (we used to call them bananas) fuselage. If you had the chance to build one straight as opposed to crooked, or go back and fix one that wasn't straght, wouldn't you? We're doing the same thing electronically. It does nothing more than take away the destraction of poor performance so you can begin to concentrate on flying well. I remember an article of Don Lowe's in RCM. He said something like, and this is remembered from 30 years ago, so fogive me if I don't get it right, the pilot should interrupt the straight flight of the aircraft as little as possible.

RE: Tutorials on Knife edge flight
 

Whats a good glow plane that will knife edge well ?

I also have a weston 50 with pipe waiting for a frame

RE: Tutorials on Knife edge flight
 

Most sport aerobatic planes will knife edge. Even the 4 star series will knife edge.

RE: Tutorials on Knife edge flight
 

I had the chance to fly an Aeroworks Edge 540 .46-60 size last weekend - very sweet aircraft. Flew like a big plane - very precise flying. Great KE, hammerheads etc - it was nice. Was being flown on a Magnum .52 - your .50 would be hot in it.

I hear that the Powerline Edge .46 is also very smooth flying.

MY favorite plane in my hangar is my Great Planes Shoestring - great KE and pattern style aerobatics as well. I'm sad to see that they have discontinued the plane this year.

Planes to stay away from for KE flight - regardless of mixing - (these are just planes I have personally owned/flown)
U Can Do .60, Hangar 9 Twist, Modeltech Majic, Hangar 9 Ultra stick .40

RE: Tutorials on Knife edge flight
 

Best planes for knife edge are pattern style designs with plenty of side area and the right ratio of rudder/vertical stab size. The best require almost no correction.

RE: Tutorials on Knife edge flight
 

This is True[8D]

RE: Tutorials on Knife edge flight
 

Mike, is that a Rhapsody, they are awesome models and in the category of little mixing required. By the way im selling mine ;)

RE: Tutorials on Knife edge flight
 

No, its a Genesis.[8D]

RE: Tutorials on Knife edge flight
 

Man all i wantto do is knife edge since i know how to mix it out
I am beginning to look kinda good now


Where can i buy the genisis and the aerowroks 540 ?

Are there any others ?


what about the futana 50 X is that good ?

RE: Tutorials on Knife edge flight
 

I was just kidding! The Genesis is a $2000 pattern airframe,,, but it does knife edge perfectly. [8D]
I really do not know of any scale aerobatic planes that do not have KE coupling. Maybe a profile or something if you want a zero coupling plane. shrug