Ever wanted to get into or improve your aerobatics?

[Peter Jenkins]

I said I'd write about the transition moves between manoeuvres.

Just to be clear, the term "standard line and height" is used in the B Schedule to describe the positioning of the aircraft when it is flown across the front of you/the examiner. It should be the same distance out and at the same height unless the manoeuvre requires a different height.

The manoeuvre I found most helpful was the P turn (because it looks like a P shape) or procedure turn. This can be used to turn the aircraft around through 180 degrees and fly back along the same path - very useful to maintain your standard line and height.

The P turn can also be used between the loop and bunt to climb to the required height and return you along the same line as the loop. The P turn can also be used at the end of the bunt to descend for the first of the 2 rolls and also return you to the standard line and height.

So what is the P turn. Having flown a manoeuvre, you continue to the end of your circuit and turn 90 deg (1/4 of a circle) in the circuit direction then reverse the turn and turn 270 degs (3/4 of a circle) to bring you back on the track you have just completed. The aircraft should now be at the same height and travelling on the reverse of the track you have just flown. This positions the aircraft for the next manoeuvre at the right distance out and the right height.

If you need to climb, that is you are going from the loop to the bunt, then start a steady climb as you begin the first 90 deg turn and continue climbing steadily while you perform the 270 deg turn. With practice, you will reach the desired height as you complete this turn at which point you roll out and level out ready to fly down the right track at the right height.

If you need to descend, then you begin a steady descent as you start your first 90 deg turn and follow the same procedure described above except you are aiming to reach your standard height and line on this occasion.

When you need to change circuit direction, e.g. after the overshoot and prior to commencing the low level circuit in the opposite direction, you use the P turn again.

If you feel really confident, then you can use a half reverse cuban eight to turn round at each end when you want to be at the same height. If you need to change height you can use an half loop and half roll. The thing is that if you get these manoeuvres wrong it puts the aircraft in the wrong place and you have to then re-position the aircraft or compromise the next manoeuvre. Since you are not being tested on your prowess in performing elegant turn around manoeuvres, my recommendation would be to keep it simple and use P turns where the chance of error is greatly reduced.

The P turn will also cope with a cross wind more easily than an aerobatic manoeuvre. With the wind blowing from behind you, you will need to perform well banked turns for the first 2 90 deg turns and then open out the bank to allow the aircraft to regain the desired track. Clearly with the opposite crosswind you reverse this procedure.

[Peter Jenkins]

OK, we’ve covered the initial circuit, the Fig 8 and the loop. The next manoeuvre is the bunt or outside loop. For many people this is a frightening manoeuvre as it involves pointing the model at the ground! For that reason, for your first attempt, make sure you are high for you first attempt. An alternative approach is to roll to inverted and then apply down elevator so that you establish the first half of the bunt travelling away from the ground and so you know that the aircraft is capable of performing the second half of the manoeuvre when it’s heading towards the ground!

Let’s assume you’ve had a couple of goes at the bunt, that you’ve convinced yourself that you are not going to crash or break the wings and go onto considering the finer points of the bunt. Again, I’ve already covered this see Page 25 and at 24/05/2014 16:57:06.

For the B, you will have completed the loop so you need to execute a P turn during which you climb to the required height for the bunt. Also, you need to position the aircraft so that it is a bit further out into the field so you don’t have it right over head. How high? Higher than the high point of your loop as most models (non-specialist aerobatic jobs) will take a bigger radius to perform a bunt compared to a loop and you don’t want to scare yourself by getting too low!

The one thing I’d add to that earlier description is that you may need to use rudder (small amounts – sort of a squeeze) to keep the average club model tracking straight around the bunt. This raises the question of which way to squeeze rudder? Well, here’s a useful tip that I’ve picked up. As you will be seeing the model as if it is inverted think of which direction you need the tail to be moved and squeeze rudder in that direction. Each model will have a different amount of rudder needed as the power comes off and then goes back on again. You will also need to move the rudder in opposite directions to cater for the power off and power on cases.

Think about this before you get airborne, and if you have a stick model (or a small model) go through the bunt slowly thinking about what you need to do at each stage. You won’t get it right every time but after a bit of practice it will start to become less of an issue.

So, as with all manoeuvres, start with the wings level and wait for the model to cross your datum point for the centre of the manoeuvre. That’s when the power starts to come off and not before. I’ve seen some pilots slow up too much before they reach the point at which they push the nose down and speed determines both the radius of the bunt as well as the effectiveness of the controls. Try and keep the speed relatively constant.

Read carefully the point about easing off the elevator at the bottom of the loop. That’s because you have the greatly increased slipstream from the engine at full power (or high power) making the elevator more effective. So easing off the down elevator allows the aircraft to come up the second half of the bunt at the correct radius to allow you to reach the same height at which you entered the bunt.

Once you have completed the bunt at the same height as entry you will also have smoothly reduced the throttle to normal cruise power. Don’t forget to fly in a straight line (no climbing or diving either) for a short period after the bunt.

Since your next manoeuvre will be the two rolls, you need to position the aircraft sufficiently far down wind during your P turn to allow a good entry for the rolling bit. Use the P both to descend and position the model on your previously established standard line and height.

[Geoff Reynolds]

Wow Peter,

where would we all be without your knowledge and help.

This all seems so easy on paper, but I'll keep following but I know there isn't any thing better than getting out there on the sticks.

Missed a great day today because of mowing the field this morning and having something to do this afternoon, but I'll definitely be out there tomorrow!

Thanks for what you are doing here, it is easily digested and to follow. You should bring out a book.

Regards

Geoff

[Masher]

The bunt is my stumbling point at the minute! It took me a long time to get comfortable with even trying it and then I had a spell of doing it Ok. Unfortunately, as I have been more critical with my training for the 'B', I seem to be unable to do the bunt properly any more! I seem to always end up skewing out no matter which direction I try - downwind or not.

I have increased rudder exponential to 60% to ensure I am not affecting that with the throttle and pay particular attention to avoid affecting aileron when I change elevator (I am Mode 2). I start the bunt at low throttle and am careful not to over do the elevator. Then gradually increase power..................but I've already skewed by then?????

Today I added some weight to the relevant wing tip to improve (static) lateral balance and still have the skewing issue. If I do the bunt upside down by approaching from inverted, I don't have a problem in getting a good shape.

Any help would be appreciated. This is with the WOT 4 BTW, I seem to fair better with the Acrowot.

[Willyuk]

Masher, I have the same problem and I think that in my case it's not having the wings absolutely level before starting the bunt. I get it right less than half the time but when it goes well it's usually because I ensure the wings are dead level. Of course by this time it's 200 yards past centre but that's a minor issue at the moment!

[Masher]

Thanks WUK, I will watch out for that - non-level wings could be the answer because I am usually practicing too far out and up (because others are flying) so it's not so easy to see the wing attitude

[Geoff Reynolds]

Hi Masher,

I used to bunt better than loop, but have the same skewing problem in both at present.

When my transmitter went back to Spektrum for repair recently, they loosened both my gimbals off as they said they were too tight, but that isn't the cause.

I'd put money on not having the plane set up right, but we'll wait for maestro Peter to tell us.

Geoff

[Geoff Reynolds]

Posted by Willyuk on 16/10/2014 17:48:00:

Masher, I have the same problem and I think that in my case it's not having the wings absolutely level before starting the bunt. I get it right less than half the time but when it goes well it's usually because I ensure the wings are dead level. Of course by this time it's 200 yards past centre but that's a minor issue at the moment!

This could be it, I'd not really thought of that.

Geoff

[Masher]

I'm so glad that it's not just me! Trouble is, it seems the more you concentrate on a problem, the worse it gets.

[Martin McIntosh]

Masher, this may be of help but I have not tried it on a high wing model.

Static balancing is a waste of time, it must be done in the air.

At height, fly exactly downwind away from you. Then, with the wings level, close the throttle fully and push down into a half bunt. One wing will probably be lower so carefully note which and add weight to the opposite side, a small nail at a time until the exit is level. It does not work if you first roll to inverted. This should be one of the very first trimming stages for a model from my experience.

Martin.

[Peter Jenkins]

Hi guys, the big problem with having the wings level is..... having the wings level. It is difficult to get used to what it should look like with wings level when the aircraft is higher than you normally fly. Most folk tend to have the wing nearest them a little bit lower than it should be. If you have a stick model, hold it at the sort of angle that your aircraft will be at height and have a good look at what a wings level attitude looks like. The other way of telling if you are wings level is that the aircraft should fly in a straight line. If it turns then the wing on the inside of the turn is low. Just fly backwards and forwards at the bunt start height until you are satisfied that you know what the aeroplane should look like when wings level.

The other check is whether you have the correct amount of sidethrust. The way to check for this is to fly into wind so that the aircraft is tail on to you. Apply full power smoothly and pull to the vertical and watch in which direction the nose goes - do not make any rudder correction, just watch. Do this a few times to make sure you are satisfied it is either going straight up (well done, move on) or if it's going left or right. If it's going left, add more right sidethrust. If it's going right, remove some right thrust or else add left side thrust. Needless to say you only want to make small adjustments and then do the flying test again. It's worth spending time on this as it will greatly reduce the amount of correction you will need when flying the bunt or any other manoeuvre that requires a lot of power - most of them!

With my Wot 4, I also get it skewing out of shape unless I use some rudder despite having the side thrust sorted. I'm out flying tomorrow so will take the Wottie and experiment with it. Generally, as power comes off the nose will tend to swing to the left needing a squeeze of right rudder to keep straight. As power goes on, remove this rudder and be prepared to squeeze a small amount of left rudder to keep straight. As you come round to the top of the bunt remember to return the rudder to centre.

Hope that helps.

[Masher]

Thanks Martin & Peter - some things to check. I think it's a matter of not being careful enough with the trimming procedure - I've listened but then failed to be meticulous enough.

[Peter Jenkins]

Good point Martin.

I read of another way of checking that involved flying vertically downwards with the throttle closed and then pulling sharply to the horizontal. You do not need to have wings level before you pull but just need to make sure that you don't introduce any aileron (if you are Mode 2!) into the proceedings. Then look carefully to see which wing is low. Repeat several times to be sure that the aircraft behaves in the same way for most of the time. The wing which is low is the heavy one. Martin's described the cure above.

I've found this easier to use to check for a heavy wing than any other method which always requires you to start with wings level and high.

[Martin McIntosh]

I think that my method is more accurate Peter, since when flying vertically downwards you cannot easily tell if the wings are level when you start to pull out.

Some more for newbies.

If anyone is wondering, the reason that you cannot do this from inverted is because at the top of the bunt `G` will be zero so any imbalance will not show. By the time that you get to the bottom you will probably already be adding aileron correction subcontiously because the model is much closer and you can see better what is happening.

The reason that this is done with a fully closed throttle is so that thrustline cannot affect the results, whereas starting from the bottom it could have a great influence.

[Peter Jenkins]

The reason I like the method I described Martin is because I always find it difficult to be absolutely sure that my wings are level when the model is high. With the vertical dive you can roll the model so when you pull out it will be flying at you and it should be much easier to see if the wings are level in that case. At least, that's been my experience. However, folks can try both methods to see which they prefer.

[Martin McIntosh]

I suppose that both methods have their merits, so suck it and see. I have found that flying away then doing a reversal and coming out towards yourself having positive `G` does not seem so effective as the negative `G` method but I do not know why this should be. Maybe something to do with the vertical cg of a low wing model.

["L"Plate]

It might be to do with the fact the model was trimmed upright reducing the effect, as it is supporting the weight but when you go Neg G it adds to the weight.

Just a thought.

[Peter Jenkins]

Yep, my Wot 4 needed a healthy dose of left rudder as the power came on in the bunt. I have to say though, that after flying a 2 mtr aerobatic aircraft for most of the time, the Wot 4 feels like an agricultural beast! Still, it's jolly good fun especially when you have a throttle pipe on an Irvine 53 that gives you virtually unlimited vertical performance!

[Peter Jenkins]

I forgot to mention in the post above that the reason for LEFT rudder is that the aircraft is upside down (negative g) and the rudder movement is now reversed. If you look at your inverted aircraft and apply left rudder you will see that it moves to the RIGHT as the rudder is now upside down. It's a bit confusing until you realise that like the elevator the rudder effect is reversed when the aircraft is upside down when viewed from the pilot's perspective. The ailerons continue to function as you'd expect i.e. left stick produces a roll to the left.

[Peter Jenkins]

OK – we’ve completed our bunt, successfully (!) and carried out a P or procedure turn to position for the first of the 2 rolls while reducing height back to our standard line and height. We are now heading inbound and about to commence our double roll. It is good practice to aim always to roll away from yourself. That is, if the aircraft is flying from right to left, your first set of rolls will be rolling to the right.

The B does not require you to use both rudder for the roll but you must use elevator and it must be obvious that you are using it. The roll rate needs to be quite slow so that you cannot get away with a set of twinkle rolls and no elevator input. Aim for about 3 secs per roll. The roll rate must be constant so you need to think about how you will achieve that.

As I had the ability to set 3 rates on my transmitter, I set a very low aileron/elevator/rudder rate to allow me to apply full aileron but only get the desired slow roll rate of about 3 secs per roll. This allows a constant roll rate and leaves the pilot free to concentrate on when you push or pull on the elevator. Paradoxically, the slower the roll rate the easier it is to time you elevator input. For both the push and pull you need to apply them for the same amount of time either side of the wings horizontal position – say around 10 deg before to 10 deg after wings level – give or take! The main thing is that the application of elevator is symmetrical about the wings level position so that your flight path is not dragged one way or the other.

Oh yes, don’t forget a very quick pull of up elevator before you commence the roll. Don’t pull the aircraft up and leave it to climb for a bit – just a quick pulse of up followed immediately by the roll but don’t start the roll with elevator applied or your ground track will be dragged off centre before you’ve even started.

When you first start this set of manoeuvres, try establishing a 45 deg climb and then roll. That way, if things go wrong at least you are heading away from the ground. As you get more confidence reduce the angle progressively until you end up entering the rolls from straight and level.

The biggest problems with the 2 rolls is that pilots mistime their elevator input and lose direction or else use too much elevator and pitch the flight path up too far.

Finally, it helps to fly this manoeuvre faster than all the other manoeuvres. This gives you more control over the aircraft. So, open up the throttle a bit more as you roll out from your P turn onto your standard line and height.

If you wish to use rudder for the 2 rolls, then the easy way to remember which way to push the rudder is when you start the roll the rudder goes in the opposite direction to the stick. So, if you roll right, you start with left rudder. Maximum left rudder is reached with wings vertical and then the rudder is reduced to neutral as the aircraft reaches fully inverted. Rudder is then applied progressively in the same direction as aileron to a maximum until wings are vertical and then progressively returned to neutral as the wings come level. Of course, you also need to feed in the down and up elevator commands as the aircraft rolls. It is a good deal easier to cope with just elevator so many B test candidate stick with just elevator. However, if you can introduce rudder as well then you are well placed for when you want to fly true slow rolls.

I’ll try and post a picture of how much aileron movement I have on my Wot 4 to get the desired roll rate for the 2 rolls in the next post.

[chris Bond - Bondaero]

Just thought it was a while since there was any pictures in this thread Couldn't resist

 

On topic though

Edited By chris Bond on 23/10/2014 14:26:45

[Geoff Reynolds]

Checkmate, or should that be check everything before you fly, mate!

Great

Geoff

[Peter Jenkins]

It's amazing what's included when you buy an Oxai Axiome and Galactic these days! It used to be that you only got fuselage, tailplane and wing bags!

[Martyn K]

I can see why they are so blooming expensive now. Mind you, I would be distracted from flying..

[SR 71]

Not a lot of weight in those models, i do like the look of F3A