Ever wanted to get into or improve your aerobatics?

[Malcolm Blake 1]

My friend and I were practising for our "B" certificate and were specifically trying to master the Bunt.

He performed one and seemed very pleased with it but I commented that it was too small. He then decided to do another but this time it was too large...BOOM.

We don't practise together anymore.

["L"Plate]

Sorry to hear that Malcolm, I always like practicing with others and listen and share ideas but at the end of the day, it is the pilots decision how to use those suggestion and their own responsibility to keep the model and others safe. I can not blame any one else if I crash unless they grab my TX or fly into my model (with the latter even then thing happen and I wouldn't hold it against them).

I hope you pal gets back to flying with you or you find someone else to practice with.

[Peter Jenkins]

Hi Malcolm - sorry to hear about your friend's predicament but it does bring home the issue of not flying too low when you start learning new aerobatics. It's also a good reason with the bunt to try it out by rolling inverted first and then pushing into the bunt. At least that way you are always going away from the ground on the first half that sets the size of the manoeuvre. I hope your friend decides to put that one down to experience and comes back to practicing with you.

As Bear says, it helps enormously to have someone with whom to practice.

[Peter Jenkins]

The Stall Turn

In aerobatics, the stall turn can be used as a turnaround manoeuvre, a centre manoeuvre or even as part of a the figure M which extends across a wide part of the centre of the aerobatic box – I’ll describe the Figure M later on.

So, the Stall Turn is quite a useful manoeuvre but it needs to be executed well to have the desired appeal to both the pilot and those watching.

The first thing to remember is that you should build up to the elegance of the full stall turn. Most pilots will have performed stall turns but not everyone will be aware of the requirements of a stall turn used in precision aerobatics. When I first started practicing for my B certificate, I noted that the description for the stall turn included a requirement to allow for any cross wind so that you had to lean the aircraft into wind to prevent it drifting with the cross wind on the vertical leg. This I found rather difficult especially when the crosswind was coming from behind me but the B required me to turn the other way, away from me and the crowd, in order not to be failed on the manoeuvre.

Well, several years after that “slight” difficulty I am now used to doing this but in precision aerobatics you are not required to stall turn away from the crowd – an important difference between the B and an aerobatic schedule. Never mind that, what are the issues to be considered before we even get airborne?

A stall turn is rather a strange name since the aircraft doesn’t actually stall. What is meant is that the aircraft must be flown vertically until it stops and then, by application of full rudder, rotates about its CG and flies vertically down the path it just came up. Well, depending on how much power you have available, you might find that you need to reduce power otherwise the aircraft will keep going vertically upwards till you lose sight of it. Where this is not the case, you will be at a high throttle setting so as the aircraft comes to a stop, you will have a good amount of slipstream blowing over the elevator and rudder with none over the majority of the wings and ailerons. Clearly, the wing centre section will be subject to the slipstream.

As you apply rudder and the aircraft yaws, it is possible that the aircraft will roll in the direction you applied rudder. There is also a balancing act in when to reduce power and when to apply rudder. All you want the rudder to do is to nudge the aircraft off the vertical when going straight up, or, if you the aircraft is canted over to counter the cross wind and you need to turn in the other way, you will need much more rudder force to do that and, in this case, it is better if you start to feed in rudder earlier than you would otherwise do. In this case, engine power needs to be maintained while the rudder is applied in the direction of the required turn to overcome the natural tendency of the aircraft to just fall in the direction in which the aircraft is tilted. So, engine power needs to be maintained at a good level to allow the application of rudder to turn the aircraft in the desired direction and for the power to be cut as the fuselage passes through the vertical.

More in the next post.

[Peter Jenkins]

Stall turn continued.

The other thing to consider is the headwind or tailwind depending on where the manoeuvre being performed. Now, we’ve covered this with the loop and bunt already so as you fly the vertical section of the manoeuvre, what you want is for the aircraft CG to be going vertically up and down. So, for a headwind, you need to lean the aircraft into wind on the way up and then push the nose past the vertical on the way down. This will allow the aircraft to track vertically up and down despite the wind although the aircraft attitude will be such that it is not vertical. The opposite applies for a tailwind situation.

So, putting this all together, the sequence of events for an end manoeuvre stall turn is as follows:

• Fly the aircraft towards the edge of the “aerobatic box” and perform a ¼ loop to the vertical
• Fly vertically upwards – as you get more practised, you can extend this vertical leg to a considerable height but you need to work much harder to keep it in the right place in the sky – then smoothly reduce power to say ¼ throttle – do not close the throttle at this stage.
• As the aircraft comes to a halt apply full rudder in the direction you wish to turn
• As the aircraft begins to turn – and you are aiming for a pivot around the CG not a wing over – close the throttle completely
• as the aircraft fuselage passes the horizontal, centralise the rudder and allow the manoeuvre to be completed by the weight of the aircraft
• This next bit is really important – allow the aircraft to accelerate in a straight dive before performing a ¼ loop to exit at the same height at which you entered

If at the top of the stall turn, your aircraft flops either forward or backwards, then you either had insufficient power applied or you closed the throttle before initiating the stall turn. The next stall turn you do, add a click more power and keep the power on until you see the aircraft turn through at least 15 degrees before closing the throttle.

The other problem you might encounter is the aircraft rolling in the direction you applied rudder. Simply this is caused by the outside wing generating more lift than the inside wing as the fuselage rotates and rolling the aircraft. Applying a touch of opposite aileron as you apply rudder helps to sort out this problem.

As I said at the beginning, start with the basics and gradually build up towards being able to fly the stall turn using all the techniques that I’ve described above.

You can also use a stall turn in the centre of the aerobatic box. Generally, once you have pulled to the vertical, you will need to perform some sort of rolling manoeuvre so that you can see the plan form of the aircraft. This can either be a ¼ roll either to present the top surface of the wing or, if you want a challenge, the bottom surface of the wing. In the latter case, your rudder controls appear reversed so you need to go back to thinking “which way do I want the tail to move?” and moving the rudder in that direction. It’s certainly not as easy as the stall turn when looking at the top surface of the wing!

You can also perform other combinations of the roll. For example a 1 ¼ roll up or a 3 or a 4 point roll up with a similar or different combination on the way down. You can also choose to exit a stall turn into inverted flight – exciting the first time you do it – for preparation into another manoeuvre that requires an inverted flight entry for example. So, there are quite a number of variables that can be introduced into the basic stall turn manoeuvre.

Edited By David Ashby - RCME on 31/01/2014 05:21:39

["L"Plate]

Thanks Peter for a great description of the Stall Turn.

I would just add a couple of things from my experience.

1st You should as Peter said enter and exit the stall turn with a 1/4 loop, lot of pilots tend to put too much elevator to try and make it too much of a tight corner, this kill a lot of the airspeed and unless you have a lot of power in hand will chop your stall turn off lower (so not as nice to see) or if you have the power you could end up fighting the torque reaction to keep straight up straight.

2nd When you first start it is often found easier if you fly down wind as the wind will help your recovery, the same as flying into wind for the loop or down wind for the bunt.

As Peter said to get a nice Stall Turn you need to practice the balancing act with the throttle at the top to get that nice static (well near) rotation. I think the Stall Turn with 1/4 Rolls in the centre of the box look fantastic (if I get it right) and onlookers seam to like it as well.

["L"Plate]

A diagram to show correction for wind coming from the right.

["L"Plate]

Again from wind from the right.

["L"Plate]

 

 

Edited By Bear on 13/01/2014 10:58:54

["L"Plate]

With referance to my post above "2nd When you first start it is often found easier if you fly down wind as the wind will help your recovery, the same as flying into wind for the loop or down wind for the bunt." and a talk with Peter the reason for the stall turn down wind being easier is that you have to pull out less than 90deg from the down line to level flight (even though you have to pull more than 90deg in the up line, if you are compensating for the wind). I am sure Peter could explain it better, we didn't come up with a reason for the bunt being down wind or loop into wind, other than a convention.

[Martin McIntosh]

Hi Peter, me putting my oar in again I am afraid.

The usual way to guarantee a stall turn is to blip the throttle just after shutting down and applying rudder. This may have been frowned upon at one time but with the current trend to electric no one will know that you are doing it anyway. I believe that it is now accepted that this is the best way to do it and that this practice is not downgraded.

[Peter Jenkins]

Hi Martin

Delighted to have your input!

As you say, with electric predominating in today's F3A, it's difficult to detect the blip! Perhaps Kevin Caton, who is a current GBR team member could comment on this technique. However, the competitors who are still flying ic in comps do not obviously appear to blip the throttle but then again I might not have been focusing on that.

I have to say that I do not blip the throttle on my electric F3A machine and all goes well provided I carry around 1/4 throttle into the stall turn.. When I screw up, it's because I didn't leave enough power on and the model just flops onto its front or back depending on which way it was leaning at the time. When I get my next bird sorted out, I'll give it a go and see if I can up my percentage of successful stall turns. The difficulty with electric is judging how much you blipped the throttle as you never hear it.

Peter

[Kevin Caton]

The idea of the "blip" of power is to get some airflow over the rudder just at the point the plane comes to a stop in the vertical climb. This gives some rudder authority and gives you some confidence the plane will stall in the direction you push the rudder. I suggest that if you can't hear the increase in prop speed with an electric, then you haven't increased the airflow over the rudder! I am not the only pilot to have flown a stall turn on full power to stop it going the "wrong" way - a sure sign that you have under compensated for a crosswind. In theory you should not be downgraded for the amount of power you use. In practice, you are...

The key to getting the stall turn right is to stop the plane with just enough power to be able to fly over the stall at the tight radius required. This just takes practice. One tip is to concentrate hard on the CG of the plane as it flies over the radius at the top. More often than not you will see the plane "fall through" the turn.

I can't understand why the BMFA B certificate requires a stall away from the flightline because this is incredibly difficult if the wind has any component from behind you. If it is for "safety" then ask yourself what is more dangerous, a couple of wing spans towards the line at 2-300 feet, or turning from base leg to land on the strip perhaps 30 feet in front of you?

[Martin McIntosh]

Kevin, I agree with every word you have said. The B cert. is not a test of aerobatic ability but to show that you can fly safely in front of a crowd amongst other things and I am an examiner.

When I used to do it in anger it was nice to get the perfect stall turn but if you fluffed it - zero points, so it was better to use a blip of power to guarantee the manoeuvre.

The rules at the time stated that the stall should be no more than two wing spans but I do not know what the case is now.

Anyway, how come that you are still at it and so good after all this time? Congratulations on your achievements.

Martin

[Peter Jenkins]

Many thanks to Kevin and Martin. I do hope that those of you following this thread appreciate what tremendous input you are getting from these two experts. We should take very careful note of what they say and make use of it to improve our flying. I know I will!

Peter

[David Ashby - Moderator]

Excellent thread Peter, I'm quietly lurking and learning and, as you say, it's great to see the contributions too.

 

 

Edited By David Ashby - RCME on 15/01/2014 07:09:06

[Kevin Caton]

Martin the "two wingspans" rule still applies today - some things don't change!

I'm still at it simply because I love flying and I don't fly as often as I would like to. Anyway Wolfgang Matt is still going strong and he last won the World Championship when I was still at school!

[Peter Jenkins]

Spare a thought for those of us who only found F3A after they had passed 60!

[Peter Jenkins]

Figure M

The Figure M consists of 2 stall turns linked by a half loop. The diagram below shows what I mean. The manoeuvre is flown on the into wind leg. Thanks to the GBR/CAA for allowing me to use some of the diagrams they have on their judging presentation.

So, you commence the first stall turn, some distance before the centre of the aerobatic box, in the usual way with a half loop. The next manoeuvre is a ¼ roll so you are looking at the top of the model. The height of the stall turn is judged by placing the rolling manoeuvre in the middle of the vertical path. The stall turn is as before. On the way down, you perform a ¼ roll, then carry out a half loop and then repeat the sequence for the second stall turn. After your second stall turn recovery you can decide to go straight into a turn round manoeuvre or stagger off round the circuit to get your breath back!

There are many more variations of rolling and looping manoeuvres that you can use so that the stall turn is done with the belly of the aircraft facing you or you can introduce a knife edge half loop or an integrated roll into the half loop. I wouldn’t recommend these alternatives unless you are really on top of your game – build up to them slowly!

You want to aim to have the bottom of the half loop on the centre line of your aerobatic box and both stall turns as symmetric as you can get them. Done well, it’s a lovely manoeuvre to watch.

Of course, you will need to introduce wind correction as discussed earlier in the Stall Turn description and this time you have to do it twice.

[Peter Jenkins]

Half Square Loop on Side

This is primarily used as an end turnaround manoeuvre. With this manoeuvre, you both gain height and reverse your direction. There are a number of alternatives to the basic manoeuvre shown below.

The basics are:

• Perform a 1/8 normal size loop i.e. 45 degree climb angle
• Then fly a straight portion – the side of the square
• Then fly a ¼ normal size loop
• Then fly a straight portion – depending on how you have trimmed your aircraft, you will need to maintain a small amount of down elevator to fly a straight path
• Then fly a 1/8 normal size loop to return you to straight and level (S&L) but inverted

Thanks again to the GBR/CAA for the graphics!

Options are:

• to perform a half roll in the second straight leg so you perform a 1/8 bunt to recover to S&L upright
• Roll to knife edge in the first leg, perform a knife edge ¼ loop, roll to upright in the 2^nd leg and recover to upright S&L
• Combinations of full and half rolls and so on.

You will also need to apply wind corrections as we’ve discussed with other manoeuvres.

Although I’ve never seen it in a schedule, there is no reason why you cannot fly this from the top other than if you fly too long a first leg you might frighten yourself on the second leg as the ground leaps up to bite you!

If you wanted to fly a full square loop on side, you would do that as a centre manoeuvre. In that case you would need to perform a 1/8 loop to enter the manoeuvre, then 3 quarter loops with 4 straight parts and a 1/8 loop to exit.

[Peter Jenkins]

Immelman (half loop and half roll)

The true Immelman manoeuvre was invented by Max Immelman, a German WW1 fighter pilot. It comprised a diving attack from the rear on a British 2 seat aircraft with the intention of killing the rear gunner. Immelman then flew under his prey, and then using his excess speed pulled up in a loop in front of his target and when he had performed ¾ of a loop he would roll level and attack his prey head on.

In today’s aerobatic description an Immelman is a half loop followed immediately by a half roll. Note the word immediately. In competition, you will lose points if you fly a straight line before rolling. Now, you can fly an Immelman from the bottom up (loop) or top down (bunt but if you started inverted then a loop). The manoeuvre is always the same – a half loop followed immediately by a half roll. The half roll can be turned into a full roll or a ¼ roll so you exit in knife edge or point rolls. Where a single Immelman is called for it is always performed at the edge of the aerobatic box as a turn round manoeuvre. The diagram below shows the Immelman as a turn round manoeuvre at either end of the aerobatic box.

Sometimes a double Immelman is called and that will be a centre manoeuvre – so you would fly 2 Immelmans equidistant from the centre line. The manoeuvre can be entered from either upright or inverted flight.

Remembering all the previous guidance on allowing for wind, both cross and head/tail wind; applying power and controlling diversions in yaw; keeping the aircraft a constant distance from you and making the figure look as large as reasonable and graceful!

Another point to remember is to keep a good amount of power applied as you roll, especially if you have flown a climbing half loop and are required to do a full roll. There is nothing worse than staggering round a roll at low speed as you will have difficulty rolling while maintaining heading and altitude – keep that power on. It also helps if you roll with the engine/motor – i.e. roll to the left. Why? Well at least you have the engine/motor torque helping you rather than you having to roll against that force. That is, unless you have a contra rotating propeller set up- in which case you won’t be reading this advice!

Graphics courtesy of the GBR/CAA.

[Peter Jenkins]

Split S (half roll and half loop),

This is the opposite to an Immelman. The Split S is a half roll followed immediately by a half loop. Again, you can be asked to fly a full roll before commencing the half loop and the half loop can also be a half bunt.

[Peter Jenkins]

I can see that there are a few folks following this thread but the input seems to have dried up. Is this still useful? Would you like more or less information? Have you got any questions? If you prefer, you can always PM me and I promise to reply.

Peter

[graeme jones]

Peter - still following. I have a couple of questions too, but I need time to re-read the whole thread again first. Back soon.

Graeme

[karl grey]

Still following Peter, just waiting for decent weather to get out and practice