Ever wanted to get into or improve your aerobatics?

[Peter Jenkins]

Glad you are enjoying it Steve. Now for the loop!

This is much more than apply full power and haul back on the stick! One of the reasons that aerobatic models are fairly lightly built and have powerful engines/motors is so that you can fly large manoeuvres, gracefully, at a constant speed. That means the control response is the same all the way round the manoeuvre and, for the spectator, the manoeuvre looks really nice. The other point about manoeuvres is to make them as large as your available power allows. A bigger manoeuvre looks much better than a small manoeuvre. The downside is that you need to fly the aircraft all the way round as well as be ready to correct for the changes in yaw brought about by the changes in power.

Talking of power, the throttle is not an on-off switch. Unless you have a low powered aircraft you will not want to just bang on full power at the bottom of the loop and select idle at the top – indeed for a really low powered model you’ll want to take a run at the loop so you’ll have gone to full power a good 2 secs before you start the pull. For others, as you start the pull up for the loop, power gets smoothly increased until you are at a maximum with the aircraft ¼ of the way round and pointing vertically up. From just after this point you need to be gradually reducing power until you are at normal cruise power setting at the top of the loop. From then on, aim to have the throttle smoothly closed by the time you reach 2 o’clock (or 10 o’clock if looping the other way). You then need to smoothly increase power from around 4 o’clock to your cruise power setting as you pull level at the bottom of the loop. Just remember that gravity is your enemy on the way up and your friend on the way down.

This is just a start point for your manoeuvre since each aircraft type will have different drag characteristics so you will need to adjust your throttle and elevator controls to achieve a nice round loop that looks like it is being flown at the same speed all the way round. You’ll know when you’ve got there because it will look effortless to a spectator, and in due course, to you!

Now, while all this is going on, you need to keep the wings level. So, you are using all 4 controls all the way round the loop – and not just the loop, all aerobatic manoeuvres. Indeed, all the time you are flying - well, you knew that anyway didn’t you?

Now, that pesky cross wind will give you grief. As you have set up the aircraft track to be parallel to the runway in use, as soon as you start the pull up for your loop if you do nothing about the heading of the aircraft you will, as Algy pointed out above, end up with a loop at an angle to the vertical plane which will come in to you and then go out again. So, you can do one of two things.

Let’s say you are flying right to left with the crosswind blowing in your face. You will have used right rudder to set the flight path so the aircraft tracks correctly parallel to the runway but with the nose pointing to the right of track – you will have used rudder to establish this position and then gone back to neutral rudder. As you start your pull up, you need to do two things. Look for the effect of any yaw induced by the increase of power and keep the aircraft tracking straight AND gently squeeze in some right rudder to keep the aircraft tracking correctly in the vertical plane. What you are trying to do is to fly a slightly barrelly loop to prevent the wind blowing the aircraft towards you but so you pull up, you need to introduce this change of direction. Note also that wind speed will probably be higher as you travel upwards through the loop and you will face a decrease in wind speed on the way down.

The second way of dealing with this situation is to use a small amount of bank. Using the same conditions as above, as you start your pull up, you introduce a small amount of right bank to start the barrel. You don’t need much and do it smoothly so it doesn’t look obvious. Once you’ve established the bank keep your eye on the flight path and either take some bank off or add a touch more to keep the loop in the right place. As you are coming down on the loop, you need to consider that your wings must appear to be level at the bottom of the loop so keep that in mind.

Choose which ever technique suits you – both work

Clearly, when the cross wind component is from behind you then the opposite control movements to the above case are needed.

So, there is a lot going on in a simple manoeuvre such as a loop. Break it down into smaller digestible chunks to begin with before you go for the full monty I’ve described above.

This brings me to another point. How often do you think about what you are going to fly and how you are going to fly it before you get airborne? If you want to fly proper aerobatics, you need to think about what you are going to do before you get airborne. Competition pilots use a small model aeroplane to fly through their schedule before getting airborne so that they can remind themselves what the aircraft will look like as they go through the schedule, what wind corrections they will need and so on. So, as part of your process of flying aerobatics you need to get used to being a bit more deliberate with your pre-flight process. By all means use a small model to talk your control movements through the manoeuvre. Simple things, like which way am I going to apply rudder to keep tracking into the cross wind, is easier to settle when the aircraft is on the ground than trying to do so when it’s airborne.

[Kevin Caton]

Hi Peter

I'm really enjoying reading this thread since stumbling across it a couple of days ago. Thanks for taking the time to write about trimming and the "building blocks" of aerobatics - something we all need to review from time to time. It's great to see some of aerobatic legends posting here too. It reminds us that trimming should be much easier these days with programmable mixers etc. when aerobatics was for men (and I was a mere boy) trimming often involved using a saw to change dihedral and stop adverse roll.

how about another new pilots' open day next year? I'll check my diary early and make sure I can attend.

Kevin

[Peter Jenkins]

Hi Kevin

I'm just negotiating with a club to hold another NPOD next year. Will try and get some dates organised in the next week or so and will compare notes with you then.

Peter

[Peter Jenkins]

Inverted flying

Although not strictly an aerobatic manoeuvre, you are going to be flying inverted when doing aerobatics for a good part of the time. So, it’s worth practising it until you get used to it. Some pilots have a real fear of flying inverted and either avoid it or keep it to a minimum.

So, what makes it easier, if anything? One thing I have found that is a definite aid in flying aerobatics and inverted in particular is using a Tx tray. Now, there will be lots of people who have grown up flying with thumbs only or thumb and forefinger but holding the Tx. If you trained to fly using a tray then you can ignore this bit. I used to fly with a neckstrap and using thumbs. This got me into competition aerobatics but then I noticed that as I got tense, I twisted the Tx towards my body and found that the movement of my thumbs became restricted. I also struggled to fly inverted. I was encouraged to try a tray and initially it all felt very strange. I persisted and it took me roughly three months to re-train myself to fly with the tray. Needless to say, during that time my aerobatics suffered – even more than they did when I flew them with scrunched up thumbs! However, what I found as soon as I started flying with a tray was that I could use the stable base of the Tx on its tray as a way of bracing my fingers in order to fly very smooth and accurate inverted flight. That’s what convinced me to persevere with the tray as everything else felt a bit odd. So, my recommendation is to try flying with a tray but give it several weeks before you decide whether to continue with the tray or to go back to holding the Tx. I stress, this is my experience and not something that I think you should do.

OK, the easiest entry into inverted is to fly a half loop at one end of your aerobatic box. This automatically gives you extra height to allow you to experiment with flying a long straight track to the other end of the box and then fly another half loop to return to upright flight. If you found it easy to fly a straight, level track all the time you were inverted then you are ready to move onto the next stage.

If you didn’t, then read on. Well, why are you having difficulty? Firstly, you will have the elevator function reversed and the only way that you can get used to this is to keep practicing flying inverted. Secondly, if you haven’t already noticed, the ailerons work in the same way as when you are the right way up. Thirdly, the rudder, like the elevator, is reversed. Well, what’s the problem there you ask? Remember that we are using rudder to hold our track over the ground to cope with cross winds. So the question is, which way do you move the rudder. Easy when you are on the ground to say “well, it’s the other way of course” but when you are flying it seems to get a bit more difficult. I heard this tip from a friend. Move the rudder stick in the direction that you want the tail of the aircraft to move. It was so simple but removed so much confusion from my mind. Try it and see how you get on.

When you feel comfortable flying a long, straight inverted flight path, try flying an inverted figure of 8. That’s a good way of building up your inverted flight experience.

[Ultymate]

I fly thumbs only and one thing I found helpful when learning inverted flight is as soon as I go inverted I put my thumb behind the elevator stick so that I can only push rather than pull, over the years I've seen so many models lost by pulling back stick when inverted. I must admit I fly mode1 and suspect this may not work so well for mode 2 guys as you need to maintain aileron control as well, that said I still use rudder when inverted and still keep the habit of thumb behind the stick when inverted

[Peter Jenkins]

You Mode 1 guys have it easy when it comes to slow rolls! If I'd known that when I started flying radio I'd have gone Mode 1! I know that some people can switch between Modes 1 and 2 but I'm not that clever!

[David Hardaker]

Hi Peter

Why struggle with Mode 2 when you could avoid all that pain !! It's never too late to change.

I'd flown 10-channel reeds so when I got my first proportional set it came with throttle left (cos they all did). So I taught myself to fly with that gear. I was at a comp at Elvington and one of the Lancashire lads was there when I handed in my tx. He asked me why I flew "that" Mode and I replied "well what other way is there ?" So he enlightened me, wherupon I swapped the stick units around and re-learnt how to fly Mode 1. That was 40+ years ago.

The plain advantage for Mode 1 is the 2 primary controls are physically split so this guarantees no interaction. I'll admit you still have to stir the rudder when using elevator but that's a minor problem. What Mode 2 isn't is like flying a real aeroplane. (Which is also something I've been doing for 40 years) Why the BMFA promotes Mode 2 is beyond me !

You mention tx trays and thumbs or finger and thumb. I've flown finger and thumb for a long while. We flew in Belgium Internats in 1973 and saw numerous fliers using trays. I tried a tray and found it alien. But having quite large hands I have no problem holding the tx and using finger and thumb as well..

I was never keen on soft sticks ! Doug Spreng once said "soft sticks sell radios, hard sticks win competitions"... Food for thought.

I will say this only once, the essence of all aerobatics is to be smoooooth !!

David

[Martin McIntosh]

I`ll second all of the above, hard sticks and all. The heavier the better. I am at a loss to know how mode 2 flyers ever manage an eight point roll.

[Peter Jenkins]

Hi David

What I should have said in my post on trays, is that I went from Tx with neckstrap and thumbs to Tx on tray and finger and thumb on each stick. That's what took me the time to get used to the set up. I was told this was the only way to get precision control and, despite having struggled to make the conversion, I have to admit that it's true.

I also, wind up the spring tension to maximum on the sticks and I'd like them to be stiffer still as I find that it's easier to feel what you are doing control input wise with stiffer sticks. Doug Spreng was quite right in his saying I suppose! Mind you, I never could afford a Sprengbrook radio at the time.

Having come to proportional RC from flying full size gliders and powered aircraft I just felt it would be more natural to fly Mode 2. Also, all my instructors were Mode 2 types. I think the only area which I would say was clearly superior on Mode 1 is when rolling as your right hand merely has to establish the roll rate while your left hand performs a diamond pattern that automatically modulates rudder and elevator to produce the ideal slow or, as Martin says, point rolls. Having observed a number of today's F3A pilots flying, they seem to me to handle 8 point rolls without too much difficulty - guess it comes down to what you practice and, as we all know, practice makes perfect. Guess, I don't practice enough!

Peter

[Peter Jenkins]

Square Loop

If you combine the loop with inverted flying a good way to practice this is with the square loop. It is a very satisfying manoeuvre to fly and is quite often used in competition schedules with additional manoeuvres in the straight lines. Before you start, you will have worked out what the wind is going to do to your track over the ground and thought about which way you need to point the aircraft to achieve the desired track over the ground.

Now a square loop doesn’t mean you pull sharp corners to the looping bit. Treat the manoeuvre as a normal loop that gets cut into four quarters and then spread apart by straight lines each of the same length. This is what I mean.

Unlike the loop, you do not start the loop part of the square loop until you pass the centre point of your box. As you cross the centre line count, zero, one thousand (i.e. one second) and then perform a normal loop but stop when the aircraft is pointing vertically upwards - you will have used throttle in the way you normally do for a loop but you keep the power at the same setting for the vertical climb.. Now count 2 secs (zero, one thousand, two thousand) and start the second quarter of your loop – begin backing off the power as you would for a normal loop and end with your usual cruise power setting. Now you are flying inverted so concentrate on flying level and keeping your track over the ground parallel to your runway using the rudder. Again, count 2 secs and enter the 3^rd quarter of your loop – close the throttle smoothly from the 2 o’clock position. Ideally, you want your aircraft to fly at the same speed downwards as it was going upwards. If you can see that your aircraft is flying significantly faster downwards then don’t count the full 2 secs before you start the final quarter of your loop remembering to start powering up from 4 o’clock onwards till you reach cruise power when you are level. Then count 1 sec and you should pass the centre of the box.

No? Well don’t be surprised if you didn’t get a symmetric square looking manoeuvre at your first attempt! Some of us can’t manage it consistently after years of trying. Don’t worry, just keep practicing this manoeuvre and you will begin to get the feel for it. Don’t make it too big otherwise you make it more difficult for yourself. As you get better, and if you’ve got an aircraft with a good reserve of power, then you can start to make the manoeuvre bigger but note that you need to work on keeping the aircraft tracking vertically. That doesn’t mean the nose is truly vertical as you will have to lean the aircraft into the crosswind to allow for the drift that would otherwise occur using the rudder while keeping the path truly vertical. The same applies on the way down. We have also to keep the inverted part of the manoeuvre on the desired track as well. That’s where the rudder comes in and the trick of thinking which way you want the tail to go gives you the direction in which you must push the rudder stick.

So, there is quite a lot going on in something as apparently simple as a square loop. When you get it right, it is a lovely manoeuvre to see and gives you a real feeling that you are getting to be a real aerobatic pilot.

[Peter Jenkins]

By the way guys, don't be afraid to post if you have any questions or are having difficulty with following what's being said in this thread. If I can't answer it I'm sure some of the more experienced guys who are keeping an eye on this will be able to do so.

Peter

[Terence Moore]

Peter, I am new to this thread, and am currently building a 1970/80 F3A style model "bootlegger" ( + 10%) which plan shows everthing set at zero, incidences/thrusts etc.

I thought about modifying this to +0.5' wing; 0 tail;0 engine thrustline, but with 1.5' right thrust.

By the way it has an anhedral tail as per the period.

Any thoughts???

Terry

[Martin McIntosh]

Hi Peter, that was a very good explanation of the basic square loop but are you assuming that in this situation there is a full crosswind or even none at all? If flying into wind then counting seconds will see you blown far downwind and will only result in a rectangle surely? I have always judged the downline start from a central point because the ground speed along the top will be much greater than that attained during the one second entry. I remember a judge from years ago who would downmark you if all legs of a rectangular landing approach did not take the same time!

[Peter Jenkins]

Hi Terence

I'd stick to the designer's recommendations as he may have built in some down and side thrust in the design. 0/0/0 was the way these aircraft were set up at the time and flew very well. I'm not sufficiently familiar with the design to comment further but have you tried posting on the UK CAA threads for information from folks who are flying Bootleggers?

Interestingly, anhedral tailplanes are makein a comeback with some modern F3A designs.

Peter

[Peter Jenkins]

Hi Martin - yes, you are quite right! I ducked out of the headwind compensation as I was going to deal with it a bit later on. However, as you have raised it now let's talk about the problem of headwind on the square loop.

Martin you know all this but it's worth spelling out for those who have not come across the problem.

While you want to fly a square loop, you will be doing so in a parcel of air that is moving downwind (and across the flight path) at the prevailing wind speed/direction. Since all model aircraft aerobatics are viewed from a stationary position, for an accurate shape to be observed we have to fly our aircraft in such a way as the CG of the model moves only in the way we want it to appear. If we were to fly this manoeuvre in the same way in a dead calm, it would appear very odd and would have the visual impact of being flown inaccurately and heading upwind.

First of all, ground track is what gives our square loop its shape. As you fly into wind your ground speed is reduced and as you fly downwind your ground speed is increased. Your airspeed should be the same going both ways of course. So, the amount of time you spend going upwind needs to be longer than the time you spend going downwind for the two vertical arms to be equidistant to our datum, the middle of the aerobatic box.

I discussed the cross wind compensation earlier, but you also need to compensate for the headwind. As you carry out a vertical climb, the aircraft track over the ground will be backwards rather than showing no movement as would be the case in still air. So, to compensate, we don't pull the aircraft to vertical but a bit less than vertical so that the aircraft moves vertically upwards because we are causing it to fly into the wind.

On the down leg, you need to pull the aircraft to past the vertical so that you are again pointing a little into wind so that the track you make into wind is cancelled out by the track the wind pushing the model downwind.

For a round loop, you also need to compensate for the headwind component. As your ground speed will be low for the first part of the loop, you have to stretch out the pull up so you make progress into the wind. As you go past the vertical the wind is now increasing your ground speed so you need more elevator to bring the aircraft round the top half of the loop quickly and then as you come down through the vertical you need again to stretch out the loop so that it appears round to the stationary observer. That way, you don't get blown down wind. If you didn't compensate the loop would never look anything like what you intended.

I hope that makes sense to everyone.

Yep, even more to think about as you fly your manoeuvres. Best thing to do is to try and deal with each problem and accept the error till you are able to put them all together. Whenever I watch one of the top pilots flying in strong crosswind it looks like they are flying in a dead calm. Loops are round, the aircraft remains at a constant distance from the pilot never getting blown in or out! But then, they'll have spent years practicing to get that good. Don't beat yourself up if you find flying this accurately is difficult. It is difficult but enormously rewarding when you get it right after struggling for many months to do so.

Actually, that's one of the reasons for trying your hand at competition as you learn so much from watching other pilots of similar standard flying and get hints and tips on how to improve your own flying - more on this at the end.

[fly boy3]

A wonderful thread, very very interesting indeed. Although the part about Reynold numbers was in a "simplyfied" prose, it was still too much for my old head. Are we saying that a larger model will have a larger R number so it will fly better due to the smoother flow of air over the wings ? Cheers

[Peter Jenkins]

Hello FB3

It is all to do with scaling. If you remember back to the old wartime films with special effects using model boats it was obviously a model because the water didn't behave like it would in the full size world. Water and air are both fluids but with hugely different densities and viscosity but they follow similar rules for flow and turbulence.

So, putting it simply, what Reynolds number tells you is that you airflow will either behave in one of 2 ways. For Reynolds numbers above around 750,000, airflow will generally stay attached to an aerofoil from leading to trailing edge of the wing provided you remain below the wing's critical angle of attack. Below that Reynolds number, the chances are that the airflow will detach before the trailing edge of the wing causing loss of lift, drag and strange control responses.

Put another way, if you had a 50 size aircraft and scaled it up to a 150 size aircraft the bigger model aircraft would have much better flying characteristics and handling. Indeed, the bigger the model, the better it handles turbulence and other destabilising tricks of the wind. It is quite true that flying a bigger model aircraft is a lot easier than flying a small model aeroplane. Mind you, it costs more to build, equip and fly as well as more to repair which is why more people fly small model aircraft. Don't turn down the offer to fly a big one though as you'll find it a great experience.

Have I answered your question?

Regards

[fly boy3]

Thanks Peter,you have indeed answered my question, much easier this time around. Been flying ic for over 25 years mostly up to around 80 inch span. I am still finding this thread most helpful. Have a quarter scale cub in the attic, never flown (by me). Time to give it a go next year when weather is suitable. Thanks

[Shahid Banglawala]

Hey guys,

Just thought I'd chip in. Mode 1, 2, 3, 4 even mode 4 throttle reversed makes no difference to your aerobatic flying. I have seen world champion pilots in all modes. Grenot Bruckmann - Mode 1. Mark Leseburg - Mode 2. The legendary Martin Muller - Mode 4 throttle reversed. Check 'em out on YouTube!

[Ultymate]

Posted by Shahid Banglawala on 08/12/2013 22:59:58:

Hey guys,

Just thought I'd chip in. Mode 1, 2, 3, 4 even mode 4 throttle reversed makes no difference to your aerobatic flying. I have seen world champion pilots in all modes. Grenot Bruckmann - Mode 1. Mark Leseburg - Mode 2. The legendary Martin Muller - Mode 4 throttle reversed. Check 'em out on YouTube!

So long as you know what you're doing (not like me) I would totally agree, how you keeping Bango

[Shahid Banglawala]

Ey up Bryan! I'm well mate thanks. Ducking and diving trying to stay busy. How about yourself?

["L"Plate]

I used to fly Mode 3 (throttle aileron left stick elevator rudder right stick) but changed to Mode 2 as most of the clubs I have flown the majority have used Mode 2 and as an instructor I found myself teaching and testing models set up in Mode 2 so I changed.

I have been thinking about changing back to Mode 3 as it has the advantages of Mode 1. That said with all the practice I have done over the years in Mode 2 I wonder if it is worth it whether I should just stick to Mode 2.

Answers on a post card please.

[Peter Jenkins]

Tough call Algy.

In the mean time.....

Just picking up on David H’s comment, you should be aiming to make all your manoeuvres as smooth as possible if flying precision aerobatics. Flying 3D demands a different set of rules – if you want to look at it that way. You should also be aiming to fly as large a manoeuvre as your aircraft is comfortably capable of performing. If you have “unlimited vertical performance”, choose a sensible size!

Now rolling next. There are essentially three types of roll. The normal speed roll, the slow roll and point rolls. By point rolls, I mean a 4 or 8 point roll. For a 4 point roll starting from upright, you roll 90 deg, stop the roll and hold that position for a fraction of a second, then roll a further 90 deg and hold etc until you are back upright again. By definition, you roll 45 deg for an 8 point roll.

The key point to remember with rolling is that you will need eventually to coordinate aileron, elevator and rudder inputs. Initially, if you are performing normal rolls you can get away with just using elevator. I would say that a normal roll will be one that take around 2 seconds to perform while a slow roll takes around 5 secs to perform. Normally, you set the power before you start the roll. It is easier to perform a slow and point rolls if you push up power from your cruise mode as the increased airspeed gives you more control power which is what you need.

The type of aircraft you fly will determine how much you need to use the rudder when the aircraft starts to lose its wing generated lift and has to rely instead on lift being generated by the fuselage and engine demanded by the rudder.

When you first start rolling, a nice safe way to do this manoeuvre is to first pull up to a 45 deg climb putting on appropriate power and then roll. If you have never used rudder before, just concentrate on pushing in down elevator when the aircraft is inverted. Without rudder, you need to time the elevator input quite carefully to occur equally on either side of the roll as you pass through the inverted position. If you don’t do this the aircraft path will be altered. As you get more confident, reduce the 45 deg climb progressively until you feel comfortable rolling on the horizontal.

So why do you need input from both rudder and elevator? As soon as you roll the aircraft the direction in which the lift is being generated, right angles to the wing, will change and try and turn the aircraft. This also means that the amount of lift supporting the weight of the aircraft is reduced, so you need to increase the lift by easing in some up elevator – not much though. You also need to apply rudder in the opposite direction to the aileron to stop this turn. The rudder also pushes the fuselage to an angle to the airflow to generate lift (and more drag hence one reason for pushing up the power before you start the roll) as well as getting some help from the engine thrust which is now inclined upwards (another reason for increasing power).

So, as the aircraft rotates around its axis you will need to:

• Keep the roll rate constant
• Feed in rudder, initially in opposition to the aileron and then, once past inverted when the rudder is neutral, in the opposite direction to avoid the lift force generated by the wings from dragging the aircraft off track and to maintain the vertical lift being generated by the whole aircraft to balance its weight and to oppose the elevator trying to alter the track of the aircraft.
• Feed in elevator, initially up, then decreasing to neutral, or whatever produces zero lift from the wing, at 90 deg and then increasing to down so that when fully inverted you just have down elevator, then decreasing to neutral at 270 deg then increasing to up and then neutral as you approach level flight. This also acts against the rudder to prevent the aircraft track being altered.

You may want to read that through a few times. Also, if you type in “perfecting the roll” into the search box on this page you will be taken to an excellent article with some great diagrams. As a picture is worth a thousand words, it’s well worth taking a look.

For the slow roll, you really do need to use rudder and elevator otherwise the aircraft nose will drop or you’ll have to begin the roll by pitching the nose up. That’s OK for a B certificate test but doesn’t cut the mustard if you want to fly a truly axial roll. It also loses you points in competition!

Point rolls demand rudder and elevator. The 4 point roll is easier to perform as you every time you stop you only need either rudder or elevator. The 8 point roll requires both on 4 occasions and since you have to hold the point position for a short time, accuracy is the name of the game otherwise the manoeuvre looks horrid!

[Ultymate]

Posted by Shahid Banglawala on 09/12/2013 11:37:36:

Ey up Bryan! I'm well mate thanks. Ducking and diving trying to stay busy. How about yourself?

I'm fine thanks Shahid, still miss 3DRC days but that's history now

["L"Plate]

Peter,

I have found that when I am doing consecutive rolls (like those needed for the "B" test) that a slight further increase in power after the first 1/2 roll helps to maintain the roll rate and other control functions. I put this down to the increased drag slowing the model after starting the roll and as the airspeed decreases so to the control sensitivity. I have found this even with a high power start. I agree with you description and it works very well for me for one roll but it is always when I am stringing together more than one I find I need that little extra, but not so with point rolls, I assume because the roll rate is hesitated and therefore masks the decreased roll rate.