Ever wanted to get into or improve your aerobatics?

["L"Plate]

Sounds spot on Martin, two and a half turns with the wings pointing straight up and down was it for the Zlin as well, if you tried for more it fell into a flat spin and as you started to pink out at that you wouldn't want to do more. I only had a few flight with the Zlin but tumbles of any type was the Zlin's thing, big controls and light control loads in its time it was a winner, no wonder Chris Foss based his Acrowat on it.

[Peter Jenkins]

I think that mass and inertia have a lot to do with many of these stalled manoeuvres as indeed does Reynolds number. Indeed, if you saw a Pitts doing a flick roll, because it's such a small, compact machine, its rate of rotation is very fast compared to a monoplane that has to have much longer wings to provide the equivalent wing loading. I believe that it's very difficult to do a single snap with a full size Pitts and easier to do two - perhaps someone might know if that is indeed the case.

Gyroscopic action from the prop also comes into play with full size much more than for model size. Although our model props are rotating much faster than the full size I suspect that the gyroscopic effect is much less in comparison to aerodynamic damping forces than for the full size.

["L"Plate]

I was also told this by a Rothmans pilot (Philip Meeson I think, I was a fan of the team back then) that the single seat Pitts was hard to stop after just one flick but the two seater was easier as was the Eagle, he put it down to (again) the prop / power plant combination.

[Steve Colman]

Posted by Peter Jenkins on 03/01/2014 13:36:43:

Well Happy New Year to all the viewers of this Thread!

I have previously described how to perform a loop, a square loop and a roll.

Is there interest in learning, what is and how to perform a host of other aerobatic manoeuvres such as

• bunt,
• square loop on side,
• Immelman (half loop and half roll)
• Split S (half roll and half loop),
• Cuban 8,
• reverse Cuban 8,
• stall turn,
• Cobra roll,
• Fighter turn,
• Humpty Bump,
• inverted spin,
• change spin direction,
• knife edge,
• positive snap,
• negative snap,
• avalanche (loop, or bunt, with snap at top)

Any others? Apart, that is from integrated manoeuvres, such as rolling circles etc – more on those later on if you want it.

Yes please Peter, Lets keep this informative thread going.

I'm really enjoying reading it, I'm learning many new things (some of which I didn't even know that I didn't know) and look forward to putting things into practice as the new year unfolds.

Steve.

[ben goodfellow 1]

looking on you tube is basically a horizontal knife edge spin or close to it any way.... fly low

[Andy Green]

...Roll Tape.

Sorry couldn't resist. A point for anyone who know the reference,

Andy

 

PS would have worked better if my post hadn't gone to a new page

Edited By Andy Green on 03/01/2014 22:35:02

["L"Plate]

I don't know about others on the forum but the Outside loop (bunt) is probably one of the scary manoeuvers for a pilot now to aerobatics and can be hard fo rpilots to get round, often finishing at a much lower hight then they started.

I normally teach pilots by doing an outside loop from inverted and then to move on from there by flying a half inside (normal) loop and roll out at the top (known as an Immelman), so they at a safe hight.

So Peter please add some meat to this and let me know if you start pilots the same way.

[Peter Jenkins]

The Bunt – or outside loop

Well, here goes! Before you start flying this, I’m assuming that you have a properly trimmed aircraft as otherwise you will be fighting to fly the aircraft when what you need to focus on is flying the manoeuvre.

As Algy has already said, the bunt, or outside loop, is something that worries pilots who are flying it for the first time. The good thing is that the longer you fly manoeuvres such as this the better your flying becomes and the less you are fazed by seeing your aircraft in some strange positions. At this point, you are well on your way to becoming an accomplished pilot and not just an aerobatic pilot.

There are, as Algy has pointed out, two ways of approaching your first bunt. The first one is to climb to a decent height and then push the stick forward to fly the bunt from the top. The second way is to fly slightly higher than you would for a loop, roll inverted, hold steady for a moment and then push forward with the stick forward to fly the bunt from the bottom.

Throttle control, as in the loop, is also very important as is keeping the wings level and keeping the direction straight. Don’t worry about being too pernickety for your first attempts – just focus on getting the manoeuvre done. Accept that you may go off the desired line so position the aircraft a bit further out from you for your first attempt. Avoid ending up with the aircraft right over the top of you!

So, what you are aiming towards is the following sequence of events. You don't need to inject all the control inputs from the word go, but you will need them all to fly a perfectly shaped bunt.

Climb to your selected height (about 1.5 times as high as your model goes in a loop), position to fly downwind parallel to your runway with normal cruise power and when you get to the centre of the field (ideally you need a marker like a tree that you can see out of the corner of your eye) begin by smoothly pushing the elevator stick forward while at the same time smoothly retarding the throttle to idle. This is not a snap closure of the throttle at the start of the manoeuvre, but a progressive closure of the throttle from, using clock notation, 12 o’clock to 2 o’clock. Remember that gravity is helping you in the first quarter of the loop but that as you go past the vertical, gravity will work against you as you push round the bunt. Now, when you reach the 4 o’clock position begin to open the throttle smoothly aiming to have full power (if you have a very powerful model you may not need full power) at the bottom of the bunt.

As you close the throttle, remember that the spiralling slipstream that induces yaw has just been turned off so the aircraft will yaw to the right. A small application of left rudder (just a gentle touch) will help to keep your aircraft on track. Try this without using the rudder first to check by how much the aircraft yaws.

As the aircraft comes level, check to see if your wings are level and, if not, level them remembering that your ailerons work in the same way as when the aircraft is upright. So push the aileron stick towards the lower wing to get the wings level. If you don’t do this, the aircraft will lose direction and the bunt will screw one way or the other.

As the aircraft speed has built up in the first half of the bunt, the controls will be more responsive – that is unless you have managed to truly keep the speed the same all the way round the first half of the bunt. What that means is that you need to ease off on the down elevator as your aircraft starts to climb back up the second half of the bunt as otherwise you get a tightened second half of the bunt and you finish the manoeuvre lower than you started.

Remember also that now you have lots of power on, the spiralling slipstream is now going at full blast and will induce a yaw to the left, so, be prepared for a small application of right rudder (remember, just a touch) to keep the heading straight.

Once you have the aircraft past the 10 o’clock position, start smoothly bringing the throttle back to cruise power, and releasing the breath of left rudder you have been holding in, to coincide with reaching the top of the bunt. Use the elevator to maintain the shape of the manoeuvre all the way from the bottom to the top of the bunt. You are aiming to reach the same height as that at which you started the bunt at which point you release the down elevator and fly straight ahead.

As you can see, there’s quite a lot to think about to do a really nice bunt. I’ve also not covered how to allow for the wind and the almost inevitable cross wind and what that will do to the shape of your bunt. I’ll cover that in the next post.

Please feel free to comment or seek clarification on the above.

[Martin McIntosh]

Sorry to disagree here but if your model yaws one way or the other depending on the throttle setting then you should look again at the amount of right thrust. I have done just the odd one or two bunts over the years and never experienced this phenomenon! Correctly set up models do not yaw when throttled back during a vertical climb which can effectively be part of a loop.

Also, I know that a lot has been written about spiralling prop. wash causing yaw but I cannot go along with that. It is the torque effect coupled with gyroscopic reaction which causes a roll and a bit of yaw to the left. Push a gyro away from you and it will respond at 90deg. to the force which is why right thrust works for us.

Try a small model with a very large prop. and it will roll violently left compared to the small amount experienced with a normal prop. size, without a large thrust line offset, even though the spiralling airflow must be similar.

Well, you did say feel free to comment Peter!

Anyway, keep up the good work since most of this tutorial will be of benefit to a lot of people.

["L"Plate]

Please could you help me out here.

I can see that spiral airflow can be countered by thrust line to a degree. (Agrees with Martin)

With a clockwise rotation see from the cockpit a pitch nose up would gyroscope will swing model to left so if pitched nose down would swing nose right. (Would give Peters 1st 1/4 input)

Now for another bit, the torque reaction would roll the aircraft Port wing low (to me thrust line can't get rid of a rotary effect) so with the change of power the torque effects will still need to be balanced. Surely this would need aileron? (As Peter says keeping the wings level)

I have to say I have never looked at the controls I use for a bunt in detail like this, I just try to fly it and correct what ever pigs ear appears. It would be interesting to see a video of the TX as someone flies a Bunt (in still air) and see what they do, I feel we would see all controls needed at some point, unless they have an expensive contra-rotating prop system.

[David Hardaker]

Bear

Gyroscopic precession ... (clockwise prop rotation as seen from cockpit)

The effect is seen 90 degrees after the application. So with a clockwise rotation prop, a pitch-up applied at 6 o'clock will appear at 9 o'clock. So pitch up = yaw right.

This is one of the forces acting on a tailwheel aircraft when the tail is raised prior to takeoff. (others are torque and P factor)

David

["L"Plate]

Hi Dave,

Yes you are right so would be the opposite, so would make the aircraft yaw left as we pitch down for a bunt.

Now I do remember needing right boot on entry to an outside loop and right aileron on the up line with the Zlin and it had a clockwise rotation.

I can't say that at my model flying skill I have noticed a yaw effect on a model when doing big bunts or loops (or even small ones probably because they are over too fast to spot the error), mind you I do end up having to correct for the wind that never seams to be down the strip and all the other errors I put in. I am sure that most of the line correction I need is to do with, not being level to start with or inadvertently putting in roll or yaw as well (I have increased my stick spring tension to help with that).

[Steve Colman]

I can foresee a very long learning/training curve ahead of me.

I can do most of the basic aerobatic moves; not particularly stylishly by any means but, I do my best. However, when I read of the minute corrections necessary to execute a manouvre precisely I realize that I'm light years away from becoming even semi competent.

Today, I decided to try some four point rolls for the first time. It's one thing to visualise the various stick inputs beforehand, but out in the real world I found my aging mind going blank at times. Never have four point rolls looked so comical as my attempts today!

Steve.

[David Hardaker]

Bear

I agree with your last sentence... I know from teaching aerobatics that what some pilots perceive as straight and level has many variations !

I watched a comp a few years ago and saw some turn-round manoeuvres that were started with a vertical upline that wasn't, and then "rescued" with not-so-sneaky rudder inputs. Not good to look at !!

David

[Peter Jenkins]

Martin

Thanks for your correction. I was trying to take a short cut, and, as we all know, they can be self defeating! Gyroscopic forces, slipstream and torque effect. As you say, fitting different size propellors can affect the gyroscopic effect as can fitting light wood or heavy props. Torque effect is also damped by aerodynamic damping which is provided by the wing whereas spiralling slipstream has very little damping. Anyway, let's not get too wound up about which of these three forces is predominant and just accept that if you have not got the right amount of sidethrust on your engine you will get some yawing as you apply and reduce power - so best to trim the aircraft out with the correct amount of side and down thrust and, if you are left with some residual effect, either apply correction manually or mix in some compensating control by slaving the rudder to the throttle.

I would observe, however, that as these three forces are non linear it will be very difficult to get an aircraft trimmed to go in a straight vertical climb forever!

The basic aircraft design also has a major effect on how each of these three forces affects the flight path. For example, one would not expect a Wot 4 to be as well behaved as a proper F3A design.

Peter

["L"Plate]

Hi Steve,

1st off well done on doing your 4 point roll, it will get easier.

Yes it is hard to get the figures perfect, but it is less about not making errors and more about learning how to make less (in competition it isnot a perfect score that wins but the lest wrong).

Before you did the 4 point roll had you flown you model in Knife Edge? I always fly a new model through inverted and knife edge both sides before doing a point roll or slow roll, just to get the idea of how much rudder to use. As long as you remember rudder opposite to aileron in 1st 1/4 and the same as aileron in the 3/4, down elevator at the 1/2 way point you are doing well, oh and just turn it into a twinkle roll to upright if it goes wrong. Well that's my way. With a model that is trimmed (or has correctly set up mix) you will not have any (or very much) roll couple with rudder input. The more pure the model is with each control the easier it is to fly.

[Peter Jenkins]

Dealing with the Wind and Cross Wind

Now, the one thing we can be sure of is that there will be a wind blowing when we want to fly and generally a cross wind component as well. I discussed this in my description of the loop.

The key thing to remember is that as you fly downwind to perform your bunt, you will have varying ground speed as you transition from flying in the wind direction to flying against the wind direction and back again. For an observer standing next to you (and you for that matter) you will not see a nice round bunt unless, as described earlier, you fly what would be a really funny flight path in still wind. Put the wind back in the equation and that funny looking figure becomes a nice round bunt.

Dealing with the wind parallel to your flight path in a bunt is similar to the technique in a loop. You need to perform all the bits where the aircraft is going downwind “fast” and all the bits going into wind “slow”. At the beginning of the bunt, by “fast” I mean that you need to apply down elevator slightly faster than you would do in a flat calm until the aircraft is at the 3 o’clock position (flying from left to right) but pointing a bit more into wind than truly vertical as the wind will stretch out your flight path downwind. Then you need to ease off the down elevator as the aircraft needs time to track back up wind – don’t misinterpret this and allow the aircraft to get too low! You then need to reduce further the amount of down (controls more effective) until the aircraft is at 9 o’clock but with it leaning into wind before tightening up the bunt by pushing a little harder as the aircraft passes 9 o’clock as the wind will again push you downwind.

Remember, it is the shape made by the aircraft’s CG which determines how good you bunt is not the attitude of the aircraft.

Let’s say you also have a cross wind component from behind you which is tending to push the model away from you. You will have set up your flight path running in to the bunt so that the nose of the aircraft is pointing a little bit into the wind to maintain the correct ground track. As you begin the bunt, you will need to apply a small amount of left bank (not much) so that the aircraft would in still air perform a bunt coming towards you. With our cross wind pushing the aircraft away from you, the two effects, when done right, keep the aircraft track along the ground without coming in or going away from you. The amount of bank is very slight. It’s not easy but, as with everything to do with aerobatics, practice will make it easier to do.

The alternative is to use the rudder and keep the wings level throughout the bunt. In this case, it would be the application of small amounts of right rudder to keep the aircraft’s nose pointing into the crosswind direction.

You will know when you have done it right as your bunt will end at the same height and the aircraft will be the same distance away from you as you started.

Again, open to any comments or advice on how to do it better.

[Martin McIntosh]

Hi Peter, I certainly agree with your last two posts so we are now both back in synch.

Martin

[Martin McIntosh]

Steve C. Practice point rolls one point at a time. Firstly, put the model into knife edge for about two seconds ( assuming that it is near enough set up for this) then roll out. Then progress to rolling to inverted from there and again roll out. Now start inverted and roll to the opposite knife edge and maintain this for two seconds. Roll out. You should then be confident to put the parts together. Now try it rolling the other way at the start.

Another manoeuvre which will really test and teach you is the reverse point roll. This is 3/4 of a four point one way then back again in the opposite direction. Do this left to right, right to left, rolling in opposite directions as much as you can and in a few days this will become natural and you will not have to think about the rudder direction.

The same applies to eight points. Slows are much easier.

[Steve Colman]

Thanks very much for that Martin.

The model, an Acromaster, (my practice machine) is trimmed as best as I can get it for knife edge. Perhaps It's not the most suitable airframe but I know it well.

However, perhaps I might be better flying my Calmato as it tracks so much better........more lipo's needed methinks.

Makes much more sense to practice as you've suggested and I'll certainly be giving it a go next session.

Steve.

[Peter Jenkins]

Well done Steve for saying you are going to persevere and to Martin for his helpful guidance.

In addition to Steve's comment about the "long training/learning curve", it has been put to me that I am going into too much detail which could put folks off. I would be grateful for any comment on this matter before I write any further descriptions.

It was not my intention to make life difficult but just to provide as full an explanation of what needs to be done to fly a manoeuvre to a high standard. You do not need to follow all the detail but my reasoning was that if the detail were not there you would not have a bench mark to aim at.

So - what say you folks?

[Masher]

Hi Peter

I think you have it just right as it is. I must say you are now quite a long way past my ability level and I am struggling with some of this stuff. But PLEASE don't dumb it down. There is plenty of stuff about that just scratches the surface but this thread is providing so much more. I think it's also a case, as with so many other things in life, that this stuff is not easy - we need to put some effort in to understand/learn/achieve or whatever it is that we are trying to get from this thread.

Keep it up please!

[Max50]

For me , the detail is fine Peter. It is a forum for reading and asking questions if not sure.

At the moment i can't put in to practice what you've outlined, due to this weather,but i've got the thread bookmarked, so i can start from the begining again when the weather improves.

Thanks for this topic and help; Peter. I'll be still reading if not practicing.

Mal.

[Max50]

Masher got in before me.

That's what's so exciting about this hobby. You're learning and trying to improve all the time. Always something new.

[Peter Jenkins]

Well, on the basis that two readers of this thread think the detail is about right, I shall continue in the same vein.

I would just make the point that you are not going to become super aerobatic pilots by reading this thread and then going out to the field. As we all know, once you get the aircraft into the air, everything gets much more difficult! So, the best solution is to take small bite sized chunks, just as Martin has suggested for point rolls above, and build it up gradually.

It is always best if you can find a more experienced pilot to mentor you or at the very least a fellow clubmate to join you in tackling the learning curve. It is amazingly helpful for a fellow clubmate with an interest in aerobatics to act as a second pair of eyes and to describe what it looked like to them. As your experience builds up and you start thinking about stringing a set of manoeuvres together It is also helpful to find someone to call out the next manoeuvre for you. It's amazing how hard you have to concentrate when trying to fly good shapes in our typically windy flying days.

One thing I will guarantee is that if you persevere, you will find that you will feel more confident to fly in more windy conditions than you had considered acceptable before. An example is the last New Pilot Open Day I organised. The morning was sunny with a little wind. The wind strengthened and swung more across the runway by the beginning of the afternoon and the sun had long since disappeared. However, everyone continued flying according to the plan. A group of pilots told me that at their Club they would have long since packed up flying as they considered the weather unsuitable. What the NPOD taught them was that they could fly safely in far windier conditions than they expected and this opened up the number of days when they would now fly. So, just think what a boon it is to greatly increase the number of days that you will be confident to fly when before you embarked on your aerobatic "career"! Add to that, the reduction in the number of times the ground leaps up to grab your pride and joy and all the effort you will be putting in will pay off handsomely.

Right, that's the end of the commercial and I'll next post on the Stall Turn. However, as I'll be tied up for a couple of days you may not see that till Sunday.