Ever wanted to get into or improve your aerobatics?

[David Hardaker]

Hi Peter

I have an opposite view about doing a negative flick in the avalanche. Positive is easier to do as you already have some up applied. All that's needed is an extra bit of up and rudder, and round she goes. Slightly reduce the elevator once the flick has started to avoid losing too much speed. Stopping a flick is all about timing.

I find it odd that a pitch up or down prior to any flick is a pre-requisite, as you mention earlier.

After all is said, a flick-roll happens when ONE wing is stalled and the other isn't. So why bother to stall them both in the first place !??!

David

[Peter Jenkins]

Hi Martyn

David H has a good suggestion above, namely to back off the elevator a bit (not enough to slow things down) once the flick has started making it easier to stop at the right time. As for a spin, you need to "learn" how much time your particular model will need to stop. That's why I always start by holding the controls in for the flick until I'm passing the 1 flick point and then pushing them back to centre. Look at how far past the desired exit point the flick stops (or spin for that matter) and begin your recovery by the same amount before the exit point. That's a first approximation, but, as you say, practice is the only way to become consistent so that you build up the feel for these manoeuvres. A lot of the time in aerobatics it is just getting the timing of control inputs right and in the right direction! I just wish I could be a bit more consistent!

Your second point about a good flick having impercepticle change in rotational velocity is, I fear, wide of the mark. A flick roll is quite a violent manoeuvre. The rotational force is similar if not higher to that in a spin and moments of inertia come into the equation. A short wing aircraft will have a lower moment of inertia than a longer span aircraft. It will also have better aerodynamic damping to overcome the inertia forces once you centralise controls. A Wot 4 flicks so fast I find it difficult to do a single flick accurately. Conversely my proper aerobat stops almost immediately I centralise controls.

Perhaps those with classic F3A airframes could post on how they feel their aircraft react to entry and exit of flick manoeuvres.

Peter

[Peter Jenkins]

Hi David

Oooo just noticed we've passed 10,000 views! I am amazed!

How would you achieve the necessary stalling AoA without first pitching the aircraft, and hence the wing, to a higher AoA than the flight immediately preceding the flick entry? You do need to stall one wing as you say. Application of rudder provides the necessary input to unstall one wing but the AoA pulled has to be very accurately flown. There is a higher probablility of success if you get the sudden pitch to stall both wings and then application of rudder from this repeatable position unstalls the outside wing.

The other reason I would give for doing a negative snap is that while at least half your lift has gone gravity has not. Pitching the nose down imparts a velocity in the wrong direction while the obverse is true. It is certainly what I've found. Especially after watching a fellow competitor and speaking to him. I then tried a negative snap and the shape of the loop at the top while flicking was much better. I accept that it may well be down to my lack of ability but that's what I found so I thought I'd share it on this thread.

Peter

[Ultymate]

I agree that the positive snap is harder on the avalanche Peter you have to be ready with a small amount of down as the snap comes to an end to maintain the shape of the loop and I always try to hold a little more throttle than for a normal inside loop. Most of the schedules I recall flying in IMAC actually specified positive snap on the avalanche.

Edited By Ultymate on 08/02/2014 11:57:58

[Peter Jenkins]

Daviid - I forgot the other reason for given a positive, or negative, pitch before the flick roll. In F3A judging rules, you score a zero if there is no visible break in the line.

Ultymate, I found that as well which was why, as the schedule gave a negative snap as an option, I started using the negative snap.

Peter

[Peter Jenkins]

Canalisers

Some of you may know about canalisers and some may not. Before I explain, consider what happens to the airflow aft of the canopy. As the fuselage cross section decreases from its maximum thickness the speed of the airflow also decreases and the air pressure increases – a similar situation to passing the thickest part of the wing. If you can cast your mind back to my description of Reynolds number, you will know that with a laminar flow situation, the boundary layer will detach in a situation where it is flowing into an area of increasing pressure. So, the flow separates and a the fin and rudder now see a turbulent separated airflow making both less effective.

Now, introduce a canaliser. What is a canaliser? Well it started as a small wing mounted above the fuselage just behind the canopy. The job of the canaliser is to increase the energy in the airflow behind so it needs to be set at a small positive incidence. The effect of this is to discourage the separation of the airflowing down the fuselage and so the fin and rudder now receive a nice clean flow of air. This makes both much more effective in operation – in other words they become more powerful.

Today, some canalisers are a bit like a small wing and that is also why the ultimate canaliser – a biplane – is now beginning to become quite popular.

Christophe Paysant le Roux with his Axiome Plus

If you want to try a canaliser, try and make one that can have its incidence adjusted . Start with an incidence around ¾ degree more than that of the wing. Then go and fly it and see if the rudder has become more effective. Best way to see this is to fly in knife edge and compare the amount of rudder you now need. You could try increasing the canaliser incidence (if you arrange for a lead screw arrangement you can just turn the screw a half turn (making sure you know whether this increases or decreases the canaliser incidence!) and see if it makes things better or worse.

So, that’s what a canaliser is, what it does and why it does it.

On the other hand, Brian Hebert, the designer to whom I have referred before, takes the view that a canaliser is another lifting surface that you need to spend time trimming and his triangulation trimming technique is, he claims superior to the use of a canaliser. Christophe Paysant le Roux, the current F3A world champion has a huge canaliser on his Axiome Plus with which he won. You pays your money ………

[Peter Jenkins]

Why fly in Competition?

There are a lot of pilots who start out by saying they are not interested in taking part in competition. That’s OK because that’s their decision. However, it can put off those who might be considering taking this step. So, the question is, why bother with taking part in a competition?

There are, of course, a number of answers. One which might not be obvious at first is that you learn so much more when you fly in a competition. You have other pilots flying the same schedule as you so you can watch how they cope with the same manoeuvres. Competitors, in my experience, are only too happy to discuss the finer points of their flying with another competitor and to provide pointers on how to improve your performance. It is rare that you will get such input when flying at your Club. If you are lucky, there might be another pilot who wants to fly aerobatics or who can help you to improve. Add to this the opportunity to speak to experienced judges to give you pointers on how you can improve and competition is absolutely the best place to move your flying standard forwards in huge steps.

It can be nerve wracking if you let it get to you. My best advice is to try and think of a competition flight as being another training flight back at base. Yes, it’s easy to say but difficult to achieve that level of mental calm! However, that’s part of the fun. You can swap stories with your fellow competitors as friendships are quickly formed with other pilots whom you may only have met that day.

The other reason for flying competitions which isn’t obvious is that it gives you the opportunity to fly at a strange patch. All your usual sky markers have vanished and while you almost always have the three markers giving your straight forward and 60 deg either side you will find it odd to deal with this situation. This helps to build your confidence that you can fly safely from strange fields – another useful skill to be learned.

Many pilots put off entering a competition till they are good enough. Well, if you read my first point, you will never get to be “good” enough by practising on your own. You might as well go for broke and learn at a competition. If you start in the lowest class, Clubman in the GBR/CAA, no one is expecting you to be an ace so there is no pressure on you – just what you place on yourself!

The key thing is to have a well trimmed aircraft and to have practiced the schedule so you know it by heart. In competition, you can use a caller. That is someone who tells you what is the next manoeuvre you have to fly. All the best pilots have a regular caller who can help enormously by giving advice on key points. The basics are calling “Centre” as the aircraft passes through the centreline and warning you that you are approaching the end of the box – ideally you will have practiced with your caller and worked out what they are going to say and when. There is also the case of having an experienced pilot to act as your caller. They can help by telling you that the aircraft is coming in or going out from the required line. They can give you a count-down to centre, particularly when you are going for the centre spin manoeuvre. If you are not lucky enough either to be able to practice with a caller, or to have a regular caller, then it can be a bit difficult to get used to flying with a caller. The only advice I can offer here is to discuss with your caller exactly what you want them to do and what you don’t want them to do! You must make sure that you have a calling card, containing all the manoeuvres you need to fly printed in order on it. It is easy for an inexperienced caller to forget where they are and either to call the same manoeuvre twice or to miss one out. Either way, you are in the poo but it’s your fault for not pointing these problems out and discussing how you and your caller are going to avoid getting into this hole in the first place.

So, there it is, the main reason for flying in Competition is to improve your flying. Winning is a really nice by product of that.

[john melia 1]

when climbing at 45º and rolling inverted to check cg , where is the throttle set at , once inverted is the throttle shut off , half , or full

["L"Plate]

When I do it, I use a throttle setting that allows me to maintain a contestant speed around the same as my normal level flight cruising speed. I find this throttle setting by flying a few 45deg climbs upright and when I am happy that I know the throttle position, I fly along the line pull to 45deg and hold it so the speed stabilises then roll inverted (maintaining the same throttle setting) and see what happens.

I hope this is in line with the method Peter recommends.

[Peter Jenkins]

Hello John. Apologies for not making that clear. The idea is to establish a 45 deg climb which will be at the same speed as your entry speed so you will need to advance the throttle sufficiently to maintain that speed. It depends on how much excess power you have available as to how much power you need to fly at a comfortable manouevering speed straight and level (S/L) and then how much remains to cope with vertical manoeuvres. Relatively few sports aerobats, if fitted with the recommended 40-46 engines will have the power to maintain a vertical climb at your S/L speed. Fitting a bigger engine or a tuned pipe usually solves this problem. At that point it becomes much easier to fly nice round large vertical manoeuvres.

Back to your second point, once you have established a 45 deg climb at the same speed as your S/L entry speed, you leave the throttle alone and roll to the inverted and continue with the same throttle setting. That way, you are not introducing 2 changes to the aircraft state - inverted flight and power cut - so any change to the flight path will be due to just the inverted state.

You can also do the same test from S/L but make sure you have a good bit of height in hand lest you have a very forward CG at which point the aircraft will have a pronounced downwards flight path when you are inverted. The 45 deg climb gives you a safety margin to any downward pitching by your aircraft - that's all.

Hope that helps. If I've missed your point please post again.

Ah - crossed posts with "L" plate!

Edited By Peter Jenkins on 13/02/2014 09:16:13

[john melia 1]

 

thanks peter the aircraft in question is my 30cc sbach , so there will definately be sufficient power I woud hope . My second question is , in the manual for the sbach it states the cg is 33% of the wing chord , but the wing is obviously tapered , so how does that work ?

Edited By john melia 1 on 13/02/2014 10:46:02

[Peter Jenkins]

Hi John, quite often with tapered wings the CG is quoted as either percentage of chord or so many mm back from the leading edge at the wing root. In your case, it appears that the instructions just say 33% of chord. For a straight tapered wing this could be the mean chord so the chord at mid span. The other way to do it is to measure root and tip chord, add them together and divide by two. Measure back from the leading edge at this point by 33% and then project that to the root rib so you know where to stick your fingers to check the CG.

Be careful which of these two is really meant by the instructions.

If the wings taper just at the rear, so LE at 90 deg to the fuselage, if there is any doubt about what the instructions mean, going for the 33% at mean chord will have the CG further forward compared with 33% of root chord. That's safe.

With a tapered just at the leading edge then 33% of mean chord will be behind 33% of root chord - i.e a more rearward CG than intended - not conducive to a worry free first flight!

With an equal taper to leading and trailing edges the CG position will be slightly further aft along the fuselage datum when comparing the tip measurement with the root measurement.

I would opt for a forward CG for first flight to avoid the first fright syndrome! After that, adjust the CG to suit your flying style. I used to try and get CG absolutely right for first flight. Now I just err on the side of safety and fly the aircraft then make adjustments to the CG. That way, I often don't know precisely where the CG is and, in truth, it doesn't matter unless someone asks you. Then you'll have to measure it!

[john melia 1]

This is the wing ....

[Peter Jenkins]

John - looks like the angle of taper will give pretty much the same result for the 33% CG position thus allowing you to measure it at any place spanwise. That being the case, you might as well measure it at the root. I'd go for 30% for your first flight though. Better to be safe than sorry unless you know someone who has flown one successfully with the CG at 33% or even further back.

[john melia 1]

Thanks peter sorry for being so dumb here , do I measure the chord at the root and tip devide by two and measure the cg anywhere along the span . How do I get 30% as opposed to 33% . All the rest of my models have had the cg in mm from the leading edge , this is the first time I've done this

[Peter Jenkins]

Hi John, not a problem. Looking at your wing planform I would just go for the wing root measurement. To get to 30% of root chord, measure the root chord and multiply that figure by 0.3 (or 30/100) that will be 30%. i.e.

root chord = 300 mm then 30% = 300 x 0.3 = 90 mm - measure 90 mm back from the LE for CG position
(33% = 300 x 0.33 = 99 mm)

Now measure back from the leading edge at the root by that amount and that is where your CG should be. If the CG if behind that point, try moving the battery pack forwards or add weight as far forwards as you can get it.

Once you've had your first flight by doing either the 45 deg climb or just rolling inverted you'll be able to tell if the CG is too far forward. If the aircraft pitches quickly downwards immediately after rolling inverted then the CG could be moved back. If the CG is too far forward you may not be able to get the aircraft to spin or remain in a spin but you might also find that you run out of up elevator when landing. So, you then need to move the CG aft in small increments and then fly it again. Continue like this making small adjustments and flying the aircraft until the aircraft behaves as you would like it to.

You will know when you have gone too far as after rolling inverted the aircraft will just continue on its flight path without deviating up or down. You will now have reached neutral stability. If it pitches upwards slowly you are now entering the unstable area and you should land and move the CG forwards. Different rules seem to apply if you wish to fly 3D but what I am talking about is principally aimed at precision aerobatics or F3A aerobatics.

[john melia 1]

Many thanks peter , brain in gear now

[Ultymate]

Peter I like and totally agree with your post about nothing improving one's flying like competing. I think the tendency is for most pilots to reach a certain level of competency at their club field and then settle into their comfort level of flying in both what "schedules" they fly and in what wind conditions they will fly. Whereas once competing you get exercised outside your comfort zones

[Peter Jenkins]

Ultymate - you are so right! In my first competition flying my trusty Wot4/Irvine 53 combo, I had to fly in a 20 knot 90 degree crosswind. I'd never done this before so it needed a bit of getting the mind straight before take off. We had to take off cross wind but we were allowed to land into wind as indeed were the big 2 mtr boys. Now, I am prepared to fly in far worse weather than I used to think was acceptable before I started flying competition. That means you are able to fly on more days when others stay on the ground. You need to do this as, for some reason, the weather during most competitions is almost always horrible and if you don't practice in horrible weather you won't do well in a competition. Once you get over the fear factor, your flying skills improve out of all recognition.

[graeme jones]

Peter - as promised I've now re-read all of this from the start. It's taken longer than I thought as it keeps gaining on me! I now have some complaints, questions and observations.

First the (very tongue-in-cheek) complaints. This thread is at the wrong time of year! By the time my field is no longer under water I'll have to come back and read it all again. It's also, for me, at the wrong time of life. Like you I'm over 60. My reaction times never were good but now I simply can't move the sticks quickly enough to, for example, compensate for cross wind in a loop. How do you do it? And reading all this stuff has had a serious effect on this winter's model building program. Between this and a couple of other threads I've been following I could have built a complete model in the time taken.

Questions -

1. You wrote on 02/12/13 about mixing up elevator with rudder to achieve flat turns, then on 30/01/14 about mixing elevator with rudder for Knife Edge. Since this will be down elevator, to reduce the AOA of the wing to zero, there seems to be a contradiction. I suppose you could use a 3 position switch to control which mix is in use, but it seems overly complicated. What am I missing?

2. Since we don't want rudder to produce a roll, why do nearly all modern aerobatic model have a swept wing? This gives a (slight) dihedral effect.

3. A couple of people have mentioned rudder rake angle (back or forward) giving an up or down elevator effect. I thought this was a modelling myth, leftover from single channel days when some models were built with pronounced rudder sweepback "to keep the nose up in turns". It didn't work, because all it actually does is make the rudder less efficient (think what would happen with 90 degrees of sweep). Do the small amounts used on some aerobatic models actually have any effect?

4. Why do some models perform better stall-turns than others? In the late 1970's I had a Barnstormer 72. This was a parasol wing, 3 channel model with no ailerons and a fairly small rudder. It would do better stall turns than most 4 channel aerobatic models of that era, simply pivoting about it's centre with just a nudge of rudder. Some modern models need a blip of throttle and a lot of rudder to even come close.

5. You wrote recently about "canalizers". Is the 3/4 degree of incidence more than the wing correct? I've just checked the only two models I have with them, a Kyosho Osmose 70 and a Hobbyking Rainbow. They are both set parallel to the tail, giving around 3/4 degree LESS than the wing. Is that why they don't appear to do much? I've flown the Rainbow with and without and can't detect any difference.

6. I like many others I am put off competing by the cost, not of the models but of travelling. Why are all comps. in the South East or North of England? Is it just a chicken and egg thing? Are there no comps in Wales because nobody is interested, or is nobody interested because there are no comps? On a connected point, if larger models are easier to fly, why is F3A only limited to 2M X 2M? Smaller models would be harder to fly and cheaper to build.

And an observation -

No mention has been made of the model's colour scheme. I find this can make a big difference to the way I "see" the model in the air. My Osmose for example has a very "fussy" scheme with 10 different colours. At any distance it's good camouflage. I found from watching other models that a simpler scheme is better, at least for me. Best combination I've found is yellow/black chequerboard underside, yellow with large patches of black on top.

Here's hoping we get some flying weather this year

Graeme

[chris Bond - Bondaero]

MMM bit late to the party here not read everything but briefly Graeme

Not sure the canaliser incidence is that critical

Ah the Barnstormer 72 DB? I wonder if that High wing smoothed the flow over the wing like a canaliser and the old engine was ticking over fast making the rudder effective

Wales Secure the site for a day for an NPOD and we will be there promise

Why do some f3a planes have upthrust and the Japanese don't like yellow planes

You don't have to know all the answers to fly f3a

Shocked to find that Peter is over 60

[Peter Jenkins]

Graeme

Well, where do I start!

First, the issue of not having quick enough reactions can be countered, for the most part, by thinking ahead to visualise the control movements that are required and practising and practising and practising and…. You get the idea. Once you are ahead of your aeroplane you have time to think! As someone once said, they’ve noticed how naturally gifted pilots practise so hard! The thing with Aerobatics is that you have to address each challenge one bit at a time and then put the whole lot together one bit at a time until eventually you find that you can after all fly that manoeuvre that used to defeat you. I don’t think you ever stop learning in aerobatics by the way! Each new schedule presents new things you have to learn – but that’s the charm.

As for the right time, well my B Certificate chase started in earnest in November so that by the time I’d succeeded, it was March. That meant I was in a good position to enter competitions with a fair chance of being able to fly consistently – that doesn’t mean to say that I was good – just that I could maintain a consistent standard! Of course, the winter of 2010/2011 was a paradise in comparison to the present.

Answers.

1. Well, all things end up being a compromise since for the most part we are dealing with non-linear effects – that is, you cannot predict accurately how a particular control will affect the aircraft in different attitudes. You need to fly a number of flights to check the effect of each change of trim so that you are seeing consistent behaviour. Each change in trim will usually have an effect in some other flight characteristic. If you have a situation where one adjustment causes a problem with another flight regime, pick a mid-way position and remember that you will have to apply some small correction. That’s why picking a specialist aerobatic design will give you a much less bother to set up than a standard club sportster – more on this in later posts.
2. Tapered wings have some structural advantages. The rudder and its geometry with respect to the aircraft centreline – looking from the side – has a much bigger effect on rudder induced roll. Most aerobatic designs have an equal amount of rudder area above and below the aircraft’s centreline of roll. Also, that’s why some aerobatic airframes have anhedral on the wings or the tailplane. Again though, it’s not that simple since getting the full aerodynamic package do only what you want it to can take quite a few iterations.
3. Rudder can only have an effect in its yawing sense. Unless you have a V tail, rudder has no elevator effect – by that I mean the rudder produces yaw and the elevator pitch. Secondary effect of rudder is to cause the aircraft to roll, usually but not always, in the direction of rudder application. Once the aircraft starts to roll, the vertical lift vector reduces and so the nose falls. Pushing opposite rudder will, by yawing the nose above the horizon, appear to be acting as elevator but then secondary effect of rudder rolls the aircraft level. So, I don’t agree with the fact that raking the rudder hinge line has an “elevator” effect.
4. Why do some models fly better than others? This is a complicated question to which there is no easy answer since there are so many factors than can act for and against. Suffice to say that you will always need to carry some power into a stall turn otherwise there is a chance of the model flopping forwards, or backwards, or tail sliding. Propeller effects, e.g. gyroscopic, prop wash also have an impact.
5. You need to inject energy into the airflow to get it to remain attached to the fuselage as the airflow starts to slow down aft of the thickest part of the fuselage. The canaliser’s incidence should be relative to the airflow which will be influenced by the wing. So, you could have a canaliser at the same physical AoA of the wing but the upwash caused by the wing will present the airflow at a positive AoA to the canaliser. Ideally, you want an easily adjustable incidence for the canaliser so that you can find the optimum AoA for the canaliser. A canaliser at zero deg AoA to the local airstream will have no effect at all.
6. As for colour scheme, that’s always dependant on a number of factors. Some colour schemes are great on grey days but when you have the aircraft at the top of the box in bright sunshine against a deep blue sky (I do have these dreams sometimes!) you can find it difficult to see particularly whether you have wings level or not. At that point, you have to resort to sticking on bits of contrasting colour trim or spraying a canopy silver or black (works sometimes). However, almost any strongly contrasting colour schemes between top and bottom is good. Complex finishes which look great close up are impossible to see at normal flying distances – for example a chequer board pattern just appears as a slightly fainter version of the dominant colour. A wing covered in a quartered pattern (black and white or red and yellow) will be seen far better than a chequer board. But whatever works for you.

Gasp!

[Peter Jenkins]

Oops - left out the answer to Question 6. There are no competitions held in Suffolk, Norfolk or Essex either at the moment. So, that's why I run New Pilot Open Days, which Chris has very kindly supported, to get more people exposed to flying precision aerobatics. That way, I'm building up to having a large enough group of pilots in this corner of the realm who might then support a competition being run in one of these 3 counties.

[SR 71]

Hi Peter do you know of anything happening in Cyprus in the F3A ?????

["L"Plate]

Just thought I would throw this in for those how may think they are too old.

I remember once seeing a TV program with a: Fighter pilot, F1 Driver, Teenager, a retired chap in his 70’s and a few others. They checked out reaction times and found only a small difference (measured in milliseconds). The results after several practical tests showed that the retired gent was middle of the group in every test. The Fighter Pilot couldn’t handle the F1 car sim any better than the older chap neither could the F1 driver couldn’t fly the aircraft sim any better. The teenager did well in some tests and badly in others. The conclusion from the scientist on the program, was that it is less about reactions and more about conditioning, allowing the person to anticipate what was going to come up next, which they said comes from (guess what) “PRACTICE”. Older people may take longer to learn but they also than to retain regularly used practical skills better, so age is not a barrier, in fact if you are retired you have more time to practice to you should get even better.