Ever wanted to get into or improve your aerobatics?

[Martyn K]

Hi Peter

If you are coming in banked (wing down), would you lose points for not having the wings level?

I have to admit that I find cross wind landing difficult - for some reason my AcroWot seems harder to land in these conditions than my other models but I normally(!) get it down in one piece. As I go for the tracking into wind approach, the biggest risk (and what I have experienced) is that when you kick the model straight just before touchdown the model gets blown over or drops the downwind wing tip.. If you don't kick it straight there is a risk you will rip/snap the u/c off (this has happened twice to me now on the AcroWot)

I appreciate that practice is the key, but cross wind landings in blustery conditions can be a horrible experience...

Martyn

[Peter Jenkins]

Hi Martyn

Cross wind landings in blustery conditions are HORRIBLE but.... provided you persevere with the technique you will get better at it.

One very important fact that I forgot to mention. Unless you have mixed out the secondary effect of rudder, as you squeeze in rudder to align the aircraft with its direction of travel, you will have to contend with the associated roll induced by application of rudder. Generally, this is in the direction of the rudder application but can be opposite. You need to know which characteristic your particular aircraft has. Assuming that the roll induced is in the same direction as the application of rudder. So, let's say you need a squeeze of right rudder to straighten out the aircraft, apply a squeeze of left aileron to keep the wing not just level but down on the upwind side. That will prevent the situation you describe of the model being blown over or the downwind wing dropping. Apologies for forgetting to make that point above.

See how you get on with that and, as I say, if you have the space try landing with just a small amount of cross wind and then build up to a large amount while perfecting your technique.

Anyone who saw me trying to land my aircraft at the last competition where we had an 80 deg cross wind will laugh at all the advice I'm tendering here. Suffice to say that I was out of practice in cross wind landing technique and the aircraft was a fairly expensive one - that makes the anxiety stakes rise which doesn't help with rational thought and control application!

Peter

[Peter Jenkins]

Oh sorry, missed your bit about losing points with a wing down landing. The answer is no as this is the technique you need to employ in those circumstances.

[graeme jones]

Peter - still following. I'm hoping to get to the comp. at Hurley on Sunday as a spectator, to see what it's all about. Weather forecast at the moment is for heavy showers with a 16mph westerly wind. Don't know which way the strip faces but how is it likely to affect the flying? I believe there is a wind speed limit of around 20 mph for comps. Does that take into account the cross wind? I'll happily fly in a 20mph wind if it's straight down the strip but not if it was 90 degrees across (except for my 363 delta which will fly in almost any conditions).

A couple of posts ago you mentioned the 60 degree box. Do the judges and pilot have separate markers for this?

Graeme

[Peter Jenkins]

Hi Graeme - the 20- mph limit for comps says nothing about cross winds! At the last comp, Stansted, we had an 80 deg variable thro 90 to 80 deg the other way all day with 15-18 mph and gusting to probably 25. Take off and landing was interesting as was trying to keep a constant distance out! Sadly, very few comps have good weather so I take every opportunity to fly in gusty cross winds - doesn't seem to improve my flying much but does boost your confidence to handle difficult conditions. The Hurley strip is aligned roughly SE to NW and has quite a large take off/landing area.

There is only one set of markers for the aerobatic box. A couple of pages back Kevin Caton posted a picture of himself and the three marker lines. The judges sit 10 mtrs behind the pilot and use the same marker lines. That means only one judge is on the centre line but in practice this does not affect the judges view of the box at all.

Peter

[graeme jones]

Peter - thanks for that. Weather forecast for Hurley now light showers with a WNW wind at 14 mph, which isn't too bad if the strip is SE to NW.

Graeme

[Peter Jenkins]

I was going to start on a more detailed description of how to fly the Clubman schedule when something I saw earlier in the week when helping a clubmate to perfect his B Cert technique went off like a photo flash. Setting up the throttle! The proper use of the throttle is vital in precision aerobatics if you are to achieve well controlled manoeuvres.

What I saw was a throttle stick that needed to be almost at half throttle to reach fast idle leaving just half the available movement for a very non-linear action. As the Tx being used was a high end Futaba I asked why he had not put a throttle curve on it? The answer was that he didn’t know how to! Well, all I can say was that he was making life difficult for himself needlessly.

If your Tx does not have a throttle curve try setting up a mix using THRO to THRO to produce something similar – you need to have a switch to activate and deactivate this function. What you should be aiming to achieve is idle at the bottom of the stick travel, half throttle at mid-point and full throttle at the top of travel with smooth progressing all the way up ensuring that there are no dead areas where movement of the stick produces no increase or decrease of engine power – sounds so obvious and yet I rarely see this set up used by a good many club pilots. It is worth the effort to match throttle stick position to the above. You will find your aircraft becomes a bit more controllable once you have set up the throttle stick to give you as near a linear response to its movement. We all know that quite often you get to full power with the stick at ¾ open and the final ¼ travel does nothing. That’s very unhelpful.

While the above is primarily aimed at ic engines, electric motors are also worth tweaking in the same way. One particular issue is setting an idle. The way the ESC arms means that you cannot have the electric motor idling like an i/c with the stick fully aft otherwise the ESC will not arm. The answer is to use either a throttle curve or a mix to set up a second position that does give you idle with the stick fully aft. This is particularly helpful during landing when instead of having to push the stick several clicks up from closed to get a small increase in power you can just lift it by a click or two. Once I’d worked this out I found it much easier to control my electric bird on the approach since you don’t have any i/c/ noise to tell you how much power you have put on!

[Kevin Caton]

Graeme

the Hurley flight line is set up so that you will be facing East. With the current weather forecast for Sunday that means that the rain will be hitting straight on your back...

We'll all be there waiting for the sun to come out though!

Kevin

[Kevin Caton]

Update - I've just found out the Hurley comp is postponed due to poor weather forecast.

[Peter Jenkins]

These notes are intended primarily for those who have never flown the Clubman Schedule but may also be of use to some of you who have. I set out the Clubman manoeuvre descriptions and judging criteria earlier on but they can be found here starting at para 5.1.5.11. Note that the words take precedence over the calling card diagram which can be found here. It’s definitely worth reading this section. I was with a club member training for his B and he said he knew the schedule by heart. He then proceeded to do the stall turn heading into wind when, had he taken the time to read the B Certificate description, he would have found he was doing it at the wrong end of the field! So, read what has to be flown because, in competition, if you perform what is called a “wrong manoeuvre” you score zero no matter how good the manoeuvre was!

The first point to make is that your straight and level flight needs to be just that. Wandering around the sky in the general direction in which you wish to proceed does not qualify as straight and level flight in the aerobatic context. You also need to work on smooth entry and exit to all turns and manoeuvres. 80 deg banked turns make it hard to maintain a constant altitude. 45 deg banked turns with a smooth roll in and smooth roll out onto the desired heading is where we want to be. This can best be achieved by setting up progressively lower rates and flying the aircraft to see the difference it makes in the stability of the flight path.

I have a Wot4 set up with its lowest rates (I do have a 3 position rate switch) to allow full aileron stick deflection to give me a roll of the required rate for the B Certificate. I have flown the entire B schedule on those very low rates and it does work out OK. When I’ve given others a chance to fly my Wot4 on these low rates they look impressively smooth where before they were jerky and looked rushed in the way they flew. Experiment to see how the way your flying looks can be changed by reducing your lowest rates.

Before we get to the first manoeuvre, here’s what the aerobatic box looks like:

The distance out from where you are standing will vary with the size of your aircraft. For a 50 size aircraft, you should be aiming to be around 70 to 80 meters out – this is a good deal further out than you normally fly. Pace out 70 meters and try and get someone to hold your aircraft up in the pilots’ box while you look back at it. The reason for this is to give you a better view of your aircraft while you are manoeuvring it and to give you the horizontal space you need without running out of the aerobatic box. A 2 mtr aircraft will need to be flown at the 150 mtr line with a 110 size at around 110-120 mtrs. The aim is to get all the aircraft looking roughly the same size to the pilot and judges.

[Peter Jenkins]

OK – the first marked manoeuvre is the Take Off and the book says

“The model is placed on the runway, takes off, then turns 90o towards the line defined by the upwind and downwind marker. When approximately over this line the model turns 270° for a downwind trim pass. When approximately even with the downwind marker the model performs a 180° turn, reversal, or other turn-around manoeuvre of the pilot's choice.”

The acceleration along the ground needs to have the model going in a straight line with the take-off direction maintained after lift off on a steady climb out until it’s time for the first 90° turn. You continue climbing while on this crosswind leg until you reach your required altitude. You are aiming to be a bit higher than you would fly for the B Certficate i.e. around 80 to 100 feet.

The rest of the circuit needs to be planned to allow you to position your aircraft running into wind in the same direction as you took off .

If you just want to fly a square circuit that’s OK. Remember to fly out on your first cross wind leg to allow you the space when you turn off the downwind leg to be able either to perform a 180° turn or two 90° turns so that you end up with your aircraft tracking into wind around 70 mtrs out. Your downwind flight path would have been flown at a steady height – no obvious climbing or diving – and using the rudder to achieve the required ground track while keeping your wings level. I found that one of the most difficult things to master as my initial reaction to being off course was to bank and fly to the correct course. In competition aerobatics, you keep your wings level and use the rudder to slide the aircraft into the right position when you are supposed to be flying S&L!

Like trying to fly a perfect circuit, this first manoeuvre is not as simple as it sounds! However, there are up to 10 marks with a K factor (level of difficulty) of 2 which means you could earn a score of 20 with a perfect take off manoeuvre.

[Peter Jenkins]

The first true aerobatic manoeuvre in Clubman are the two loops. For maximum marks these need to be round and superimposed one on the other. This opening manoeuvre looks deceptively simple but throw in a strong headwind or a cross wind and you need to have thought through what the wind is going to do to your flight path so that you can make the necessary corrections to achieve not just one but two round loops through the same bit of sky.

I wrote about flying the loop earlier on in this thread (6^th Dec to be precise!) but to avoid you having to dodge to and fro I’ve reproduced some of what I said then in this post.

Loops look really good when they are large but not so large that they overtax your model’s capabilities – or yours for that matter. You need to have the wind effect issues uppermost in your mind as otherwise you will get twice the grief in this two loop manoeuvre!

The guiding principles when flying into a strongish wind are to stretch the into wind part of the loop by not pulling as much elevator as you would for a still air loop to begin the manoeuvre. This allows your aircraft to fly more distance into wind and with the wind blowing your track backwards by combining the two motions you get your desired loop diameter. As you pass through the first quarter of the loop, your aircraft should not be heading vertically up but rather be inclined slightly forward so that its ground speed at that point is zero.

Now, as we start the second quarter we are flying in the same direction as the wind is blowing us to our ground speed rapidly increases. So, as the aircraft starts the second quarter inclined slightly into wind, we need to remain slightly behind the attitude of the aircraft in zero wind so that in effect we are climbing more while the increased ground speed has the effect of bringing the aircraft back on its still air track. You know when you have this right as at the top of the loop, you will be on the centre line and the aircraft will be horizontal. Any other attitude and you’ve either pulled too hard or too soft on the elevator stick!

Now, as we get into the 3^rd quarter of the loop, you now need to fly inside the still air track so that the wind blows you back into position. So, you do that by pulling harder on the elevator – it’s the opposite of the second quarter. As you pass into the final quarter your aircraft should be pitched more into wind than vertical so that again your ground track speed is zero.

The final quarter requires you again to try and fly inside the still wind track so that the combined effect of that and the wind pushes your aircraft back onto the correct track remembering to ease off the pull as you are coming to the horizontal to allow the aircraft to make progress against the wind so that the loop bottoms on exactly the centre line. That’s one aspect of the loop and I’ll cover throttle control in the next post. So having completed one loop, you now need to produce its twin by doing exactly the same thing – provided you produced a good loop for your first one. In any reasonable blow, most pilots struggle to get the geometry right for the first loop and are then under pressure to perform the second loop starting from the wrong place – it all gets much harder and the adrenaline is flowing more freely as well!

[Peter Jenkins]

Just reflecting on the post above, if you consider what the flight path would look like in still air it rather resembles an egg on its side with the pointy bit facing the wind direction - sort of!

As I’ve said on a number of occasions, the throttle is a proportional control and you must use it as such in order to achieve the desired shape in the sky. So, for the first quarter of the loop into a strongish breeze you can help yourself by applying more power than you would for a still wind loop. Watch the flight path carefully as with the combination of more power and less up elevator you can end up stretching the first quarter too far upwind.

Now, as you get into the 2^nd quarter, your power needs to stay higher for longer as you want the aircraft to climb faster than in the still wind case. Be careful that you start your power reduction in good time to you don’t end up making life difficult by adding unnecessarily to your downwind ground speed by holding too much power for too long.

The third quarter power management is again a case of power reduction a bit behind the still wind case as you will be pulling harder with the elevator so your drag will be higher. Do not hold the excess power for too long though as you are being helped by gravity in this part of the loop.

Once you are into the final quarter look at the aircraft’s position and use power judiciously to drive the aircraft back to the centre point of the loop. The combination of a lot of power and going easy on the elevator pull will allow you to juggle the aircraft back to the centre to coincide with your low point. You are now well positioned for the second loop.

I’ll cover dealing with a cross wind in the next post.

[Willyuk]

Hi Peter,

a bit of advice on setting the cofg if you can. I have just put together a cheapo artf for practise purposes. To get the correct cofg it needed 294 gms of lead under the engine. 1st flight yesterday, did the 45 degree inverted test you recommended and it was clearly nose heavy, it also needed a bit. Of up trim to fly level at 1/2 throttle. So I took out lot of lead, leaving 150 gms, it now balances about 1/2 inch behind recommended point. Test today showed it still drops the nose when inverted, needs a lot of down to keep level. I am just a bit worried about moving the cofg even further behind the recommended point.

So someone give me some confidence to just keep moving it back! How can I tell when it's too far? Sorry but bit of a newbie to all this trimming

thanks

[graeme jones]

Willyuk - what aircraft is it? Many ARTF's show a balance point way forward of the optimum position. Some kits and plans do as well, and I've also seen a few over the years where the point shown is too far back, which can make the first flight interesting. For aerobatics you probably need to move it back to 25% of the mean aerodynamic chord. Finding that depends on what aircraft you have.

Graeme

[Peter Jenkins]

Hi Willyuk

Don't get too hung up about the recommended c of g as they can be quite badly out - in both directions!

Provided you make the CG adjustments in small increments you will not run into trouble. As you move the CG aft, you will notice that there is less down elevator needed for maintaining level flight when inverted. When you reach the point that you do not need to push down elevator for level flight the aircraft is now at its neutral point. Take if further aft by the same increments you have used to get there and you will notice that you need up elevator to maintain level inverted flight. That's when you go back a bit so that you need some down elevator for inverted level flight.

Given that you have removed almost 150 gms of lead, I would reduce by 50 gms and check and if you still need a handfull of down elevator for level inverted, then an other 50 and check. If you get to the point that you have removed all the lead at the front and the aircraft is still pitching down when inverted, get hold of some sticky weights and put 10 gms as far back on the underside of the tailplane (not elevator) as possible without fouling the elevator. Check again. Proceed with further 10 gm increments reducing to 5 gms for fine tuning. As I say, making small changes is perfectly safe and once you find the CG position where the aircraft gently drops its nose when inverted that's where you stop.

You can then start all your other trimming activity. Every time you move the CG you will need to re-check all your other trim points.

With the CG further aft than you have it at present, you should find that the aircraft will spin (where before it might not have) and you will also have more elevator power for rounding out when landing.

Let us know how you get on.

Peter

[Willyuk]

Thanks for the help. Aircraft is a blackhorse cobra, not many of those about!

luckily i have time tomorrow to experiment more and I will report back

[Willyuk]

Pics of cobra, note the silver disks mark the cofg as called for in the instructions.

[Martin McIntosh]

For a large amount of single sweepback that looks way too far forward to me My similar style models tend to be nearer 45% from the LE., but you need to work out where 30% or so of the MAC is.

Martin Mc.

[Willyuk]

Martin,

yes, using a very handy online calculator, a rough set of measurements showed the cg to be at at 147 mm of root chord. The instructions call for 95mm. So tomorrow I will remove more nose wieght and test again.

Thanks to you and Peter.

[Martin McIntosh]

Do it a little at a time won`t you. I do not want to be responsible for any calamities!

[Willyuk]

Hi Martin and Peter,

update on the cofg. I eventually removed all 294 gms of lead and now it seems to do what is suggested. This has brought the cofg back from 95mm to 145 mm. Spit on for the mac at 26% or thereabouts. Thanks for your help. I had carried out the same exercise with my trusty acrowot but only needed 10gms at the tail to get it right, so such a huge difference in the plan v actual had me worried.

on to the next step. Still can't fly in a straight line but that is another issue.

thanks again

[Willyuk]

Sorry, I meant 125mm was the original, now 147mm

al

[graeme jones]

Peter - finally managed to get out today and practice the clubman schedule. I learnt three things -

1. It's not easy, even for a pilot with 45 years experience.

2. Flight time is much shorter than I expected, around 2 min. 30 secs. That leads me to think about using smaller capacity batteries (for E-flight) and smaller fuel tanks for IC, to reduce weight and increase performance. Does that make sense?

3. Pattern aerobatics gives me a headache!!!

Graeme

[Steve Colman]

I'm planning to give the clubman schedule a go this coming weekend with my Angel S30.

Graeme, I imagine you're referring to the concentration required? It does the same to me; even when I'm just practicing a couple of manoeuvres.

Just ordered something a little different to fly as an antidote.

Steve