Ever wanted to get into or improve your aerobatics?

[SR 71]

Hi Peter been flying my O/D f3a but it needs a bit more thrust in the verticals, im running 10s lipos and my model came out a bit over weight , thinking of going from the 20x10 on it now to a 20x13 is that the right way to do it

Thanks

Tony

["L"Plate]

Depending what you speed is like in level flight and provided you have clearance, I normally go for a bigger diameter, to get the vertical (some times with a little less pitch.

Is this wrong thing to do?

[Ultymate]

More pitch will not help it's like selecting a higher gear in your car

[chris Bond - Bondaero]

Hi Peter/Martin

Not actually OXai so not that expensive really

SR 71 Moving to a 20x13 will help as the motor and esc will be asked for more power so amps will rise 20x13 is a reasonably common prop in F3a. It is the right thing to do as long as your motor and esc can cope with the additional current draw What motor and ESC do you have and we can assist more

[Peter Jenkins]

As Chris says.

For electric motors more pitch generally brings in more power as they operate differently from ic engines. With ic you'd want more power so more revs so reduce the pitch or diameter - not always the case with electrics.

Key issues are the motor's Kv - that is per volt how many revs will it do? For F3A you're looking at around 230-260. For a motor for a ducted fan you'd be looking a much higher figure since they will be doing around 25,000 rpm off typically a 3S LiPo - say 12 v when they are just off charge and you've got the throttle stick forward = over 2,000. For an F3A motor on a 10S LiPo say full power drops the volts to around 38v then you'd expect around 8,000 rpm from the prop.

The other important measure is the current draw for both the motor and the ESC. A watt meter is essential equipment when you are experimenting if you are to avoid blowing the ESC or motor with excessive current draw. As you load up a lecky motor it just keeps drawing more amps and amps rather than volts are what kills motors and ESCs.

I've used 20 x 13, 21 x 13 and 21 x 14. You just have to try out various props to see which you feel most comfortable with. I've used AXi 5330 (outrunner), and Hacker C50-13XL (geared inrunner) and Dualsky XM6355DA-13 all with 20x13. I ended up with a 21x14 on the Hacker which just seemed ... better but don't ask me to explain "better"! Oh yes, different makes of prop also demand different current draws and don't always translate this into thrust. I'm told that some props are more power hungry than others but the the APC electrics are the most efficient if not the lightest.

[Peter Jenkins]

Just going back to my earlier post about putting a photo of the aileron movement I use for the 2 rolls in the BMFA B schedule, here's the photo. I use one of my rates to give me 4 mm aileron deflection with full stick - the photo shows aileron deflection with full right stick. I use about 3/4 power or a bit more if necessary, and full stick then gives me a steady roll rate for which the examiner will be looking. This also gives you time to make your elevator inputs. I can actually fly the whole B barring the stall turn and spin. Most people who've flown my Wot 4 with this setting have suddenly looked like they were flying on rails! It's worth trying to see how you get on with these low rates.

[Peter Jenkins]

Oh and the associated elevator movement is 6 mm as per the photo below. This allows nice big loops if you have the power. As I have a piped Irvine 53 I can fly loops with around just over 1/4 back stick. If you're going to do a bunt with this setup make sure you start high! Don't forget, large manoeuvres while looking good need constant small corrections to retain their shape and to combat the wind speed and direction effects.

["L"Plate]

Hi Peter,

I may be doing things wrong, but I feel that a Watt meter on its own is a good tool but I also use a tacho, as a motor may draw more power but that may not translate to effective air movment. I also know of other who use a spring balance to check trust.

I have had motors draw large amounts of power but with a small reduction in pitch have produced a large increase in RPM and duration, giving much better vertical performance.

I know of some speed models and EDFs that unload in the air and become far more effective, but I don't think this is the case with F3A as constant speed (so traction) seems more the order of the day.

Have I got it all wrong?

[SR 71]

As its an O/D i have used cheap and chearfull gear, i have had a lot of success with the xyh motors and hobbywing escs from G S , so i have a 6364 xhy 230kv motor in this one and a hobbywing 100A esc

The first one i built had the same motor but with a 270kv, i hooked the 270 kv one up to my digital scales and it pulled 18lb thrust on 10s on the ground so i think the 270kv one is the better motor for what i am experimenting with

I lost the first model and motor to a stuctural failure of the wing and GS sent the wrong one when i replaced it so thats why i have the 230kv one

[chris Bond - Bondaero]

The 230KV motor will be fine you just have to load it more with a bigger prop than the 270kv motor A 20x13 will pull around 70A I would think so go ahead and try it . I think the XYH motors are the same as EMP fine but a little heavy

[Peter Jenkins]

L Plate

Did you use the same make of prop or did you have different props at the different sizes? I understand that there are significant differences in efficiency between different prop makes.

My experience has been that you can change props in both ic and electric and provided that you are not pushing the envelope with them then there are small but important changes as you change props. However, with ic if the engine doesn't produce the power or the model is too heavy changing props does not solve the problem - you just need a more powerful engine! With electric, given the motors I've described above, they are not short of more than adequate power! Full power with the AXi 5330 F3A gave too much vertical speed - going from half to full throttle while pulling to vertical would produce a visible acelleration in the vertical. My main problem has been over use of the throttle to flatten the batteries before the end of the schedule. So, I've learned how to manage the throttle to give the desired size of manoeuvre without killing the cells - most of the time!

As regards using spring balances - I did use one on my first electric F3A and the answer was most satisfactory. Since then, just hanging onto the model while someone opened up the taps was sufficient to tell me that there was more than enough power when static so expect some improvement in flight - always assuming your model is not overweight! My Capiche 140 tips the scales at 6.5 Kgs empty so it's always going to be at a disadvantage to my electric birds which have always been around 5 Kgs. 1.5 Kgs extra weight does nothing for vertical performance.

[SR 71]

Thank you guys for the help i will get a 20x13 and report back, (although it will take two weeks to get here to Cyprus the disadvantage of living in the sun )

My O/D came out at 6.5 kg ready to fly

Chris your spot on at 70 Amps for the motor

Thank you all

Tony

["L"Plate]

Hi Peter,

I used the same make of prop for the tests. You are right that different makes, do change performance, probably due to changes in aerofoil and flex.

I did do a bit of testing using a wind tunnel on a speed model as the prop was over square (more pitch then diameter) and static testing proved nothing, but in a wind tunnel at 200mph proved to have significant thrust. The model needed a bungee launch and took a few seconds for the prop to unload, before the model would accelerate. The model got to a speed of over 220mph before the prop throw a blade at an estimated 47,000rpm and the motor was ripped loose. We think, using data from the telemetry that the model might have got to 250mph, in level flight.

I must admit I have been an exponent of diameter over pitch for vertical performance (the added advantage is more prop drag in the down line) and pitch over diameter for speed.

With IC I have always stuck to the recommended prop for the engine.

[Peter Jenkins]

Just coming back to the B Schedule and rolling, if you want to use rudder during the 2 rolls, first look at how strong the rudder's secondary effect is. With a Wot 4, application of the rudder will cause an immediate roll in the rudder direction. So, when using rudder to control the roll you have a bit of the fight between the rudder and the ailerons to maintain an even roll rate. As you roll into the first roll, you would apply rudder in the opposite direction to the bank to hold up the nose. Well, that either stops or slows down the roll rate as the rudder is trying to roll the aircraft in the opposite direction to the ailerons. As you come round the roll and go from inverted to upright, the rudder will go in the same direction as the roll and speed up the roll rate.

The solution I found is to mix out the secondary effect of rudder, if you have that capability on your Tx, so that application of the rudder merely yaws the aircraft and the rudder induced roll is countered by mixing aileron. So, when you use rudder in the roll you do not need to worry about the secondary effect of rudder.

Incidentally, I helped a clubmate set up his new Wot 4 recently. He had set the full and low rates as per the instruction manual Even when flying on low rates, the aircraft looked twitchy. So, we gradually reduced his low rates (ail/ele/rud) so that the roll rate was similar to the lowest rate on my Wot 4. He found this was a great help in making his flying look and feel a lot better. He was not quite as on edge as he'd been before. That makes for a much better environment in which to learn any manoeuvres. Try it for yourself. The old adage, you can't have enough control movement is not conducive to producing smooth flying aircraft.

[Martin McIntosh]

Peter,

I feel that I must come in here as an examiner and oppose some of what I have read regarding the two rolls in the `B` test.

3 secs. per roll is just ridiculous and is more or less a slow roll. A candidate in this test is only required to demonstrate elevator input, not rudder as well.

1 1/2 seconds, or about three rolls in 5 seconds is the norm.

I feel that you are putting people off even trying for this with this statement which bears no resemblance to the guidelines.

Sorry if the above ruffles your feathers again but I am just stating what it says in the handbook more or less.

[Peter Jenkins]

Martin

In our Area, the Achievement Scheme Coordinator holds standardisation meetings for ACEs, Club Examiners, Instructors and any candidates for A & B who are interested in attending. The roll rate that I was discussing above, was considered by the assembled company to be the right roll rate. I used this to pass my B as well as now to teach it, It does not require anything other than aileron and elevator - no rudder is used at all.

The rate of roll I quoted should perhaps have been expressed as between 2.5 and 3 secs. I took my Wot 4 to the field yesterday and had two colleagues to help with timing. I flew a dozen double rolls half to the left and half to the right. The roll rate was observed to "look about right" by those watching. The rolls were flown using aileron and elevator only. I then flew a 1.5 second roll and this required a much faster application of elevator to maintain height and a consequent higher chance of losing direction if the elevator was applied early or late. I have found that B students find it easier to control height and direction if they use the lower rolling speed I describe here. The timings that were recorded for two rolls averaged over 6 instances of each were:

Left roll - 5.5 secs = 2.7 secs each

Right roll - 6.2 secs = 3.1 secs each

I put the difference down to the torque effect of the engine helping roll rate in left rolls and hindering it in right rolls.

Incidentally, I have a set of rates for a slow roll on my Tx such that full aileron gives this roll rate. That allows one to concentrate on elevator input rather than also having to worry about keeping a constant roll rate. This is again, something that my B candidates find very useful when flying the 2 rolls. As a matter of interest, I find that I can fly the whole B with this rate with the exception of the stall turn, spin and landing (you run out of elevator as the elevator rate is also turned down).

So, I think your comment that 3 secs per roll is ridiculous and I am putting people off from trying to get a B is a little wide of the mark. My experience has been that faster rolling rates cause candidates more problems than the slower rates I suggest. Hence, I am sharing with the readers of this thread what I have found to be helpful in achieving the required standard in the B. If you wish to teach a faster roll rate then that's up to you. At the end of the day, quoting from the current Guidance Notes for the B, it merely states:

"Twinkle Rolls" that are so fast that no visible elevator input is required are NOT acceptable. You have to be sure that the pilot is using the elevator. Slow rolls which require elevator and rudder input are acceptable if the pilot can perform them but are NOT a requirement.

["L"Plate]

Funny thing, today flew my monolog and timed the roll rate using the tx timer. Doing three in each direction, so get an average roll rate, timer read 16sec so that works out about 2.5sec a roll (I thought it would be about 2sec per roll). Then just for fun I repeated the test twice more with the same result.

I don't think I would want to slow it up much more as the model uses a lot of sky going down wind at that rate (but I was doing three rolls), but a slower model that I flew was timed and it was very easy to achieve a 3.25sec per roll, roll rate. I also find that timing the elevator easier with the slower rate and still not need rudder. For the slow roll I do need ruder on both models (timed at between 5&6sec each and needing more throttle on the slow model as the rudder struggles to maintain hight in knif edge without speed but the Monolog can be flown at the same airspeed as the double roll)

So I think Peter must be on the money with this one.

[Geoff Reynolds]

Posted by Martin McIntosh on 29/10/2014 19:52:11:

I feel that I must come in here as an examiner and oppose some of what I have read regarding the two rolls in the `B` test.

3 secs. per roll is just ridiculous and is more or less a slow roll. A candidate in this test is only required to demonstrate elevator input, not rudder as well.

1 1/2 seconds, or about three rolls in 5 seconds is the norm.

I feel that you are putting people off even trying for this with this statement which bears no resemblance to the guidelines.

Sorry if the above ruffles your feathers again but I am just stating what it says in the handbook more or less.

Having joined this forum because I wanted to get my 'B' certification, having become very interested in GBR/CAA, meeting Peter at an NPOD and needing some great help to and encouragement to 'GET ON WITH IT', I'm afraid I have to disagree with you Martin.

I'm with Peter on the roll rate. I've found I need the time to input elevator now that I've practiced it.

I initially thought that a fast roll rate would get me through without needing elevator assistance or any adjustment, but everything just gets out of hand the faster you travel and roll.

One guy at our club was put off his 'B' test when he found that fast rolls (basically 'twinkles' weren't accepted by the examiners, but is now keen to be tutored by our two instructors and examiners to re-attempt the test alongside a few others of us. We agree, slower is better, although not timed, what comes natural per model flown/pilot ability.

I think Peter, you are doing a great job with your forum training column, as it isn't easy to teach 'long range', especially when you can't see the results, but from the majority of comments I've seen, I think many of us are very satisfied with your efforts.

Please keep up your good work Peter and others who chip in and let’s hope we don’t get Martin taking our tests! (Sorry if that ruffles Martin's feathers)

[Martin McIntosh]

Thanks David,

I am glad that someone who was a former national champion and world championship team member as I was agrees with me.

Twinkle rolls, Geoff, are those normally performed with 3D type models with huge ailerons, not F3A types which are generally incapable of such.

Three rolls in five seconds is actually quite slow and when performed, as they usually are, downwind will use up an enormous amount of sky.

There is no way that these can be done without down elevator input.

[Masher]

Doesn't this all depend on the size of the strip and cruising speed? Without looking back through the thread I can't remember the dimensions of the ideal "box" but most strips have practical limits set by trees and no-fly zones etc.

So if the box is, say, 200m long then what would be the cruising speed and how does that fit with time to do the 2 rolls? I would have thought that as part of demonstrating 'B' competence, the pilot has to choose appropriate speeds and rates?

[Ultymate]

Could've sworn this thread was about aerobatics it now seems to have morphed into an extended discussion about the "B" test which although it does contain a minimal amount of aerobatic content is not aerobatics as such. Surely a separate thread discussing said "B" would have been a better route JMHO

[Masher]

You may be right but isn't everything about getting the basics right? I think Peter went into the 'B' stuff because nobody seemed to be coming up with suggestions for what to cover next.

Ulty - why don't you suggest what you want covered specifically instead?

 

Anyway, weather's good here, I'm off to do some timing flying 

Edited By Masher on 01/11/2014 08:44:07

[Sam Wragg]

The B test is to prove piloting ability with a knowledge and understanding of rules and regulations including safe practices and it NOT a test on how good you can perform such maneuvers.

The B test allows you to fly at public events and that is why its so important to prove these points.

In my experience ive witnessed well practiced F3a pilots get into an unknown situations and cant handle it because its out of their comfort / practice zone. Whereas a natural pilot with good abilities can handle the situation

I'm with Martin

Sam

[Geoff Reynolds]

Posted by Martin McIntosh on 31/10/2014 23:50:04:

Thanks David,

I am glad that someone who was a former national champion and world championship team member as I was agrees with me.

Twinkle rolls, Geoff, are those normally performed with 3D type models with huge ailerons, not F3A types which are generally incapable of such.

Three rolls in five seconds is actually quite slow and when performed, as they usually are, downwind will use up an enormous amount of sky.

There is no way that these can be done without down elevator input.

Thing was, he wasn't using either a £D model or an F3A model, just one of his own models, something he'd built and kitted out himself, but was considered good enough to do the 'B'. He has always been a bit of a throttle off/on, max rates on everything flyer, so couldn't adapt readily to the 'discipline' for the 'B'., not just being able to fly all the manoeuvers well, but doing it with the use of all controls.

I still think that plane and conditions will have some bearing on how some of the 'B' will be flown and it doesn't have to be flown in a 'box' like F3A, but is meant to show that the candidate can carry out the required elements to the satisfaction of the examiners.

With the new move of trying to get all examiners signing off on tests in the same way countrywide, I still believe there will be a certain amount of differences, because personal/aircraft/conditions and venue differences will all have an impact on how the flight is completed.

I'd just be happy to complete the practices consistently, let alone get over the nerves and put in a good performance on the day.

I'm not knocking what you or other experts say, but I will only improve by following a set plan of training that includes good clear instruction and help on flying and correcting mistakes. The way I eventually end up performing the required roll elements will be how the plane performs (an Acro-Wot) and how I can make it complete the two rolls as smoothly and in line/on height that satisfies the examiners I have to do it for.

[Peter Jenkins]

Ultymate, as Masher says, no one came up with any suggestions on what to discuss after the Clubman Schedule so, as you need a B to enter competitive aerobatic flying, I thought it might help those who were trying to get their B if I were to discuss some of the issues. There is also Andy Ellison's set of articles which I found very helpful but what I'm adding here is a bit on the set up and technique that I have found help those who I'm guiding through the B. I hope that those who do get their B will be inspired to try competitive aerobatic flying. However, even progressing to the Clubman Schedule (mostly B level manoeuvres) find that the need to fly manoeuvre after manoeuvre without the comfort of a circuit to steady the nerves takes your flying to the next level and so on.

The B Certificate is a BMFA Achievement Scheme rating and nothing more. Contest directors use this as a mark that someone has learned how to fly safely to a set standard. They can then choose to use that as a measure to decide whether to let the pilot fly in front of the public. The B is not a test to allow you to fly in front of the public. I have seen some pilots who hold a B Certificate who have allowed their skills to deteriorate that I wonder whether they would be able to fly an acceptable A test.

Anyway, please let's not turn this thread into a debate on the B test as that will defeat the object of the exercise. Once I've completed my input on the B test - WHAT WOULD YOU LIKE ME TO COVER NEXT IF ANYTHING?