IMAC Primer finally run !!

Just a few days ago on Saturday 28th November, despite the horrible weather forecast, we managed to finally run an IMAC “Newbies” day at Waharoa. Here’s a bit of a run down to recap the day.

Jarrod and I arrived at the field around 9:45am, to find the weather not too bad, low grey clouds, and a bit windy. But not a sole to be seen. Hmmm … I’m sure there were half a dozen guys who all said they were coming. Where could they all be ? With breakfast pies disposed of, we ventured over to the other side of the Airfield near the Hangars, to find half dozen keen guys waiting by the club rooms. “Come on Bogan, Where’ve you been ? You said if it was crap to meet over here” … Bloody great I thought, all that printing after I got out the spa at 1am last night will not be wasted.  8 attendees in total, 4 from North Shore club, Foster, Derek, Aaron and Johan, two Waikato guys Gavin and Steve, another guy Lance from Tamaki, and last but not least Kerry Oakley from the top of the Coromandel. Also John Butler had come down to lend a hand.

As the weather was a bit rough, we setup in the clubroom first, and with the help of a whiteboard, and a stick plane, I gave the guys a bit of a crash course in IMAC, how to read Aresti, and the manoeuvres that make up the Basic sequence. Tons of info to soak in, but soon it was a case of, stop talking Bogan, lets go for a fly. As we drive back over to the field, Jarrod says, gee its pretty tricky to describe all the ins and outs of flying IMAC to the newbies ay Dad. Yep, all that stuff you’ve taken in over the last 10 years seems easy now doesn’t it. But for a newbie, I can imagine its information overload. During the white board session there were some good questions from the guys, like what to do if you stuff a manoeuvre, how the whole judging thing works, where to fly while other models are in the box, and what, we have to use the rudder too now ?

Over at the flying field, the weather was getting slightly better. But still pretty windy, and blowing a direct crosswind from behind us, prob about 15 to 20 knots at a guess. The guys all started to assemble their models. Mostly 50cc airframes, and a couple of Great Planes Super Sportster’s. Usually in that kind of wind, it would be a pretty mean Contest Director who would put Basic up, but these guys were all happy to have a fly. But first off, a demo flight. Jarrod and I pulled out the trusty old $109 Mark 2 Skyraider. Imagine the most ugly low wing box section model, with a plank wing, and no curves at all … yeah that’s the Mk2 Skyraider. Only ours is electric now, and fly’s on 4 cell. No more slimey mess to clean up, and enough power to get around the basic sequence in 15 knots of crosswind too !! I ran though the sequence, giving as many helpful tips on the way. We ended up doing a number of spin entry’s to finish with. How to stall it, and wait till the nose / wing drops before the spin, vs how to get a zero by not waiting quite long enough. Without a doubt, the most common reason a basic flyer will get a zero, it will be for the spin entry.

Everyone had a fly, and we dodged a few showers. Soon it was time to try and work though a few model setups. Ok, hands up who’s on Mode 1 so I can fly their plane and dial it in for ya. Hmmm, not many … what you guys are all Mode 2 ? But this is NZ not the US ? What on earth is going on here, how are guys supposed to learn to fly in a Mode 1 country, when they are sold a Mode 2 Trainer !!! Certainly doesn’t help does it. Ok, lets buddy lead then. Right hands up who’s on JR ? As you can imagine it got harder from there, but with a bit of sorting, I was able to fly a few of the Mode 2 models on Mode 1, and give some tips on setup.

As the day went on, the wind dropped, the sun came out. But one more shower of rain around 3pm ended the fun, and after it cleared up, everyone left fizzing to come and have a go at the next comp, mid December.

Ok, for the guys that were there, here are some follow up notes off the top of my head.

First off, CG position. Not surprising, most of the models I flew were tail heavy. Its a problem with 50cc models. The motors are so light, as are the batteries we run these days. So even with everything as far forward as possible, those two heavy elevator servo’s down the tail are your enemy. Find the lightest tail wheel assembly you can, and do what ever you can to keep it light behind the wing tube. Use a canister muffler to get more weight up front. For CG position, the best point to start with is 30% MAC. Forget about where the wingtube is, or where the book says. Here is a website you can use to figure out where 30% MAC is on your model.

Measure the wing, and sweep, and stick in the dimensions. Tell it you want to be at 30%. MAC is Mean Aerodynamic Chord. Eg the Average chord point on your wing. We usually have wings with a double taper, so an MAC calc is needed to find the magic spot. If you are flying a zero taper plank like the Skyraider, then its just 30% at the root. The cool thing is, the calculator will let you put your existing CG location in, and then it can tell you what percentage you are currently running at. If you need to add lead to the nose, don’t be afraid to do so. Do a Jimmy Page, and get out the lead !!! Our 50cc Raven needed about 250g on the firewall, and that was with batteries all on the motor box, super light elevator servos, and a tiny tail wheel setup. A tail heavy model is horrible to fly, and even worse in the wind. Remember the “in the sky” test, after the model is trimmed to fly straight and level, on full bore, pull a 45 degree upline (make sure its steep enough), then roll to inverted … now  then let go of everything (but keep the power on). It should gently arc down toward the earth with gravity. If it keeps going up on a perfect 45, you’re tail heavy. If it actually pushes up towards the wheels, eg an even steeper line, then you are really tail heavy. Models like this will be a handful to land, because they want to balloon up, and you actually need to give some down elevator to get the thing on the ground. Not good. Get the CG where it needs to be. On a scratch built model, I go to great pains to get the CG right, with no added weight. If this means moving the wing back, then we do it. My Rudder servo’s are usually as far forward as they can be, right up near the u/c.

Next thing. Throws and Expo. A modern 50cc aerobatic model will have pretty big ailerons. But for flying an IMAC sequence, you only need about 10 to 12 degrees of throw. The first manoeuvre is a full roll. When you give it full aileron, it should take about 1.5 to 2 seconds to do the roll. If it goes WHAM, and your roll is over in a blurr, drop your low rate till its slower. This means in the other manoeuvres when you only have to do a half roll (like on the humpty, 1/2 rev Cuban, split ess, etc), it will be easier for you to do the half roll, with out over rolling and missing wings level. Expo – start off at 50%. This will make it feel nice and soft around the middle. You can go higher if you like. I run 70% on my big models. Makes it really easy to keep ya wings level mon ! (Ask Jarrod about that joke when you see him next)

Elevator – as per the ailerons, usually the elevators on a 50cc model are massive too. Great for 3D flying after the comp, but you only need 10 to 12 degrees for doing sequence flying. Most guys have way to much elevator in low rate. Set it so you can almost pull full up when on 1/3rd throttle, and rather than dropping a wing and doing a wild tip stall, it should pull around a really tight loop. This means if you get in trouble and you pull full up, its going to fly a radius rather than stall and crash. 35% Expo s about right in low rate elevator though. Too much expo here will make it hard to fly a level line, and the plane will porpoise.

Rudder – Ok here you want tons in low rate. 45 Degrees. But crank the expo up to about 50%, or even 60%. This means you will have plenty of throw to kick it over on the top of the stall turn, but the expo will still keep it smooth in the middle.

The dreaded spin. If your low rate is setup properly, you should find that is hard to stall the model even with full up. So here is where you need a second rate. Turn on flightmodes in your TX, so you can have everything on one switch. Make it easy, and in a spot you can get to without looking down to find it. After the Immellmann turn, flip into the spin rate. You need a bit more up, (eg 15 to 20 % more), a bit more Aileron, but the trick here is less Rudder. Try 60% throw on the rudder to start with. The extra elevator will allow you to get the nose up for the spin entry. But the rudder needs to be less, otherwise its gunna spin too fast. As you fly it in, slow the model down, and gently start to pull the nose up, feeding in more and more elevator until you get to full up, and it stalls. If you feed to much up too early, it will zoom up. So you have to practise that bit lots, to get it to a stall, but not having gained altitude. As for when its time to spin, Bogan says WAIT MAN WAIT !! Don’t touch the rudder or the ailerons until the nose has actually dropped, or is dropping. At that moment in goes the rudder. Be careful not to give too much aileron at this point, as some models have got such massive ailerons, and even though its stalled, they can still have enough air going over them that the wing will come up and over,. So instead of dropping into the spin, it has snapped in, and at this point I’m afraid the judge sitting behind you will be forced to give you a big fat zero sorry. Remember if the canopy is pointing directly down at the ground at any stage, then you probably snapped it in. The wing and the nose are supposed to drop at the same time. You might find you can spin on just rudder and elevator. Eg no aileron at all. So try that out and see how it goes. But if you try to spin with just elevator and aileron (eg no rudder at all), its going to be a downhill roll I’m afraid, and that too will get a big sugary donut from the judges. The tricky thing about the spin in Basic, is its only 1.5 turns. So its time to start getting out of the spin not long after you have started it. The slower you can get the rotation speed, but still actually spinning properly, the better. On exit its just a matter of timing. Let go of everything at the right time, and walla !!! Give it a dab of down elevator as you finish rotating to get it on line again, and what ever you do, make sure you’ve flown a bit of a down line before you start to pull out. Pull up too early, and with too much elevator, and you risk going straight into another spin, then it can be a balsa shower if you were too low to start with. Don’t forget to return to your normal low rate after you are back flying level again.

Practise spin entries into the wind to start with. If the model wanders off as its leading up to the stall, its because the wind is blowing on one side of the model, and its weather cocking. So keep the heading straight with the rudder, and the wings level with the ailerons.

For the expo settings in the spin rate, you can up the elevator expo slightly, so it feels the same as in low rate. Same with aileron. But you actually need to back off the rudder expo a little because it has less throw in spin rate.

Last thing. Props. A few guys were running 23×8 on 50 / 55cc. Great when its dead calm, but it can be hard work in the wind because you’ve got no speed. Try a 22×10. If you can handle that, try a 20×12. That is what we used to run on the 50cc Raven. Super quiet because its less diameter / more pitch. Tons of power too. But the 20×12 fly’s with a bit more pace, so try the 22×10 first. And if its too noisey, that stick with the ratchety thing on it is called the throttle, and guess what, it also controls the noise. Soon you will need to learn throttle management If you have plenty of power, then only use it when you’re going up.

Well that’s enough for now. Great to see some guys keen to have a go at Basic, and we will see you in a couple of weeks at the next comp !!! Waharoa Dec 12th.



P.S. Bugger … I was so busy on the day, I didn’t get any pictures. If you took some, send me some please.