Sunday, 3 March 2019

Twister Pilot Notes

The following is meant to help anyone who has yet to fly their Twister and should not be taken as any kind of instruction - it is merely a guide.

As I've only ever flown G-FUUN this is type specific - your results may vary :)

(This is for a fixed gear, integrated tailwheel Twister with a UL260iSA engine.)

How I fly a Twister.

Preflight:

I start my pre-flight inspection at the prop, checking it for any damage and general secureness, I look underneath the cowl for any leaks and at all 3 tyres to see they are inflated correctly. 
Then the oil level is checked, then all cowling fasteners.
I then visually check the contents of each fuel tank. 
After that I walk around the wings running my hand along the leading edge to check for any damage before stopping at the pitot to check it is clear and the ailerons to check they are operating in the correct sense and are free. I also check the aileron linkage at this point. 
Proceeding back along the fuselage I check the static vents are clear and then that the fail safe screw for the tailplane attachments is in place. The elevators are checked next for integrity, full and free movement and no play.
Next the rudder is checked, that both pins are in and both cable attachment bolts and nylocks are secure, also checking for full and free movement.
The walkaround continues to the other side of the aircraft with the same checks as above where appropriate.  

Start: 

After getting strapped in and applying the parking brake the canopy is closed and locked (you should never even start a Twister, let alone run one up with the canopy not locked down). Throttle is set to just above idle and all switches are set to ON from left to right. A brief pause to check you have correct fuel pressure and then looking outside for any people who may have strayed close to the prop before shouting "clear prop". Starter is then engaged. Oil pressure is monitored closely and must come up in 5 seconds or less or shut down. Battery voltage should also begin to rise.

Checks:

Whilst warming the engine I perform all pre-take off checks (bar one). Controls, full free and in the correct sense (the most important check in any aircraft). Straps, secure and any loose ends tucked in. Instruments, set altimeters to local QNH, turn on radio and transponder. Flaps, set to first position, 10 degrees down. Trim, set to slightly forward of centre. Engine, check battery voltage is now 14.5, then check each ignition coil in turn by turning them off one at a time there should be a small rpm drop of only about 20-50 rpm each time. Oil temps coming up, I taxi when it is 35 degrees using only low revs, no more than 1,500rpm.

Taxi:

The view for me over the nose is possible but a shorter pilot will not be able to see over the nose so you should use the Pitts method of taxiing in a series of left and right curves. The turning circle on the integrated tailwheel Twister is quite poor so you need to take that into account before taxiing into a confined area, this takes up quite a bit of your attention when at an unknown airfield. Braking won't help tighten up a turn either as the standard brakes act on both main wheels simultaneously. If the surface is bumpy then it's best to hold the stick hard back to ensure the nose does not tip over.

Take off:

Final check before take off is a full power static rpm test after first checking oil temp is at minimum 50 degrees C. Depending on the outside air temp and wind direction I get between 2,500 and 2,600 rpm. 
Once the take off roll has begun do not be tempted to raise the tail too soon, wait until you have 30 knots or so and have good rudder authority, the integrated tailwheel will help you greatly to keep straight but not when it is in the air! Once the tail is raised your view ahead improves greatly and the usual footwork will be required to keep straight, at this point I glance down to check that my ASI is live, when you get to 50 knots things will become light and shortly after it will want to fly off. Let it accelerate in ground effect until you have 60 knots before easing it up into a climb attitude.

Climb:

On the initial climb out I leave the flaps down at 10 degrees and climb until I have about 300 ft or more before raising them. Once raised the Twister will naturally assume a lower angle of attack and the speed will come up.
At this point I let it accelerate to 90 knots before turning onto the crosswind leg. I continue to climb at 90 knots, this gives 1,300 fpm in the Winter (and as little as 500 fpm in the Summer when hot, heavy and high). There are many good reasons to 'cruise climb' at 90 knots rather than try to climb out at a much slower speed. Firstly you have a much greater margin over the stall giving you much more time to react to any emergency, Secondly you have a better view over the nose for possible conflicting traffic, Thirdly the climb rate is no worse at 90 than it is at 70 because with a fixed pitch prop the engine is not able to rev out (and therefore produce more power) when you fly it slower, Fourthly when you are actually trying to go somewhere then a faster climb speed will make your journey time less, and finally, Fifthly, the cooling is better for the engine when at a higher airspeed and a lower angle of attack.
Caveat to this; my Twister is probably the heaviest one out there and I may also be the heaviest Twister pilot(!) so your combination may climb better at a slower speed, but I have found this is the best speed for me.

Cruise:

I climb above my target altitude by 100 feet or so then shallow dive down to the target altitude to accelerate quickly to cruise speed and get on the 'step'.
I typically cruise at 2,700 rpm giving a TAS of 125 knots with a fuel burn of just under 15 litres per hour. 
If I'm just flying around at low level for an evening 'bimble' then I'll reduce the revs to 2,600 or even less.
I change fuel tanks every half hour to keep the wings balanced.

Descent:

The Twister is a slippery beast so it is best to plan well ahead with your descents. I tend to reduce power a little and then head down at max rough air speed - which is 120 knots indicated.

Circuit:

The more familiar I am with an airfield the tighter I will fly the circuit. I tend to fly the downwind leg quite fast - at 120 knots indicated and then go below circuit height on the last bit of the downwind leg while setting the throttle to idle. Then as the speed comes slowly back I will raise the nose by quite a lot to slow it down further until the flap limiting speed. If you don't raise the nose it would take forever to slow down to approach speeds. Flaps come down in stages. Only use 20 degrees of flap if you have a strong crosswind and plenty of runway length available, otherwise I always use full, 30 degrees, flap.
If you're starting out then fly a big wide circuit and only go at 100 knots until you get used to everything.

Approach:

A steady approach at 60 knots is what you are after, nail that 60 knots and make sure you carry that speed all the way until the roundout. The Twister side slips quite well, so if you are too high then throw in a side slip to lose height.

Landing:

A minimum runway length of 500m is a good idea for a Twister - certainly in the early days of flying one. (In nil wind I personally would not try to land anywhere that was not at least 500m)
The Twister floats quite a bit on landing but don't try and slow down your approach below 60 knots to land shorter you will only end up running out of energy to round out and hold off if you do. Stick to 60 knots and you'll be fine, just accept the long hold off period until touchdown.
I virtually always 3 point for a landing. What you are trying to do is come down very slowly in the last foot or so above the runway so that you touchdown without much vertical speed at all. If you have a sudden drop to the runway it will bounce, the undercarriage does not have any kind of damping effect and is more like a spring so you end up going back up to where you came from. If this happens then hardly anything needs to be done, just be patient and let it come down again gently with a very small back movement on the stick at the last bit (do not pole forward!). Unlike most other aircraft you should not stall a Twister onto the ground as you are landing, the reason for this is that it has a sudden wing drop at the stall (for me it's the right wing) and if this were to happen with any height above the runway you would come down very quickly on one side. It has happened to me once and it was not nice.
Due to the Integrated tailwheel the Twister is a pussycat of a taildragger. As soon as that tailwheel is on the ground you have good directional control (unlike most other taildraggers). So that's why 3 pointing is a good idea, even in a crosswind. I have done some wheeler landings (where you touch down on both mains in a level attitude and then lower the tailwheel later on) but to be honest they are no better than a 3 pointer if you have the integrated tailwheel.


Aerobatics:

So you're ready to have some fun then? Good stuff. Here are a few things I've learned while aerobating the Twister.

Safety first: Do it high so you don't die. If you're trying anything for the first time then do it high - minimum 3,000 ft or preferably 5,000 ft.

The main thing to watch out for in a Twister when doing aerobatics is speed control when you are heading ‘downhill’. The Twister accelerates much faster than more draggy airframes so if you are not careful it can get away from you a bit. If in doubt always roll out of any manoeuvre rather than trying to pull out (if you are upside down) if this is happening.

The Elevator has a nice feel to it, the Ailerons are heavy (spades are needed really) and the Rudder is much too light and so quite sensitive.

The roll rate is pedestrian - 90 degrees per second - which is very slow for an aerobatic aircraft. Also it has a low power to weight ratio which makes it lose energy going 'uphill' quite quickly. Conversely as it is so slippery it accelerates and gains energy going 'downhill' very quickly (as cautioned about above). 


120 Knots is a good all round entry speed for most manoeuvres.

Loop, Stall turn, Half Cubans etc.

A big input of right rudder over the top of any Looping manoeuvre is needed to stay on heading.


The Immelmann requires a higher entry speed, 140 or even 150 if you can manage it as the Twister loses so much energy and has a relatively slow roll rate at the top.

Any other figure which requires a long up line - first half of a Goldfish or reverse half Cuban for instance - also require a higher entry speed - 140 is good.

Snap (Flick) rolls should be entered at a much lower speed, well under Va. 80kts is fine for those.

Normal aileron rolls and hesitation rolls can also be done at a lower speed. Around 100 to 110kts or so gives a clean look to those.

Stall turns should be to the Left. Once the nose has passed the horizon on the first half of the turn then I go to idle with the engine. This helps in two ways. It lets you make a long down line without gaining too much speed, it also gives you much more right rudder authority to 'stop' the turn on a vertical downline with the wing leading edges parallel to the horizon, it also reduces the torque effect of the engine.

With spinning I prefer to spin to the left as it gives more control and enables you to stop it on a heading better (more right rudder authority at idle). Spinning to the right it happens quicker so is harder to stop on an exact heading, normally you should start recovery from a spin 1/2 of a revolution before you want to stop to get it to come out on the right heading.

Enjoy your Twister and be progressive in exploring it's limits (and yours).

3 comments:

  1. Hi, my name is Ross turner and I competed in the Breighton competition at sportsman in g-eeek. I was just wondering what your personal opinion was for the twister in terms of class viability. Is it capped to sportsman at the moment or do you think you could take it to intermediate? Not suggesting you do or trying to push you out or anything lol. Just wondering how viable it is compared to planes like g-eeek which normally cap at advanced national or lower from what I’ve seen

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    1. Hi Ross,

      Good to meet you at Breighton. You flew very well for your first comp.

      Personally I am struggling to make some of the Sportsman figures look right for the judges and even at the best attempt it is still a compromise so I know I lost points on certain figures. Immelman being the worst. I think the Twister is just capable at Sportsman level but would not be able to compete in Intermediate due to the energy (time) required for some vertical figures in that class. The Twister only has half the horsepower of the Extra 200 and it shows. Also the roll rate is only 1/4 of the Extra so any errors show up much more to the judges with the Twister and you take longer to complete any figures which uses up energy again. Maybe with more power and an improved roll rate the Twister could be used in Intermediate but as it stands I honestly don't think it would be capable let alone competitive in that class.

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