Stability

Hey all,

I have spent the last 8 hours just trying to fly a circuit with the spit.

It is a great challenge as expected, which is part of the fun for sure.

I have a question though about the directional stability and effectiveness of the controls.

For some reason I can't get a combination where the aircraft is capable of going straight.

During taxi at low power, (1100 RPM), after centring the tail-wheel with the differential brakes, I expect that when I release the brake, keeping back pressure, the rudder should be effective enough to at least roll in a straight line. It is not, however, but even the slightest dap of the brakes, (I have tried with buttons and with an analogue input, same results) there is no way of actually keeping it going straight, not even for a second.

I know that the CG is aft of the wheels and hence when there is more drag on the wheels, the tail wants to go forward. However with the brakes fully released, full aft pressure on the stick, 1100 RPM to blow the tail wheel down and get some airflow over the rudder, still there is not enough rudder authority to go straight. to me that doesn't seem right.

I have attempted over a hundred take-off's now, I can manage to stay on the runway about 3/10 times. I get airborne about 7/10 times.

I have not managed to find the magic combination of powersetting, airspeed and pitch.

when I slowly apply 8lb of MP, the aircraft goes off the runway to the left with full right rudder. Only when I am already off the runway, the rudder becomes effective but it's already too late.

So I have tried to first gently apply 0 or 4 lb of MP but then the aircraft always swings left and right resulting in wingtips bouncing off the deck.

I'm not saying that you haven't modelled the spitfire correctly, but at the least with my hardware in its current configuration, it is almost uncontrollable.

I have watched a few YouTube videos of real spitfires taking off, paying especially attention to flight control deflections. I haven't seen any videos where full deflection is required. Actually it looks like the stick is slightly checked forward from brake release and variable amount of right rudder is required to stay straight. I can't see the use of brakes of course from the outside, but I would think during take-off, surely using brakes shouldn't be required?

Once airborne, the aircraft flies like the CG is slightly too far aft. Stick force per G is virtually zero which means that at a certain trim setting, the aircraft can fly 140 in trim as well as 300.

With the CG a tiny wee bit forward, the aircraft would fly much better I'm sure. and this is not cheating, In real aircraft there are often tail or nose ballast weights that can be added or removed to adjust the CG. Of course you already knew that! :pilotfly:

Looking forward to your feedback and the golden tip to get me off the ground safely!

My hardware BTW: VKBsim Gladiator, CH pedals, CH throttle quadrant.

Cheers

PilotNL

In the Stickies above there are 3 good essays about controlling the Spit. She is a eal bitch on the ground. The read did help understand a few things a little better.

The center of gravity issue: With trim to 0, it will pitch downwards. The engine is pretty heavy, I don't believe it too far aft.

I can keep the Spitfire straight with brakes. That's just a matter of practice. If you have trouble, set a curve for the axis you're using. You also don't need to kick the rudder completely left and right for brakes. You can see the left/right brake pressure displayed on the gauge in the bottom left of the front dash. Watch this to get an idea of how much you're braking on each side.

The way you describe takeoff is either confusing or straight up odd. Or a bit of both. I've never had the Spitfire behave the way you describe on takeoff. Hold brakes, 2000RPM, release, slight but not full deflection of the rudder to the right.

I also trim for takeoff. Take the rudder trim wheel and rotate it clockwise until it completely stops. Trim the elevator until it is about +0.5. For some reason, the trim setting upon spawning in is more appropriate for landing.

Also make sure your axis controls are set up correctly, and that rudder and take off assists are completely off.

I hope something I said helps. The Spitfire is a joy to fly. Setting her down on a grass field is so very satisfying. Don't give up! Persevere!

Your slow power up is the reason you're struggling to keep her straight during take-off. The Spitfire had a free casterting tail wheel and has little rudder effectiveness at low speed. In otherwords, it requires significant airflow over the rudder to maintain directional control. Here's a video I made a couple years ago but the basics are as follows:

Trim nose down so the the indicator just touches the top of the circular mark.

Right rudder trim, roughly 5 keyboard clicks right, so the word 'Rudder' is roughly straight.

Full RPM

Power up quickly to Boost +10

You'll require full right rudder initially and about 1/4 right aileron.

Trim as advised above.

Hold the stick fully back.

Don't dilly dally on the throttle - straight to 8lb+.

Full right rudder initially then come down to half as speed builds, then watch for the swing to the right starting and go left rudder.

Once you have some speed built, stick to neutral. Nose should come up soon. After that I find I usually take off successfully although I like to slam it to full boost once the nose is up.

All of the above, with the stick pulled to you, but pitch trim set to just a mark above the middle / horizontal position, so which is still "down" because null pitch happens above that, around 3 o'clock...

But I use no rudder trim and prefer to use the rudder myself to control the takeoff.

Also check you do not have "rudder trim assist" enabled the the "Special" options tab !

Trim rudder one notch down.. trim rudder right until the First R in rudder is pointing straight up, boost up to eight and dance on the rudders,,, if you need a hand I can host give you some TS details and talk you through it

Red

Seems we all have different preferences for takeoff trim.

Official notes on Spit mk9

Open in Google chrome

http://zenoswarbirdvideos.com/Images/spit/SPIT9MANUAL.pdf

Red

Official notes on Spit mk9

 

 

Open in Google chrome

 

 

http://zenoswarbirdvideos.com/Images/spit/SPIT9MANUAL.pdf

 

 

Red

Take the rudder trim wheel and rotate it clockwise until it completely stops. Trim the elevator until it is about +0.5. For some reason, the trim setting upon spawning in is more appropriate for landing.

Pretty much this

It's also important to note that not only do you have to be quick to respond to any deviations from the desired course but you have to anticipate what the aircraft will do before it happens. And obviously you have to be delicate with the controls so as not to overcorrect.

Moreover if it's getting out of hand stop and try again. Trying to fight with the plane won't get you very far. If the takeoff doesn't start well it probably won't end well.

Ok! first of all,

Merry Christmas and thanks for all the kind comments!

It took me another many broken aeroplanes, but indeed I needed to adjust a few things:

I now take-off with full right rudder trim (thanks for that manual! epic!)

Pitch trim at 1/2 division down, half aileron right, hard back-pressure.

Franctic efford on the rudder to go straight (and I was thinking the supercub is a handful!).

Just before airspeed is alive, ease on the stick.

get off at 90knots, accelerate in ground effect.

Brace for the 120mph killer tug-under, but with anticipation its not so much a problem.

140kts, start breathing again and consider cleaning up, powerup to 12 boost, canopy and trims.

I must say, I have done some basic aerobatics:

Half roll and slpit-S, Loop, lazy eight, spin, hammer-head and stall turn, chandelle, spiral and side slip, it behaves nicely all through and even an unintentional inverted spin (I was being naughty) was easily recoverable. I may or may not have gone through a hangar or two as well.

Jolly good aeroplane above 140mph!

So again thanks all, I will keep practising and hopefully one day see you either on the wing tip or the cross-hairs.

blue skies!

Ok sorry to bother again, but seriously, that free castering tail wheel is a pain in the backside for taxiing.

Just a request for any engineers out there, could you put a little less grease on the bearing, so it is still free-castering, but that it may take more than 0.1N to move it.

Thanks! :pilotfly:

Yes to all the above.

I find it also helps to hold the brakes on until a lot of power has been applied.

This gives good airflow over the rudder and makes it easy to catch the initial swing.

After a week, I could taxi the Spitfire wherever. After a month, the Spitfire was under my dominating control during taxi. Taxiing is really not that difficult.

After a week, I could taxi the Spitfire wherever. After a month, the Spitfire was under my dominating control during taxi. Taxiing is really not that difficult.

Ok, now set a landing mission with turbulence ( set it at or above 100 ) and x-wind of 10 m/s which is aprox 20 knot... Try landing without wing tip strike or runway excursion :-)

Same applies to landing under such circumstances in the 109 K-4.

The P-51d is a lot easier to control, and, just as IRL, helicopters are even easier under windy / gusty / "turby" conditions...

Ok, now set a landing mission with turbulence ( set it at or above 100 ) and x-wind of 10 m/s which is aprox 20 knot... Try landing without wing tip strike or runway excursion :-)

 

 

 

Same applies to landing under such circumstances in the 109 K-4.

 

 

 

The P-51d is a lot easier to control, and, just as IRL, helicopters are even easier under windy / gusty / "turby" conditions...

Curious, I tried this. I didn't set turbulence to 100, or crosswind speed to 20 knots. Instead, I set the weather to the summer thunderstorm preset. And umm...

I actually made two attempts only. First one, I came in too fast and stuck my prop. Rest of the plane was intact though. Second was this. Wingtips never struck the ground, never left the runway.

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