J400: Keeping it straight when starting

[mch]

Hi,

 

yes, not when landing but when starting :).

 

I come from 10 years of flying a Cessna 172 and that plane has a start roll like a truck. Now the J400 with just the pilot (me) is a lot more nervous, OK so far, it's got more HP per kg at less than 500kg.

 

But at every start I notice that at about 40kt it starts to get nervous to a point that I seem to jitter slightly to the left or right. It's not much, just to make me feel uncomfortable that one day I might sort of overcorrect and leave the centerline of the runway more than I'd like.

 

Has anyone noticed the same?

 

Maybe I should alter my starting technique? I'm currently keeping the nose actively down until around 55 or almost 60 kts and the lift of gently. Once in the air it all is well.

 

I start with trim almost fully nose down and flaps 15 degrees. All tyres are at nominal pressure and they are all of the "round" type. (Round in the sense that they contact the runway in the middle of the wheel, not from edge to edge ..)

 

Maybe I should start with neutral and let her lift of the nose earlier?

 

I'm not sure.

 

Any input?

 

On landing the same does *not* seem to happen. It just rolls down once it has settled. Of course, then the engine is idling and there is no pull forward.

 

Mike

 

J400, Germany

 

 

[mAgNeToDrOp]

Hi Mike

 

I have not flown the j400, but have flown J230 and J160 and I would say the general rule with Jabs is get that nosewheel off as soon as possible, i.e. lift it and hold it just off the ground on your takeoff (and landing) roll. Jab nosewheels don't like any weight on them and will make directional control difficult. I've been told with cessnas and the like you can hold the nosewheel on the ground on takeoff as you described, but always been told by my instructor to treat the jab nosewheel as if it were made of tissue paper - keep the weight off it for as long as possible..

 

Edit: oh and yes, was also taught to have trim neutral

 

The torque effect on the 230 is also quite noticeable and needs plenty right rudder to keep her pointing straigh down the strip when you bury the throttle...have heard a few stories of pilots testing the jabs offroad capabilities when the torque has caught them by surprise by veering off the strip... :)

 

 

[Tomo]

Yeah, same as mAgNeToDrOp. Get that nose wheel off ASAP, and with the trim in neutral, that's what I've been taught, and do. I haven't flown the J400 either but it should be the same as a J230 or similar type Jab

 

 

[Guest Brett Campany]

...have heard a few stories of pilots testing the jabs offroad capabilities when the torque has caught them by surprise by veering off the strip... :)

Yup, I was bitten like that as well! They can be temperamental at times!

 

 

[HEON]

My time in J160's while learning was to get the weight off the nose wheel as soon as possible. As that is happening use the rubber! As nose wheel authorty reduces, rudders authorty increases.

 

 

[Guest Qwerty]

Better still, lose the nosewheel altogether. Fly tailwheels. :stirring pot: :rilla:

 

 

[mch]

Hi,

 

thanks for all the input which fortunately went all in the same direction.

 

Well, with the exception of loosing the nose wheel altogether, that one I like to keep - I hope, I never force a divorce :).

 

Will try neutral and an earlier "let it go" when it stops raining over here.

 

I think the reason I did not notice the problem on landing is partially that I indeed keep the nose wheel off after the flare (same as in the C172, but there you can't keep it off that long) and to the other part that the torque from the engine is missing when it finally comes down.

 

Mike

 

 

[Bruce Robbins]

Hi Mike,

 

I've only got a few hundred hours in various 172 sized GA (General Aviation) aircraft, but many hundreds in the various Jabiru models.

 

All the Jabirus have shorter travel on the rudder pedals than most GA aircraft and a nosewheel that is closer to the mainwheels. The pedals are also physically shorter, so combine the short pedals, shorter pedal travel for a given nosewheel movement, and closer coupling of mains to nosewheel and you end up with much more sensitive steering on the ground. The shorter pedals and throws also give a "stiffer" pedal feel. (particularly on the larger models like the J200/400).

 

I think that once you re-program your feet to a new tactile feedback loop, you will find the J400 easy to handle on takeoff. Remember to think rudder pedal pressure, not rudder pedal movement.

 

Having said that, I would use some different takeoff techniques.

 

The Jabs are much more sensitive and responsive to nosewheel steering on the ground, and most people get into trouble because they overcontrol and end up in a PIO. By using full forward trim you're loading up the nosewheel even more, and delaying the changeover from nosewheel to rudder steering.

 

So:

 

Method 1) Set the trim Neutral. Lift the nose wheel just off the ground once it is happy to do so, and then let the aircraft fly it self off in that attitude (which should be pretty much your initial climb attitude). The speed to lift the nosewheel will vary depending on the aircraft weight and CG. I have only flown J230s in the J200/400/230/430 series, so cannot comment specifically on the J400, but in some of the 230s I've flown with full fuel and only a light pilot, the nosewheel almost jumps off the ground by 30 kts and can require some forward stick. The response to rudder inputs is "softer" with the nosewheel in the air and avoids that darting from side to side you get if you're overcontrolling slightly.

 

Method 2) Set trim neutral, leave the stick neutral and let the nose wheel stay on the ground till you get to 50-55 kts or so (depends again on the weight). Rotate positively and the aircraft should lift straight off. During the ground roll be sensitive with the rudder pedals, and keep thinking pressure, not movement. If you develop a bit of a side to side swerve, put pressure on BOTH pedals till it stops, then gentle corrections again to regain your desired track.

 

Regards,

 

Bruce

 

btw: There are a few guys on this forum who fly the J400s, so you should get some more model specific advise soon.

 

 

[Derby]

g'day Mike, on my J400 I lift the nose at about 40kts,I have trim set to just aft trim the plane will then fly off at 65kts then flapps off at 70kts and clime out at 100kts, depending the day usually at or above 1000fpm. Mine won't lift off at much below 65. Landing you should keep nose up as long as possible depending on the weather i.e wind

 

Rory

 

 

[Yenn]

Normal nosewheel practice is to take the weight off the nosewheel early in the take off run. You will then be steering with the rudder and it is a lot easier.

 

 

[mch]

Much better now

 

Thanks to all,

 

all of you have advised to lessen pressure on the nosewheel during takeoff and today I tried that. The takeoff run is much better now, in fact, there is no "nervousness" left now.

 

I still don't lift off the nosewheel ASAP because I feel that the aircraft has not enough speed at that point to be fully controlled by the rudder.

 

I tried that also in calm wind condition and control was too soft for me initially and my limited experience. With more wind or a sudden gust it might be hard to keep her on track.

 

However, with now neutral trim and almost no elevator input she lifts the nose at about 45 and then flies off gently at 55 or so while still accelerating fast. Computed stall speed in this configuration is about 43.

 

There is no jitter in the wheel left (at least I could not feel it) and I feel quite happy now.

 

Thanks a lot!

 

Mike

 

 

[Tomo]

Great to hear Mike!

 

Ps. I've heard that some people put full back trim on, on finals for the landing stage... (trying to think where now?!) obviously holding the nose down with the stick!

 

But anyway, what do you all think of that? does anyone here do such a thing? Has anyone seen/heard of that before, or am I just dreaming!!? It just seems to me to be a bit dangerous. Like for instance, if you got distracted by something and let the airspeed wash off... could be disastrous!

 

True it would help keep the nose wheel off the ground during the landing run, instead of holding the stick back. I usually pull the trim back once It starts slowing down, Ie. flaps away, trim back, fuel pump off etc...

 

 

[jcruffle]

Great to hear Mike!Ps. I've heard that some people put full back trim on, on finals for the landing stage... (trying to think where now?!) obviously holding the nose down with the stick!

 

But anyway, what do you all think of that? does anyone here do such a thing? Has anyone seen/heard of that before, or am I just dreaming!!? It just seems to me to be a bit dangerous. Like for instance, if you got distracted by something and let the airspeed wash off... could be disastrous!...

My J230 requires full back trim on approach. Gazelles I have flown also require it. It depends on the aircraft, load etc.

 

John

 

 

[jetjr]

Yep, I can, turn base (at cct height) throttle off, trim right back, turn final, flap out 1 stage and it will pretty much glide in. Do have to keep an eye on airspeed but rarely a problem till very close to the strip. Usual problem in J200/400 is trying to slow down enough to put out flaps, pulling trim right back early solves this mostly. Ive never been close to stall with this approach, more often pushing too fast for flaps, smaller wing might have something to do with it compared to J230.

 

I do find that now I release the trim a fair bit late final, just so I can "feel" things a bit better, but still holding back.

 

On take off get the nose up as soon as you can, it wont fly until its ready. I have to have trim slightly fwd or it will tend to climb too fast on take off - helps on hot days to to climb with a bit more speed too.

 

I was taught with landing, ideally the stick should be fully back and held by the time nosewheel comes down, it really has stopped flying by that point, you are going much slower and still decellerating. (older J200's had really weak brakes too)

 

When you drop the nose too early, you are still at "nearly flying" speed and thats when a gust will really hurt, get flaps up too as soon as nose is down.

 

JR

 

 

[mch]

Full trim back: same here with only the front seats loaded. To remain within W/B limits I have about 15kg in the "baggage compartment" behind the rear seats.

 

In that configuration full back trim results in the approach you describe. However, for me that type of approach feels to steep, remember, I come from the tin GA planes.

 

So I prefer a 3 degrees descent which requires some power on the final, let's say something in the order of 1400 rpm.

 

I just feel better with that type of approach as the round out is very smooth then with less change of attitude. When the flare peters out she just sits down on the mains gently. It will take more runway, I concede. Here in Germany we have a lot of tarmac runways, usually in the 700m+ category, so this is no problem.

 

With a 500m or less strip your steeper approach technique is probably better and also with obstacles in the final.

 

Mike

 

 

[Yenn]

Full back trim on the approach? What will you do if you have to go around in a hurry? Surely the correct trim position is where it just cancels out all loads on the stick. Of course if you can easily overcome the trim it doesn't matter, but in that case why do you need it.

 

 

[jetjr]

Your right, full back trim is about where the load is taken off - it isnt full back on the stick

 

Jabiru trim is just a spring setup on the elevator so pretty easy to overcome, even if you did apply full power not much untoward happens, you just fly it like normal and when you can adjust trim

 

Why using trim on descent? same reason you do other times and in this case it sets up near perfect base and final approaches (assuming circuts are the suitable size) Can just give a bit of power if too short, second stage if too long

 

JR

 

 

[Guest watto]

I cannot use full back trim on approach, I prefer to have a bit if authority left if I need to go around or hit a patch of sink.

 

I trim slightly back from nuetral depending on load.

 

 

[Tomo]

I cannot use full back trim on approach, I prefer to have a bit if authority left if I need to go around or hit a patch of sink.I trim slightly back from nuetral depending on load.

That's basically what I do in the J120, sometimes it's just Neutral trim, depends on the load, and then glide it in on finals on second stage of flaps at 65-70kts...

 

Thanks guys for answering my question, It obviously is what a lot of you guys tend to do. It just sounded a bit backward at first... In the Drifter you have a tad of forward trim in on finals to keep you descending at 50-55kts.