Jabiru flap stress

[sseeker]

Well it's not all that 'important' but I can see it being an issue for some pilots and students, especially those who train in or own a hire and reward Jabiru. During my preflight inspection I noticed, what appeared to me as wear on the rubber boot where the undercarriage leg connects to the aircraft (underneath door). Turns out it was just some paint peeling and it was normal... Instructor showed me what I should be looking for and most of it was on the flaps. Where the control horn connects to the actual flap on the underside of the wing, the laminate was coming off quite a bit (still safe to fly however because it's just laminate) but this is because students & pilots are deploying the flaps above 80kts (I think the specific speed is 84kts) this can apparently lead to cracking in the flaps and a nice bill for the flying school, not all that fair is it? BUT that's just a minor problem out of whats unfolding, not only was it damaging the laminate on the flaps it's also damaging the control horn sticking up out of the wing on the inboard section (right above the doors) and this means the flaps are coming loose!

 

For example in our aircraft (J160C) the left wing flap is fine and sturdy, however the right wing flap is coming loose and rattles around quite a bit (once again still safe to fly... or is it?) So what happens when you have air flowing under the wing and into the flaps? Of course because the right flap is loose, it pushes out a little bit meaning the right wing has a lower angle than the left wing meaning the left wing is generating more lift than the right wing so you bank to the right... Right? Well I thought the flaps were fine and there was nothing wrong with them, surely being a little loose can't cause that much damage right? Wrong... Instructor threw an activity at me that I've never done before, late downwind he said, "Right your controls are locked, fly the plane..." My first reaction was to keep the attitude good and the speed alive, so I monitored that with power (more power = nose up and loss of speed etc... etc...) next thought was, right I need to keep the wings level but my ailerons are locked, rudder works good in a situation like this... (For anyone that doesn't understand, when you push the right rudder pedal the outside wing (left) accelerates and generates more lift, therefore you roll to the right as well as yaw. & visa versa) But of course our little flap issue comes into account now.

 

I had my flaps stage 1 due to being on late downwind (about to turn base) so of course as stated above, the left wing was generating more lift than the right. This caused us to bank to the right, at first it was controllable and I was able to maintain flight but it got much worse. It got to a stage where me nor the instructor could control the bank to the right using FULL left rudder. At that stage we were at atleast 30 degrees bank so the exercise was aborted and I levelled out and went out, turned around and rejoined the circuit. Obviously it could be avoided by raising the flaps, but that wasn't the point of the activity. Your engine has failed, the last thing you're thinking about is a control lock, and your flaps are damaged, but you've already put them down and some how your electrics/flaps fail (possible fire). I can assure you, you wouldn't walk away from the crash.

 

It's something everyone should take into account, look after your flaps. They're brilliant and make landing a fair bit easier, but they're also very dangerous if damaged. I just thought I'd share my story and hopefully everyone can learn something from it.

 

Thanks,

 

Andrew

 

From the way I explained things in this article, it seemed like a crash. It wasn't a crash, just a simple training exercise.

 

 

[Tomo]

Thanks for that Sseeker, very informative. :thumb_up:

 

You can actually adjust the flaps so it fly's S/L -- but yeah, that's not your point. Look after your aircraft and fly by the numbers people.

 

 

 

[sseeker]

No worries Tomo, I mounted the camera I purchased near the flaps bar but it fell down during takeoff (first time that's happened) but it gave an excellent view of the instrument panel/rudders so I can upload the video if you like.

 

Thanks,

 

Andrew

 

 

[Bruce Tuncks]

flap maintenance

 

Some years ago, a glider pilot was killed when one flap of his glider (an HP14 I think) became disconnected as he was close to landing.The disconnected flap of course rose up to wherever the airstream blew it. He would have had only a split second to raise the other flap before the rolling effect took over, or maybe even this wouldn't have worked.

 

SO...... Be very careful with the structural strength of your flap-drive system.

 

I completely agree with the idea that overspeeding with flaps down can apply excessive load to the system. What is not so widely known is that the more the flaps are deflected, the higher the loads. Electric flap drives prevent you from feeling the forces involved.

 

Personally, I only use the first stage of flap to land normally, leaving the second stage for short-field stuff.

 

Bruce

 

 

[sseeker]

Thank you all for your input.

 

Cfi, good point! The airspeed indicator is usually clearly visable and should have a white arc in it, really you have no excuse to fly outside of it with flaps deployed.

 

 

[bra83d]

If you want to really get a feel for the stresses involved in a flap system fly a Beech Sundowner with manual flaps, unless your speeds are correct you will struggle to get the handle off the floor, also extending above Vfe puts some big loads on the rear spar!!!

 

 

[nevjoll]

When I first started flying my Jabiru SK there seemed to be much more to remember than when flying a Gazelle.

 

One of those things was remembering to retract the flaps at 70knots. So easy to forget.

 

I made up a small metal box which sits above the flight instruments on the dash. It's very simple, a switch and a flashing red light.

 

Whenever I pull the flap lever down, I now automatically switch on the red flashing light.

 

It's a constant reminder to me to retract the flaps before reaching 70knots. One could use small batteries, mine is 12v

 

It's bright enough to remind but not bright enough to dazzle. Works well.

 

There is a UK guy who sells a kit which lights automatically when the flap handle is moved.

 

nevjoll

 

 

[sseeker]

Hi Nevjoll,

 

I could imagine going from an aircraft with no flaps to one with flaps could be pretty tricky, a nice solution though!

 

-Andrew

 

 

[poteroo]

There are actually 2 important considerations with flap extension....

 

(1) do it below Vfe as already indicated, but (2) is even more important,

 

(2) reduce power before flap extension sufficient that the aircraft doesn't pitch up and 'balloon' ....usually <1600-1700 rpm. If your power is set just right, all that happens is the aircraft slows a little,and you lower the nose a bit more to hold IAS.

 

Have a look at the flap 'tracks' on any flying school C150/152 you might pass. If there is a lot of slop when you lift the flap from the lower edge, then check the edges of the track slot. If they have a burred out edge - someones been using the flaps for Stuka practice.

 

happy days,

 

 

[zodiac3813]

I have an LSA and I think this movement is a natural function of the fact that the L) side flap is adjacent to the fixing point (lever/location holes), whereas the R) side flap is way out the end of a torque tube that is subject to torsional movement.

 

For it to be the same on both sides, it would have to be firmly attached on both sides. As for the small difference in airflow over each flap, you would be compensating for it with aileron/rudder without even realising it.

 

Just my humble opinion......

 

Jim

 

 

[sseeker]

Thanks Jim you have a valid point. That's all well and good in normal flight but my 'what if' was your elevator/aileron becoming jammed.

 

-Andrew

 

 

[zodiac3813]

I guess that, in that unlikely event, I would use rudder for banking and throttle for pitch control. Only half flap for landing.

 

The chances of losing both aeleron and elevator control are far, far less than the chances of the engine stopping/losing power by all accounts! If really concerned, adjust the right flap down slightly.

 

Cheers, Jim.

 

 

[sseeker]

Jim,

 

Aviation is full of 'what if' situations, I've never had any type of failure so far but I'm sure they don't happen in a perfect environment.

 

-Andrew

 

 

[Bruce Tuncks]

On my older SK (330 hours) I noticed flap play more than I liked, and it was nearly all in the inner pivot points. And yes the starboard flap has more flexibility in its drive as has been pointed out.

 

Now the pivot is an AN3 bolt, and I've bought some brass tube which is a nice fit on the bolt. This will be a tighter fit in the worn holes, maybe a tiny bit of filing out will be needed. So my plan is to bush the AN3 bolt, effectively making it a bit bigger .

 

I'm not suggesting this is urgent at all, I've never heard of a problem with a Jabiru in this area.

 

cheers, Bruce

 

 

[zodiac3813]

A quick bump...

 

I just remembered an incident with an LSA 55 some years ago, in north Tas here, where one of the flap ROD ENDS broke off where the thread finished, while on short final. This was due to the ball part having seized up... the nett effect was that the plane suddenly rolled violently, and only the quick reaction of the pilot in countering the roll with aileron, taking off flap and adding power (all at once!) avoided a nasty crash.

 

ALWAYS check the rod ends for free movement...as we all know...

 

Cheers, Jim

 

 

[Tomo]

Was reading an article the other day, in a Decathlon, the elevator movement jammed, and she had to land it using the trim instead.

 

 

[dazza 38]

Was reading an article the other day, in a Decathlon, the elevator movement jammed, and she had to land it using the trim instead.

There is a fair few document cases,over the years, where pilots have had to land using trim alone.Thats why one if the reasons that i like a trim wheel, instead of electric trim.Very rare, but it does happen.

 

 

[dazza 38]

Gidday Tomo,Don't know if you have ever flown a Decathalon or Citabria (should do if you get a chance), the trim control is a small lever and is extremely responsive, in fact so responsive it is sometimes difficult to trim to an accurate attitude to hold a particular altitude.

It would be very easy to use the trim control as an elevator substitute given its extreme response.

 

Regards,

 

David

Sounds like a similar set up, as per the Savage Cub.A lever, which is very effective with pitch changes.It is also a lever with a locating male tooth that engages with a multiple row of female teeth.In the cub, between one tooth to the next one.There is a big difference in pitch change.Where as a trim wheel, you can spin the wheel quickly, to make big changes, or move it slowly, to fine tune the setting.Its to do with the trim wheel being geared down.Every model A/c is different.

Ps- Hows your holiday David.I wish i was over there, i could do with a holiday LOL

 

 

[djpacro]

The Decathlon/Citabria elevator trim system would be even more simple than the Savage Cub (as I understand it from dazza's description). As David said, it is very effective - only a small part of its range of travel is needed (I don't see how an extreme cg position could require much more either).

 

If the elevator control system became disconnected it would work fairly well. Different kettle of fish if the elevator is jammed (more likely in my opinion) and not so easy to simulate that situation for practice.

 

 

[facthunter]

Flap overstressing.

 

The most dangerous aspect of this ,(and it is an operator/maintenance problem) is that a failure will MOST likely be assymetric in nature. Ie will only apply to ONE side. This will command a rapid roll, which may not be able to be opposed by ailerons alone. Rudder can always back up aileron to cause/[prevent roll, but this is not the way to approach the ground and hope to have the required control during landing. You have to equalise the flaps , if possible, and you have to be pretty quick.

 

Operating above the flap speed is a seriously BAD idea, because of the chance of causing a failure of the flap . Some planes have a flap operating speed that is far too close to the speed that you should be doing CLEAN in moderate turbulence, so there might only be a small margin.

 

The Cessna high-wing family even buckle the top surface of the wing when the flaps are extended too fast. Limit speeds are LIMIT speeds. Nev

 

 

[dazza 38]

Hi David, I just read it mate.Sounds like your having a great time.Its on my Bucket List, to go there.

 

 

[Spin]

Was reading an article the other day, in a Decathlon, the elevator movement jammed, and she had to land it using the trim instead.

Remember too that in this case the trim will work in the reverse sense, ie, move trim wheel nose down to get plane's nose to rise. We had an incident when I was training for my PPL where a low time pilot had the elevator sieze after rotating, he was able to stagger around the circuit and land with a combination of trim and throttle management.:ah_oh: My instructor later replicated the situation by grabbing the stem behind the yoke, preventing me from using the elevator to control pitch. Doable, but I'd hate to try and cope with turbulence on final.

 

 

[eightyknots]

I made up a small metal box which sits above the flight instruments on the dash. It's very simple, a switch and a flashing red light.

Whenever I pull the flap lever down, I now automatically switch on the red flashing light.

 

It's a constant reminder to me to retract the flaps before reaching 70knots. One could use small batteries, mine is 12v

 

It's bright enough to remind but not bright enough to dazzle. Works well.

 

There is a UK guy who sells a kit which lights automatically when the flap handle is moved.

 

nevjoll

This sounds like a good idea! I wonder why something like this is not used more frequently?

 

 

[eightyknots]

I made up a small metal box which sits above the flight instruments on the dash. It's very simple, a switch and a flashing red light.

Whenever I pull the flap lever down, I now automatically switch on the red flashing light.

 

It's a constant reminder to me to retract the flaps before reaching 70knots. One could use small batteries, mine is 12v

 

It's bright enough to remind but not bright enough to dazzle. Works well.

 

There is a UK guy who sells a kit which lights automatically when the flap handle is moved.

 

nevjoll

Any idea who the UK guy is that sells the kit?

 

 

[jetjr]

Instrument panels

 

Vic Leggot Id say

 

good guy easy to deal with