TYABB biplane v fence

[Ben Longden]

It was going to be a great day for the Tyabb air show - their major biennial event that draws hard core aviation buffs from around the nation to see some of the rarest aircraft in history.

 

Loads of spectators were arriving by air, including the rather beautiful RAA rotary engined biplane that had been seen at Benalla only a few days beforehand.

 

Without pre empting any investigation (THREE Casa inspectors were on hand) this beautiful aircraft has had the engine and undercart amputated following a collision with the fence at the end of the runway.

 

Uber aviation photographer Jen Clark (and student pilot) said she was photographing this plane because it was rather cute, and noticed a series of rough bounces and the AC was heading for the grass.

 

Alas, for some reason, the AC hit the tyres at the end of the runway before meeting the fence.

 

This is the beautiful before pic.... and the sad "During"

 

 

 

If there is any good news, it is that the pilot was out of the aircraft and walking around before help arrived.

 

Lets just hope he can get this gorgeous and unique aircraft rebuilt and back into the sky.

 

 

[turboplanner]

This is the second RA aircraft to hit the end fence at the busy Tyabb Mornington Road. The road fence is still marked by temporary orange netting.

 

This is a good example for the people who were recently discussing setting up an airstrip of pretty much matching the minimum landing specification of a Jab.

 

Runway 17/35 is reported to be 3223 feet long, yet this aircraft made it all the way to the end at speed.

 

In setting up a runway with due care, you have to allow for the person rather than the specification.

 

 

[Bubbleboy]

I think this is the aircraft that was at Natfly a few years ago in Temora. Just stunning! If you look hard enough you can see some of my drool on it!

 

Hope he gets it back together.

 

Scotty

 

 

[geoffreywh]

I wonder what went wrong with the landing? The pic shows the aeroplane down on all three wheels, I would have thought that the biplane would have stopped pretty quickly with that stiff northerly blowing. Plus the BUSY Mornington _ Tyabb road was closed , thus not so busy

 

 

[dazza 38]

I heard a rumour that the aircraft may have had a stuck throttle, but being just a rumour it may be true and it may not be true. It is plausible though.

 

 

[metalman]

I'd heard the throttle stuck as well, I was on base when it happened and the RV7 in front ( and me) had to go around till they had the runway sorted, I've got YouTube footage of this plane landing at one of the lethbridge toyruns a couple of years back, damn shame it was a beauty ,

 

Matty

 

 

[Keenaviator]

Stuck throttle, mixture control and mag switches perhaps?

 

 

[turboplanner]

I think his foot slipped off the brake on to the accelerator.

 

 

[metalman]

I think his foot slipped off the brake on to the accelerator.

It happens!!!

 

 

[Head in the clouds]

Stuck throttle, mixture control and mag switches perhaps?

I think his foot slipped off the brake on to the accelerator.

This is something that's rather close to my heart and I think worthy of a mention because many of us might not be aware that it could happen to us easier than we might think.

 

It's all very well for those who build their own plane and for those who have maintainer's tickets but I wonder whether the average LSA buyer/owner is aware of what happens when they have a 'stuck throttle'? If indeed it is a stuck throttle, because it's more likely to be a broken throttle cable or disconnected throttle lever.

 

In a car or motorcycle, with cable operated throttle, if the cable breaks a spring will return the throttle to idle and you aren't going anywhere fast. It's quite different with an aero engine because the throttle lever at the carburetors or fuel injection unit is sprung to the fully open position which means that if you have a broken cable it doesn't go to idle it goes to wide open throttle. That's because in aero systems the throttle cable pulls the throttle closed, just the opposite of a car.

 

This subtle difference means that many folks who bought their plane and might not be overly mechanically minded are blissfully unaware of what will actually happen if the throttle cable fails. The reasoning behind having aero engine throttle sprung to the full open position is that if your throttle cable fatigues and finally snaps in cruise, or during during the critical phase of climb perhaps, then it will go to full power allowing you to climb to a safe height before switching off and making a glide to a landing, or perhaps controlling the power with on/off bursts of ignition.

 

That's all very well, and probably good, but if the cable snaps when you've just about completed your landing roll and might be close to the far end of the airstrip it's quite a different matter. Shock and surprise would be complete if you didn't know that a broken cable or linkage means instant full power and the first instinct would be to pull back harder on the throttle and so waste a valuable second or two. While you're pulling the throttle and holding the control stick you don't have a spare hand to switch the mags even if you'd thought of it. So I write this in case there are any out there that didn't know about the broken cable/full throttle thing and so hadn't pre-thought what to do if it happens i.e. switch the mags/ignition off quick, or pull the mixture if you have one.

 

Further - there's very good reason why a failure of this kind is far more likely than most people might think. Where amateur built planes are concerned I have seen many which do not have a throttle control lever stop and that means that every time you pull the throttle back to idle the full force of the pull is on the cable itself and not on the control stop. Consider that the lever might be 150mm long and the cable connected about 1/3 the way up the lever from the hinge point so the force on the cable is three times the force applied to the lever, and most folk pull back on the throttle quite firmly to make sure the engine is idling as slow as possible and so to reduce the rollout after landing.

 

That's the amateur homebuilt, so of course this doesn't apply to the factory-builts that you fly does it? Well it very likely does because I have seen many factory-builts, with a throttle control stop but where the cable is still taking all of the load applied to the lever. And the reason is simple. You know how the revs tend to creep up while you're taxying? That's because the spring which opens the throttle (remember the cable only closes the throttle, a fairly strong spring opens it ...) is constantly urging the throttle open unless you keep your hand on the throttle lever and keep pulling it back. And also it's hard to get the revs down low enough - even with the throttle lever right back? These situations so frustrate many owners, and this applies to rental and school planes too, that the maintainer, instead of carefully and accurately adjusting the idle stop at the carbies, and re-balancing the carbies very delicately, has often backed-off the adjusting screw on the control stop to the extent where it's not doing anything, so the cable is taking all the load. Something to check on your next pre-flight perhaps?

 

As for not thinking quick enough about what to do if the throttle does go to full at the worst possible moment i.e. when looking at the boundary fence, well I won't be the one to laugh because I was a slow thinker about something very similar a while ago. I'd just finished restoring a nice sports car that had previously sat in a paddock for several years. I'd had to replace some unusual components specifically because it had not been used for a while, things like the plastic brake fluid reservoirs had disintegrated, and so on. Anyway, the day finally came when I could road test this beauty and all went exceptionally well and I was heading home toward the town centre and gave it a last squirt of power then backed off the accelerator but the power didn't reduce, the car just kept accelerating. In just a second or two, very close ahead were cars almost stopped at traffic lights and nowhere much to avoid slamming into them. Mercifully the pavement was clear and my brain switched back on at that moment so I swerved left, mounted the kerb, hit the brakes and switched the ignition off at the same time.

 

That wasn't quite the end of it though, I just missed a lamp-post and then tried to steer down the pavement next to stopped cars but instead the car kept turning left, demolished a hedge and hit a trampoline in a house front yard. Gladly the young girl who had been playing on the trampoline had vacated it seconds beforehand and was standing watching wide-eyed a few feet away. What happened? The throttle cable was rusted internally and some strands broke, they became little barbs inside the cable outer and prevented the throttle closing via the spring return. Then when I switched the ignition off, the steering lock ...

 

 

[skeptic36]

Yep, that steering lock happened to me, when I was a kid, I had the experts fit a new stereo in my LX Torana, they neglected to put the little plastic plugs back in the trim beside the accelerator so when I put the pedal to the metal the trim moved out over the accelerator pedal...... Got interesting for a moment

 

 

[ayavner]

I've had that happen to me both in a car (jag e-type, stuck carb linkage) and a motorcycle (don't remember which) and I think in both cases quickly giving it clutch then killing the ignition kept me from running up someone's backside. One of those real world demonstrations that knowing how your engine/system works makes you a better driver, but certainly gets your attention!

 

 

[geoffreywh]

The biplane in question has a Rotec motor fitted. Chances are it has a Rotec throttle body too. These are sprung neither open nor closed. The throttle slide is controlled by a solid 1.6 mm or so wire in a flexible tube. VERY unlikely to break. Should it break then your only option is to push the throttle to full open.....................But having said that I am very sorry for the pilot and his lovely aeroplane. I hope it is not too badly damaged.

 

 

[Teckair]

I had a carburetor slide stick part way up on one carburetor on a 582 on a Drifter once and someone said that should not have been much of a problem. Well they were dead wrong about that, we were doing circuits and the first thing to happen was the plane did not want to land it just kept flying. So we ran out of strip then we had to do a go round without full power. By this time I had worked out what was going on so after struggling around the circuit with part throttle we shut the motor off and landed. Some thing so simple can make life quite difficult.

 

 

[howe]

I had a carburetor slide stick part way up on one carburetor on a 582 on a Drifter once and someone said that should not have been much of a problem. Well they were dead wrong about that, we were doing circuits and the first thing to happen was the plane did not want to land it just kept flying. So we ran out of strip then we had to do a go round without full power. By this time I had worked out what was going on so after struggling around the circuit with part throttle we shut the motor off and landed. Some thing so simple can make life quite difficult.

Was it premix or oil injection?

 

 

[Keenaviator]

I

 

I had a carburetor slide stick part way up on one carburetor on a 582 on a Drifter once and someone said that should not have been much of a problem. Well they were dead wrong about that, we were doing circuits and the first thing to happen was the plane did not want to land it just kept flying. So we ran out of strip then we had to do a go round without full power. By this time I had worked out what was going on so after struggling around the circuit with part throttle we shut the motor off and landed. Some thing so simple can make life quite difficult.

If the carby slide stuck wouldn't the rpms have been higher than normal? Perhaps the next step would have been to cycle the throttle or better yet switch off the mags rather than flying the full length of the runway in ground effect? I once had an experience like this in a trike running out of strip with the motor idling a bit fast so switched off and stopped no worries. My mate did the same thing the next day, showing off to work mates on a golf course on dewy grass but didn't switch off. Ended up rolling the trike and putting it out of action for several months. Laurie

 

 

[turboplanner]

Does anyone have am actual cause yet? Another source reported it as a bounce.

 

 

[Teckair]

Was it premix or oil injection?

Premix.

 

 

[Teckair]

If the carby slide stuck wouldn't the rpms have been higher than normal?

Yes but I was in the back with no tacho and did not realise. There was a student in the front.

 

Perhaps the next step would have been to cycle the throttle or better yet switch off the mags rather than flying the full length of the runway in ground effect?

I practice glide approaches so what happened we throttled off turning base and I did not pick any change in engine noise the first red flag was we were much too high approaching the strip. We did not get into ground effect, I decided to go around which is when I realised we did not have full power. Cycling the throttle would not have helped, shutting the motor down mid final would have done the trick but we did not know what was going on at that point. Remember the student was flying the plane I only took over when things went wrong. Hindsight is a wonderful thing.

 

 

[Teckair]

Was it premix or oil injection?

From memory there was small object caught between the slide and carb body and it was unknown where the object came from.

 

 

[Keenaviator]

Thanks for this post teckair, a valuable lesson for all to bear in mind. Laurie

 

 

[howe]

Been debating whether to go to premix or oil injection on a new 582 motor at least with premix the slides and fuel pumps are lubricated, any thoughts?

 

 

[Guest Maj Millard]

Go premix..............Maj....

 

 

[Teckair]

Thanks for this post teckair, a valuable lesson for all to bear in mind. Laurie

No problem a seemingly insignificant thing like that can turn out to be more of an issue than one would imagine.

Richard.

 

 

[horsefeathers]

Been debating whether to go to premix or oil injection on a new 582 motor at least with premix the slides and fuel pumps are lubricated, any thoughts?

Carbs and fuel pumps run fine on straight petrol - ask our 4 stroke brethren.

 

I have 40 hours on a brand new 582 with oil injection without a hiccup in sight.

 

And if you look at the (literally) millions of 2 stroke motorbikes using oil injection, why would you go pre-mix?

 

Like anything, oil injection MIGHT break. Just like you MIGHT put the wrong amount of oil in premix.

 

So much in the 2 stroke world seems based on hearsay, innuendo, and plain wrong thinking. EG Adjusting your jets and needles from factory setting to "fix" EGT/CHT temps, with no understanding of how propeller pitch influences temps.

 

Stick with the factory made oil injection. They have a bigger R&D department than most flyers.