How far to inspect?

[pylon500]

Had a slightly heavy landing with a student the other day, and the tail leaf spring snapped!

 

Only minor damage, but makes you wonder just how far do you go inspecting at 100 hourlies?

 

Arthur.

 

 

 

[Student Pilot]

Looks like it's been going for a while Arthur. On training with a tailwheel, I'd give it a pretty good look over at 100. Including delaminating the spring and checking the mounting bolts.

 

 

[barandbrew]

Arthur

 

Is there a publication on inspecting chrome molly structures I would like to make sure that our 100hr inspections are as professional as possible

 

Regards

 

John

 

 

[pylon500]

Bearing in mind that the original photo depicts a piece of spring steel, to do inspections on 4130 (chrome-moly), I guess the best resource would be good ol' AC 43.13-2A, try chapters 2 and 7.Generally though, once a steel tube structure has been built, it's enclosed to such an extent that the only inspection option left would be complete re-bagging or X-raying.Both prohibitive for the average 100 hourly! The best you can do is figure out the most loaded sections of the structure and inspect the welds at those points as best you can with a touch and mirror.Anotherway is to look for loose or rippled fabric on the structure, and question why the fabric is not tight? For those that are building, be warey of painting tube structures a dark colour, much harder to find cracks on a dark background!

 

Arthur.

 

 

[pylon500]

We must be having one of those months!!After the tail spring broke, I noticed one of the tangs holding the brake band had a crack!

 

This annoyed me a bit, but I got it welded up and we continued flying.Two weeks later while checking the brakes on a daily, I find the other brake band has almost cracked through!In repairing the tailwheel, I had also rebushed the pivot point, and the steering was a bit heavier while the bush bed in.The need for more braking to steer must have hastened the crack!I guess you just have to be extra vigilant with these things.Arthur.

 

 

 

[Admin]

How true Arthur - and glad you caught it in time. I think this is a message to us all

 

 

[Student Pilot]

Do you do the brakes every hundred Aurthur? how long does it take to do a hundred with your usage?

 

 

[pylon500]

Currently we are opperating only one plane (we have two) and seem to come up to a hundred hours about every four to five months. In the past when checking the brakes, it was usually the brake cables, the brake lining and the roundness of the drum that required attention.This year is the first time I've seen cracking (metal fatigue?) in the support structure or band itself!

 

It is possible that the band was refitted at some stage, but not aligned with the rim, then fitted tightly instead of floating a little, which applied the side load that started the crack. Will have to go back through the logs.will be having a lot more work done next 100 hours.

 

Arthur.

 

 

[pylon500]

Trouble happens in Three's!

 

On doing a daily on our LightWing Last Saturday, I found a crack in the plastic 'Body' of our Brolga/Ultraprop hub. While initially thinking that it was only the plastic with a crack, and that the steel plate within wold be OK, I decided to pull the prop off for a quick look. What I found was bad enough, but when I pulled the prop apart, it was freightening! It looks like the plate had cracked earlier and only when flexed far enough it had split the plastic hub body.The crack is on the rear hub half with the trailing hole having the crack, so I'm not sure if it could be from a prop strike?It could have been from a problem we had some time back with the 912 having odd bad starts in the morning.

 

When starting cold with choke, the engine would wind, then fire up for about two revolutions and then stop dead very abruptly, almost like a backfire.(Apparently the 912S's are really bad for this?)After completely stripping the prop I found that;

 

1. Rear hub cracked at one hole

 

2. Possible cracks at other holes

 

3. One pitch-block split in half (rear block)

 

4. ALL other blocks have cracks

 

5. ALL retaining bolts (correct AN series) show signs of bending

 

6. Bolt at the failure point was Cracked!

 

All (but the cracked bolt) had the correct torque at the nuts, but there is a problem in that the bolts torque down onto a plastic surface. The hub kits are usually supplied with normal AN-960 series washers, I'm thinking that we should use a larger washer format to apply the torque load over a greater surface of the plastic to avoid crushing.My only fear in uploading this post is that we could start the same hysteria that occurred with the GSC props.

 

As I posted in a previous forum, I believe propellers are to aircraft as tires are to cars, they all work, some better than others, they just perform in proportion to their cost, reliability is not usually an issue.As such, I have ordered another hub and pitch block set for the Brolga, I just might notate in our logs to strip, inspect and rebuild the prop every 100 hourly, it would only take about a half hour., and after all, we all rotate our tires don't we?

 

Arthur.

 

 

 

 

 

 

 

 

 

[Guest TOSGcentral]

Scary stuff indeed Arthur!

 

What did Dave at Aerofibre have to say about it?

 

To support your comment about 'calm' - in the ten years TOSG has been going I have only had three reports in on Brolgas (and I get a LOT of incident reports!).

 

1. The 90 degree returns on the sharp end of the pitch blocks cracking and the ends eventually breaking off. Easily visible on pre-flight. Cause - blade not being seated correctly before being torqued and so putting pressure on the end lug. Comment - The blades do not 'auto-seat' as appears to be the case and do need checking that they are flush against the pitch blocks before tightening them.

 

2. Main retaining bolts shearing in flight. Cause - incorrect spec bolts in use. Comment - The Brolga is a very safe prop and it is difficult to lose a blade entirely in flight! In this case when the first bolt went the prop ran out of true and caused enough vibration to occassion a forced landing, but not enough to do any further damage. A second bolt was then found cracked but had not yet separated. I had occassion recently to talk to Dave about prop bolts and the standard factory issue is: Grade 8, 80x8 mm, at 1.25 pitch. These are a good match for ANs, are cheaper and easier to get hold of. Dave particularly said to stick with these and do not start sticking in very high tensile bolts!

 

3. Cracked hub from retaining bolt hole. Cause - over-torquing. Comment - The Brolga props are not very complicated but owners do need to know how they are actually supposed to work. There are a couple of traps for the unknowing! There are 12 bolts in the hub in two pairs of six each. 6 of these hold the prop hubs together and clamp the blades. The torque needed is 10 ft/lbs and is applied through the lock nuts. That is not much and it is easy to over-torque, especially with a poor quality torque wrench, or by failing to 'warm up' a wrench before using it.

 

The second set of six bolt the entire prop to the engine drive flange. The torque setting is 14 ft/lbs. This is applied between the bolt and the drive flange itself that is tapped - NOT the usual lock nuts you find on the other end. In fact you do not need lock nuts at all and some people use drilled head bolts and wire lock them instead! If however the owner does not realise all of this and tries to apply the torque through the bolt/nut combination the actual torque to the drive flange could be all over the place - particulary if it is one of those people who like rotating the bolt to tighten it (because it is easier to get a swing on) rather than bringing a nut down on a stationary bolt!

 

None of the above was a defect in the prop or its components - it was the product of indifferent maintenace, not using standard parts, not using the excellent factory instructions that come standard with these props, and/or a straight lack of basic knowledge of the task!

 

The damage to Arthur's prop really is frightfull! I would opine accumulated fatigue rather than a prop strike. To do that level of damage there would be very noticeable damage on at least one of the blades.

 

Arthur, I would very much like to use some of your photos and background data in my next TOSG Bulletin. May I have your permission to do so please?

 

Aye

 

Tony.

 

 

[Student Pilot]

Sheeeeeeeeeeeeet!

 

 

[pylon500]

Grade 8, 80x8 mm, at 1.25 pitchG'Day Tony, yes, feel free to use any of my photos you find on the web.I'm supprised to hear you say the Brolga supplier specify the non A/C bolts?I'm fairly sure we were using the prop as we got it, with the AN-5's shown in the photo. These are only used to retain the blades as the prop is held by fixed bolts coming forward through a spacer on the front of the 912

 

(this is as supplied by Howie, don't ask me why he ounted the engines half an inch BEHIND the cowl lip?)

 

We have in the past noticed an odd harmonic vibration at around 4500rpm, but put it down to unbalanced carbies, which we seemed to spend a lot of time curing. I think we'll still use the Brolga as it's a good hard working prop, and with the years I've delt with the Vampires, I never noticed a problem with the Ultra-Props other than lack of performance.Arthur.ps, the brolga guy is currently in Napal.

 

 

[Guest Guest]

Woops! Yup - tks Arthur. I should have specified that I was talking about fittment to 582/503 motors! Sorry if I gave anyone a confusing time!

 

Comes from specialising on one type these days.

 

The bolt specs are exactly as recited to me by Dave. They surprised me as well.

 

The reason I checked was another little possible error that can creep in and I did not mention. On the bolts attaching the prop to the drive flange they are only long enough to take one washer each. I have found a LOT of people insist on putting a second washer under the head of the bolt. So I was mainly checking how long the bolts should be.

 

This makes it impossible to get the nut the required minimum 1.5 threads to be 'in safety'. On the other hand I find an alarming number of people who do pre-flights who are not conversant with the term 'in safety' - which is a bit of a worry!

 

T.

 

 

[pylon500]

UPDATE;Have just recieved the new Ultra-Hub for the Brolga containing an assembly and maintenance sheet. Apart from saying you need to recheck torque values after, 1,2,4, and 8 hours of operation, you also need to check every 20 hours and then dismantle the prop every 200 hours.It also suggests replacing the bolts every 1000 hours.Fortunately the blades themselves are deamed to have indefinite life after regular inspection.Arthur.ps, Hub Halves (x2), Pitch Blocks (x6), Bolts (x6), Nyloc Nuts (x6) and Washers (x18) plus post = $353.20.

 

 

[Student Pilot]

The body of the hub seems to have some discolouration from being in the sun. Is the machine hangered Aurthur?

 

I'm sure the exposed sun time would have some bearing on the life of the hub. That price sounds pretty good.

 

 

[pylon500]

This (and most of our) aircraft is kept in a three sided hangar that faces the East.We have a 'Shade Cloth' curtain drawn across the front, more to keep out birds than the sun.For the last two years this LightWing has sat at the front of the hangar and yes, the hub was starting to fade.The irony is that it was the rear hub half that failed.

 

It's a bit annoying actually, in that I take my students to the prop before each flight as part of our preflight, and spend that time inspecting the blades because they are showing signs of fading.I guess I became a victim of doing a routine, but boy, am I adding to that list!! Actually I suspect that the crack in the plastic occoured suddenly in that the weekend before I saw the crack, I had actually been told about it by the last pilot to fly the aircraft the day before, he noticed an increasing vibration, so landed and found the crack.He called me about it, but never mentioned it's size. As I mentioned in the first prop post, I suspect that the inner steel plate possibly cracked some time earlier, and after growing in size, eventually stretched the hub plastic until it craked.I guess the thing to do at each walkaround is to look at the blade retaining bolts for signs if cracks radiating from under the washers, or signs of the washers having moved.

 

Arthur.

 

 

[TechMan]

Arthur,

 

Can you please submit an incident/defect report to RA-Aus, downloadable from the RA-Aus website for the Propeller and all other defects that you find.

 

Or call the office and we can fax or mail you a form.

 

Thanks

 

Chris