Engine shock-loading
 

What sort of damage does actually derive from engine shock-loading, anybody knows? I mean, what component does actually take the shock: crankshaft, bearings, any gearbox (e.g. Rotax engines)?
And say that while I'm taxiing on bumpy grass, the propeller strikes the ground (without the engine stopping): does that make the engine not airworthy until inspected/repaired?

Thanks for sharing your knowledge!

Deeday

Regarding the parts of the engine: anything from nothing, to pretty much all of it...and anything in between.

Regarding a suspected prop strike: one of my co-owners in the Pitts had one of these at Elvington last year; it was indeed a heavy landing, but unaware of prop damage, he did taxy the aircraft the best part of a mile to the apron where I was waiting to climb in and fly a competition aerobatic sequence. Imagine our surprise when, upon shutting down the engine, that a good proportion of the propellor had been removed.

In summary: yes, it bloody does matter if you have a prop strike on bumpy grass..or one of the largest pieces of smooth tarmac in the country...or a fuel bowser that you didn't see, in fact, pretty much anything. In fact, being confident you have a complete propellor and engine to go with it is right up there with counting the number of wings during the walk round, and if you finish counting with an odd number or a fraction, best to ask a responsible adult for advice.

Now then, is there something about your last flight you think you need to share with anybody?

You have to remember your life can often depend on that thing whirling around in front of you, it is better to be sitting on the ground thinking "damn that cost me a fortune" than to be sitting in the air in total silence thinking "damn I wish I had spent that money"

This is how Lycoming defines a prop strike, and it will suprise a lot of you.

http://www.lycoming.textron.com/supp...dfs/SB533A.pdf

Rotax's is similar see

http://www.rotax-aircraft-engines.co...kus/d04167.pdf

http://www.rotax-aircraft-engines.co...kus/d00288.pdf

The fact that you are asking means if you have had one you have concerns over it. Which brings me back to the top of this post.


An Essex Flyer’s Diary prop strike

Deeday

As you only have definitions so far.

The run out of the crankshaft is usually checked first to see if it has bent the crank.
I have seen a couple of very hard shock loads (a twin at full power with an early gear selection!) the cranks were fine and no damage anywhere in the engine/s!
Then a landing on grass at low/ idle power which bent the crank well out of limits?

The Magneto drive gear is inspected/checked/tested as this can fracture many hours after the shock load incident, I have a gear wheel with a very small crack in it and one with a tooth missing both removed from aircraft after hitting hard runways under power.

The bearings and other parts are inspected/replaced as a precation and some items must be replaced after they are removed/disturbed.

I'm sure someone who does the job/s will give a clearer description?

hehe, I didn't notice that my post sounded like an admission of guilt. I'd like to reassure you all that my last flight was OK (and the one before... etc), and I always own up to my mistakes, especially if they can affect other people. Having said that, my grass airfield is rather bumpy, in some places, and striking the prop is always at the back of my mind.
It's just that this expression - shock-loading - seems to come up in every other accident report, but without much detail on what actually happens to the engine. Anyway, thanks for the links, they are spot on.

Deeday

so if my prop chews through a pigeon on take off

is this a prop strike?
should I do a couple of circuits to make sure there is no vibration, before carrying on my way?
or should I RTB, and get an engineer to have a look?

Things can get bent or cracked, and the cracks can be internal. They can also be in the crankcase... That's why one has to NDT the whole engine.

In the past, and it may still be true, Lyco allowed an engineer to countermand the shock load inspection if a) the engine did not totally stop in the strike AND b) the crankshaft flange was still running true. I imagine many took advantage of this but it's IMHO very poor risk management, especially in a SE.

Many prop strikes are unreported and unlogged. One clue might be prop hours differing from engine hours, but somebody with a brain will fit a new prop (to replace the damaged one) and transfer the S/N from the old one, or just change the blade(s). Then it breaks years later....

Shock loading an engine is serious and expensive.
It means completely stripping the engine and checking for damage in the crankshaft, prop governor, magnetos, gear box etc..
Of course when the engine is stripped the other non related shock items may have to replaced due to wear or ADs.
Crankshafts and crankcases are expensive if they need to replaced because there is no core value for them. You're probably aware that these items get used over and over again even when an engine is 0 timed.
Think thousands of £'s. Best not to try it!

It was about £6k for an IO-540 a few years ago. And that was done by a well known cowboy (since gone bust) in the UK. It's really hard to find a reputable engine shop in the UK; I would send the engine to a specialist in the USA.

Plus the cost of the prop. Often, the hub had to be replaced and then a whole new prop probably doesn't cost any more. Mine cost £12k or so (with a JAR-145 form of course :yuk: ).

That's why one needs to be a bit paranoid about driving on grass, and especially grass/hard transitions. The renters queued up behind (paying brakes off to brakes on) may not be happy about you getting out and checking the ground for potholes but that's what you have to do. The airfield which owned the pothole can probably be sued but in practice will do absolutely everything possible to wash its hands of any liability. The insurance pays out but it knocks your premiums for years. Been there, done that ;)

I would recommend Maclaren and Nicolson ( Spelling) in the UK

Another vote for Nicholson-McLaren Aviation

Beware of some - all that glitters may not be gold (or even grey...)

We had a nose gear collapse on landing, was a grass runway.

Was a 3 blade prop on an IO360A1B6, stopped in 12 blade strikes.

Repaired to the full Lycoming sudden engine stoppage service sheet.

300 hours later the engine nearly fell to pieces due to very high internal wear.
Comments from engine overhauler was he had seen far better 2800 hour engines.

We think the case hardening on the ancillery gears was micro cracked, due to shuttling on the sudden stoppage. We believe this then shed hardened steel particles into the oil and caused all the wear. The ancillery gears are not on the must change list, but I think they should be.

50 hours after the rebuild the case then cracked. Low rmp sudden stoppages with two of a three blade prop digging in on grass put a very high bending strain on the crankcase.

Any sudden stoppage is expensive and serious, beware.

I've just gone through NDT (eddy current, magnaflux, ultrasonic, etc) training which involved checking a number of shock loaded components. Many of the crankshafts had minute cracks around and through the flanges, some also had cracks through the journals. Unfortunately there was no information to hand about the seriousness of each strike but seeing the results made me realise how important it is to have engines checked following any prop strike.

H/Flyer - the metal you describe would have shown up in either the oil filter or in oil analysis.

OK, we know that almost nobody does oil analysis because they don't know or because it adds £10 to each 50hr check ;) but the oil filter should be cut open and it is clear this is not always done either.

Reports from U.S. engine shops suggest that some 95% of shock loaded engines are OK but they only NDT the gears, not change them. However, IMHO, your problem was not the gears (if the engine stopped in soil over several revs) but a bent crankcase which caused a lot of bearing interface material to be shed into the oil. I gather the gears are very rarely found to be damaged.

Oil analysis............. cheap at 10x the price.

Nicholson Mclaren
 

I used N-M for the first time this week for a problem Cylinder. They turned the cylinder around in three days, they did a first class job at a reasonable price.

With the level of service that they have shown I will be sending more work to them in the future.

Reputable Shops
 

I've heard rumours that N Mclaren and Ronaldson are both having internal problems with key staff going from one to the other. Anybody heard how their quality is being affected??

still-learning
 

The "goings-on" in the engine business would make a good soap opera, the only problem is that if you presented it to a TV production company They would reject the script on the grounds that it did not have "credability".

The only other comment that I will make is that I think it highly unlikely that the Quality of the work that N-M turns out will suffer.

This was some time ago and was resolved as far as I know in Ronaldson's favour. Ronaldson's are busy expanding their facilities and I've always found their work excellent. I believe that some of the guys from the now defunct CSE engine shop are working there.

A year ago I sent my engine to Barrett Precision in Tulsa, Oklahoma. They were the most reputable engine shop I could find. (Yes I know their website is a bit naff...)

Prior to that I did extensive "due diligence" on every engine shop over here and could not find two actual users who would trust any of them as far as they could throw them.

To be fair, this could be as much a reflection of the poor work done by many as the difficulty of finding past customers to talk to (via the inevitable internet means) but the bottom line is that an engine shop in the USA will quickly get a very bad name if they do any poor work, never mind consistent poor work, because they are so much more widely discussed on the huge American pilot forums, and in pubs like Aviation Consumer.

The drawback of going to the USA is shipping. Air freight is cheap at about £500 each way (for a big engine) but can be appallingly unreliable due to the low grade personnel involved. Been there, done that, and at work we struggle with AF too, time after time, right down to some moronic delivery drivers. Next time I would just use DHL at some £1500 each way and it would still cost no more than a UK job picked up in a van.

The other drawback is warranty, which a US shop would tend to work via a UK engine shop, but the chance of a properly assembled engine needing anything is very remote, and the warranty is 1 year anyway.

I paid $12k+shipping for the same job for which the now-defunct CSE quoted £16k, so the recent moves in the exchange rate are nowhere near making up the difference, and I most definitely could not find two happy CSE customers... and hey how much a warranty from CSE be worth?

If installing to anything other than an N-reg, make sure you get an 8130-4 form (an FAA Export CofA, a special form signed by an FAA DAR) which is about $300 extra. For an N-reg, 8130-3 is fine and comes standard.

There are some big US firms which can generate an EASA-1 form (e.g. Pen Yan) but their quality reputation is not exactly spotless. But if you have a G-reg on AOC then that may be the kind of firm you have to go to.

The whole engine was statically and dynamically balanced and runs very smooth.

Anybody wanting more info, email me.

jxk
 

I am sure that both smarthawk and myself could comment but won't.