Damage due to pulling/pushing on Propeller

[abgd]

I always understood that he would keep a little upward load on it as well to make sure it would not flap downwards.

That may be true, though I believe naval helicopter pilots sometimes use downthrust after landing on a moving deck.

My favourite youtube rotorblade clip:

[foxmoth]

Could not understand a word!

[Aviater]

Yes you can bend an ali prop and damage a composite prop by pulling on it. Prop shops do it all the time. It's called cold working. Looks like there's a lot of opinion here so without getting all technical I'll add this.

I've seen damage to both kinds of prop. Ali and composite.

Props are under incredible load during different phases of engine operation. Granted. But they are specifically designed to carry those loads.

If you point load a prop blade in exactly the right spot with enough resistance + force, you will bend it.

But most things people have said ring true and if you stick to your common sense, you'll never have a problem. ie; Don't pull a 421 out of the mud by a single blade tip and take extra caution with wooden or composite blades. Which are easily damaged by mishandling. I've pulled 3 composite props this year that have been damaged without the engine running.

[Capot]

Fascinating clip in abgd's post.

Thread drift again, sorry....

Is it just coincidence that - in that clip at least - the blade flaps downwards, fairly consistently, as it passes the tail rotor? I can't think of a reason why it would do that.

[riverrock83]

Originally Posted by Aviater

I've pulled 3 composite props this year that have been damaged without the engine running.

You need to be a bit more careful then!

It does show however that this isn't an old wives tale.

I have seen elsewhere mention of not to pull "wobbly" props as this can damage the hub. Does anyone have any opinion on this (and isn't it difficult to tell for most non-engineers whether a prop is variable pitched or not without looking at the controls?

[CJ Driver]

Props are bigger than you think

I always imagined propellers as "flimsy" and worthy of delicate handling until I had the opportunity to see one NOT attached to the front of the aircraft. I'm talking about a C172 propeller - nothing fancy. When it is leaning against the hangar wall it transforms from my little propeller to become HUGE. It is built like a girder, but beefier, and I can hardly lift it, because it weighs so much.

Suddenly it went from being the most fragile part of the aircraft to the toughest. So, if you are looking for a part to push or pull, don't choose the cowling, or the spinner, or the strut, or the wing - grab hold of the propeller instead!

[mad_jock]

levers and application of force are not obvious to the majoirty of the population.

I did a consultancy job for a court case for a police force that was sueing a stiff cuff manufacture for supply faulty goos which wern't fit for purpose.

BAsically they were bending and failing while making an arrest.

So we did material tests on them which proved that the metal that they were made out of was over spec'd for the contact.

We put them in a the testile puller under various conditions using scafolding poles as the levers. Again passed with flying colours compared to the spec and contract agreement.

Put them in the hands of one Her Majestys finest drug enforcment officers who has years of practise subjecting people to the maximum legal amount of force as required tackling a druggie who is out of there tits they bent like a twix in the tropics.

With the forces involved we couldn't understand how the person being arrested arm was still on afterwards never mind not broken.

We got asked to foxtrot oscar and they lost the case 9 months later. If they had asked us we could have told them that there specs were wrong and that all they needed to do to the current ones was super glue a metal spacer to torsionally stiffen the cuffs and you could have rolled a car over using its towbar hook using one of them.

Its all in the application of force not the amount or how strong the thing looks that your apply it to. If its not been designed to take a load in a particular way you can break it.

[peterh337]

I've pulled 3 composite props this year that have been damaged without the engine running.

How (precisely) was it damaged?

[mad_jock]

I would have presumed Peter the matrix will have started delaminating around the stress point down at the hub. As soon as it does that it will start wicking moisture and bit of a freeze a prop failure here we come.

Always did think that making props out of composite was asking for trouble.

[A and C]

Jock

I have to totally disagree with you about composite props, the advantages outweight the disadvantages.

As this thread is about damage the main advantage is that you can repair a composite prop and return it to its new size & shape.......you can't do that with a metal prop.

[mad_jock]

I will bow to your experence fixing them.

My none aviation experence of comporsite structures were they were a royal pain in the arse when damaged both fixing them and proving that they were still fit for purpose. But this was in applications which wern't weight sensitive and throwing a couple of tons of steel at it might piss the product design mafia off but wouldn't result in any real penalties.


Has anyone ever made a titanium prop?

[ChrisVJ]

I have seen props used for pulling aircraft for years, though personally I wouldn't do it to a wobbly. Jemima has a composite ground adjustable prop however since she is a pusher and the prop isn't accessible for pulling or pushing I had not really thought about it for a long time.

I can see how a composite prop might be susceptible to damage even though designed to be robust enough for flight.

Jemima has an IVO 3 blade. Each blade is held by two bolts and goes about 3 inches into the hub behind the front plate. The prop is hollow too with a steel rod down it for adjustment., With the right hub it can be adjusted in flight by twisting along it's length by twisting the rod at the hub. (So the hub end is not just solid composite material.)

During flight there is a strong centripetal force which might mean that the prop is 'advancing' and applying force at the hub but not a leveraging force, (ie, it works like a helicopter blade.) When stopped and a load is applied to the prop the force at the hub would be all leverage and the point of the hub in contact with edge of the front plate could receive a load several times the actual load applied, say, 10 or 12 inches along the prop.

Not saying it could not take it. Just thinking out loud

[mad_jock]

There is a huge difference (well just times it by how far out you put your hands)

Between hauling on the thing next to the root and pulling at the tips.

One hand either side of the hub and close in won't do any damage.

The further your hands are out away from the hub the more chance you have of damaging something. Also as well pulling only one side ain't to bright either.

And that goes for metal, wood and any other material that takes your fancy.

[A and C]

Jock

Composite structures are a very different thing from metal and this is a big problem within the industry, a lot of the major players within GA have a very worrying lack of knowlage and ability when it comes to composites.

Almost all of the Daimond and cirrus approved maintenance shops in the UK are not capable of all but the most minor repair work, this leads to the aircraft becoming expensive to insure as the aircraft get written off for damage that could be fixed. One example is a DA40 that was scrapped on the south coast simply because the maintenance company had no idea that the damage was repairable, the aircraft could have been back in the air within a month or so had it been looked at by the right people. (NOTE this sort of damage would be repaired IAW a manufactures repair scheme ). Unfortunatly this also is true of parts, things that should be repaired are being scrapped due to lack of Repair knowlage within the industry and it is the owners that are bearing the cost!

The knowlage of the long term durability of composite structures is mostly to be found in the renewable energy industry as these structures are having to last up to thirty years with minimal inspection, I know of one aviation based company that is in the renewable energy sector and they have fatigue numbers for composite water turbines that say the turbines are good for thirty years running. The boss of this company is of the opinion that compared to water turbines aircraft get a very easy life with lots of inspection and so are far easier to maintan safely.

[BackPacker]

The knowlage of the long term durability of composite structures is mostly to be found in the renewable energy industry

The gliding sector also has a lot more experience with repairing composite structures. In fact, whereas most powered composite aircraft are still built of glass fiber, most high performance gliders will have a substantial amount of carbon fiber content since it's even stronger and lighter than glass fiber. But reportedly even tougher to work and repair.

[A and C]

Backpacker

You are quite correct in saying that the gilding sector has a lot of experience with composite structures, Unfortunatly almost no one from this sector has taken the step of getting the EASA145 approvals enable them to repair whole aircraft.

In terms of calendar life with composite structures the gliding industry has some experience but due to the nature of gliding the airframes don't do a lot of flying hours, this has to be contrasted with some water turbines ( the blades are about the size of a GA aircraft wing) that will operate underwater and have an expected fatigue life of 250,200 operating hours.

I would be interested to know the number hours that the highest time GRP glider has flown.

[BackPacker]

A and C, all true. The only thing I can add is that gliders do have a lot of cycles (starts/landings), which arguably puts more stress on the airframe than flying hours.

And I think gliders suffer minor (repairable) damage more often than other aircraft, due to hitting stuff during outlandings.

[mad_jock]

Its a big problem in every industry that uses them.

I would say that the marine side of things has more experence than the rest put together. And I know a couple of lads from sailing who have been pinched from boat yards to work on wind turbines etc.

But still to this day I believe that most repairs are in the hands of god and also the person that fixes it. The anal attention to detail of the fixer comes into play more than anything else. The same of course is the same with fixing metal structures but at least with them you can NDT them and carry out other checks to prove that they are fit for use.

Unlike the comporsite repairs where you have to trust that it has been carried out in exactly the right temprature, right humidity, there isn't any contamination of the matrix such as hairs or dust etc , the weave direction has been aligned exactly as per requirments (may need a full engineering analysis because it may be different to the original) Then you have issue with the interface between two matrixes and not actually knowing whats been damaged you can have sections where the fibre has gone but the matrix looks fine and you wouldn't have a clue.

I know I am an ex engineer that mainly worked with metal but the state of affairs when I stopped working as an engineer was that the compersite side of things was at the same level as pre liberty boats and the Comet with metal. You asked any of them if they could prove anything and they would start talking statistical proberbilitys of failure.

I know things have improved since then on the production side of things but the fixing them still isn't a science in the same way as fixing metal is.

[A and C]

Mad Jock

You do have a very good point about quality control with composite structures, we inspect the job at each stage to make sure that all has been put together correctly, the post cure temperature and time are monitored by two independent systems, a sample of the resin is kept for analissis and if it is a spar boom we are repairing a test sample of the rovings and resin are made as the spar is being assembled. This test sample is tested in the same rig at the manufactures as they test samples of new spar booms.

Composite quality control is not a problem if it is done at the time of assembly but is as good as imposable once the assembly has been compleated, this is unlike most metal repairs were it is clear if a repair is not up to standard just visual inspection.

[mad_jock]

Yep would agree with that.

I would also say as a pilot I can visually inspect a metal prop and "not flying that, its fecked"

Compersite prop you wouldn't have a clue until it failed for 50% of the time. All because some plonker was bouncing the aircraft through a rabbit hole holding onto the prop tips.