Could it be safer to *not* replace Rotax hoses after five years and/or overhaul at 2000 hours?

[APenNameAndThatA]

I suspect that the answer is a definite "no", because preventative maintenance prevents breakdowns. On the other hand, maintenance is the most significant cause of engine stoppages in large Boeings (or was in the early 1990's.) Does anyone have any anecdotal evidence? One factor is that if manufacturing gets better and better (a big if), breakdowns and unscheduled maintenance would become less and less likely. On a related note, are there any particular gotchas for oil changes and 100 hourlies? 

[kgwilson]

While a Rotax 912 et al is avery reliable engine it is somewhat more complex that an air cooled direct drive engine. There is a fair amount of plumbing, radiator and gearbox so it is pretty important that these things keep going and the replacement every 5 years or whatever the timeframe is I would consider absolutely mandatory even if the existing hoses look perfect.

 

It is certainly true that the risk of failure increases dramatically after maintenance so it is important to understand that aspect and deal with it wisely like test flying and checking stuff after the first engine run, flight etc. Even brand new quality controlled and tested parts can fail. The worst I've experienced was a brand new spark plug failed after the first flight & I was frustrated by murphys law as it was plug No 12 out of 12 checked.

[RFguy]

come on 5 years or 2000 hours isnt much to ask.

 

[onetrack]

While I agree that the chances of powerplant problems increase after maintenance, it is also a comparable point that rubber components have a higher failure rate after a few years.

 

Rubber and rubberised components degrade quite rapidly, with the effects of heat, ozone, UV light, coolant additives and other chemicals, and constant cycles of heat & cold, and pressure.

 

I would opine that the 5 year changeover time is not unreasonable, nor exceptionally costly, and properly done with due care and attention, I see no reason to avoid it.

 

Edited June 11, 2021 by onetrack

[Kyle Communications]

Well if you dont do it you are a candidate to be a statistic for sure. Fuel hose is notorious for breaking down with age and heat as KG says.

In the scheme of things it is cheap to do if you buy all good quality hoses from elsewhere that Rotax. There is plenty of parts that are far better than what Rotax supply. Now you must also replace the fuel pump every 5 years. I didnt think it was that necessary until my mate has had his fail. Luckily he caught it before any drama by always monitoring his engine parameters while flying.

 

 

 

[RFguy]

Jab in recent times reduced their hose replacement to 2 years.

 

Some of the hoses around the oil cooler plumbing are pretty close to the exhaust manifold, and also, they are unrestrained and flop about a bit. fatigue.

 

The fuel hose is also not well restrained as it might be, looks like the fire sleeve does alot of the stiffening job.

 

I wouldnt hesitate to do hoses 5 years or 2000 hours. Alot of far more intensive aircraft maintenance tasks would go past in that time !  

 

Edited June 11, 2021 by RFguy

[planesmaker]

I do have to wonder about rotax’s financial interest in the five year replacement especially with their pricing of mandatory replacement parts 

[Kyle Communications]

All Rotax parts are outrageous in cost  Each slipper half shell is $100.00 each  the fuel pump is $400. Sprag clutch is almost $1000 the CDI are $1650 each

 

 

 

[planesmaker]

Yes the new fuel pumps aren’t near as good as the old  pierburg pumps. I’ve had some failures of the new pumps even as low as 15hrs

[Kyle Communications]

We have just got in a new pump we are looking at using as a replacement. It is a Pierburg one...looks like it will be perfect. out of England...40 euro

 

[planesmaker]

That’s more like it

[Kyle Communications]

I got a new sprag clutch plate out of England for $140 landed here...the only issue is the outer is produced by Rotax so thats a issue but iy is usually the plate and springs not the outer drum that is the issue

 

[planedriver]

WOW! so it looks like you don't have to be in the aircraft, to be taken for a ride 

[facthunter]

Beware of statistics. Not doing replacement as being safer is ridiculous. Things used to be test flown. Cost has stopped that. IF a maintenance process can cause a safety concern adjust the process to eliminate that possibility as much as possible. Lets get REAL. There's also some CRAP stuff around so avoid it and PAY for good quality. Your PLANE is not a lawn mower that you can just leave where it stops and have a coffee, Nev

[Kyle Communications]

Yes. My engine for the S-21 only has parts in it that I could not get from elsewhere. I had to get the slippers, valve springs and cotters, studs and various shims and thrust washers...this totalled $2500 !!!!

The rest like roller bearings and gearbox bearings and all seals and Orings, the valves and pistons and cylinders were from the big bore kit all have been obtained from elsewhere and mostly are even higher quality that supplied by Rotax

Engine rebuilds can be done at a far better reasonable price if you know where to find stuff. I have a mate who is in a business that deals with all sorts of mechanical stuff and is a whiz at sourcing all this stuff. Oc course you cant do this with anything certified but for experimental or 19 rego its not a issue and you literally can save 10k on a rebuild

 

[Kyle Communications]

I agree Nev...all the parts we have used are either what Rotax actually use from a manufacturer but we got them from the source. The sprag clutch is from a BMW bike, Bearings are SKF or Fagg Orings and seals are all high end quaility most likely better than Rotax ones but being obtained from reasonable sources the cost is far far cheaper

 

[facthunter]

Kyle you can do this stuff and I'm a born and bred rebuilder out of necessity mainly but with spares the cost and quality they sometimes are I'm inclined to just regard the whole thing as a consumable and toss it when it's  expired. Life's too short to try to prove things and make silk purses out of sows ears. . Labour costs too much and Planes are full of Labour costs .Nev

[Kyle Communications]

The cost of the Rotax parts is a big part of what makes aircraft costs being expensive. Let alone the labour costs which are high of course. Most of the genuine parts costs are just off the planet when they are just repacked parts off the shelf from Joe Bloggs auto store

 

[facthunter]

It's relatively low volume  but you would think the design and development costs had been amortized by now. It IS possible they don't make much from their engines and how will the chinese made copy affect things. you might get  your "cheaper Parts" Now

  Ok where is the D motor, the Werner radial the Rotec Radials  and numerous other motors going. Older"certified" motors when rebuilt are usually less reliable than when they were first marketed. Two strokes are generally out due to being two strokes. the iconic Gnome and Rhone rotaries were likely to do 5 hours without major attention admittedly at the front line. Where is OUR future in powerplants.? The RR merlin got to 650 hours TBO max in civil use and was not legal at all in many countries. Nev

[Kyle Communications]

The future is electric of course...but the biggest stumbling block has not been solved enough yet...The batteries or for a more rounded solver...the fuel source

 

 

[RFguy]

It's getting closer.  25 years I reckon for batteries good enough.

.

Gasoline is about 15MJ / kg (taking into account ICE efficiency) 

Common batteries are 0.78 MJ/kg best. so, 16:1 right now.

!

For an hour of circuits for training, the electric is a no brainer (about 135kg of batteries) .

otherwise, not so much...

For short run times, the battery weight is offset by the light electric motor (15kg versus 75kg), so that buys you your first 60kg of batteries 'for free'. leaving 75kg of batteries to go in the wings.

 

at the moment one useful endeavor would be a hybrid =- along the hybrid  lines of ICE driving  alternator/generator  then prop motor. and 20  minutes of batteries to deal with an ICE failure + TO/climb  thrust. Ideally, the ICE would drive the single shaft  via a clutch the prop+generator/motor (single component).

This would eliminate the need for the ICE and motor to be oversized for TO, and provides for 20-30 minutes of run in case of EF. I think something similar to this already been done.  But maybe not motor in charge and discharge mode (dual purpose).  

 

 

Edited June 12, 2021 by RFguy

[Kyle Communications]

Certainly as a interim that would be a good solve

 

[facthunter]

Regenerative motors on a plane are a waste of time unless there's no weight or reliability penalty. Where you might use them you generally could have commenced your descent earlier and saved battery power that way.  A plane generally uses about 75% power for cruise so unless your ICE motor is above that it's not going to charge a battery at the same time OR power the plane. Nev

[skippydiesel]

With way less technical knowledge than you guys , I get a buzz/benefit out of finding lower cost parts for my Rotax/aircraft. Lower cost but the same part, often the same part number. I purchased  the upgraded "radiator" cap from a Ducati shop for about 1/2 the BF price (same PNo) brand new spark plug caps through a generous "mate" on this forum for less than 1/2 price. Get all my coolant hoses (less the specially bent one) from Repco/Gates. Still get my oil hose from BF as I have never found a good quality 17mm ID elsewhere. My oil pressure, coolant, volts, oil temp, sensor/gauges are by Speco, work flawlessly & a fraction of the cost from VDO. My CO monitor is a caravan/marine stand alone unit from Bunnings ............. etc etc I am very careful note to use anything that is likely to have a negative impact on my lifespan

Edited June 12, 2021 by skippydiesel

[RFguy]

(Nev) yep.

 

The kicker is that to keep a  plane flying , lets say a ubiquitous J230, will need something like 25kW to keep it airborne S&L. 25kW and 20 minutes  needs something like like 50MJ of batteries - about 75kg of them !

but decreasing at about 5 % per year for lithium batteries, and then at some point there will be a 2:1 jump on another chemistry.