Rotax 135 HP Engine

[deandob]

West Oz Flyer - excellent post that explains some of the details of the rotax & turbo implementation, and has helped my understanding. Consensus seems to be for a newbie like me to go for a cheaper/lower power/smaller gyro and practice on that before graduating to a more sporty / larger / power machine.

I just have to get over my trepidation of the feeling that the smaller gyros are basically a seat on the front of a motor, a prop, rotor and tail - nothing between you and the elements, and as a beginner this is a significant confidence challenge to overcome. Also to eventually graduate to my 'dream gyro' at a later stage (when more experienced) means having to sell the old one & purchase another machine, which is a hassle.

I'm sharing this as these are the thoughts going around my head as a new person interested in learning & being part of the gyro community but trying to work out the best pathway to entry (safety and getting the right instruction are the other dimensions). What I like about the larger more powerful new generation gyros is that they feel like a small fixed wing, factory built / tested (so takes away some of the mechanical / structural concerns) and (in my opinion) make it easier for new people to come into the sport. But I can also see that the smaller more agile gyros will be more fun to fly, but not until I have the confidence / experience.

[WEST OZ FLYER]

Fourth time lucky, I have been trying to post this for awhile but it wouldn't let me.😠

Automotive turbo failures are normally a result of high engine loads (especially at low rpms), high boost pressures, poor maintenance and poor operating proceedures. Aircraft engines operate at maximum load at maximum rpm as determined by the pitch of the prop, hence maximum continuous rpm in the aviation world. Additionally the boost pressures are very conservative.

Turbo bearing failures are generally from poor maintenance, poor oil quality, over fuelling, very high oil temps, putting too much load on the engine/turbo before it is at operating temp and shutting down the engine when turbo is still hot turning the oil into carbon on the bearings.

Sure high egt's can damage a turbo but there is generally low boost pressures associated with aviation engines. Theoretically there is a "safety" margin in there so overspeed should not issue for turbo failure. The extra boost from the extra speed could cause an issue. As aviation engines don't need instant boost reponse running a bigger than normal turbo will supply larger volumes of cooler air (from not working as hard to compress the air - heat) in the upper rpm region where the power is most needed for aircraft applications.

Setup properly the Bing carbs lend themselves well to turbo application but they do have their limits. Turbo engines add alot of extra complexity, especially on the fuelling and ignition timing side of things. I am still unsure as what is done with the timing on these engines. The compression ratio has been lowered. At 5psi and 8.0:1 static compression ratio, the effective compression ratio will be roughly 10.7:1. That is not much more than the standard 10.5:1 but anymore boost could be bad without timing modifications.

My concern is how thin the piston crowns are. A lean mixture will cause pre ignition or detonation and possible melting. The 9 series Rotax have liquid cooled cylinder heads and air cooled barrels unlike automotive engines that are fully liquid cooled which can dissipate the heat more efficiently. One of the earlier guys pioneering this 100 hp Rotax turbo was welding the underside of the piston to allow for extra crown thickness. Mind you he was pushing out more than 135 hp.😁

There are also weak spots in the crank case if you look in the right spot.

Extra power can get a inexperienced pilot into trouble as well so my humble advice is get yourself a second hand single seat gyro powered by a suby EA 81 & go fly that around for a couple hundred hours & then you will have excellent base to work off. - That is the best advice you will ever receive.

Flying marginally powered machines has saved my bacon on a few occassions. You actually have to fly the machine and not rely on the power. The extra power is good when you know how to use it effectively

[deandob]

Wow, that is a lot of experience. You must be dizzy with all those circles

I drove a Subaru Leone in the 80's for a number of years and worked on the EA81 (usual things teenagers did to hot up their cars....) - I'd never imagine it strapped to a gyroplane back then. I guess this engine is popular due to the Boxer configuration (lower center of gravity, reliable, good power to weight ratio).

Regarding open frame single gyros, I can't get over the raw experience of hanging out there in the breeze at 500 feet up and 60 knots.... Even the open cockpit models like TAG I have some hesitation but could get used to it. Closed cockpit & especially side by side gyros are a little easier for newbies like me (and will attract more new people to the sport) - but I can see that a gyro like the TAG would end up being more fun in the long run. I definitely want a 2 seater (likely tandem) that I can be trained in / get used to, and eventually take a passenger when I'm competent enough.

[Brian]

Thank you Brian for the advice.

No problems dean, only too happy to help, I have been fortunate to see a fair bit & have learnt from watching & listening plus having a few thousand hours of flying around in ever diminishing circles. My first gyro was an open frame single seat powered by a EA 81 suby. It was a bit heavy, cruised at 4200 revs & wide open at 4400 revs so I learnt a lot about rotor management plus managing speed

[deandob]

Thank you Brian for the advice.

[Brian]

Quote from Dean "Good advice Brian. Agree having the extra horsepower if implemented well is actually a safety benefit to help power out of trouble. Being new to aviation and gyros I can't avoid the temptation to look at the gyro crashes on youtube and sites like gyroaccidents.blogspot.com and it does seem that having more horsepower would have helped avoid a number of accidents especially on takeoff (I'm still learning gyro theory - not having the rotor up to speed before climbing seems to be the most common takeoff accident cause though)." End of quote.

Crashes on takeoff can be mainly attributed to rotor management & I'm not going to delve into that here except to say that the lack of this basic skill is a big factor into all sorts of things going pear shaped & resulting in destroying beautiful machines. Extra power being applied during takeoff where the rotors are NOT up to flying speed will see disaster happen very quickly.
All instructors should be able to teach the student pilot all about rotor management. The big influx of the European gyros that call for the pilot to run the blades up to 200 revs or whatever specified for that particular gyro whilst being held stationary by the brakes & then release brakes whilst applying power if not done exactly right will see lots of pretty gyro being spread over the runway ! So it pays to learn, practice until you can do it in your sleep !

Extra power can get a inexperienced pilot into trouble as well so my humble advice is get yourself a second hand single seat gyro powered by a suby EA 81 & go fly that around for a couple hundred hours & then you will have excellent base to work off.

[Brian]

I can fully understand Bert not commenting on turbo 912 's & why would he condone someone adding a turbo & then wanting Floods to honour a possible warranty problem which could be as much as a blown motor.
Gets down to the owner taking the risk for paying for a stuff up should it happen which is the way it should be !

[deandob]

I doubt that.

West Oz Flyer - care to explain? That hasn't been my experience with auto turbos - local heating by an overdriven exhaust turbine is severe, causes the oil to breakdown, warping and even metal fatigue. But the failure modes for a turbo on the rotax motors may be different, so I could be wrong.

[WEST OZ FLYER]

One thing I don't understand is why rotax don't use fuel injectors for the turbo motor especially if they have added additional electronics / safeguards to control boost.

The 914 has an enrichment solenoid operated by the TCU. It's not an injector but does what you describe.

[WEST OZ FLYER]

I think the bearings in the turbo would fail before any heat damage to the engine (and higher performance turbos have an oil cooler to help).

I doubt that.

[Waddles]

Thanks Rick for that info on turbocharging. I'll stand corrected.

The Xenon is the one from the hunter that you enquired about in an earlier post.

I reckon that Bert doesn't talk much about these modified Rotax engines because they don't come from Rotax and he is the exclusive Rotax dealer here.

Waddles

[RickE]

Rick, were you thinking that the blokes at Bert Flood thought that the modified aftermarket turboed 912 was a 'good thing' or 'not so good'?

Not sure Trooper. From memory though I think that the guy's modifying the 912 were taking on the warranty side of it as well.

[deandob]

While we are talking about the rotax engines, I just read up about the new 915 fuel injected turbo motor, and it delivers an extra 20HP over the 914, which is nice, as well as the fuel savings, even though it is more expensive. This motor apparently is just about ready for use by the gyro manufacturers, and as I have started to look at a what gyro to buy, I'm wondering if waiting to buy a new gyro with the 915 would be a smart move, not just for the extra power & fuel savings, but for the resale, as depreciation is a large part of the ongoing cost of ownership. I assume in a couple of years time the resale on a good gyro with the 915 would be better / more desirable than the same machine using a 914.

Would be interesting to see the torque curve difference between the 914 and 915, as a fuel injected motor has more flexibility for tuning versus one with a carby. If the torque comes on stronger at lower revs the motor will feel stronger and more responsive.

Also I couldn't find the price list for the 914 and 915 - anyone have these?

[RossM]

Looking at the gyro accidents blogspot link, may have to take a photo of the ASRA website now, as G3500 looks a bit worse for wear.

[deandob]

Good advice Brian. Agree having the extra horsepower if implemented well is actually a safety benefit to help power out of trouble. Being new to aviation and gyros I can't avoid the temptation to look at the gyro crashes on youtube and sites like gyroaccidents.blogspot.com and it does seem that having more horsepower would have helped avoid a number of accidents especially on takeoff (I'm still learning gyro theory - not having the rotor up to speed before climbing seems to be the most common takeoff accident cause though).

Rick, the trick with getting more boost from a 914 is likely similar to the auto bolt on 'chips' which modify the data coming from the sensors to trick the engine management computer or even remapping the timing/fueling tables.

One thing I don't understand is why rotax don't use fuel injectors for the turbo motor especially if they have added additional electronics / safeguards to control boost. Allan and I discussed this on the weekend at Caboolture as carburettors aren't as reliable as fuel injection and require regular tuning. Fuel injection has been around since the '80s in the auto world, and the new rotax motors with fuel injection apparently costs a bit more (and the fuel savings won't pay back the extra cost). In fact these rotax motors are pretty expensive for what they are, even without the fuel injection.