acw

My Feedback: (1)

About 2 weeks ago, I had a flame out with my Ares L. The engine made some unusual noises and then silence. I almost made it back to the runway but slightly damaged the front gear mount after landing in a rough area. After inspection I noticed the electrical connection to the engine popped of. I assumed airflow from intake did that.

I repaired the plane and went back to the field a few days later. The engine failed to start with a bad glow plug message. At home, I removed the engine and found out traces of rubbing on the compressor and a missing blade on the turbine wheel (hot section). The obvious became apparent. I became more comfortable with the plane and was practicing some 3d maneuvers such as hovers, flat spins and square loop. I was having a lot of fun and likely over G'ed that engine causing it to break in flight. The electrical connection popped of due to vibrations after a catastrophic failure.

Obviously when something like that happens, my next step is to understand how to prevent it. One thing I can do is to add some voice warning when the plane exceeds some G limit. But the question becomes: what is the maximum G limit our micro turbines can handle at full power? So for example, if the limit is 15 I could set a warning at 10 etc...

Note: I don't wish to discuss what brand turbine I was flying or which brand X is better than Y. They all have limits. Just trying to figure out what the limits are.

Thanks!

cetigershark

Hi there
I do not know how many Gs you put on the airframe during a typical flight, But with an ARES I think you will not get over 10Gs, the wing will stall before that value. What really makes the turbine assembly suffering is the gyroscopic effects. I mainly use Xicoy turbines and they explicitely do not recommend 3D flying (or extreme 3D flying) with their turbines. When you look at your compressor/intake section from the front, where is the rubbing/abrasion? If it is on the side (like 3 or 9 o'clock..) then it can be clearly from too many positive or negative Gs by a massive dive or pull up maneouvre.

Regards
Chris

scoeroo

My Feedback: (9)

The design of our turbines is based on the single / common shaft design , these are susceptible to torsional harmonic issues at certain attitude's - attitude's not altitudes
If it were possible to design in such a small package the turbo fan free shaft style it would make torsional issues a non event
In time we know a manufacture will come up with such design , till then ..... we have what we have

JSF-TC

My Feedback: (2)

It is not the G level that is causing the issue. Turbine rub (and subsequent damage) is primarily caused by the gyroscopic forces induced by very high Pitch Rates and/ or Yaw Rates.

Remember how hard it is to rotate a spinning bicycle wheel, or when playing with a gyroscope - our rotating turbine components are exactly the same, but ours are now spinning at 100,000rpm or more.

The gyroscopic forces generated by these pitch/ yaw rates are huge, and are transmitted through the bearings and into the case. With both the compressor and turbine wheels hanging off the end of the shaft, and only supported by the two bearings, they will naturally deflect, to include gyroscopic precession, and may start to rub.

Rubbing at 12/6 o'clock is signs of too much yaw rate, and rubbing at 3/9 o'clock is due to too much pitch rate. Precession effects show up 90degrees away from the applied rotation rate.

If you don't get rubbing and/ or catastrophic failure, you'd at least have to expect not to make the full 25hr bearing life.


There's been more than 1 full-size engine that has had major rub issues by flexing of the rotating parts due to gyroscopic forces. Leading to multiple aircraft losses and loss of life too. And they were designed top handle it too.

Our model engines survive this abuse more by luck than design.



Paul

David Gladwin

Much if what has been written here, particularly about gyroscopic forces, makes eminent sense.
These engines are not made with 3d type flying in mind.
I don’t fly my jets “hard” but I found typical Gs about 4 for a loop or max rate turn. About the same as a fullsize jet trainer.
Even doing square loops with a 120 powered Reaction never exceeded 6 G and that was enough to slightly bend the aluminium wing tubes !
If you want real data, the V Speak vario pro. has a 3 axis a accelerometer, G meter, incorporated.

acw

My Feedback: (1)

Great information on this thread. Thanks all!

But then the key question becomes: how do people with 3d planes mitigating the very real risk of destroying their engines? Is there maneuvers that should clearly be avoided or only be done within some parameters (ex: low speed)? Where is the limit in practice? It appears that the line is blurry and to make things worse, we aren't in the plane to feel it.

V Speak vario pro is interesting and I could setup some warnings for over acceleration on each axis. I'll definitely try that.

JSF-TC

My Feedback: (2)

In my opinion, low speed is the worst of all. This is where maximum pitch/ yaw rates can be generated, and with the engine at high power. Just watch how quickly a low speed nose up or down tumble occurs - 1 to 2 seconds to flip fully around. At conventional (higher) speeds there is no way to generate those pitch/ yaw angular RATES, so the induced gyroscopic forces will be way less .

Note that high roll rates don't affect the engine at all.

Personally, like David, I only fly scale type maneuvers. 3D (prop or jet) does not interest me, so I can't comment on long-term engine issues that may be attributed to this style of flying.


Paul

FlyJ

There are engines available that are plenty capable of handling the glycolic loads induced by extremely high rate flat spins. I’m currently using a Swiwin 220 on a CARF Diablo and it has been great. The flat spin rate is ridiculous. My estimate is close to 540°/second at full throttle. I’ve seen similar results with the Kingtech 210.

My guess is that you’re using a Xicoy which I’ve seen have issues with rubbing even without high gyroscopic loads. If you have an Ares, you shouldn’t be limited by the capabilities of the turbine. There are several turbines that can handle the torture of 3D flight, though you may need to send it in for bearing service at 18hrs instead of 25hrs.

JSF-TC

My Feedback: (2)

Part of the solution to getting higher thrust out of our modern and smaller engines is to reduce the clearances between the rotating parts (compressor and turbine wheels) and the adjacent static parts, to reduce the leakage of air.

With reduced clearances, there is less room available to allow the rotating parts to deflect under gyroscopic forces. Adding more structure on the fixed side adds weight, and adding a stronger/ stiffer shaft adds to the rotational inertia, slowing down engine response, so you get into a vicious circle of trying to make a small, powerful, responsive, light-weight and abuse-tolerant engine.

It sounds like Xicoy may have focused on the efficiency, size and light-weight goals, while some other brands may have traded some of that off resulting in it appearing to be more tolerant of the 3D flying style. It's all al balance.



Paul

acw

My Feedback: (1)

I have many Xicoys but that's not what I had in the Ares...

So you guys flying 3d, what specific engines are you successfully using? Success being defined as 10+ hours of runtime flying 3d without any problem?

FlyJ

Kingtech, jetcat and Swiwin have all been used successfully in 3D jets.

Swiwin 220s and 240s had a recall on the compressor wheel about 12 months ago. There are still many floating around that didn’t receive the new compressor wheel.