Water Brake Dyno for High Altitude Simulation

Welcome back to another episode of Dyno Insites! In today's episode, we're diving into the exciting world of aerospace high-altitude testing. Join Chris Middlemass and Mike Golda as they unravel the complexities around a test project which required simulating altitudes of up to 40,000 feet.

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Transcript

Diane Nossal [00:00:09]:

Thank you for tuning into Dyno Insites. In today's episode, Mike and Chris describe a test system designed to simulate high altitude conditions of up to 40,000 ft.

Mike Golda [00:00:22]:

So ever work on a test project where you had to simulate altitude?

Chris Middlemass [00:00:26]:

That's an interesting one. We've completed a big project there, and it's quite something. It's not practical, obviously, to put a dyno in an airplane and take it up to altitude and test there, that's for sure. But therefore we have to create a false altitude on the ground. And in doing that, it brings some challenges to using a water brake. So you say, well, why use a water brake? But in that case, because of the speed and power that we're running at, really, a water brake was the only realistic solution.

Mike Golda [00:00:57]:

 So Chris, high altitude. What does that mean? How high are we talking?

Chris Middlemass [00:01:02]:

Well, to start looking at high altitude, we're typically looking at 35 to 40,000ft. And at that altitude, the air pressure is a couple of inches of mercury. And the temperatures are around about minus -50 -60 degrees centigrade 

Mike Golda [00:01:23]:

So is that like commercial airliner type heights?

Chris Middlemass [00:01:27]:

It's testing a bit above that to cover eventualities when an aircraft might have to go above some weather or maneuver. So we try and have a higher capability than we'd be running in as under normal flight.

Mike Golda [00:01:41]:

Okay, so what other challenges were there that you experienced besides the water brake? So you mentioned the water brake, right? So what's different about a water brake that operates at altitude versus high altitude.

Chris Middlemass [00:01:53]:

If it was operating at altitude, that will be fine. The simulated altitude creates some issues where we're pumping water through the Dyno to do the power absorption. But it then has to drain from the Dyno under natural sort of gravity. If you have a simulated very low altitude, then you're also running at a very low temperature and there is a situation where, because of the temperature, the water can try and freeze, but because of the low pressure, it's actually getting close to boiling point within the machine. That's interesting sort of variation of temperatures we have to deal with.

Mike Golda [00:02:31]:

So you kind of broached the second question I had, which is obviously simulating altitude and being at a different pressure is one thing, but also you've got the temperature aspect that you need to focus on as well or potentially control.

Chris Middlemass [00:02:45]:

Yeah. If we're creating a true altitude condition, then we'll have a very low atmospheric pressure that's clear with the altitude. But the same. What comes with that is running at a very low temperature, actually getting down to more like 60 degrees negative centigrade and having to deal with water at those temperatures becomes a big challenge.

Mike Golda [00:03:05]:

That's pretty cool.

Chris Middlemass [00:03:07]:

Yeah, we have to have a lot of thermal insulation around the machinery to protect it during the cold. But then when it starts operating, it generates its own heat which we have to let escape. Otherwise, we'd start creating some overheating issues. So a strange set of conflicting conditions.

Mike Golda [00:03:26]:

So is that commonplace? Is altitude testing, is that a one off or does that happen frequently or is it the requirements?

Chris Middlemass [00:03:34]:

We're seeing quite a few of them, I think, as the engine manufacturers are looking to develop their engines for different conditions. Testing them in aircraft is very expensive so there is more interest in testing on the ground under simulated conditions.

Mike Golda [00:03:52]:

So are there other considerations that you need to be on the lookout for in regards to operating under those conditions? Or have you had experience with other things, other applications on top of that, other requirements on top of that?

Chris Middlemass [00:04:06]:

Not as extreme as the altitude one. I mean, we're looking at how do we incorporate different capabilities within that testing, how we expand the range of testing that can be achieved under those conditions. The altitude one in itself took some time to solve because we've got to deal with this water condition and the different ceiling expectations in the Dyno. Having got past that, you can then look at how do we create more, in this case, flying conditions on the ground under these simulated conditions.

Mike Golda [00:04:37]:

What do you mean by flying conditions?

Chris Middlemass [00:04:39]:

Well, for example, there are times when we look to run the engine, run an aircraft engine under no load or even under sort of a failed condition to simulate different fault conditions in the aircraft. And so there we may have to provide zero load from the Dyno to the engine, which for a hydraulic Dyno, we need to have some assist system to balance the load, the sort of parasitic load that the Dyno has at very low, high speeds.

Mike Golda [00:05:09]:

How do you do that?

Chris Middlemass [00:05:11]:

Well, in this case, we're running an electric motor behind the Dyno to effectively provide a drive into the back of the machine. So that way you can balance the drag and the engine sees a zero load condition referred to as a backdrive system.

Mike Golda [00:05:25]:

So back it up a little bit. I'm real interested in the temperature aspect. So you've got a dynamometer that's used to operate in normal conditions per se and you have to put it in a condition where you said below minus -60 degrees. What do you actually do to the product or the dynamometer to protect it from freezing.

Chris Middlemass [00:05:46]:

Interesting one. If we weren't running the Dyno, we would just drain it the water out of it and it could sit there at negative temperatures without any issue. The challenge comes when want to run it under those conditions. And bear in mind that once an engine's operating in a test cell under those conditions, it's going to generate heat and create its own environment because it'll achieve a running temperature. So for the Dyno, we've got to have a situation where we protect it from the cold so that the liquid inside isn't freezing, that it can still operate as a hydraulic dyno. But we have to then have the ability to reduce the cooling, to allow it to reach its operating temperature and run under normal temperature conditions through most of the test.

Mike Golda [00:06:34]:

Interesting. And again, I'm trying to get a picture in my head of what you're describing. So you're explaining a dynamometer, and then you said to simulate the zero load conditions. Now you're attaching an electric motor to it to overcome the parasitic losses of the dynamometer and the drive line. Have you had applications where you had more than just a motor and a dynamometer, like you mentioned, simulating the airframe? Have you had applications where you had to simulate the airframe itself or the inertias of the airframe?

Chris Middlemass [00:07:02]:

Yeah, in some cases, because the Dyno is driving sorry, the engine is driving the Dyno shaft. That's typically a lot less inertia as a rotating system than it would be if it was driving a turbine or propeller for an aircraft or a helicopter. So what we typically use is a flywheel attached to the Dyno and the engine and use the weight of the Dyno to simulate the inertia of the engine operating in an aircraft.

Mike Golda [00:07:31]:

Interesting.

Chris Middlemass [00:07:32]:

And in some cases, we can supplement our flywheel with a braking system so that we can decelerate the shaft more quickly, or we can lock it in a non-running condition to simulate the change from an engine operating. Coming to land and then stopping and being locked in the stationary position sort of quickly after a running condition so we can simulate more operating conditions.

Mike Golda [00:07:57]:

So what I'm visioning in my head of what you just described is you basically have the customer's engine. You've got a drive shaft that connects to a dynamometer, then a dynamometer that connects to a flywheel, and then a flywheel that connects to an AC motor or electric motor.

Chris Middlemass [00:08:14]:

It almost sounds like a song, doesn't it?

Mike Golda [00:08:16]:

Doesn't it? So it's quite the system, then. Yes. I can only imagine from a controls perspective, there's challenges associated with that as well.

Chris Middlemass [00:08:25]:

Yeah, you're quite right. It becomes very complex in trying to match the conditions all the time and create the right running situation to replicate a test.

Mike Golda [00:08:36]:

Now, would you consider this type of test stand, something that's a steady state, something that's very dynamic? How would you describe the operation of a stand like this in those conditions?

Chris Middlemass [00:08:47]:

Well, I think that's, on the whole, this would be a steady state, but with the flywheel, we've got the opportunity to run transients and use the inertia to simulate the acceleration of the engine with its propeller.

Mike Golda [00:09:01]:

Okay. So with this, I can only imagine things don't go as planned. With a system as complex as that is, there's probably some challenges along the way that make it that much more challenging to design, engineer, and build and then operate. So I'm assuming that nothing goes as planned. Typically, when it seems like when you're putting together a test cell and nothing goes perfectly. I would envision that this one would be even that much more complicated or complex to start up and commission something like this.

Chris Middlemass [00:09:35]:

It does get so. Again, one of the issues with the simulated altitude, as I mentioned earlier, is the water conditions under very cold and low pressure. We finish up with the drain from the Dyno, becoming a challenge to make sure we can take the water out of the Dyno, move it away from the Dyno, and move it away from the low-pressure condition before it then is reintroduced into the cooling system of the test cell. So you finish up with some quite complicated plumbing, which is beyond the complexity of the Dyno, but was really quite a serious challenge in how to accommodate that in the test cell.

Mike Golda [00:10:13]:

So, Chris, that was pretty intense podcast in regards to a system application.

Chris Middlemass [00:10:18]:

Well, that's what makes it fun, Mike.

Mike Golda [00:10:20]:

Yep, you're right about that.

Chris Middlemass [00:10:21]:

Good talking.

Mike Golda [00:10:22]:

Same here.

Diane Nossal [00:10:24]:

Thank you for listening to Dyno Insites presented by Froude. If there are any engine testing topics you would like us to discuss, we'd love to hear from you. Please email us at podcast@froudedyno.com.