Turbo "S" - Water Injection installation instructions - Sept '88

[euromobile900]

I've sent him a PM. I'll do some hardcore googling for some duplicates of the files as well.

[nordwulf]

I found them on the website and updated the first post with the new links. I also combined the images into a single PDF file and saved it on this site with a download link.

[nutcase]

Thanks guys

[euromobile900]

Yes, thanks, Wulf! You have succeeded where I have failed! I should have locally hosted them myself when it first happened, but I think I was new at the job?

[s900t8v]

Thanks,

its very interesting to see saab injected the water pre turbo. I guess they did this because there was no intercooler? It's really handy to have the nozzle size 150ml/min and the opening pressure (although probably not 100% useful as these were low comp engines.

[euromobile900]

Yeah they were low compression--what, 7:1 with no APC?

[s900t8v]

would love to know the specs of the pump! If anyone had the system and let me know that would be cool. It's handy they tell us it's a 150ml/min nozzle.

I'm trying to figure out the best setup for my 900 WI wise. It seems like Saab used a very basic WI system (on/off) it flows at 0.7bar (10psi) with a 150ml/min nozzle, maybe I'd use a 100-150ml (somewhere in middle) to open around 8psi ... Or set it up to pulse the a water solenoid in the line with the 150ml/min nozzle...

[nutcase]

I think it was injected pre-turbo to allow for a low pressure (cheaper) pump. The downside is it erodes the turbine blades.

[s900t8v]

not sure how much it erodes metal turbine blades, I know it's shocking for ceramics. It only happens too if it's not atomised properly? Or did you know people who said first hand their c900s had eroded blades?

[rpiereck]

Well, you have to remember that water doesn't compress, and that a turbine blade turns at several thousand rpm, getting up to 120,000 rpm at full throttle, high engine rpm. The water molecules, however small, will erode the blade tips, starting at the tip, less severely at the root. The blades end up having a rough texture on the leading edge.

This same thing happens with our helicopter compressor turbine blades, the ones that are exposed to dirt and water in flight. An automobile turbine blade has the advantage of being protected by an air filter, on our helicopter all we have usually is a steel mesh to keep the big stuff away, but sand, dust and water still makes it in. On highly dusty environments, like Iraq and stuff, we actually have a centrifugal particle separator that spins the air before it enters the turbine, which removes most of the sand and cleans the intake air. That system however, is unreliable and breaks a lot.

We usually will blend and root the blades as they erode, but only to point, we always have to measure first before blending. Good thing is that the blades that erode the most are the ones on the first section, and they're exposed to the outside of the engine, we can blend them without opening the negine, but you need tiny hands to reach in. I can't do it with my meaty paws. Once they're blended too much you have to remove the engine from the aircraft, open the compressor section and replace an entire section of blades. On the turbine section, we can replace each individual blade is they are eroded, but that is rare on the turbine section as anything that went in through the compressor is likely on fire in the turbine section.

The picture below hows one of the turbine vanes, with the individual blades installed on the left, and removed on the right. Notice the root looks like little Christmas trees, which locks them in with centrigugal force. When replacing those individual blades we have to replace a pair, always 180 degrees apart for proper engine balancing, they always come in matched pair and we have to weigh them before installing, and will trim them if the weight difference is more than on thousand of an ounce between each pair.



I got carried away, but yeah, water will erode them.