Necessity of anti-ice systems for hobby runs?

[cursorkeys]

Does anyone have any knowledge of the speed of ice formation in commercial/military gas turbines?

I know that intake/IGV icing can occur well above 0°C and/or the dew-point temperature but nothing out there seems to say how fast the ice can possibly form.

Thus far I haven't connected any of the anti-icing systems on my engines up. But, as as the temperature is hovering around freezing here and damp I'm wondering if quick 10 minute runs are likely safe or if any ice could form in that short time?

[gidge348]

Not sure, but I have removed all the anti icing from my Nimbus just to cut down the number of things that can go wrong.

But I will be just running it in the middle of a salt lake in temps 30-45°C with very low humidity.

Having said that, a friend of mine (Black Hawk maintenance pilot) had a look at the engine and expressed some concerns that I should keep an eye on it because the formation of IGV ice can be very different from engine to engine.

I personally don't think it will be a problem with 10 minutes or less but just keep an eye on it. If it does generate ice that dislodges it will be pretty small in 10 minutes.

Ian...

[gidge348]

Hi Jon,

Just had an "Oh Bugga" moment thinking about your question on icing.

I was planning on running a 15L/min water/methanol injection system as suggested by John Wallis.

As mentioned before I have removed all the anti icing, but now I am wondering if the water/methanol may drop the temp and increase the dew point to a point where icing may occur?

I was wondering if some smart person out there would have a calculation or idea on how to calculate icing conditions?

Ian...

Ps. have you had a go at starting your engine yet?

[cursorkeys]

Hi Ian,

Thanks for the info, that's very helpful.

I've managed to talk to a retired RAF pilot who said that it was policy for them to use engine anti-ice below 10°C. He said that below 10°C in low visibility conditions dangerous levels of icing were considered to happen nearly immediately. Sadly he didn't have any equations or data to give me.

I've found someone's thesis on gas turbine icing which appears to have all the information needed to calculate icing so I'll have a go tonight and see if I can get an Excel thingy together.


Nope, I haven't run mine yet. I'm saving up for an arbor press currently as I can't persuade one of the support pins to go back in by hand and I don't want to have to hit it.

Cheers,

Jon

[Richard OConnell]

If you are looking for some headache math, heres an interesting and non ctrl+f friendly PDF:
www.dtic.mil/dtic/tr/fulltext/u2/770069.pdf

I found some interesting bits of info around page 27 and 42, but it looks like there are a LOT of variables to consider including size of droplets encountered, pressures, and so on. Based on my reading I can tell you that you should prepare yourself with some aspirin before approaching this

[gidge348]

Hello Richard, thanks for the details, I agree the formulas are way beyond me, but the text looks really interesting. I will go over it over the next few days and try and get a handle on it.. good bedtime reading.. aspirin's ready

Hi Jon, one tool I have found invaluable when you need to shift something that does not want to be shifted is a "Dead blow hammer"
www.gotstock.com.au/deadblow-hammer-45mm-face-90mm-head-handle-length-220m-o-all-length-290mm-nom-wght-500g-jbs.html?gclid=CL2vvtK2_LsCFYdcpQod4HEArA

You can really whale into it without any chance of damage. It's basically a plastic hammer with lead shot inside.

[racket]

Hi Guys

Re ,icing ...............page 332 of my "Aircraft Gas Turbines Powerplants" states .................it might appear that anti ice should be used at much higher temperatures than 40 to 45 deg F to prevent freeze up , but industry testing has proven that it is a safe limit . It takes time for water suspended in air passing through the inlet to turn to ice , and if the temperature in the inlet is no lower than 45 deg F ~7 deg C , ice will not form.

Theres an ~10 deg C "static" drop in temp due to the velocity increase of the inlet air , same total temperature though, so any impact of air on inlet parts should "restore??" the static temp to the higher "ambiant".

An inlet air temp probe will be an useful addition to your cockpit instruments , as with all aircraft, an OAT gauge is a mandatory piece of equipment .

If theres water alky augmentation into the inlet air during high ambiant temp operation , as long as the temperature at the engine's inlet is above that 45 F - 7 C , things should
be OK.

Hope this helps :-)

Cheers
John

[gidge348]

Hi John, thanks for that very helpful makes total sense.

Also I have just got off the phone with my friend the Black Hawk pilot and got his take on things and they match your comments very well. My notes on his comments below.

1. 3 things needed for ice formation a. Moisture b. Low temp c. Low pressure. all these with some caveats.

2. P₁ V₁/T₁ = P₂ V₂/T₂...........ie P= pressure V= Velocity T= Temperature.... the total is a constant.

3. 2 types of moisture visible and invisible.

4. Black Hawk anti-icing set to go on at 10⁰C- 13⁰C regardless of moisture.

5. Key to icing is the difference between dew point temp and ambient temp. Big difference = no ice possible.... Small difference = ice is possible.

6. Signs of IGV icing from the pilots perspective are increasing EGT & no increase or a small decrease in power or FPT rpm.

Interesting side note, he got back 2 years ago from Pakistan/Afghanistan in winter running UAV's for the army and even though the temp was well below 0⁰C they were not icing conditions because of very low humidity. Also Antarctica is mostly an aircraft ice free area while the clouds are absent.

Anyway interesting subject all this.


Cheers

Ian...

[racket]

Hi Ian

The blackhawk engine runs a very high through flow rate with its transonic axial compressor so there'll be a fairly large temp drop , the 10-13 deg C ambiant ( OAT) point for de-ice would be warranted as actual comp face temp would be within a degree or so of freezing .

LOL......yeh , once ambiant temps are below 5 deg F - minus15 deg C theres no icing problems as air is considered "dry" , great for our Members in the "frozen north " ...........I hope you're coping with those plus 40 C temps at the moment :=)

Cheers
John

[gidge348]

Hi John, yep it was pretty bad, we were about 2 kms north of where the big fire started but luckily (for us at least) the fire basically headed east.

Unfortunately 2 of our friends each lost their houses.

We have a silly system here where you can go to jail for cutting a tree down and you can't burn off to reduce fuel load because they stop the burning season when everything is still green. So we are going to see this again and again.

I feel sorry for SA, they are copping is now.

Ian...