White Waltham

Any VC10 related discussions.....
bobisqueen
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Re: White Waltham

Post by bobisqueen » Sat Feb 18, 2017 10:23 pm

Just to say I'm not being picky! Just trying to help you make it better although I understand it's not quite that simple!!

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vololiberista
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Re: White Waltham

Post by vololiberista » Sun Feb 19, 2017 9:18 am

bobisqueen wrote:
Sat Feb 18, 2017 10:06 pm
vololiberista wrote:
Sat Feb 18, 2017 2:52 pm


The EGT rise and fall in the video is slowish I think due to the ambient temperature. Which in the video is 1°celsius. At ISA on the runway at Shoreham (which is where I do all my sea level testing!) it rises and falls much more quickly and also to the correct maximum for those conditions. As for hot and high airfields yes it rises even quicker and to a much higher temperature. I have the panel set so that the temperature switches above the EGT gauges are set to Norm which as I understand/believe operate the duct bypass into the airframe anti-ice system at 595c. The duct temperatures themselves are controlled by a heat specific formula that ensures that the different temperatures of the airflows into the duct mix to the correct temperature. Thus I "usually" get the correct temperatures showing up on the anti-ice gauges. In this image (engines off) the "ambient" wing temperature is higher because it's receiving more sunlight.ice.jpg Doing the anti-ice panel was a bit of a challenge in that in the sim there is only one hard coded variable! Easy peasy for the likes of 737 models. But when you have to model an entire panel with switches, MIs different temperature gauges etc. It gets "interesting" as everything the user sees has to work. Which it does surprisingly!!


As regards the EGT rise at/after 11%n2 there is a way of doing it but can you remember by how much the temperature rises before ignition. And I presume it rises quite slowly in comparison to when ignition occurs.
The EGT rise still seems slows for +1 compared to real life experiences. The ignition starts as soon as you hit the start switch and the HP cock is also opened then hence you get light up and EGT rise at 11ish%

The switch next to the EGT gauges is for the top temp monitor on the engine. When in Normal it controls the Max EGT to 595c. This is the temp at the rear of the HP turbine in the hot stream and is nothing to do with the bypass or anti ice ducts.

The anti ice duct temperature is control by the temperature control valve and it's controls the anti ice temperature by controlling the amount of P3 )HP compressor outlet) air is mixed with LP4 (LP compressor) air. The temperature is controlled around 230c

The switches on the anti-ice ice panel. The 4 HP stop valves allow the HP compressor air into the anti-ice system. The 2 PRVs ensure the duct pressure doesn't exceed 45 to 50psi. If the HP stops are shut and the PRVs are open, LP compressor air is still allowed into the anti ice system. If the HP stops are open and the PRVs are closed, nothing will get into the anti ice system.

I will dig out some diagrams if that helps?
Hi,
Any diagrams would be useful many thanks. The ati-ice system works pretty much within the parameters you have described. And the gauges show the correct temperatures. I did find a video with a view of engine no.4 EGT gauge. Not very clear but it seems that EGT rises to about 300c and stays there for a few seconds before rising to max and falling back. I am wondering if that is related to the HP cock setting. If I recall the HP cock has three settings. closed, start and full or to that effect. Is that correct? I have tried a couple of experiments and they don't work correctly as the sim's hard code steps in. So I will have to fake it from 11%. Still, not nearly as bad as calculating P7!!!! Thanks again.

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vololiberista
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Re: White Waltham

Post by vololiberista » Sun Feb 19, 2017 6:19 pm

bobisqueen wrote:
Sat Feb 18, 2017 10:23 pm
Just to say I'm not being picky! Just trying to help you make it better although I understand it's not quite that simple!!
I am working on a solution. However, it is not perfect. The sim will not ignite the fuel until 22%n2. So I have had to make an "overlay" code that moves the needle from about 11-12%n2. In the mean time the sim code catches up and passes the overlay code. However, this results in a pause at around 300c for a second or so. I can slow down the overlay code to reduce the pause but obviously there comes a point when the perceived needle movement is too slow. So at the moment it's a bit of swings and roundabouts to find the best compromise which unfortunately it will always be.

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vololiberista
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Re: White Waltham

Post by vololiberista » Sat Feb 25, 2017 9:25 pm

Ollie aka Bobisqueen does this float your boat? It had better lol as it was a lot of work. I did have help from an expert at FSDeveloper.com who specialises in creating look-up table formulae.
https://www.youtube.com/watch?v=DNaiRo9o5q0 This all works nicely now. I would still like to see a close up video if and when you have the time. So that the numbers can be more accurate. Also if your technical notes contain max EGT at various ambient temperatures like -40c, +15c, and +50c.
Currently I have programmed rough estimates. I'm working on the needle speed as it rises a little too fast. Having said that I think it is quite convincing even so!

This is the current profile for the needle movement for engine 2. It traces the movement for the whole light-up process and to engine stable. Where it hands back to the Sims EGT once the two numbers are equal.
rate2.jpg

bobisqueen
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Re: White Waltham

Post by bobisqueen » Sun Feb 26, 2017 8:06 pm

It looks much better :D

I don't think there is anything in the AMMs that talks about EGTs at different Temps. The engines are so different and due to older manufacturing techniques and Wear and tear each engine would behave slightly differently. Something you couldn't easy replicate in a sim!

The EGT so behaves slightly different when the start temperature go's over 595c. This is because the limiter starts to trim fuel back so the EGT appears to stagnate slightly. Somethings that's easier to see during a start.

I'll dig out the test bed figures I have and see if the start parameters are recorded

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vololiberista
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Re: White Waltham

Post by vololiberista » Sun Feb 26, 2017 9:18 pm

It's quite easy now to programme any specific engine to start-up a bit hot but the EGT is already programmed to be affected by ambient temperature and if you try to start in Kuwait for example you will get a nice hot start. There might be a way to reduce fuel flow at 595c but currently that is hard wired to the physical throttle position. And doesn't respond to enforced changes.
Currently I have set the max/min parameters as
@-40c, max EGT385c
@+15c max EGT545c
@+50c max EGT630c
they seem to be in the ball park at least.
Wear and tear each engine would behave slightly differently. Something you couldn't easy replicate in a sim!
Actually it's not that difficult. The start-up with this new coding is entirely customisable for each engine. And engine vibration is already programmed as the sim permanently records the number of hours for each engine. The vibration meters (bear in mind these are the meters at the base of the EO's panel in the civilian version) are running above 4 so the sim will need some new engines soon!!

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vololiberista
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Re: White Waltham

Post by vololiberista » Fri Mar 03, 2017 6:36 pm

Made some adjustments and now the EGT indications are as smooth as a babies undercarriage doors!! An outstanding question though regarding hot starts. 595c is the max. Does the EGT indicate a rise beyond that with the top temp switches at norm? Or do the needles stay at 595c?

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Re: White Waltham

Post by Jelle Hieminga » Mon Mar 06, 2017 4:24 pm

bobisqueen wrote:
Sun Feb 26, 2017 8:06 pm
The engines are so different and due to older manufacturing techniques and Wear and tear each engine would behave slightly differently. Something you couldn't easy replicate in a sim!
I think wat Ollie means is that there is a lot of variation in parameters even on one engine that is started on different days in different ambient conditions. I once had a go at modelling EGT values over longer periods to see if we could use that to predict engine removals (as engines age the EGT at peak performance increases). As the conditions were so different from day to day my graphs were sometimes more of a child's scribble than anything else. I managed to get a reasonable approximation that may actually have been useful but based on that experience I would say that the true variation in parameters is not something you want to put in your model. As a sidenote: that was done on a more modern engine than the VC10's Conways.
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vololiberista
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Re: White Waltham

Post by vololiberista » Mon Mar 06, 2017 4:57 pm

Jelle Hieminga wrote:
Mon Mar 06, 2017 4:24 pm
bobisqueen wrote:
Sun Feb 26, 2017 8:06 pm
The engines are so different and due to older manufacturing techniques and Wear and tear each engine would behave slightly differently. Something you couldn't easy replicate in a sim!
I think wat Ollie means is that there is a lot of variation in parameters even on one engine that is started on different days in different ambient conditions. I once had a go at modelling EGT values over longer periods to see if we could use that to predict engine removals (as engines age the EGT at peak performance increases). As the conditions were so different from day to day my graphs were sometimes more of a child's scribble than anything else. I managed to get a reasonable approximation that may actually have been useful but based on that experience I would say that the true variation in parameters is not something you want to put in your model. As a sidenote: that was done on a more modern engine than the VC10's Conways.
Hi Jelle,
I would think that one can only get "consistent" data on new engines and even then there will be some variation. I've set it up so that engine 3 runs a bit hot on start-up about 580c+. Engines 2 & 4 are not quite as bad and engine 1 peaks at around 560c at ISA. I have tried to match the number of engine hours in my sim. Engine 3 having the most with 2,238 hours. I would not like to be in a place like Kuwait in the Summer with engines that run that hot!!!

bobisqueen
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Re: White Waltham

Post by bobisqueen » Mon Mar 06, 2017 7:07 pm

With the top temp switch set to Norm, the EGT limit is set to 595. However during start, esp in hot conditions the max EGT may swing past that. (hence the max EGT during start is higher. MK301s fitted to the RAF max start temp is 690)

Because you get a rapid EGT increase during start its possible that the EGT may swing over as the limiter is only basic (if the temp goes over 595 the top temp monitor sends a signal to the fuel control unit to trim back the servo fuel which in turns reduces the output of the HP pump which means less fuel to the burners)

Because it fluid and not electrics, Theres a small delay and the limiter cant control rapid changes, so when the start temp swings over 595 the limiter will try and control it to 595. This means as the limiter starts to take effect the over swing will start to slow and stangnant and drop back. Does that take sense?

I had a quick look at the test bed data I have. It only shows basic start data. a max EGT of 620 @ 19.8c

hope that helps!!!

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vololiberista
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Re: White Waltham

Post by vololiberista » Tue Mar 07, 2017 5:06 pm

bobisqueen wrote:
Mon Mar 06, 2017 7:07 pm
With the top temp switch set to Norm, the EGT limit is set to 595. However during start, esp in hot conditions the max EGT may swing past that. (hence the max EGT during start is higher. MK301s fitted to the RAF max start temp is 690)

Because you get a rapid EGT increase during start its possible that the EGT may swing over as the limiter is only basic (if the temp goes over 595 the top temp monitor sends a signal to the fuel control unit to trim back the servo fuel which in turns reduces the output of the HP pump which means less fuel to the burners)

Because it fluid and not electrics, Theres a small delay and the limiter cant control rapid changes, so when the start temp swings over 595 the limiter will try and control it to 595. This means as the limiter starts to take effect the over swing will start to slow and stangnant and drop back. Does that take sense?

I had a quick look at the test bed data I have. It only shows basic start data. a max EGT of 620 @ 19.8c

hope that helps!!!
Hi Ollie,
Yes, that's how I imagine it. It makes perfect sense. At the moment the equation feeds the difference betweeen 595c and the actual EGT into another variable and that is subtracted thus the needle stays at 595c. I will have to introduce another variable to make the needle slow down and back-off as it were.
I had a quick look at the test bed data I have. It only shows basic start data. a max EGT of 620 @ 19.8c
is that a max allowable temperature or a generally expected temperature?
In this video engine 4 seems to get up 590c before dropping back https://www.youtube.com/watch?v=jD8AOw9uyUs

bobisqueen
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Re: White Waltham

Post by bobisqueen » Tue Mar 07, 2017 5:13 pm

That's yours truly at the controls :-)

From memory that was a coldish day. Maybe 8c?

bobisqueen
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Re: White Waltham

Post by bobisqueen » Tue Mar 07, 2017 5:54 pm

620c relates to the max recorded start temperature of the engine while it was on the test bed. In this case it was a Mk301 engine SN 8085. It was under going test post a visit to the repair shop.

I really think there's no such thing as a average start temp on the Conways!

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vololiberista
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Re: White Waltham

Post by vololiberista » Tue Mar 07, 2017 6:52 pm

bobisqueen wrote:
Tue Mar 07, 2017 5:54 pm
620c relates to the max recorded start temperature of the engine while it was on the test bed. In this case it was a Mk301 engine SN 8085. It was under going test post a visit to the repair shop.

I really think there's no such thing as a average start temp on the Conways!
Curently Engines 1,2 and 4 get to the 570's and engine 3 gets up to 591 at Shoreham on an ISA day. I'll repeat the exercise at Bruntingthorpe at 8c !!!!
At Bruntingthorpe +8c the EGT's are about 25C less for each engine. So to match the Bruntingthorpe temperatures I'll have to add that amount to the equation. That would mean that all the engines are at risk of a hot start at ISA SL. I suppose with the engines not being new that might well be the case.
Last edited by vololiberista on Tue Mar 07, 2017 7:57 pm, edited 2 times in total.

bobisqueen
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Re: White Waltham

Post by bobisqueen » Tue Mar 07, 2017 7:01 pm

Also it was the first time in 6 months that those engines had been started

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