White Waltham

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vololiberista
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White Waltham

Post by vololiberista » Mon Feb 06, 2017 11:25 am

Jelle,
I noticed in this topic on the main site http://www.vc10.net/Memories/testing_earlydays.html wishing that there was a video. There is one as you probably already know. Here https://www.youtube.com/watch?v=DqdM9xvxBaA
You might like to add the link to that article.
Oh, and btw the engines sound to be at 80%n2 not at idle as described by the onlooker. 80%n2 actually would be the correct procedure (80%n2, flaps 2, no gear down) otherwise the same fate would befall the 10 as did the A320 at Habsheim.

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Re: White Waltham

Post by Jelle Hieminga » Tue Feb 07, 2017 8:01 pm

That particular video is on my site, but as you noticed not on that page. It is on the page about G-ARVM, so if you click on the registration you'll find it. Actually, I am in the process of reorganising the pages with 'memories' and one of the things I'm doing is grouping smaller collections of stories with a similar theme together. One of those themes will be the White Waltham airshow, so that will get its own page, including the video.
Buttons . . . check. Dials . . . check. Switches . . . check. Little
colored lights . . . check.

bobisqueen
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Re: White Waltham

Post by bobisqueen » Mon Feb 13, 2017 9:56 am

To be honest, the Conways sound like there there fairly close to idle, and not at 80% HPRPM.

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Re: White Waltham

Post by vololiberista » Tue Feb 14, 2017 9:27 pm

bobisqueen wrote:
Mon Feb 13, 2017 9:56 am
To be honest, the Conways sound like there there fairly close to idle, and not at 80% HPRPM.
They do seem to be spooling down. As right at the end of the clip they sound much less than 80%. I think he pulled the throttles back floated for a while on ground effect and just before the engines wound right down gave them full welly for the climb out. Unfortunately we'll never know as that's when the video stops. Bear in mind that there is only 20%n2 plus from 80% down to idle.

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Re: White Waltham

Post by bobisqueen » Wed Feb 15, 2017 7:46 pm

What gives it away for me is theres little to no black smoke coming out of the engines and also you can hear the engines whisting. Both signs the engines are at lower power settings. At 80% HPRRM the engines start to roar more. Theres also only 20% HPRPM from 80 to max!

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Re: White Waltham

Post by vololiberista » Thu Feb 16, 2017 12:56 pm

bobisqueen wrote:
Wed Feb 15, 2017 7:46 pm
What gives it away for me is theres little to no black smoke coming out of the engines and also you can hear the engines whisting. Both signs the engines are at lower power settings. At 80% HPRRM the engines start to roar more. Theres also only 20% HPRPM from 80 to max!
You don't get that characteristic Conway roar and thick smoke until about 92%cn2plus in ISA conditions. At 80% you will hear them sing and that's all. To be honest such a low fly past with the engines "already" at idle is a very risky manoeuvre as there is no power left in the engines to climb out safely as was clearly demonstrated at Habsheim (and I don't think he was in ground effect either). Think of the number of accidents there have been where engines were closed to idle leading to too high a sink rate which could not be recovered from once identified.

I certainly would be loath to close the throttles to full idle doing this even though at White Waltham he was clearly in ground effect. Here are a couple of graphs I did to correct David Maltby's air file tables for his FS9 model. He used the stock MS tables for all his aircraft. They all suffer from engine surge at start-up and all have exactly the same thrust be they a Super VC10 or Comet.

thrust2.jpg
The first graph is the real actual thrust from a Conway 550. You can see that it really doesn't do much until above 85%n2. Most of the thrust is generated in the last 15%n2. That is typical of this type of jet engine. The numbers along the top are the polynomial curve that I used within the sim and subsequently corrected as seen in the second graph.
thrust.jpg
The second graph shows corrected n2 which is done to calculate actual thrust at different altitudes/temperatures etc and that is what is used by the desktop sims. Particularly a problem with FS9 and FSX as the way they work means that at both ends of the curve there is not enough thrust. So the real thrust curve has to be adjusted so that the correct thrust is seen in the sim. You can also see in the second graph why slamming the throttles to max at hot airfields like Kuwait is a no no! As n1 would overspool big time! All that has to be modelled in order to get the correct thrust at various altitudes and temperatures.
thrust3.jpg
This graph was the original transcription from the data I had. It shows a much steeper curve only because of its scale. But you can see clearly demonstrated that all the useful thrust is generated only at the top end. The difference in scale between this and graph no.1 is to scale it to the relevant air file table in the sim.

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Re: White Waltham

Post by bobisqueen » Thu Feb 16, 2017 6:09 pm

I'm well aware of the facts and figures, having spent 8 years working VC10s and now look after 241 at Brunty. Engines where also my Base trade. Any figures I use are based on Maintenance manual or mk301 test bed figures I have.

I can guarantee you at 80% HPRPM she generates plenty of black smoke and she certainly doesn't sing at 80% HPRPM. The distinctive conway noise is produced at around 96/97% and a lot of that distinctive noise is made by the cabin compressor.

The conway produces half thrust at approx 90% (I have test bed results to confirm this) and the throttle position matchs this. Ie 90% = HPRPM = half throttle = half thrust.

Also you can slam the engines in any condition as the FCU will control the accel in within limits and regardless of where you are they will not stall. This was part of a post engine change check regardless of conditions. Around 3ish seconds idle to 90 and 1 to 1.5 seconds 90 to max.

The engines are certainly within the lower power setting and if the flypast was conducted with lots of energy with a relatively light weight, there would be no need for loads of power, however I never said they were at idle.

For me you can't compare it to Habsheim. It was a different aircraft, flown differently and to this day there's disputes over the cause of that crash! At least with the Conway there's no FADECs or FMS to worry about

Regardless it's a impressive Feet of flying

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Re: White Waltham

Post by vololiberista » Thu Feb 16, 2017 10:34 pm

As regards Habsheim as far as I am aware the only person who disputes the accident findings is the pilot!!!! Your figure of 90% pretty much coincides with the 90% shown on the graphs. When I was remodelling the engines for FS9 I put the real thrust table into the air files to see the outcome and it required full thrust to get it moving at all. Also in the sim it is pretty much impossible to restrict the engines. i.e. create a limiter to prevent overspooling as that affects the throttle position. I also worked on the throttle position so that it matches as close as possible to the real thrust/position relationship. Thus I was able to eliminate throttle creep which was previously in the model.

Actually it is quite a task trying to get the correct responses from all the instruments, matching the sound, climb power, cruise settings etc.. All dependant on the ambient temperature and pressure. I have to say I have a close match!! I modelled the duct temperature as well (somewhat rudimentary but it works).The worst was calculating P7. The P7 max graph was not so difficult but finding a curve that matched the actual temperature and pressure at any and every airfield to the instruments was difficult. Thus the applied thrust has to match the graph at every location even El Alto!! I am still having problems with the initial P7 values which should match ambient pressure but for some reason don't quite. work in progress as they say.

It would be really great to see a model created for P3D. That is far beyond me as hundreds of photos would be needed and I don't live in the UK.

Have a gander at this. Constructive criticism accepted. I skipped a lot of the checklist, but everything in the real checklist can be checked and tested if you want to. Even the Precision altimeter test works. Only the Electrics and Hydraulic panels are not yet modelled.
https://www.youtube.com/watch?v=WF1PVEVdQDo

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Re: White Waltham

Post by bobisqueen » Thu Feb 16, 2017 11:50 pm

I've had a quick look and it looks very good. One thing I've noticed is the start sequence is not quite right. The oil pressure light normally goes out quicker and you would normally see a EGT increase around 11-13% HPRPM. I don't know how easy that is to adjust?

I'm at Brunty in March and will be carrying out a ground running on 241. I could video the start and engine panel for you?

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Re: White Waltham

Post by vololiberista » Fri Feb 17, 2017 2:19 pm

bobisqueen wrote:
Thu Feb 16, 2017 11:50 pm
I've had a quick look and it looks very good. One thing I've noticed is the start sequence is not quite right. The oil pressure light normally goes out quicker and you would normally see a EGT increase around 11-13% HPRPM. I don't know how easy that is to adjust?

I'm at Brunty in March and will be carrying out a ground running on 241. I could video the start and engine panel for you?
That would be very useful thanks. In the sim EGT temperature is linked to fuel flow so that might be tricky one to correct. I'll have to check what is behind the oil pressure as it is a hard coded variable by the sim itself. That said in the original model the oil pressure and LP cooling air lights lights on the main panel were coded as something different and the lights stayed on even longer. The EGT does seem to work well otherwise especially at hot airfields with the risk of hot starts.

I have modelled ambient cooling as well. So simmers who are stopping over as it were have to wait until the engines have cooled down!

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Re: White Waltham

Post by vololiberista » Fri Feb 17, 2017 2:54 pm

I have the oil pressure lights as on at less than 12psi. So this may only be a timing issue. The start-up is controlled by the time to n2 airfile
time.jpg
This was completely revised from the original MS stock graph. MS had misenterpreted their own SDK!!! As it is not what the title says. It is in fact "Time to n2" i.e. time from initial start to idle. Here it really only starts to get going from 39%n2 the third vertical line from the left. To me it has always been sluggish especially when the engines run down when the throttle is closed. More work need there.

You might find this interesting as the sort of problem simulating engines can be.
http://www.fsdeveloper.com/forum/thread ... up.389153/

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Re: White Waltham

Post by bobisqueen » Fri Feb 17, 2017 8:24 pm

12 psi is right for the low pressure oil light to come on. As an aside, 18psi was the minimum required for a ground running.

I've looked at the start sequence again and the EGT rise and fall is slowish compered to normal and it happens later in the start sequence then in real life. Out of interest what happens to the EGT in the sim when you start in hotter Temps? I also notice you have a max start temp of 650 rather then 690?

I'd have no ideal were to start coding flight sims and I take my hat of to you.

As I say I will record the start sequence on 241 for you as comparison for you. I will also record any else you want if you let me know.

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Re: White Waltham

Post by vololiberista » Sat Feb 18, 2017 2:52 pm

bobisqueen wrote:
Fri Feb 17, 2017 8:24 pm
12 psi is right for the low pressure oil light to come on. As an aside, 18psi was the minimum required for a ground running.

I've looked at the start sequence again and the EGT rise and fall is slowish compered to normal and it happens later in the start sequence then in real life. Out of interest what happens to the EGT in the sim when you start in hotter Temps? I also notice you have a max start temp of 650 rather then 690?

I'd have no ideal were to start coding flight sims and I take my hat of to you.

As I say I will record the start sequence on 241 for you as comparison for you. I will also record any else you want if you let me know.
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!!
The reference to 650 was from when I photographed the Sultan's aircraft at Brooklands as that had/has those dymo tape stickers.
I much appreciate you doing a video for me. If you can also record the temperature, QNH and elevation when you do do it I would be most grateful. Anything to refine the model is most welcome.

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.

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Re: White Waltham

Post by vololiberista » Sat Feb 18, 2017 8:08 pm

There is another issue with slow starts at low temperatures which I don't think can be changed as it is hard coded in the sim. The sim assumes fuel is injected at 22%n2. Whilst it is possible to change this on the surface (which I have done) it has effects the further away from ISA you get towards and below 0c. In fact below zero the engines hang and have to use the 22%n2 procedure. For example for an engine restart while airborne the engines also hang unless I use the 22%n2. Most of the coding that any developer does for the sims is to get around its limitations. And indeed some developers now code entirely outside the sim which envolves very complex programming as the sim has to find out what to do through the back door so to speak. Not my realm of expertise at all!

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Re: White Waltham

Post by bobisqueen » 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?

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