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Need some clarification please.


Mike Busutil
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Leatherneck / Sir's,

 

I am working on a brand new detailed kneeboard checklist and am basically complete with it and ready to release it to those that may want it but I need some clarification on a few items because the information is either unclear or missing from the flight manual.

 

Question 1:

 

The flight manual states that the Radio switch is turned on with the RV17 switch and when this switch is in the DOWN position, the radio station will serve as an intercom station to talk to the ground crew. Why am I able to talk to ground when this switch is in the up/on position as well as the down position? (Easy communications and radio assist are both off)

 

Question 2:

What unit of measurement is used for the engine emergency o2 pressure gauge? My gauge shows just short of "10" but what is "10"? Is it "10" PSI? Is this low? Is it a normal value? Does it ever get higher that "10"?

 

9cyfxjV.jpg

 

 

 

Question 3:

What unit of measurement is used for the battery capacity? The battery capacity reads approximately "4". Is this "4"Ah? 40Ah? 400Ah or something else?

 

 

 

8ZBcBNh.jpg

 

 

 

Question 4:

What is the normal operating position for the "Aux 2 pos nozzle ctrl" switch? It is in the down position by default but the warning panel shows a green "Nozzle open" light until the needle 1 RPM exceeds 50%.

 

 

 

B4CHwSI.jpg

 

ki8xYQt.jpg

 

 

 

If the "Aux 2 pos nozzle ctrl" switch is in the up position, the green "Nozzle open" light on the warning panel will turn off.

 

 

 

jsYGzQ3.jpg

 

 

 

Thank you for any clarification on these items. :book:


Edited by Mike Busutil
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1. As I understand it, it just a way to tell you that you can talk to the ground crew regardless whether the radio is turned on or off. :)

 

2. kg/cm2

 

3. Ah

 

4. It's for emergency procedure in case of nozzle control failure. Default is down position, keep it so unless there's a failure. Manual explains it in more detail. :)

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1. As I understand it, it just a way to tell you that you can talk to the ground crew regardless whether the radio is turned on or off. :)

 

2. kg/cm2

 

3. Ah

 

4. It's for emergency procedure in case of nozzle control failure. Default is down position, keep it so unless there's a failure. Manual explains it in more detail. :)

 

 

1 does not make sense to me... :huh:

 

2, Ok thanks, do we know if it will read any higher than 10? For a gauge with a scale going up to 40, 10 seems to be on the low side.

 

3, Would that actually be 4Ah? Or is it really showing 40Ah?

 

4, Thank's. I found more information in the flight manual under the emergency section. :thumbup:

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Q1. I believe the intercom telephone taps into the transmission circuit at all times so the ground crew can hear all the time but the switch must be up to talk to ATC as well.

 

Q2. Pressure is force per area. Kilogram is a measure of mass and not force. And so a concept of a kilogram-force is invented to describe what force is made by a 1 kg mass in one Earth's surface force of gravity. In Newtons it is 9.8N for 1 kg-force if you say gravity on Earth is 9.8 m/s^2. Sometimes it is written kgF instead of kg to tell kilogram-force from kilogram but in this gauge it is not.

 

Imperial has the opposite problem because it has a very common unit of force (pound), but uncommon unit of mass (slug). And it invented the concept of pound-mass which is how much mass under Earth's gravity gives a force of 1 pound.

 

With rocket engines to give fuel efficiency in seconds it is using this trick. For an engine which has Impulse-specific (Isp) of 200 seconds it means it gets 200 seconds x 1 KgF thrust for every 1 kg mass of fuel. And they say "kg cancels kg and this leaves only seconds" but we can see that one is kg force and one is kg mass so they aren't really the same thing. This was invented to prevent mistakes when talking to other scientists which are using different mass and force units.

 

1 KgF/cm^2 is almost exactly equal to 1 atmosphere pressure (0.9678...). And so you have nearly 10 atmosphere of O2 pressure. I think this is relative to ambient so if you put the whole airplane in a vacuum chamber it would read 1 more.

 

Q3. 40 Ah (battery is 15СЦС-45Ь suggesting a total rating of 45Ah by model name).

 

Q4. Normal position is down (safety wire). In up position a medium position of the engine nozzle is set (corresponding to ~60% N1 RPM in automatic). The exception being that in afterburner it is opening to a second more-open position. These are the two backup nozzle positions (dry and wet, automatically changed between) while the normal operation adjusts to many positions based on the engine state.

 

The reason for the "nozzle open" light is for the pilot to confirm the nozzle is working properly by automatic scheduling being fully open when it should be (minimum thrust and afterburner) and not fully open other times.

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1. controls only the radio.

 

Up=On

Down = Off

 

Crew is beside you on the ladder and you can talk with them without the radio.

 

I think DCS has a small issue now that you can talk (in any plane/helicopter) with crew and rearm even with canopy closed. It used to be mandatory to either use intercom if available (example Ka-50) or open the canopy to speak directly by yelling :)

 

4. As Grunf said. The green annunciator just tells you that the nozzle is open not that is a problem with that. Is green! The switch controls it in case of failure. You close it with that switch to keep gases inside engine more to build pressure in case of malfunction.

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Thanks Zaelu.

 

Good info.

 

The intercom mode with the radio switch off must be the primary way to communicate with ground otherwise everyone on the same ATC channel as you including tower would hear the conversation you are having with ground.

 

Plus the MiG-21 is loud. Doubtful the crew would be talking to each other over the engine without an intercomm.

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Maybe they take into consideration talking with hand signs :) .

 

About the 2nd nozzle, info is in the manual on page 168. Here is a screenshot

 

voSBBYm.jpg

 

Basically, when AB is On, the nozzle is opened fully but it should close when AB is turned off.

If it fails to do so the engine will not have enough power hence the manual setting (to close) and the emergency.


Edited by zaelu

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Found on page 61 of the flight manual.

 

DWhT6jj.jpg

DCS manual, although very good, may have some things simplified. :D

 

I was referring to the real manual, which has a very detailed startup procedure, and on several occasions mentions hand gestures as a way of communication with the ground crew. However, it does not explicitly say that there is no intercom, but it is implied.

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Indeed. That thing in the manual is just a game/joke information. :)

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In 2-position mode the closed dry position is not fully closed but a half-way position. The manual suggests that the emergency 2-position will close to the full throttle position but it doesn't.

 

I haven't checked JPT readings at FT setting with 2PSN mode on or not.

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In 2-position mode the closed dry position is not fully closed but a half-way position. The manual suggests that the emergency 2-position will close to the full throttle position but it doesn't.

 

I haven't checked JPT readings at FT setting with 2PSN mode on or not.

 

 

Having a look externally, here is the nozzle position when the 2psn switch is off (down position)

 

VDJNKJC.jpg

 

 

And here is the nozzle position when the 2psn switch is on (Up position)

 

O7WXEXc.jpg

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I have my doubts Leatherneck uses "Joke information" for the flight manual...

 

If you try the training missions your doubts might vanish :) .

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Having a look externally, here is the nozzle position when the 2psn switch is off (down position)

 

 

 

 

And here is the nozzle position when the 2psn switch is on (Up position)

 

 

attachment.php?attachmentid=155131&stc=1&d=1484344369

 

What can be done to great precision is to bind a keyboard key to toggle the 2PSN switch and look in external view at the exhaust nozzle while changing the throttle lever and switch position. There is some RPM setting between idle and full throttle where toggling the 2PSN switch produces no change in nozzle size.

 

For me this RPM is 62.5% N1 (71% N2) at 495°C JPT.

 

While I cannot get any change to RPM or JPT due to switching on of the 2PSN switch I can say that it does have a thrust difference. At FT, 3000m I could get a TAS of 588 knots but in 2PSN this drops to 582 knots.

 

At lower settings (80% N1) the effect was larger, I had 271 kt IAS (F2) under normal scheduling but it dropped to 230 kt (and was still decreasing) with 2PSN schedule.

 

I was unable to easily test the "no nozzle change" point since 62.5% N1 can't maintain level flight. Considering that the dry 2PSN setting also corresponds to some normal nozzle position there should exist some 2PSN thrust which is equal to the normally scheduled thrust.

NozzleComparison.JPG.c2b6fe101bdc293229df71b0d179d635.JPG

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