investigating Bombing altimeter (MPC) incorrectly modelled?

[scoobie]

I know I'm 6 years late to the party, but has this been discussed yet? Couldn't find anything.
Thing is... the MPC "bombing altimeter" modelled in DCS seems to make little sense.

The RL flight manual for F-86F "T.O. 1F-86F-1", dated 27 May 1960, says this (excerpt):

 

Quote

10. Set index altitude on bombing altimeter red-and-white scale by adjusting the black arm.
11. Set target altitude on bombing altimeter by turning knob on altimeter. (White pointer now indicates proper bomb release altitude for the particular target selected.)

(I added bold/red myself.)

 

The last sentence MUST mean (or I'm terribly mistaken) that the "index altitude" arm/pointer is MOVED not only by your hand (first, in point 10, as given above), but also by turning target altitude knob as in point 11. In other words index arm is "friction clutched" (by means of a circular felt pad or anything similar) to the red pointer, so that turning the red pointer also "pushes" the white indexer pointer the same amount of feet.
So... you start with the knob turned so that red pointer shows 0. THEN you dial in index altitude as read from this MPC box to the left of the sight. THEN you add target alt. by turning the knob and BOTH arrows are going up - the red one (until it's set to TGT alt.) AND the index alt, together. As a result, you get a "ready to use" bomb release altitude.

 

Otherwise such contraption would make no sense IRL. Anyone (a pilot or myself) can add target alt. to the index alt. in the mind and dial the result as "index altitude", but SINCE somebody invented this red arrow for target alt. alone, they must have done it on purpose - apparently they wanted to make the job easier, I guess to reduce the likelihood of a pilot's error.
Moving the red arrow freely/alone - as it is now in DCS - makes no sense (at least to me), and MCPMPC procedure, as given in DCS F-86F, makes no sense, either. I mean, the procedur does concur RL procedure, but it makes no sense when you use the bombing altimeter as currently modelled in DCS. Why would I turn the knob to move red pointer? It does nothing in DCS F-86.

 

I may be totally wrong, though, e.g. I may be missing some important point, obvious to others. I've just started learing this vintage beauty. If so - can anyone give me a clue?

For now, I'm just adding TGT ALT + IDX ALT and dial in the result, but it doesn't seem to be the proper way this instrument should be worked with.

 

(I know it's not a big deal, I can do such simple mental arithmetic, but you know... it's the simulation, it's all about how things really work).

 

Edited January 11, 2021 by scoobie

[metzger]

On 1/11/2021 at 2:40 PM, scoobie said:

I know I'm 6 years late to the party, but has this been discussed yet? Couldn't find anything.
Thing is... the MPC "bombing altimeter" modelled in DCS seems to make little sense.

The RL flight manual for F-86F "T.O. 1F-86F-1", dated 27 May 1960, says this (excerpt):

 

(I added bold/red myself.)

 

The last sentence MUST mean (or I'm terribly mistaken) that the "index altitude" arm/pointer is MOVED not only by your hand (first, in point 10, as given above), but also by turning target altitude knob as in point 11. In other words index arm is "friction clutched" (by means of a circular felt pad or anything similar) to the red pointer, so that turning the red pointer also "pushes" the white indexer pointer the same amount of feet.
So... you start with the knob turned so that red pointer shows 0. THEN you dial in index altitude as read from this MPC box to the left of the sight. THEN you add target alt. by turning the knob and BOTH arrows are going up - the red one (until it's set to TGT alt.) AND the index alt, together. As a result, you get a "ready to use" bomb release altitude.

 

Otherwise such contraption would make no sense IRL. Anyone (a pilot or myself) can add target alt. to the index alt. in the mind and dial the result as "index altitude", but SINCE somebody invented this red arrow for target alt. alone, they must have done it on purpose - apparently they wanted to make the job easier, I guess to reduce the likelihood of a pilot's error.
Moving the red arrow freely/alone - as it is now in DCS - makes no sense (at least to me), and MCPMPC procedure, as given in DCS F-86F, makes no sense, either. I mean, the procedur does concur RL procedure, but it makes no sense when you use the bombing altimeter as currently modelled in DCS. Why would I turn the knob to move red pointer? It does nothing in DCS F-86.

 

I may be totally wrong, though, e.g. I may be missing some important point, obvious to others. I've just started learing this vintage beauty. If so - can anyone give me a clue?

For now, I'm just adding TGT ALT + IDX ALT and dial in the result, but it doesn't seem to be the proper way this instrument should be worked with.

 

(I know it's not a big deal, I can do such simple mental arithmetic, but you know... it's the simulation, it's all about how things really work).

 

 

There is no automatic needle movement.

You tune the target altitude and then the release altitude manually, then watch the altitude needle aligning with the release altitude needle and pickle if all other parameters are matched.

 

The bombing altimeter is up there so you can easily keep track of it while seeing the sight and the target and decrease your workload of manually adding and calculating everything. 

 

The MPC box on the left is not related to the bombing altimeter at all, it's there again to make it easier for you to choose and select bombing parameters,  I find how F-86 has it very handy. F-5 for example you need to pre-plan it and/or have the tables on a kneeboard.

[scoobie]

11 hours ago, metzger said:

You tune the target altitude and then the release altitude manually

Yes! That's how you do it in DCS not to get killed.
Trouble is - what you say is against DCS F-86 manual.
Bigger trouble is - the DCS manual matches RL manual in this respect. So, either the RL procedure was meant to kill absent-minded pilots (a kind or euthanasia program to eliminate silly pilots or what?) or the instrument (the bombing altimeter) IRL works differently from the instrument in DCS F-86. The sentence in bold in my previous post is - IMHO - a clear explicit indication for the latter.

 

Example on how to get killed following the manual:
8. On the MPC panel, determine the INDEX altitude.
(Mind you: it says INDEX, not RELEASE). Let's say the panel tells me it's 3,700 ft, OK?
9. Set the obtained INDEX altitude on the bombing altimeter.
OK, I have - the white pointer is now at 3,700 ft.
10. Set the target altitude above sea level (indicated by the red pointer) using the rotary knob on the left side.
OK, my target is high - 4,000 ft. Have dialed 4,000 ft with the knob. I'm worried that the white pointer still reads 3,700 ft, though, but let's just go on.
(...)
13. (...) When the bombing altimeter instrument pointer coincides with the white pointer on the index altitude arm, depress the bomb-rocket release button and start the pull-out.
NEGATIVE! I'd have to plow 300 ft into the ground to drop the bombs and only then pull out... in the soil. Bad idea.

 

[VampireNZ]

I think the RL/DCS manual assumes a level of common sense in that most pilots would realise dropping bombs after hitting the ground is less than ideal, and therefore a little maths is required to set the INDEX altitude ABOVE the target altitude by the amount indicated by the MPC.

So the super-handy MPC handily tells you the INDEX is 3,700' - you say thanks very much Mr. Helpful MPC, now I know I need to release my bombs 3,700' ABOVE the target (cause dive bombing from below the target is hard and for experts only....once), which in this case is 4,000' - so by amazing mathematical gymnastics requiring years of honing, I am able to deduce I need to set the resultant INDEX altitude on my nifty bombing altimeter instrument to 7,700'.

 

It does not specifically call this the RELEASE altitude because it is just a reference, the pilot may elect to drop sooner or later depending on many different parameters such as wind or resultant bomb behaviour etc. He may have dropped exactly at the index alt last time and it fell short for example by a set amount, so next pass the pilot may drop a little differently. We used to do exactly that while bombing in the P-3. First pass may have been out when using 'standard' parameters, so next run you adjusted accordingly with variations to the known INDEX.

 

Hope that helps a bit 

Edited January 13, 2021 by VampireNZ

[scoobie]

Thank you, but... I've written a few times I know how to work around the issue (add two numbers).
My claim is different: the instrument in DCS is CLEARLY BODGED and it's OBVIOUS, people. Come on.
How could this have happened? I think I know it, too: a guy from Belsimtek didn't figure out how the instrument works (of course they are super bright guys, they must be - judging from how crazy difficult things they do for life). Maybe the guy was in a hurry, deadline for release was close etc. It happens, even to world champions, and that's okay. Sh*t happens. No worries.

If anybody (especially from ED) cares, please bare with me.

DISCLAIMER: It is NOT a rant. What I care about is how things really work and I think I figured it out. If - at any point in future - DCS: F-86F is to be "refreshed", I think ED might consider reworking the bombing altimeter. Just a kind proposal, OK?
Why I find it important, even though everyone knows a workaround? Because it is the only true to life way of delivering bombs in F-86 (LABS is for nukes, and "normal" auto/manual release was supposedly forbidden), so it would be nice if the bombing altimeter was real, and not a fantasy creation.

 

RL manual actually says how the instrument works, though the wording could be a bit clearer. If anybody cares, READ THE RL MANUAL, PLEASE, at the bottom of the front page in the copy I have it reads: "27 MAY 1960 CHANGE 10 - 30 APRIL 1971". Perhaps other versions of the manual could work as well, I don't know.
Start with "MANUAL PIP CONTROL SYSTEM." on page 162 in PDF (which is page 4-36 in print), read the whole section (2 pages or so). Each single sentece, one by one, carefully - only then things "click" to form a coherent picture.

I attached a crude picture.

 

The instrument seems to be a (nearly) STANDARD altimeter with an additional assembly attached on top of its face. "Nearly" means there must be some way to attach that whole front assembly and hold it in place. I think it may be held by some kind of a metal ring outside of the altimeter's scale (normally covered by the front assembly), but it might be attached through the axis, too (the latter seems flimsy, but I don't know).
The assembly comprises:
1. The outer ring with a toothed surface around its lower (closer to the underlying altimeter) part. Perhaps the teeth are on the outer surface, but I don't know. The ring is "driven" by the knob at the bottom left of the instrument - as the result the knob turns the whole assembly around.
2. The target altitude pointer, which is either a physical "needle" turning with the assembly or perhaps it is just a line painted on the glass - provided that the front glass is a part of the assembly (the glass may be attached to the underlying altimeter as well - so I don't know),
3. A part of the ring is a quarter-circle white scale for index altitude.
4. A "black arm" to set index altitude on the white scale, whereas the other half of the black arm (opposite to its axis of rotation) is the white pointer, which eventually gives the pilot a PROPER RELEASE ALTITUDE (that's the purpose behind this instrument, which RL manual also explicitly states). The black arm can be rotated around the ring, but remains where you leave it and then rotates together WITH the ring if you turn the knob (friction pad or whatever of this sort).

 

PROCEDURE:
* Obtain index altitude from MPC panel.
* Set it on the white scale with a black arm. White painted arrows (one on the very arm, the other on the ring just above the white scale) tell you where you "count" thousands of feet of index altitude (this is why it says on the ring: "INDEX ALT. 1000'S FT" - to make it clear).
* Turn the whole ring so that target altitude pointer is set correctly (so now, quote: "White pointer now indicates proper bomb release altitude for the particular target selected.").
* Dive, drop, pull-out when the underlying's altimeter pointer meets the white pointer.

 

Does the picture make it more clear for anybody?
The bombing altimeter in DCS is just wrong, fake, fantasy.

 

 

EDIT: At first I didn't look carefully how the whole assembly seems to be attached to the altimeter underneath it. This is my guess, but it looks as if the alitmeter is 100% standard, not "nearly standard" as I wrote. The whole "front assembly" looks as if it was just screwed on top of the altimeter. If so, then the body of the whole assembly is rectangular outside and is screwed on top of the altimeter. Perhaps the alitmeter is screwed to the dashboard by separate screws (flat heads), which are offset to the screws visible on the picture. Or perhaps you attach both the altimeter and the front assembly by one set of screws, like a "sandwich". I'm not sure.
Anyways, if this is true, then it means this:
* This assembly doesn't need its own glass as the altimeter has it.
* Red pointer actually is a physical needle and probably it's just a piece of steel wire (painted red), simply wrapped around the center pivot (which, in turn, can be as simple as a screw on top and a nut underneath). It's okay to do it this way, because you read (set & read) target altitude on the scale, which is outside, far from the center. The important part is to attach the pointer to the ring (point-weld or hook in a cut out detent - something like this) precisely at a specific place on the outer ring. I assume so because if you look closely the part of the pointer that goes into the center, seems to be offset - disappears above the center pivot. I know it might be just parallax, but look - it's way above, so I guess it's just wrapped around and "pressed" with a screw-nut assembly (it never rotates around the center, so it's okay).

Still... it doesn't matter that much, i.e. it doesn't influence how this assembly is operated by a pilot. I was just curious.

 

Edited January 14, 2021 by scoobie

[Balion]

I have one more question to add. You can see PRESSURE ALTITUDE label on the altimeter scale. That means the bombing altimeter doesn't indicate above sea level altitude, but pressure altitude. So the target altitude pointer should be also dialed to target pressure altitude, not above sea level altitude as manual says. Thats add another complexity for pilot. Why he just don't use main altimeter for bombing as in some other aircraft?

[scoobie]

Good point!
Manual says this: "The bombing altimeter (...) consists of a standard cabin altimeter connected to the static air source and indicates airplane pressure altitude."
(Doh, silly me... so I have the answer to my previous question - it IS a standard altimeter with that whizzbang assembly attached on top... I could've read the inscriptions!).

 

My blind guess:
How do you obtain your target's altitude? If you read it from a paper map, then such maps don't have QNH knobs built in. So... gee, I've just realized I never thought about it. Apparently maps are drawn with elevations scaled in pressure altitude (1013.25 or 29.92). What else could they do - print 50 maps for some typical QNH values? Sounds crazy.
If so, this "spare" altimeter is also "fixed" at pressure altitude, so you compare apples to apples and thus get no error (in terms of when to release bombs).
But I'm floating in the clouds now, I don't know if it makes any sense.

 

Another reason for a separate altimeter is simple (this one is not a guess) - they wanted a pilot to look at the sight, keep the pipper on the target and at the same time, without any disturbances, be able to see release altitude. So they tried to put this instrument as close to the sight as possible.

 

[Balion]

1 hour ago, scoobie said:

How do you obtain your target's altitude? If you read it from a paper map, then such maps don't have QNH knobs built in. So... gee, I've just realized I never thought about it. Apparently maps are drawn with elevations scaled in pressure altitude (1013.25 or 29.92). What else could they do - print 50 maps for some typical QNH values?

You can't reference pressure altitude on map, because it depends on current atmospheric pressure (QNH).

 

Look at the picture (http://www.faatest.com/books/IFRH/4-0.htm)

 

You can obtain target pressure altitude (PA) from target elevation (ASL) via altitude correction (AC):

PA = ASL - AC,

where AC = ~1000 ft per each 1 inHg QNH above 29.92.

For example, if ASL = 1500 ft, QNH = 30.42 inHg, then AC = 500 ft, PA = 1500 - 500 = 1000 ft.

Edited January 14, 2021 by Balion

[scoobie]

Oh, damn... I WAS floating in clouds! Sorry. I don't know the answer. There must be some rationale, design decision, something, but I just don't know

I was just trying to figure out how this contraption ("front assembly") works in terms of its mechanical design - what moves together with what etc., to make sense of what the manual (RL one) is saying.

 

[Awger]

Scoobie -- you are correct, the bombing altimeter in the DCS F-86 is not implemented correctly.

 

With reference to https://forums.eagle.ru/uploads/monthly_2021_01/f86_bomb_alt.PNG.513c915ba9b0f8b756808617b37f154a.PNG :

 

• The "black arm for setting index alt" (indicating 6K) and the white arm indicating release alt (pointing at ~ 19K ft) are connected to each other (most likely not a single piece, see below)
• The arc ("set index alt here"), bumper, target alt pointer, and black outer ring (with labels "INDEX ALT 1000's" and "TARGET ALT") are all connected and move as one piece when the "ring-turning knob" is rotated
• This image reflects settings for a target alt of 12K ft with an index alt of 6K
  • for dive entry of 10K above target (22K), use 80 deg dive angle (1st card)
  • for dive entry of 15K above target (27K), use 70 deg dive angle (2nd card)
  • for dive entry of 20K above target (32K), use 65 deg dive angle (3rd card)

When the bombing altimeter is "zeroed" (target alt at sea level, index alt of zero) it looks like this: http://aviadejavu.ru/Images6/AE/AE72-4/199-1.jpg . Note that the "index arc" is rotated into the upper-right quadrant and the target-alt needle is not visible because it is covered by the release alt needle.

 

The "index alt" from the MPC unit indicates a nominal release altitude above target altitude which is pre-calculated based on aircraft performance and safety margin (bottom of dive 2,500ft above target, 5G pull-out). Rotating the knob on the MPC adjusts depression of aiming pipper in gunsight (pre-calculated in mils) based on dive entry alt, speed, and dive angle.

 

For reference: Altitude loss for a 60deg dive from 10K / .95M is 4700ft for 6G and 7300ft for 4G. For a 90deg dive, 6G nets an 8600ft loss and 4G gets you a dirt nap. Note that altitude loss referenced is for dive recovery initiated at 10K while maintaining .95M, not for a dive initiated from 10K, and not accounting for acceleration or deceleration.

 

The black and white needles (index alt and release alt, respectively) are most likely seperate pieces geared together so as to increase the indicated release alt (relative to the selected index alt) as target alt is increased. Given that all altitudes referenced are pressure alt, all airspeeds are indicated, and altitude loss from a dive in a constant-G pull-up increases with altitude, it makes sense that these needles would have to diverge with increasing altitude. In any event there is something more to it than a simple "target alt + index alt = release alt" as the indicated release alt in your pic is +1K from the simple calculation, suggesting some additional fu (both mathematical and mechanical).

 

Accuracy with this bombing method is entirely dependent on correct entry parameters. Altitude, entry speed, and dive angle can be reasonably controlled, but the exact point in space (where the dive is initiated) can only be grossly approximated based on slant-range to target, estimated by Mk1 eyeball. Over- or under-estimating the range will alter the dive angle necessary to put pipper on target, throwing the other settings out of whack.

 

Fixing the bombing altimeter may appear to be a simple matter of adjusting some graphics, but I think it's just slightly more complicated than that (heh), so I seriously doubt that ED would make the effort.

[scoobie]

I don't know how I managed to overlook your post. Late thank you for the insight and that other picture!

I guess you're right - no one seems to care about this bombing altimeter contraption, let alone ED about remodelling it true to life. Whatever. I just wonder if the white and black pointers can actually be cleverly "geared together" instead of just being one piece of metal. On one hand your explanations make sense, but on the other - this assembly is such a thin steel "sandwich" right above the glass that there seems to be extremely little space for any mechanical marvels there. Maybe the design attitude was "more or less is good enough". I don't know, just speculations.
Well, anyway, it is what it is, we're not getting it, thanks for taking time to dig into it!

[NineLine]

Can you tell me which manual you are referencing so I can make sure I am looking at the same thing? Thanks.

[scoobie]

Hey @NineLine
The document I was referring to: T.O. 1F-86F-1, 27 MAY 1960, CHANGE 10 - 30 APRIL 1971.

Secion "MANUAL PIP CONTROL SYSTEM" begins on page 4-36 (p. 162 in PDF), the photo of the bombing altimeter assembly is on the next page.

My PDF file weighs 119 049 KB.

 

[Awger]

Been away from DCS for a long while, decided to jump back in... just saw your reply.

There's a museum in TX that has an FJ under restoration, plus a bunch of aircrew and mechanics that worked on these birds back in the day (aside: the guy in charge of the FJ restoration was crew chief on that specific bird when it was in service). I know the curator, and have done some work on their T-37 simulator, but I haven't had a chance to ask them about the MPC system. Need to remember to do that next time I'm down there.

If you have any info on who actually manufactured the MPC, or any other aircraft it was used on (I'm guessing FJ but there may be others), that would help.

Hopefully info on the MPC is easier to come by than docs on old Link pits... or why Bubi Hartmann's Knight's Cross (with diamonds) is hanging on a wall there (blink and you'll miss it).

[Awger]

I just noticed that ED responded to this thread.. I'm hoping that's an indication of interest... and, considering that I'm only some random voice on the internet, I thought I'd flex just a little bit.

This is sitting in the T-37 simulator (seats missing... long story... if you know where to get seats, PM me plz-ty) ... on the left is the tail of the FJ; center frame and behind the FJ is a MiG-15 trainer; in the background to the right is Randy Ball talking to the president of the museum next to the tail of Randy's MiG-17.

I've been messing around with simulators (military, commercial, and homebuilt) for the better part of 30 years, and I've always wanted to build my own F-86 pit. Never got around to it, but Mugga got me thinking about it again...

[[MVP] Mugga]

Hey @Awger I may have a contact here in Australia that has an inventory of spare T-37 seats and spares, as they had to be removed and replaced with more modern units for flying aircraft here down-under.  Feel free to message me on +61 415 577 724 and I can liaise with you regarding these.

Regarding the F86F Sim Pit, I am starting to take a look at the Bombing Altimeter MPC atm.  I don't really want to build a replica.  Instead I would really like to source an original and convert it etc.  But to do so, I also need to know manufacturer and part number details etc.  So... if anyone in the community has information on the unit itself, it would be greatly appreciated.

@scoobie would love to get a copy of any F86F Manuals and documents that you may have in PDF.  Would you be open to sending through a download link?  You can DM me here on the DCS Forum, or you can send me an email to:  muggavirtualpilot@gmail.com

 

Edited August 7, 2022 by [MVP] Mugga

[[MVP] Mugga]

Took some time this evening to draw up the Bombing Altimeter instrument/gauge components - anyone who may have an interest in such.

[scoobie]

The assembly drawing of the bombing altimeter. Just found it. I wish I had seen it before!
I can't see the target altitude needle in the drawing.

EDIT: I can't see the "bumper" for part number 12, either. It must be a slightly different variant of the device from the one depicted in Flight Manual.

Edited August 9, 2022 by scoobie

[[MVP] Mugga]

@scoobie You beat me to it... was just chatting with our team and reviewing the parts manual.  It does appear that the bombing altimeter is just a standard cabin pressure gauge, that has a face bezel applied, with a manual adjustable needle.  The bezel can be rotated using the knob to the left and the needle on the face of the bezel can be moved freely.  It brings into question the way that the instrument is modeled in DCS.  I am not sure if there are different versions etc.  It may be correct, but I have little idea.

[scoobie]

I'm glad if I could be of any help.

Yeah, apparently there must have been different versions of this "front assembly". For instance, look at the "black and white arm" from the picture in the manual and its counterpart in the breakdown picture - part number 12. They are different, the former is "straight", the latter has this circle with a hole punched in it, near the thick end where you grab it.

Anyway, if you get a chance to get these parts somewhere, or preferably the whole assembly together, we'll learn everything about it

[Awger]

Looks like an "early" variant? Construction (specifically the support brackets, #17 and #22) doesn't look like what's illustrated in the manual.

[scoobie]

Yes, the breakdown apparently shows an early variant, a bit crude The one in the manual looks more "civilized" or polished, so it's probably a later design.

[[MVP] Mugga]

Doing some research and found the following picture;

 

Edited August 10, 2022 by [MVP] Mugga

[Awger]

Finally got an opportunity to speak to the curator about the FJ ... it has no instruments. They have -1s for FJ and F-86 (same ones available online, same info already posted) but no other maintenance manuals that reference the MPC.

However...

Randy is supposed to be around on Saturday, and he used to have an F-86; he may still have some manuals. Worst case, he knows people who know people who have stuff.

The search continues...

[Awger]

Spoke to Randy today. No joy on the MPC (his F-86's cockpit was already stripped and rebuilt when he got it) but he did give me a line on T-37 parts.

There's a guy flying an FJ somewhere north of here, need to track him down.