Flat top blind flying panel – need some help with hole sizes.

The 2 BA csk screws are one inch and the spacers are half inch (8 required) – based on experiment. 🙂

2 BA brass screws went into the prevailing torque nuts on my AH & DI without apparent damage.

I’ve looked myself for a drop-in hardware store that has them but not had much luck (well not in Sweden where everything is metric..) though you can often find brass machine screws on eBay.

http://www.ebay.co.uk/bhp/2ba-brass-screws

Should be brass instrument screws, or sometimes Aluminium. The spacers are usually turned aluminium, but I have seen Tufnol ones as well.

Hi Bruce, & OneEighth

Were there 4 separate spacers or was a spacer ring used ?.
Any ideas where I might be able to obtain the correct screws ?.

Bob T.

Can’t agree with your measurements so I did a bit more research …

from AP1275 Vol I 1937: the pcd for the fixings is given as 4.125″ (=104.8mm), dividing by root2 gives the square dimension as 74.1mm (2.917″)- not a round number of inches but no reason why it should be.

Measuring an actual instrument (MkIXE* dated 1942 with non-ribbed outer bezel) with an electronic vernier…
measured rear case diameter 85.75mm – this is a shade over the nominal 3.375 given in AP1275
measured front bezel diameter 92.4mm. This is close to EB’s 3 41/64″(=92.47) so perhaps the inch dimension for the hole should be 3 21/32″(=92.9mm)

Smirky – your numbers from AP1275 match actually with my book. It says 4.125″ PCD which is 4-1/8″ or 2-1/16″ from the centre of the dial to the centre of the screw hole as I gave in my original post. My book also gives 2.92″ as the horizontal and vertical distance between holes which is 2-59/64″ in old money and as it’s shown in a different diagram in the book.

The original BFP kits came with all the necessary screws and spacers, except for the DI, and horizon. These had screws with them from manufacture.

Bruce

Should be brass instrument screws, or sometimes Aluminium. The spacers are usually turned aluminium, but I have seen Tufnol ones as well.

I bought a repro BFP recently & am wondering if anyone could please tell me what types of screws are used to mount the instruments, & what kind of spacer is used for the turn & slip ?.

Cheer’s.
Bob T.

In my book it simply states 2BA as the screw size for the instruments. Looking at pictures of actual panels it appears that the ASI, ALT, ROC and T&S *should* use countersunk slotted machine screws and that the Artificial Horizon and Gyro compass use dome head slotted machine screws.

However that’s and observation and not something I’ve seen officially documented.

I bought a repro BFP recently & am wondering if anyone could please tell me what types of screws are used to mount the instruments, & what kind of spacer is used for the turn & slip ?.

Cheer’s.
Bob T.

Remember the ASI is also mounted off spacers, and may not fit through the hole.

Bruce

and having measured an actual Mk9 ASI instrument.

Can’t agree with your measurements so I did a bit more research …

from AP1275 Vol I 1937: the pcd for the fixings is given as 4.125″ (=104.8mm), dividing by root2 gives the square dimension as 74.1mm (2.917″)- not a round number of inches but no reason why it should be.

Measuring an actual instrument (MkIXE* dated 1942 with non-ribbed outer bezel) with an electronic vernier…
measured rear case diameter 85.75mm – this is a shade over the nominal 3.375 given in AP1275
measured front bezel diameter 92.4mm. This is close to EB’s 3 41/64″(=92.47) so perhaps the inch dimension for the hole should be 3 21/32″(=92.9mm)

The Artificial Horizon diagrams are copies of Smiths Dat Leaflets (not Sperry, but I guess they were interchangeable) but the ASI Mk 9 was I think drawn up from the leaflet for something similar and having measured an actual Mk9 ASI instrument.

I did wonder about that. As Smirky pointed out, it needs spacers. However my wartime book *does* actually give a panel cut-out hole including the corner missing for the zeroing mechanism to sit in.

I did say that but then looked at the actual panel and corrected it as the VSI is in fact flush to the rear of the panel. The older ones have a knob rather than the grub screw so that would need a cutout.

The Corner isn’t cut out, the adjusting screw is accessed through a screw hole in the panel.

I did wonder about that. As Smirky pointed out, it needs spacers. However my wartime book *does* actually give a panel cut-out hole including the corner missing for the zeroing mechanism to sit in.

I guess either/or works.

Smirky, TerryP

Thanks for that. Very helpful. I need to sit and do some backwards conversion to the old imperial fractions to compare them with the numbers in my book to see if in fact its the same but expressed differently.

I noticed for the ASI in Terry’s picture you have 2.9″ between holes and my wartime book says 2.92″ so only 1/100th of an inch difference.

Can I just ask Terry, are those numbers on the drawing from some sort of official publication or ones you’ve drawn yourself after measuring?

I’ve noticed that in the wartime book I have they give the hole diameter as being the bezel diameter + 1/64″ whereas in Terry’s drawing it’s 1/16″.

[QUOTE=OneEighthBit;2132179]All,

the climb-descend gauge needs the corner cut-out for the zeroing mechanism.

The Corner isn’t cut out, the adjusting screw is accessed through a screw hole in the panel.

Some round top panels were modified flat tops, you can tell which ones because they have both vocab sections and references but the earlier one is struck through. On that basis, all the holes and the width should be the same. The maximum height probably is.

Any help? Haven’t got anything for the T&S Mk1.

I have done this exercise for my Lancaster curved top panel, this is based on a combination of tracing, drawing from a modelling book, photos and experience so is not definitive. Also I made this part by hand so I may have fiddled it slightly but from memory the dimensions were pretty good. I have converted your dimensions to metric in brackets.

BFP general dimensions – 14″ x 10-5/8″ with corners rounded to 1/2″ radius?
Mk IX Air speed indicator – hole 3-41/64″ diam. with holes spaced 2-1/16″ from centre?[92.5]. [52.4]Mine are 92.3-CORRECTION 92.8 and 52.4

Mk I Sperry Artificial horizon – hole 3-3/4″ diam. with holes spaced 2-1/4″ from centre?[95.25], [57.15]Mine are 96.8, 60.3

Mk I Turn and Slip indicator – hole 4-1/2″ diam. with holes spaced how? [114.3], [?]Mine are 111.1,60.3

Also, is there a general rule on how the holes should be aligned?
Mine are on a rectangular grid, reading across: 104.8, 115.9mm. Reading down 104.8mm

I measure the repro panel and it seems as if the top holes are all aligned on a datum 3″ from the top of the panel and the bottom at 3-1/2″ inches but with the Turn and Slip hole its too close to the climb and descend.[76.2], [88.9]

I have 74.4 & 89.5 so this sounds right. Yes the turn and slip hole is very close.

Just checked and my VSI fits flush to the rear of the panel on three screws with out needing an extra cutout. The ASI and the T&S are mounted on spacers to even out the front projection which would otherwise be excessive.