Help Sought - Sperry Gyrosyn Compass

[Crimea_River]

I'm hoping that someone here can answer a question or steer me in the right direction. A bit of a long story to start.

As many of you know I'm helping to restore a post-war Mosquito P.R.35 as it was used by Spartan Air Services for aerial mapping. The cockpit is where I'm currently working and I'm trying to complete the Blind Flying Panel. The well-known basic-6 instruments used by the British appear to have been modified by Spartan, especially where the directional gyro was mounted at the bottom center. Here is a typical British unit seen on some late model Mosquitos on display:

I have a Spartan Equipment List dated 6 November, 1957 which confirms that a Sperry Gyrosyn C-2 system was installed. The indicator's weight of 4 lbs is consistent with that shown in a manual that I have for this unit and the moment arm of -4.2 feet is consistent with its mounting on the instrument panel.

In this photo excerpt of one of Spartan's deactivated machines dated June, 1966 there is a gaping hole where the directional gyro would normally be mounted:

It's evident that some of the original British instruments have been replaced with American units but that's another discussion. The instrument panel that came with our aircraft also has the large hole at the directional gyro location:

After bead blasting our panel, it was discovered that the aluminum that it is made of is stamped "ALCAN" and so it appears that this BFP was a complete new replacement of the original de Havilland production unit.

Here's the issue. The dimensions of the enlarged cut-out and the hole pattern surrounding it are NOT consistent with a Sperry Gyrosyn C-2 or C-2A compass and so I'm now looking at the possibility that there was yet another upgrade to the gyro compass after November 1957. I need to find out what unit would have been installed in that hole in the late 1950's or early 1960's that would have been considered the latest and greatest aid to navigation at that time. The mounting hole pattern is ROUGHLY 4.5 inches square and I neglected to measure the circle diameter but that can easily be done the next time I'm at the shop.

Does anyone have any suggestions or know of where I could pursue this question?

 

[cvairwerks]

Look at the AN-5736 series and see if that matches the hole pattern. I think it's the large diameter series, also known as a C-7.

 

[Crimea_River]

Look at the AN-5736 series and see if that matches the hole pattern. I think it's the large diameter series, also known as a C-7.

Thanks for that. I only get hits for the Artificial Horizon using AN-5736 and no hits for a C-7. I'm looking for the gyro compass - the Artifical Horizon is above that on the panel.

Sorry I'm not that proficient in these model numbers and so may be looking at the wrong thing. Can you offer any links?

 

[Wurger]

Andy , wouldn't be it one of these ? ... I don't say it has to be but it might have been one of a such serie ..

the source: Sperry Slaved Compass System J-1 & J-2 aka Gyrosyn C-1 & C-4 Service Manual | eBay

 

[Crimea_River]

Possibly Wurger Wojtek. I would need to know the key dimensions and when these were first produced to see if these are options.

EDIT. One thing I see is that the raised portion behind the adjustment knob is the wrong shape.

 

[FLYBOYJ]

I've been looking into this as well. Just an observation - many years ago I restored a 65' C150 straight tail. My partners and I gutted the airplane and put in newer instruments. In the middle of the original instrument panel was this huge directional gyro that must have weighed at least 10 pounds. Looking at your pics I would say it was about the same size as the cut out in the instrument panel shown.

 

[FLYBOYJ]

Found this - again, a shot in the dark

WWII Era US Army Aircraft Directional Gyro Indicator Gauge AN-5735-1 JAHCO Parts | eBay

Find many great new & used options and get the best deals for WWII Era US Army Aircraft Directional Gyro Indicator Gauge AN-5735-1 JAHCO Parts at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Wurger]

Possibly Wurger Wojtek. I would need to know the key dimensions and when these were first produced to see if these are options.

EDIT. One thing I see is that the raised portion behind the adjustment knob is the wrong shape.

I see.

 

[Snautzer01]

where would it sit in the cockpit?

 

[Crimea_River]

Found this - again, a shot in the dark

View attachment 690873

WWII Era US Army Aircraft Directional Gyro Indicator Gauge AN-5735-1 JAHCO Parts | eBay

Find many great new & used options and get the best deals for WWII Era US Army Aircraft Directional Gyro Indicator Gauge AN-5735-1 JAHCO Parts at the best online prices at eBay! Free shipping for many products!

www.ebay.com

No Joe, that is similar to the wartime configuration circled in the first panel pic I posted above. The calibration knob on yours is on the bottom whereas the one I need is at the 7 o'clock position.

where would it sit in the cockpit?

The indicator unit I'm looking for is bolted onto the instrument panel.

 

[FLYBOYJ]

No Joe, that is similar to the wartime configuration circled in the first panel pic I posted above. The calibration knob on yours is on the bottom whereas the one I need is at the 7 o'clock position.

Yes - seen that, also seen how the artificial horizon had the cut out to the right, thought there might be an overlay when comparing the two photographs

The indicator unit I'm looking for is bolted onto the instrument panel.

Gotcha

 

[Snautzer01]

No Joe, that is similar to the wartime configuration circled in the first panel pic I posted above. The calibration knob on yours is on the bottom whereas the one I need is at the 7 o'clock position.

The indicator unit I'm looking for is bolted onto the instrument panel.

Yes. It would. But in what place. Werent the instruments grouped to function.,?

 

[Crimea_River]

Yes. It would. But in what place. Werent the instruments grouped to function.,?

OK. Look at the first panel picture I posted. See the yellow circle? Now look at the second panel picture. See the big hole where the yellow circle in the first picture is? Thats where the mystery unit goes.

You are correct these units were placed by function. In both pictures, the directional gyro compass is at the bottom center. I need to know what type of gyro compass fits the large hole.

 

[FLYBOYJ]

Yes. It would. But in what place. Werent the instruments grouped to function.,?

Yes. Artificial horizon and directional gyro usually close to the center. VSI, airspeed indicator, turn and back indicator usually off to the one side. Engine instruments usually on the right side of the panel looking forward, some aircraft like the Mosquito had them on the left.

Now here's something interesting.

Andy - look at this bird! DG knob in the middle.

 

[Crimea_River]

OK, I guess I'm not explaining this very well so I will try again. Yes Joe the picture you just posted shows a typical wartime Mosquito Blind Flying Panel with the small Directional Gyro with the knob at the bottom. It's probably an F.B. VI Mosquito. The aircraft we are restoring has a MODIFIED Blind Flying Panel as pictured here with the cut-out for a more modern (ca. 1960) Directional Gyro Indicator shown in the red circle.

I have a good handle on what instruments I need to insert into the other 5 cut-outs (ASI at top left, Artificial Horizon at top center, Rate of Climb indicator at top right, Altimeter at bottom left and Turn and Bank indictor at bottom right) but I need to find an American Directional Gyro Indicator that will fit into the large circled cut-out with a knob at the 7-o'clock position. We're NOT restoring our Mosquito to a wartime machine but a rather unique civilian bird.

 

[Crimea_River]

Something like this, though I don't know if it fits:

I suspect the raised semicircular bit in the top right corner precludes this one though.

 

[FLYBOYJ]

OK, I guess I'm not explaining this very well so I will try again. Yes Joe the picture you just posted shows a typical wartime Mosquito Blind Flying Panel with the small Directional Gyro with the knob at the bottom. It's probably an F.B. VI Mosquito. The aircraft we are restoring has a MODIFIED Blind Flying Panel as pictured here with the cut-out for a more modern (ca. 1960) Directional Gyro Indicator shown in the red circle.

View attachment 690881

I have a good handle on what instruments I need to insert into the other 5 cut-outs (ASI at top left, Artificial Horizon at top center, Rate of Climb indicator at top right, Altimeter at bottom left and Turn and Bank indictor at bottom right) but I need to find an American Directional Gyro Indicator that will fit into the large circled cut-out with a knob at the 7-o'clock position. We're NOT restoring our Mosquito to a wartime machine but a rather unique civilian bird.

OK - gotcha now!

I'm sure you folks probably did this already, but has anybody reviewed the maintenance records for an equipment list or weight and balance report that might have all equipment listed? Perhaps a "Form 45" (I think I have it right) was completed for this installation? Just throwing out some ideas.

 

[Crimea_River]

Yep. That's how I know they had a Sperry C-2 installed in 1957 (see the excerpt from the Equipment List in the 1st post). Unfortunately, the C-2 dimensions are not consistent with the larger cutout and screw pattern so I suspect they installed something newer after 1957. Unfortunately records of W&B reports and Equipment Lists stop in 1957 but our aircraft and others continued in service until the early 60s so that's why I'm looking for help. I agree that if we had later documents then that would make things clearer. I'm pursuing another source for those docs if they exist.

 

[FLYBOYJ]

Yep. That's how I know they had a Sperry C-2 installed in 1957 (see the excerpt from the Equipment List in the 1st post). Unfortunately, the C-2 dimensions are not consistent with the larger cutout and screw pattern so I suspect they installed something newer after 1957. Unfortunately records of W&B reports and Equipment Lists stop in 1957 but our aircraft and others continued in service until the early 60s so that's why I'm looking for help. I agree that if we had later documents then that would make things clearer. I'm pursuing another source for those docs if they exist.

OK, now the brain is engaged, I don't know why I glossed over that part of the equipment list

 

[FLYBOYJ]

Do you think Transport Canada may have some additional records?