30 Seconds over Tokyo B-25 Question

[Airlift48]

My question is regarding the power to the turret in Lawson's B-25.

Lawson says in the book, that it stopped working, but would only work on reserve power which he had to build up as he flew along and was switched on from the cockpit.

What kind of system is that? Battery powered? Did the batteries have to be charged from the engine driven generators?

This part of the story always puzzled me.

Anyone know what he's talking about and can explain it in detail?

Thanks...

[agent86]

Ok ,I'm not speaking from a position of any knowledge of the system involved. To me it sounds like a Hydraulic system.I dont know but it sounds like needing to build pressure before working.Just a guess

[Steve Nelson]

Like Agent 86, I don't have any detailed info on B-25 systems, but a quick bit of Googling indicates that the B-25B used an Bendix Model-A turret, which was electrically powered. Just going by Lawson's description, I would assume that main power came from the plane's electrical system, and auxilliary power came from batteries, which had to be charged up during the flight.

SN

[bluehawk15]

Just a guess, with a little fact tossed in. Many electrical systems on the B-25 ran off of AC power, being changed from DC power through inverters. Could the back-up power have been DC and possibly the battery power was low after starting the engines and needed to have the charge restored by the generators in flight?

[mustangdriver]

I remember Lawson states that the power to the turret won't last long in combat.

[bluehawk15]

Does sound like a battery back-up power system. I wonder if it had dedicated batteries, or took power from the main aircraft battery?

Anyone have a gunner's manual for the B-25, if there was such a thing? The -1 doesn't say anything that I can find.

[turret nate]

I don't think the B25B model used the Bendix model A, more likely it was the model N.

Our B25J, Miss Mitchell, has the model A. I can speak to that turret, the power cable goes from the power box directly to the main bus on the forward side of the bomb bay. The turret draws about 20 amps on idle, 100 amps on full movement into slip stream, and nearly 700 amps briefly at start up when the amplidynes start. There is no hydraulic component.

I have no direct experience with the model N but do have the service manual. This is the earlier model with the periscope type sight (model A has the simple N-6 sight). The electric connection seems the same, but the N does have a hydraulic gun charger.

My guess is there was something wrong with the ship's component that charges the batteries. At load the turret would not take long to drain the batteries. I have not read Lawson's book. Is there any mention of other electrical components in the ship not working?

[mustangdriver]

Not sure, but I know he had some issues with the left engine.

[bluehawk15]

What is it with B-25's and the left engine? I know what it must be! That's the engine the guy in the left seat starts. Must be his fault! As co-pilot, I start the right engine on the Yellow Rose, and it's doing just fine. (knock wood)

I'll try to see if Dick Cole knows the answer to that question about the turret. I'll post what I find out.

[Steve Nelson]

Thanks, Turret Nate! That's exactly the kind of detailed first-person info that makes this forum so valuable!

SN

[Taigh Ramey]

As stated the upper turret is purely electric and would run off of the ships main buss. This bus receives power from both of the engine driven generators and the ships battery.

In flight one generator could power the turret should one have failed but if both generators quit for some reason then the turret would deplete the ship battery (batteries) quickly. If both generators did fail then they likely could have continued on the mission and rationed the battery power to essential equipment. I can see the turret as essential if fighters were around but as I said it the turret would kill the batteries in short order. As a guess maybe 20 mins of conservative operation as it used two big amplidynes which are large motor generators that run all the time and consume power quickly not to mention the azimuth and elevation drive motors.

Once in flight the other electrical equipment that comes to mind are:

The boost pumps (not normally used in flight unless an engine driven pump fails)
Fuel transfer pumps (used to transfer fuel from the aux and bomb bay tanks) essential
Fuel quantity and a few engine instruments as most are direct reading in one form or another
Oil temp indication (essential, to me anyway)
Prop feathering (hopefully not needed but essential none the less)
Bomb bay doors are electrically controlled but can be opened and closed with a manual valve in emergencies
Bomb release is normally electric but they can also be released manually
Landing gear position indications (not essential in flight)
Radio equipment (This could be a big consumer of electrical power but could be easily turned off as necessary. The ADF might be essential for navigation and homing and this did use AC power as well as DC power thus to use it an inverter or dynamotor would have to be turned on which eats amps quickly)
Interphone (uses small amounts of power as compared to other radio gear)

I am sure I am forgetting some but this are a few of the big ones anyway. If both generators did fail then it would be like an Apollo 13 thing trying to only use what battery power was essential to finish the mission/flight. I don't know what specific problems they had so this is pure speculation. I also do not know if these B-25B's were 12 or 24 volt aircraft whereas the 12 volt aircraft used roughly twice the amperage as their 24 volt counterparts to get the same job done. This could eat up the battery quicker too.

Some of the early aircraft used more selsyn instrumentation for engines and control/gear position indication thus they relied more heavily on AC power. Whenever AC was needed a dynamotor was used (see above).

Anyone know what specific problems they had?

Taigh

[mustangdriver]

Could someone ask David Thatcher?