Just my two cents, the engine definitely should be rotated through to clear hydraulic lock.
In the Connie that was 12 blades. Only then did you prime and set ignition.
On smaller GA aircraft, like my friends C195 or Stinson SR9, you would make sure the mags are off and mixture at cutoff, and then carefully pull the prop through by hand a few times.
I would also use the Boost as an ignition boost, there are separate fuel pump switches. So a fuel boost doesn’t make any sense. You are always more likely to flood an engine than to starve it.
The starter sound would be great to have a bit more prominent. As of right now it is not really there.
I did the first long flight with the 307 since I purchased it on release. And it is already a totally different and better airplane. So you are definitely on the right path.
Hmm, the DC-3 has them and they are fuel booster pump switches, with it having the same engines I’d guess they have the same function.
On the DC-6, as you rightly said, it is an ignition booster. But with this having engines matching the 3 rather than the 6 (and the 3 not having an ignition booster either), my educated guess is leaning towards fuel booster pumps.
Are we sure the DC-3 modeled here is equipped with Wright Cyclone and not Pratt & Whitney R-1830 engines?
This is found in at the top of the sound.xml file for the DC-3:
Regardless, images of Boeing “press” photos of the 307’s cockpit do not show a row of four individual fuel pump booster switches as seen in the modeled 307 we have. Seen here a “P.A.A. 307” aka 307A of Pan Am. (Note the twin levers flanking the pedestal not seen in any photos of #2003 and also not present in other images I have of 307 cockpits.)
I’ve also been intrigued as to why they have a “use only one at a time” warning label on their switch plate. Did these pumps have some significant electrical draw that turning on more than one would risk an electrical issue?
Of further interest is the B-17 manual instructs the crew to turn on all four booster pumps above 10000’.
I find the clear differences between the B-17 and 307 starter and booster pump switches to be of particular interest given the shared wing design and same engine family that they have in common.
Are the 307’s six switches associated with starting the aircraft momentary switches? Would the Boost switch be held, energizing the fuel booster pump and the booster coil at the same time? Then when fuel pressure was assured, would the Start and/or Prime switches then be held until the engine fired?
If they are momentary switches, then the addition of the four individual booster pump switches makes sense to a degree for allowing a pump to be set to on without having to hold a switch to do so. Then that begs the question of why? Why would that be needed? All early images of various 307 cockpits do not show these switches, so it would seem these switches were added later. When did the need arise to turn on a booster pump, and then only one at a time if the label warning is to be adhered to?
So many of these questions could, hopefully, be answered if Boeing or the Smithsonian would get back to me.
For the Connies we did have full sets of manuals for each of the variants, including circuit breakers and their sizes. In some cases there were diagrams that showed different settings for different stages.
This was to load-share either the draw on the generator or to ensure enough fuel pressure could be sent around the 7-tank systems valves etc to reach the four engines.
The case with use only one at a time may be, for example only relevant during startup and not after. Both to not over boost the fuel system and to verify operation of each individual pump. I did not look at available documentation for the 307 regarding tanks, manual valves, check-valves etc.
This may also explain the difference between a warplane and a civilian one.
I believe most switches involved in engine start, except for mags, are momentary only and must be held to remain engaged. It would be interesting to know for example what sort of priming system the 307 has.
Think the truly manual one in a single engine Cessna or Piper, that literally pulls fuel into the line and squirts it into the intake. Electric priming pumps that did the same?
Starting a big radial is a delicate dance that requires skill and practice and something between three and four hands usually.
But basically you get the engine turning, which generates the required compression but nothing more. Then you introduce sparks….but with a lean mixture still no bang and smoke.
But now you prime until the first few cylinders fire and then bring the mixture levers in from cutoff.
At slow starter rpm the engine driven pump should not be introducing too much fuel pressure yet.
But at least in warm SoCal we never went full rich on startup…that only happened when the engine was warmed up and rpm increased for run-up etc.
Some aircraft have electrical fuel pumps, other have manual pump.
The booster switch has nothing to do with fuel booster pump. It provides an auxiliary spark to boost magnetos during start.
The procedure is to turn ON booster pump and prime the engine. You have to use booster pump because the engine isn’t feed by gravity. If the aircraft hasn’t electrical booster pumps you have to build fuel pressure using manual pumps before priming.
And priming is used only for a few seconds. To much and will flood the engine.
After priming, you start the engine by helding both booster and starter switch.
I fully understand all of this information and then some.
What isn’t clear is how any/all of this is/was implemented in the 307.
The photo you shared is of #2003, which has 4 individual booster pump switches. I have seen no evidence of those 4 switches existing in any other image of a 307 cockpit.
Again, as I’ve stated a few times, there were only 10 of these aircraft:
1 was destroyed during flight testing/demonstrations
1 was highly customized for Howard Hughes with engines and a fuel system unique to that airframe
5 were sold to TWA with two-speed superchargers taken by the USAAF during WWII and highly modified during and after that time
3 were sold to Pan Am with single-speed superchargers – of which one is still in existence and had B-17 engines installed in it by the Haitian Air Force in 1954.
All of that makes this endeavor of determining how this – specific – aircraft was constructed exceptionally difficult. Data is sparse and Boeing isn’t sharing what they have.
In the case of these engines, you primed while starting. You want the engine spinning when you’re dumping fuel into a non-running engine. That is important, otherwise you could flood the cylinders which would then hyrdo-lock when the starter was engaged. With it spinning, if it doesn’t fire, the excess fuel will be expelled from cylinders via the exhaust. Excerpt from B-17 Pilot Training Manual:
I am not sure where I found this but I had a bookmark for it and I think it shows the startup procedure quite well for the big radials. It’s Buffalo Joe and his DC-3. If you watch him start the second engine around the 3 minute mark in the video it is quite clear what works. Starting Radial Engines with Buffalo Joe | DC-3 MASTER CLASS (youtube.com)
I hope this may help, really appreciate all the work you have done for the 307.
B-17 have inertia starters. Given the switch layout of 307, I suspect it uses direct cranking starter.
According to pratt&Whitney you prime as required before starter and booster.
With the electric priming pump on the 307, I’d be inclined to think it would be exceptionally easy to over prime (read: flood) as opposed to a manual pump.
See this except from the DC-6, which also has an electric priming pump. Engine is already in motion via the starter:
Using ITAR is such a joke. Because a 1930’s prop liner is such a high risk national security issue…
As a huge fan of the B-17 I’ve been following this abysmal release from AH since day 1, and I just wanted to commend your efforts! When one dedicated person can achieve all this, it really goes to show how little the original developer cares beyond the cash grab. You’ve got me back to considering getting this as a stop gap until us Fort fans get a proper B-17.
Using ITAR is such a joke. Because a 1930’s prop liner is such a high risk national security issue…
The only reason I could maybe possibly see is that they don’t want to give out anything thanks to the years long string of legitimately leaked secrets over on the War Thunder forums…
I would bet it has not much to do with that. I think there’s rules in place to guard legitimate things and this just gets caught in the net. It’s not worth their time or effort to figure out a way to release it. It’s easier to just say “no.”
I’ve seen this in business before. As an example, for years BNSF wouldn’t allow Train Simulator to use their livery outside of the USA for the simple reason that their attorney’s said it wouldn’t be wise as they didn’t own the trademark. All they did was make fans angry, but it was easier to say “no” than go through a couple of hoops. They can now - I don’t know what changed.
It is just odd considering how many documents can be found on the DC-3. Yes, the Boeing is built from a bomber, but the technology is so old. It is not like you are trying to obtain information about the bomb sights. The DC-3 also had a military variant. I understand the need for ITAR for a lot of things, but this isn’t one of them.
The longer I reflect on it, the more I’m finding it quite odd, too.
The aircraft was never designed by Boeing as a military variant. All of that was done independently from Boeing via the USAAF. Even then, most of it was stripping out interiors and pressurization equipment – not turning them into bombers.
I know they still hold the patent on the pressurization regulators, so there may be some desire to hold things close to the chest, but I wonder how the author of the 2012 paper presented to the American Institute of Aeronautics and Astronautics that I referenced for this project was able to gain access to the diagrams and photos that were labeled “Boeing Historic Archives”.
Perhaps, I’ll try to contact the author of the paper…
The 307 payload defaults to an empty aircraft other than Pilot, First Officer and Flight Engineer; each at 170 lbs.
I’ve noted that using the slider to load the aircraft is less than ideal as it maxes out the weight of the flight crew to 200 lbs and then evenly fills the passenger seats and cargo holds with the exact same weights. These weights end up being really unrealistic.
To setup a passenger load ends up being a bit of a pain with a fair amount of time spent on each station.
I could preset an initial load of passengers and cargo that better reflect the weight distribution of given loadout.
Does anyone have any thoughts on this? How full a cabin? How much cargo?
Also, it’s looking like the apron.flt is adding fuel and configuring the payload, too. I’m thinking that should all be removed so as to not conflict with the Payload setup via the Flight Planner.
Here’s an example of full seating. I have a “stewardess” in row 9. I don’t think I’d want the aircraft full like this, but having some sort of baseline load would be nice.
