Battery drain for startup

[gumbyk]

For a radial, you need to turn the prop through some number of blades before engaging the mags. The blades vary with the number of blades on the prop and the radial in question ... but radials ALWAYS need to turn some before starting or they can backfire and blow out gaskets with extreme ease or hydraulic lock and require a complete rebuild.

I've never seen any of the radial warbirds operators down here crank the engine before turning on the mags. Usually ignition occurs on the third or fourth blade. We've never had any problems with backfires either
Hydraulic lock should always be cleared BEFORE cranking the engine. The starter has enough energy to bend conrods if a hydraulic lock is present, this is why you pull the propeller through a number of revolutions prior to start (we do it as part of the preflight).

 

[bobbysocks]

i know on for certain ac we serviced on the ramp, once the battery went below a certain level or reached a certain temp it was classified junk and had to be removed and replaced. since we didnt stock any of those batteries and coupled with the high cost of the battery, labor, and loss of flight we ALWAYS hooked up ground power to those ac prior to start. ground power also put out higher and more consistant cranking amps than the battery alone.

 

[FLYBOYJ]

Well, there is "now" and there is "then". There is some story about the British substituting 1500 generators on some (all?) of their Tomahawks instead of the original specified 900 watt units. This lead to a number of the Tomahawks sent to the Russians breaking their generator drives due to the greater load and a rush shipment of new generator drives being sent.

I'd like to know the source of that because aircraft power is NEVER measured in watts. Volts, amps - 24 or 28V systems. A generator drives don't break because of loads, there's other mechanical issues there

The engine didn't have to be running at full throttle to get the full charge rate. That would happen at a somewhat lower RPM. and the voltage regulator would keep things from over charging at the higher rpm. But an RPM close to idle would NOT give full charging rate, so the ability to charge at a slow cruise depended on the rpm setting and the electrical load.

Again I'd like to know references for this as maintaining electrical load at engine idle was usually a before takeoff checlist item and was a reson for abort (I believe this is specifically in the B-25 and B-26 checklist - I'm on the road so I don't have access to my library)

This was in the early part of the war and more stringent requirements for both generator power and batter capacity may have soon been put in place, especially after a few accidents with planes having Curtis electric propellers. If you loose the ability to change the prop pitch landings can get really interesting.

The failure of Curtiss electric propellers were mainly due to bearing failure that did not allow the prop to feather and the prop would run away, had little to do with loss of electrical power.

Again this is one reason that engines weights are given as dry weights, generator weight is not included as it changed with the air frame the engine was installed in. "simple" planes like fighters using a smaller generator than a 'complicated" plane like a bomber or transport. Please remember we are only 10 or so years from using a generator mounted on the wing or fuselage and driven by it's own propeller

Generators and later alternators were then and now never included in aircraft weight and are actually considered an airframe part in some QEC installations

Late-war practice could be completely different and much more in line with modern practice. Please remember than the earlier P-38s and many other twin engine aircraft had a generator on only one engine.

The extra generator the P-38 was due to entire electrical loss on the left engine, not the operating load. You lost the left engine, you lost electrical power. Common sense, not electrical load dictated that fix

 

[Shortround6]

I'd like to know the source of that because aircraft power is NEVER measured in watts. Volts, amps - 24 or 28V systems. A generator drives don't break because of loads, there's other mechanical issues there

There may have been other factors like th torsional load, any any rate the story is in "Vee's for Victory" on pages 122-123. I was in error though, The original model test for the British for the C-15 engine was done with a 500 watt (that is what the book says) generator while the British specified that the plane should have generator of no less than 900 watts and the actual unit fitted was 1500 watts. Allison made quite a number of gear and coupling sets for refit and and also a different generator was used.

Again I'd like to know references for this as maintaining electrical load at engine idle was usually a before takeoff checlist item and was a reson for abort (I believe this is specifically in the B-25 and B-26 checklist - I'm on the road so I don't have access to my library)

It may be quite possible to maintain the desired load at idle if the generator/s are big enough to begin with. One of the big advantages of the alternator over the generator (at least in cars from about 1960) was that the alternator could maintain about 60% of output at idle speeds and it could hit 100% at a lower speed than a similar sized generator. I have no doubt there was a certain minimum power level that the generators had to put out as part of a pre-flight check.

The failure of Curtiss electric propellers were mainly due to bearing failure that did not allow the prop to feather and the prop would run away, had little to do with loss of electrical power.

This may be semantics. IF you got the plane back on the ground and fixed the generator or replace the battery the propeller would operate just fine, it wasn't broken or it didn't "fail" any more than the electric window not working on a car with a dead battery. Jump start the car or replace battery and the window is "fixed". The problem is NOT being able to control the propeller if the available electrical power is too low.

Generators and later alternators were then and now never included in aircraft weight and are actually considered an airframe part in some QEC installations

I think you meant engine weight and not aircraft weight but I have made plenty of mistakes in typing or wording myself. The point was that different generators could be fitted to the same engine to suit the different applications.

The extra generator the P-38 was due to entire electrical loss on the left engine, not the operating load. You lost the left engine, you lost electrical power. Common sense, not electrical load dictated that fix

Quite right, but the point was the rules, regulations and even common practice were changing quite rapidly in the late 30s and early part of WW II. what was an acceptable practice or even risk in 1939-40 would be considered dangerous or even fool hardy by 1945 let alone today. The changes in electrical needs and supplies in aircraft were happening faster than the operational experience was being acquired to form good policies and regulations. Loosing entire aircraft due to the savings (weight or cost) gained by not having a second generator (or a big enough first one on a single engine plane) seems stupid now but was fairly common then.

 

[GregP]

Hey barney,

The radial startup you posted was a non-propped engine not on an airplane. It may well have been started less than 5 minutes prior to the clip to assure it was good to go for the video clip. In a real ariworthy engine start, the plane has usually not been started for some days, even for weeks. The 8 to 12 blades are to clear the oil that had drained into the cylinders since the last run. At the Planes of Fame Museum, some of our radials are only run every few years! They need consierable rotation before engaging the mags! Go watch any real radial-powered aircaft start up.

Here is olne:
View: https://www.youtube.com/watch?v=GWBjvRSGn7E.

He turns 8 blades or more.

Here is another:
View: https://www.youtube.com/watch?v=TSpBw8vigrA

He turns 19 blades before engaging the mags. The intent is to CLEAR the cylinders of oil.

When we did an annual on our P-47 in 2009, we pulled the prop through 20 blades with the spark plugs out and got maybe a gallon of oil out. When we reinstalled the plugs and pulled it through another 15 blades, we got another couple of quarts of oil. When we used the starter later, we got another quart or more of oil out before we engaged the mags. When it startted it smoked for 4 minutes due to excessive oil before cleaning up and running normally.

Engines like to be operated regularly, not stored ...

 

[Siegfried]

The reason why the WWII Me109 had no electric starter was lack of space due the fuselage weapons (magacines). All currently flying examples in Germany have one because no weapons are installed so does the Me109E in the US
Regards
Cimmex

Are you sure this lack of electrically spun inertia started applied to ALL Me 109, eg even Me 109K4?

The Me 110 with the same engines always did have electrically spun inertia starters.

The direct in cylinder fuel injection of the DB601 and 605 meant they tended to start immediatly.

 

[cimmex]

Yes I'm sure, there was no space for an electrical motor at the starter because of the fuselage armament. At the 110 there were no cannons nearby the motor, so they indeed had an electrically driven inertia starter.
regards
cimmex

 

[gumbyk]

Greg,
The starter on most radials is powerful enough to bend conrods if you have a hydraulic lock. That is why you always pull the engine through by HAND prior to starting. Even then, I have heard of conrods being bent by an over-eager person pulling it through.

 

[fastmongrel]

Greg,
The starter on most radials is powerful enough to bend conrods if you have a hydraulic lock. That is why you always pull the engine through by HAND prior to starting. Even then, I have heard of conrods being bent by an over-eager person pulling it through.

Starter on virtually any engine is strong enough to bend a conrod if you have hydraulic lock. We recently had to swap an engine that had filled one cylinder with coolant when the head gasket had blown. As the engine cooled it sucked coolant into the cylinder, next morning customer tries to start and the engine goes clonk. A rebuilt engine for a Mercedes CLK AMG C63 does not come cheap.