EconoBoy
Posts: 152
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APUs On Piston Engine Planes

Mon Jul 25, 2005 11:12 pm

Most modern jet airliners have an APU, usually a gas turbine located in the tail of the aircraft. But what about the piston engine planes of the fifties like the Stratocruiser and Constellation: did they have APUs, if so where and what type?
 
SA006
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RE: APUs On Piston Engine Planes

Mon Jul 25, 2005 11:47 pm

No chance the Stratocruisers and Constellations had APU's back then. I'm pretty sure they didn't even have Ground Power Units.

GPU's (Ground Power Units) are used on aircraft nowadays that have no APU's (CRJ's , Dash 8's , ATR's etc)

-SA006
Proudly South African
 
SlamClick
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 12:42 am

No authority on those kinds of airplanes but I have seen onboard APU installations.

First off, since the planes ran on avgas rather than Jet-A the APUs tend to be recip rather than turbine so they could share a fuel supply.

I think it was common for 28V DC to be the primary electrical supply rather than the 115VAC 400Hz three-phase that is standard on jetliners. Accessories requiring AC were fed by inverters that were run on DC motors. Lots of heat and noise, and probably high wear. I've seen these mounted in the area between the passenger cabin and the cockpit.

The power for this type of APU which I have seen tended to be 1 or 2 cylinder, air cooled lawnmower-type engines. I've heard them called a "putt putt"

One old recip I saw had an I-beam mounted on rails to the overhead in a bag pit and it had a putt-putt on a chain hoist. They'd set it on the ground outside the plane, get an engine turning, then reel it in and lash it down.

You may recall that it was a rig something like this that caused the fire that destroyed the "Kee Bird" the B-29 being recoverd from Greenland. The fuel line separated and started a fire. Or maybe the gas can just tipped over. Don't remember for sure.

Now let the real dinosaurs pop up and tell you how it really was.

Slam
almost that old
Click
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FinnWings
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 2:09 am

Quoting SA006 (Reply 1):
GPU's (Ground Power Units) are used on aircraft nowadays that have no APU's (CRJ's , Dash 8's , ATR's etc)

Just a small correction, all CRJ's have an APU. The mad nitpicker strikes again...  duck 

Best Regards,
FinnWings
 
vc10
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 2:35 am

I think you will find that the civil version of the Constellation did not have APUs, because the airlines had them removed to save on weight. Also most civilian airfields of that time, that were big enough to handle those aircraft, would have a GPU giving the required 28v DC, and even if they did not a Connie could start on it's batteries.

Now the military versions of the Connie did have APUs and depending on their age as to what type it was. The Mats Connie [ex military 121A built 1947 ] had a two cylinder piston engine APU, whereas the Swiss Super Connie [ ex military 121C built 1954 ] had a gas turbine APU. Whichever type, they were fitted in a fire proof box to the rear of the rear pressure bulkhead and had their own fire detection and extinguisher system and supplied 28v DC ,with their controls being on the F/E panel . Either type also used Avgas obtained via its own pump from one the aircraft's normal fuel tanks

little vc10
 
Fly2HMO
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 3:54 am

DC3s have APUs, well at least this one had:


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Photo © AirNikon



I was standing very close behind this private DC3 one day when it was being started. First I heard the APU, which sounded just like those portable generators you find at the home depot. It seemed to be mounted in the tail, because smoke came out of there when they started it. Then they fired up the engines.

Gotta love the roar of those radials Big grin
 
SlamClick
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 3:58 am

Quoting Vc10 (Reply 4):
because the airlines had them removed to save on weight.

That brings up a good point. When Dougs and Connies were the mainliners for United and TWA they were operating "on line" so everywhere they went there were battery carts or GPUs available.

The ones I recall seeing were non-skeds and corporate operators of older planes and they were a hundred percent "off line" and needed to take their auxilliary power with them wherever they went.

Most awkward getting stuck in Wink Texas or Chugwater Wyoming (do they have an airport?) with low batteries.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
OzLAME
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 9:57 am

Quoting SA006 (Reply 1):
GPU's (Ground Power Units) are used on aircraft nowadays that have no APU's (CRJ's , Dash 8's , ATR's etc)

Dash 8s have APUs as well. A RH prop brake is optional on the SAAB 340 so that the RH engine may be used in lieu of an APU. There are even King Airs with APUs. One of the most horrible noises I have ever heard emanating from an aeroplane turned out to be an APU in a Royal Australian Air Force HS.748.

The HARS Connie here is the next a/c off the production line after the Swiss Connie, the APU has been removed for weight and safety reasons, as well as to stretch the donations a bit further.
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.
 
L-188
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 11:12 am

The APU on the B-17 was a generator powered by a Briggs and Stratton engine.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
aeroweanie
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 1:55 pm

The B-29 had an APU too - it was the fuel from the APU spilling that started the fire that destroyed "Kee Bird". The APU was a small piston engine.
 
L-188
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 1:58 pm

Quoting AeroWeanie (Reply 9):
The B-29 had an APU too - it was the fuel from the APU spilling that started the fire that destroyed "Kee Bird". The APU was a small piston engine.

There air museum up at Fairbanks Alaska has one of those on static display.

If memory serves it is an 2 opposed cylinder sundstand motor.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
EconoBoy
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 3:18 pm

Interesting replies! I guess the old prop liners had lower power demand anyway - no air conditioning or IFE demands for example.
 
MD11Engineer
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 4:20 pm

On the big piston engines it also depends if the aircraft has direct crankingstarters installed or flywheel inertia starters. For direct cranking starters you'll need a massive power source to provide the current required to turn the engine (a typical piston era starting GPU I know had a huge chevy engine driving six 28 volt alternators in parallel through a belt drive). Inertia starters only use a relatively small motor, which turns a flywheel to high speed. The flywheel is then coupled by a clutch to the crankshaft through a reduction gear and provides the torque. While flywheel starters have the advantage of being able to be cranked up by hand using a starter crank in emergencies (probably everybody has seen the pictures of the Messerschmidt Me-109 mechanic sitting on the left wing root cranking away on starting the engine, and sliding back to the ground over the wing prior to departure), they are much heavier than direct cranking starters and therefore cut into the airline's bottom line.
Military operations liked flywheel starters for ease of operation and independence (the little Briggs & Stratton APU could deliver enough curent to get the plane going), while airlines, which operated from big airfields with a big GPU available, would prefer direct cranking starters.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
vc10
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RE: APUs On Piston Engine Planes

Tue Jul 26, 2005 7:42 pm

MD11
The MATS Connie [ ex military ] had direct cranking starters and the batteries would supply enough power to start at least one engine as long as it did not take too long to fire up. It's APU was also just a twin cylinder horizontally opposed engine and it gave out more than adequate power.
The worst thing about inertia starters was that you had to be absolutely 200% sure that you were not going to have a hydraulic lock before you engaged the starter, whereas some direct starters had a clutch which would slip should you get a lock up while turning the engine with a starter

little vc10
 
CRJonBeez
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RE: APUs On Piston Engine Planes

Wed Jul 27, 2005 11:19 am

Quoting OzLAME (Reply 7):
A RH prop brake is optional on the SAAB 340 so that the RH engine may be used in lieu of an APU.

there are a few SF34s out there with APUs. i can personally confirm this as the company i work for sees the university of indiana's saab in here a few times a year, complete with an APU
 
L-188
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RE: APUs On Piston Engine Planes

Wed Jul 27, 2005 12:17 pm

Quoting Vc10 (Reply 13):
The worst thing about inertia starters was that you had to be absolutely 200% sure that you were not going to have a hydraulic lock before you engaged the starter

Absolutely, which is why when you see WWII video of ground crews waking up round motors in WWII you see four or five guys holding arms pulling together to turn the motor over before trying to start.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
erj-145mech
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RE: APUs On Piston Engine Planes

Thu Jul 28, 2005 9:25 pm

Quoting MD11Engineer (Reply 12):
(a typical piston era starting GPU I know had a huge chevy engine driving six 28 volt alternators

The two GPU's that I used to own were powered by Chrysler 426 hemi industrial engines, on Hobart frames, driving two 1200 amp 28V DC generators. The Douglas A-20 Havoc that I worked on had a putt-putt in the ass end of the left engine nacelle. It was the same unit as the B-17 had. If anyone is going to be in Oshkosh this week or next, go to the B-17 Thunderbird, on the Aeroshell Square, and take the airplane tour. You'll see the on board putt-putt opposite of the aft entry door.
 
L-188
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RE: APUs On Piston Engine Planes

Fri Jul 29, 2005 2:20 pm

Quoting Erj-145mech (Reply 16):
Quoting MD11Engineer (Reply 12):
(a typical piston era starting GPU I know had a huge chevy engine driving six 28 volt alternators

You have to be careful with Lycoming O-290 engines from what I understand, they where also used for GPU powerplants.

BTW: I dont' recall seeing a piston that was anything other then 28VDC.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
aviopic
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RE: APUs On Piston Engine Planes

Sat Jul 30, 2005 5:17 pm

Quoting L-188 (Reply 15):
Absolutely, which is why when you see WWII video of ground crews waking up round motors in WWII you see four or five guys holding arms pulling together to turn the motor over before trying to start.

Well not only on WW2 video's, it's something we still do today. Big grin
Eventhough we have direct starter motors with a slipper clutch it's better to be safe then sorry.



Connie's APU(2 cyl. boxer) power is rather limited.
When you have a flat battery there is no way you can start on APU power alone and you have to rely on a ground power unit.
It's a nice bonus though as it feeds the battery charger.
The truth lives in one’s mind, it doesn’t really exist
 
aviopic
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RE: APUs On Piston Engine Planes

Sat Jul 30, 2005 6:03 pm

Forgot something.
As you see is engine cranking done by one guy only as the objective is to feel if there is a hydraulic lock or not, pushing and pulling with more people might lead to damage after all if in our case the clutch doesn't function properly.
Normal procedure is 12 blades.
This is the best fitness you can think of and it even comes for free Big grin

Here you see the GPU we have in use driven by an industrial Porsche engine.
In this case supplying power to the DC2.

The truth lives in one’s mind, it doesn’t really exist
 
vc10
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RE: APUs On Piston Engine Planes

Sat Jul 30, 2005 8:40 pm

Aviopic,
I think you will find that with a flat aircraft battery you are unable to even start the APU never mind the aircraft's engines. The Dutch APU is fine and will, or at least did, have the capability of starting the main engines
There is a school of thought that actually turning the prop by hand can actually damage the engine if it has a hyd lock because the reduction gear and lever arm of the prop will allow the mover to damage the con rod.
However if unsure of the clutch then turning by hand is better than nothing, but I should imagine there are a number of different schools of thought on this subject

Be Happy little vc10
 
aviopic
Posts: 2423
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RE: APUs On Piston Engine Planes

Sat Jul 30, 2005 9:41 pm

Hello Pete,

Of course you can't start the APU with a flat battery but even if you could start it it would still not supply sufficient power for an engine start.
To my best knowledge it is also not intended to do so.
We do use the APU though to support the batteries..... oh and it is still fine.

An email about current status is in production at this moment  Smile

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Willem
The truth lives in one’s mind, it doesn’t really exist
 
Airgypsy
Posts: 130
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RE: APUs On Piston Engine Planes

Sun Jul 31, 2005 7:40 am

The most common type of "Jennie" (Generator) was built by the Ranger Engine Company. Ranger was purchased by Fairchild Hiller and diappeared into history. The early KC-135 had a larger unit. I think it wasa made by Wisconsin.
They built several versions, one off which survived in serfvice as the PE-75 DC GPU (175 Amp) used in the USAF into the 1970s. The two cylinder variety was the most common and I last saw one at the Reno Air Races being used as a GPU for one of the unlimited aircraft.
The A-26 had a two stroke engine in the back of the nacelle that provided electrical power. Don't remember it's rating.
Airgypsy

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