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When Hollywood Ruled The Skies - Volumes 1 through 4 by Bruce Oriss


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PostPosted: Mon Feb 19, 2007 7:57 pm 
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[quote="JimH"]We pre-oil and manually push through all the bomber engines. Although I have heard that the 1830's have hydo locked I have never seen it.

I have seen it twice on 1830s, the 1830-92 on our PBY and the 1830-94 on the DC-3, I also have had locks on the R-2600s on both the TBM and B-25, and the R-2800 on the A-26. I have yet to find one on the 1820 ( T-28 and C-1a), 1340s ( T-6 ) or 985 ( C-45H )

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PostPosted: Mon Feb 19, 2007 8:10 pm 
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sdennison
What you say makes some sense.
But the reason for turning the prop in the normal direction, is if there is a lock developing it can be felt. And then spark plugs removed to drain the oil. If turned backwards, things become a bit reversed. Meaning the exhaust then acts like the intake and vise versa. So if you turn it backwards what ever is in the cylinder at the time, will be forced into the intake and the same thing at the compression postition, if there is oil it would again lock since both valves are closed in that position. So nothing special is gained going backwards. Except for the fact that the intake tubes would get the oil forced into them. Then like the others say, if it is in the tubes, then as soon as it is spun the correct direction it sucks the oil back in, but this time there may be some inertia behind the turning effort, when the lock is encountered.


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PostPosted: Mon Feb 19, 2007 8:24 pm 
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JimH wrote:
We pre-oil and manually push through all the bomber engines. Although I have heard that the 1830's have hydo locked I have never seen it. The 1830 is really easy to push through one handed...9 blades an engine. The 1820's on the B-17 require a bit more effort to push through but you can feel the oil in the bottom cylinders, and you can feel it flow out of the cylinders. The B-25 is a whole "nother" animal. It usually takes two people a blade to pull the props through and when it locks, plugs are coming out. I know some owners that use the starter to "bump" the props through, counting the clutch if it locks. We don't.

As for power settings, usually no more than 40" for takeoff power and 35" for Meto power(all 3 airplanes). Part of our pre landing checklist is briefing the missed approach which is planned at Meto power, beyond that it is "whatever it takes". From what I have witnessed, pre-oiling, not allowing a reverse loading to happen, and constant monitoring CHTs has prolonged our engine life remarkably.

JimH


Jim is exactly right. I have flown with him and the Collings Foundation before and they tell you on day one to not pull the props through backwards. We always pull the props through 9 blades before start up. And yeah, the 1830's are very easy to pull through, the 1820's require a bit more effort, and the 2600's take two men and a boy to pull through. You can't get too over zealous when pulling blades or you could cause a lot of damage without realizing it. Slow and steady is the idea. And we never use the starters to check for hydro lock.

I have seen another B-25 operator use the starters with almost disastrous results. I was at an airshow a few years back and they just didn't want to pull the plugs. Almost cost them a B-25.


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PostPosted: Mon Feb 19, 2007 9:45 pm 
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engguy wrote:
sdennison
What you say makes some sense.
But the reason for turning the prop in the normal direction, is if there is a lock developing it can be felt. And then spark plugs removed to drain the oil. If turned backwards, things become a bit reversed. Meaning the exhaust then acts like the intake and vise versa. So if you turn it backwards what ever is in the cylinder at the time, will be forced into the intake and the same thing at the compression postition, if there is oil it would again lock since both valves are closed in that position. So nothing special is gained going backwards. Except for the fact that the intake tubes would get the oil forced into them. Then like the others say, if it is in the tubes, then as soon as it is spun the correct direction it sucks the oil back in, but this time there may be some inertia behind the turning effort, when the lock is encountered.


OK, so let me try this again. The four strokes are intake, compression, power, and exhaust. In the forward direction, the piston travels away from the head sucking in the intake charge. Next the compression stroke where the piston travels toward the head with both valves closed. Third is the power stroke with the piston traveling away from the head and finally, the exhaust stroke with the piston traveling toward the head forcing out the exhaust gases.

Now if you pull the engine through in either direction while in the compression stroke, you will have incompressable lock. This is when you stop and pull the plugs and drain the oil. However, with the exhaust and intake strokes being side by side and with oil possibly in the intake tubes, if you pull forward, the oil is sucked in and then you hit lock on the compression stroke. If you are pulling backward rotation, the piston is traveling away from the head sucking the oil in from the intake tubes with the next stroke now actually the exhaust, the piston travels toward the head and forces the oil into the exhaust manifold.

The next stroke is the power stroke, again a piston traveling away from the head (no lock issues) followed by again the compression stroke (now with a clear cylinder, no lock) followed by another intake stroke that could again draw any remaining oil into the cylinder from the intake tubes followed by the exhaust stroke forcing any additional oil into the exhaust manifold (no lock).

I'll grant you that if any cylinder is with oil on the compression stroke, you will have lock regardless of the direction you approach TDC, other than that, it would appear that reverse pull through is more advantageous than forward.

What am I missing here? :?

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PostPosted: Mon Feb 19, 2007 11:35 pm 
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Hello all after woking on 1830's on our r4d for 10 plus years. yes they
do lock. All i can say is PULL THE PLUGS. Clean up the mess and go fly
and have fun. Also have all people checked out on pulling the props.
we have one person that loves to help but needs all the power he has to
pull a compression stroke . And will never know even a small oil lock.


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PostPosted: Tue Feb 20, 2007 12:02 am 
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sdennison wrote:
engguy wrote:
sdennison
What you say makes some sense.
But the reason for turning the prop in the normal direction, is if there is a lock developing it can be felt. And then spark plugs removed to drain the oil. If turned backwards, things become a bit reversed. Meaning the exhaust then acts like the intake and vise versa. So if you turn it backwards what ever is in the cylinder at the time, will be forced into the intake and the same thing at the compression postition, if there is oil it would again lock since both valves are closed in that position. So nothing special is gained going backwards. Except for the fact that the intake tubes would get the oil forced into them. Then like the others say, if it is in the tubes, then as soon as it is spun the correct direction it sucks the oil back in, but this time there may be some inertia behind the turning effort, when the lock is encountered.


OK, so let me try this again. The four strokes are intake, compression, power, and exhaust. In the forward direction, the piston travels away from the head sucking in the intake charge. Next the compression stroke where the piston travels toward the head with both valves closed. Third is the power stroke with the piston traveling away from the head and finally, the exhaust stroke with the piston traveling toward the head forcing out the exhaust gases.

Now if you pull the engine through in either direction while in the compression stroke, you will have incompressable lock. This is when you stop and pull the plugs and drain the oil. However, with the exhaust and intake strokes being side by side and with oil possibly in the intake tubes, if you pull forward, the oil is sucked in and then you hit lock on the compression stroke. If you are pulling backward rotation, the piston is traveling away from the head sucking the oil in from the intake tubes with the next stroke now actually the exhaust, the piston travels toward the head and forces the oil into the exhaust manifold.

The next stroke is the power stroke, again a piston traveling away from the head (no lock issues) followed by again the compression stroke (now with a clear cylinder, no lock) followed by another intake stroke that could again draw any remaining oil into the cylinder from the intake tubes followed by the exhaust stroke forcing any additional oil into the exhaust manifold (no lock).

I'll grant you that if any cylinder is with oil on the compression stroke, you will have lock regardless of the direction you approach TDC, other than that, it would appear that reverse pull through is more advantageous than forward.

What am I missing here? :?


as it was pointed out, there are brushes and carbon vanes in starters, generators, tack generators, vacuum pumps that don't like to go backwards, also your oil pump and scavage pumps work in 1 direction only, I would rather go in the correct direction a suck some oil thru the pumps VS going backwards and pushing it away.

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PostPosted: Tue Feb 20, 2007 12:10 am 
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For this sample consider a very basic cam timing with no lead or lag times at top and bottom dead center, and no overlap.
And for what it matters, I was running an International scraper one time, and was in too high a gear for a hill I was going up. It stalled the engine, and coasted in reverse, and the engine started in reverse. This was a diesel engine. It was so funny seeing the black smoke coming outa the airfilter. And no it was not allowed to run very long, as oil pressure was nonexistant.

The strokes, Intake-compression-power-exhaust

Intake: starts with piston at top, valve open, piston moves down sucks in the air/fuel.

compression: piston is moving up and both valves closed.

Power: Both valves still closed piston moving down

Exhaust: Piston going up ex valve opening.

Now reverse it.

Exhaust valve open, piston at top and moving down sucking on exhaust pipe.

At the bottom of the stroke the piston moves up in A compression stroke,

At the top the piston starts down as if on a power stroke both valves are closed just like if it was turning the correct way.

At the bottom of that stroke piston moves up pushing what ever through the intake valve.

What is important is the exhaust becomes the intake, and the intake the exhaust. So this is why you never turn that propeller reverse to check for a hydraulic lock.

And yes in real life the timing is not correct to run good in reverse, but it can be done.


Where you are wrong is saying the piston sucks oil from intake turning the crankshaft backwards. Remember the intake becomes the exhaust. [/b]


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 Post subject: Randy Sohn
PostPosted: Tue Feb 20, 2007 12:27 am 
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I've just read Randy Sohn's treatise on "Full Rated Power on Take Off," and am wondering what others think about his writing. I didn't see many facts, other than some about "near AD's" and powerplant failures at take off, which makes sense. But I am wondering if he has put any more technical reference into his ideas. Specifically:

1. Octane calculation reformulation- I know it has happened with auto fuel, but has the calculation changed as well for AVGAS?

2. Alternative Minimum Power Settings. I don't have ready access to any manuals, but can anybody look this up in the appropriate manuals and post it here?

3. Are all the Merlin operators using lower MP at take off? I was told by a WWII P-51 pilot that he usually only used 30 inches at take off- is this true?

Very interesting discussion...

As for oil lock, I pull the O-435 through every time before I fly- it's in the manual and on the original checklist. Good way to find a stuck valve or other fun things. I don't turn it backwards- that is from training by several instructors, but I have never heard different.

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PostPosted: Tue Feb 20, 2007 12:46 am 
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Hi,
I flew as one of the crew on a former Polish AN-2 "Big Bubbinski" for several years (until the owner sold it :( ). We ALWAYS pulled the prop through 20 blades before starting (we kinda worked it into the airshow act ... "now look as the AN-2 crew winds up the rubber bands !!!! ). One thing no one has mentioned yet though is to make sure that the mags are switched off as well as fuel. I have never seen a engine fire while pulling through but was told it could happen. If it locked, then we would start pulling the bottom plugs until striking oil. By the way, make sure if it's you that the pilot has been safely locked up while doing this operation. One time I had just pulled the plug and stopped to wipe the oil off it when the pilot grabs the blade and says "here, let me help......... famous last words !!". Before I could move or utter a sound he shoves the prop forward and I get about a gallon of oil blasted down the front of my flightsuit :shock: :shock: :evil: ! Needless to say I had to do a quick change before we left for the airshow! I like the smell of AvGas and oil but I don't like to smell LIKE it! It was funny though, AFTER I got cleaned up (and he bought me a beer at the party later!).

On the manifold pressure debate, although I can't remember the numbers, Mike always kept the MP lower than the book because of the lower octane. The engine was made by PZL and basically a metric copy of a 1820 or 1830 tuned down to only a 1,000 HP.
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PostPosted: Tue Feb 20, 2007 1:52 am 
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The scenario you are missing is., if the engine stops with a cylinder on the intake stroke, and fills with oil. Pulling foreward will hit the hydraulic lock.Because the engine came up to the comp stroke
Pull plugs and clear. If you pull in reverse the oil will be pumped into the intake or the intake is already full from the valve being open and a lock never felt. Then felling like everything is great. You hit the starter,the oil comes back into the cylinder from the intake. If there is enough, it will hydraulic.
The example about the disel is a good one. Piston engines are a pump, that will pump in either direction depending which way they are turned.
Pulling in the direction of rotation will show a lock, or pump the oil into the exhaust pipes. Pulling in reverse will show a lock or pump oil into the engine intake pipes.


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 Post subject: Merlin
PostPosted: Tue Feb 20, 2007 10:50 am 
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FF. I doubt if any Merlin is taking off at 30", think you got a misprint somewhere. Some pilots(John Baugh) have gotten good life with full 61 inches on each takoff, and swear that's the way. Others use as low as 50". I belive when I flew Crazy Horse with Lee and Doug, they were using 55". If I recall, 50 inches feels a little soggy, 55 feels good and solid, and 61 is "getting with the program". A Spitfire is lighter and the wing has more lift at takoff speed, Normal takeoff at Civilan weight is 44", (+7lbs.) and 3000 rpm. +8 or 46" is plenty, +10 or 50" inches in Mk IX is really overkill and about all you can hold with full right rudder. The Spit mixture is automatic and moves from lean to richer as you go past +7 lbs. Engine life is certainly a consideration, but operating safety is imporant, a go around is another place where climb performance is also vital. A Mk IX can go around with gear and full flaps at +4 or 38", but a 51 with full flaps has a lot of drag and needs a lot more power. You do want to come in slowly and progressively with power, not torque it all at once.

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PostPosted: Tue Feb 20, 2007 11:16 am 
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OK I'm new to this column. I'm the guy that checked Gary Austin out as engineer on FIFI. When we last flew FIFI we used reduced power on take-off. We used 40" verses the normal 47". At the light weight we were operating at, we were airborne about the time, me, the engineer got all the throttles (power) set at 40". The big reason the DPE's (designated pilot examiners) don't like you to use the reduced power is that there is no flight manual for reciprocating engined aircraft (that I know of) that has reduced power take-off charts for distances, VMCG, etc. Most of the turbo-prop/ jet manuals have these charts for reduced power. In FIFI we have some fairly good charts that you can extrapolate the data from, and we also fly it in the experimental catagory, so we don't have the legal restraints others do. In regards to the octane question, All the scientific data I've seen states that there is no difference between 100/130 and 100LL in octane. This data is from a radial engine overhauler. Maybe knocking off one inch of manifold pressure for insurance???


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PostPosted: Tue Feb 20, 2007 11:18 am 
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Forgotten Field wrote:
this crappy gas made today, and the continued re-formulation of standard gasoline including aviation gasoline, I am inclined to believe them on this one.


One of my college roommates was a petroleum engineer, who said that without a doubt current aviation fuel was better than anything made in the past with respect to quality and actual octane rating.


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PostPosted: Tue Feb 20, 2007 11:38 am 
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Hey Forgotten Fields,

couldn't disagree with you more. There was no such thing as 115/145 fuel for the WW2 birds. All those engines were designed to operate on 100 octane. One of the recurring OWT (old wives tales) is that there is some big difference between 100/130 and 100LL. The ONLY difference is color and lead content. That's it. This info is available for all to see in ASTM D910; aka the fuel specifications. The alternate power settings for the B-25, and others, were because 100 octane fuel was needed in the combat zones and 91/98 octane was used at the state side training bases to ensure an adequate supply was available for combat. besides, with the war machine pumping out everyting at a rapid pace and with mechanics to train, who cared if you burned up a bunch of cylinders.

Also, since it always comes up...........the issue of "the weights we fly". The power settings are designed for engine performance, not airplane performance. Without rated TO power the carb won't provide sufficient power enrichment to keep the cyliniders cool. (if anyone wants a great resource on this try "Aircraft Carburetion, by Robert Thorner.)Went through this with a B-25 I used to fly. Took the boss flying one afternoon. We did 2 takeoffs at 44" and 2 at 40". The CHT's were 25 degress cooler at 44 every time. Thermal cycles! Get your cylinders really hot and then cool them down and watch them start to crack.

Glenn

(gladly pouring more fuel on the MP setting fire.)

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 Post subject: weights
PostPosted: Tue Feb 20, 2007 11:55 am 
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Glen, I don't operate the big boys, but the reason weight is factor is because it is such a determinate on performance. At heavy weights takeoff roll is longer, and climb to cruise level off takes longer. You may need more power at heavy weight to have the same level of safety like a go around. With higher power settings you may shorten the time til you can cruise. Jack Rouse feels the current gas is like lower octane or leaner; like so much of this info it is as much folklore as scientific fact, neither proven or disproven. I thought there was 130 or 145 gas Near the End of the war. Merlins in Spitfires had an ok to use a brief overboost on 145 to, I think 20 lbs or 80" which was 2050 hp, but really reduced engine life.

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