do people pull the prop through on geared engines?

[snj5]

Basic question for the pros on radial engines: after a recent 1820 accident due to a failed rod that was bent, it has posed a question:
In a geared engine, is there any value in pulling through the prop prior to starting. I did this with a direct drive 1340 for years. The mechanical advantage seems to work against bending the rod in a geared engine, and I have always heard to use the starter motor which will not bend a rod from hydraulic lock.

Many thanks

[Cvairwerks]

Everyone that I know of and every radial powered a/c I've crewed, it has been standard practice to do it. It's not nice to find a lower cylinder full of oil with the starter motor...it tends to be very hard on the clutches if it doesn't kick off the drive dogs.

It's also easier to listen for strange clunks without the starter grinding away...

[snj5]

that makes good sense to me as well, but I'm told T-28 NATOPS says on page 3-7: “Caution: Do not pull the engine through by hand before rotating with starter as engine can be damaged by hydraulic lock.”

I just cannot imagine one guy generating enough umph to do that.

I'm not one to question NATOPS, but thinks it does warrant discussion, especially if it may prevent a failure.

[Robbie Roberts]

A starter motor will not feel the resistance of a hydraulically locked cylinder: to pull a radial through by hand is the best method.

Hydraulic lock from the oil in the bottom cylinders will do quite a good bit of damage to the engine by causing a rod to bend after attempting to compress an incompressible liquid... The starter motor, as I mentioned, with a geared engine may have enough torque to bend that rod- when you turn through by hand, you will feel that resistance, and know there is a lock probem: the starter don't feel a thing..

The other method would be to leave a bottom cylinder lug out, and make a drain piece to allow the run-down a place to exit the cylinder. Of course, you'll have to reinstall the plug each time you wish to fly!

Smile

Sorry to hear about the rod-

Robbie

PS- Sounds like a mistake in the NATOPS manual: might check for a revision. Unless the gearing makes the feel go away, come to think of it...

[coldaffyduck]

For what it is worth, on the "Tracker" (which had 1820-82B's) that we had, we were told by a resident "expert" that we did not need to pull the props through before start-up because the starter was clutched such that if there was a hydraulic lock the starter would kick out automatically. The one thing that the pilots did ensure of though was that we turned at least nine blades before turning on the mag switches. On a side note, our NATOPS manual for the US-2B says nothing about pulling the prop through by hand but it does say to turn the prop through for 6 blades with the starter before switching on the mag switches.

The really weird part was that on the "Lodestar" (which has 1820-71) that we have, it is required to pull the props through by hand.

[bdk]

I've seen plenty of photos of troops pulling through radials on everything from fighters to bombers during WW2.

[snj5]

See, that's the thing - the more you try to understand the general principle, the more that inconsistancies show up. Jus' trying to make sense of it all.
From my small pilot manual collection, here is a list of planes with geared engines that the official printed military manual all say to pull them through 4 - 5 blades or 2 - 3 revolutions:
C-47 (R-1820 & R-1830)
P-47, F4U, F6F (R-2800)
TBF/M, SB2C (R-2600)

In my case, an R-1300, the engine is 1/2 of an R-2600.
Thanks for the discussion everyone. Would be interesting to know if someone can state the reason the NATOPS was written that way. A specific incident, perhaps?

[Robbie Roberts]

B-29- turn through 16 blades...

[t28pilot]

DO NOT pull an R1820-86 by hand unless you have a very good feel for what you are doing. What most people fail to understand is the different -#'s all have different geared ratios. With a .666 to 1 on the T-28 1820's, yes a person can easily bend a rod. And if your starter is correctly setup it will release if there is a certain resistance. Just because its a radial doesnt mean you can or should pull it through!! It never fails to amaze me that people sometimes think the NATOPS books are incorrect or that there is a better way to start the engine, or even run it. CW, P&W, The NAVY, Marines and Airforce spent so much time and money over time refining the procedures that one should not think they are better than that experiance.

[Jase]

*Assuming* the starter is correctly set up to declutch. I have seen two that were set up wrong straight from the overhaulers. One was set way too loose, and the other way too tight.

[Robbie Roberts]

DO NOT pull an R1820-86 by hand unless you have a very good feel for what you are doing. What most people fail to understand is the different -#'s all have different geared ratios. With a .666 to 1 on the T-28 1820's, yes a person can easily bend a rod. And if your starter is correctly setup it will release if there is a certain resistance. Just because its a radial doesnt mean you can or should pull it through!! It never fails to amaze me that people sometimes think the NATOPS books are incorrect or that there is a better way to start the engine, or even run it. CW, P&W, The NAVY, Marines and Airforce spent so much time and money over time refining the procedures that one should not think they are better than that experiance.

That sounds like a better, more experienced answer than mine, so I'd defer to the gent with more experience!

I would also say, however, that military manuals do have, from time to time, mistakes in them- no matter how good or the source. Be that as it may, sounds like he knows his stuff, and the manual is probably correct then.

Robbie

[snj5]

All of the user manuals are the defining reference points, and are written initially based on contemporary tests and engineering data, then refined through use. Having been (albeit small) a part of that process in the Air Force, a good safety mindset is to follow the proceedures, but always be willing to discuss them and look for improvements if any are there. If we did not ever have this safety mindset to continually better understand and refine our proceedures if there were reason to, the original manuals would never have been changed. And, these manuals were written for a military environment a bit different than our civilian use. And, they were written for the most part by people like you and me.

I'm certainly not advocating everyone going out and pulling T-28B props through - quite the opposite - rather a discussion of the principles involved in the decision to better understand them. And, obtw, having pulled many different engines through myself according to the manual, one person would have to be pretty unobservant and pull like a mf to bend a rod, so I do disagree a bit with the 'easily' adjective. Does a starter disengage mechanism cut out at less torque than one guy pushing a blade? How about the old shotgun shell starters? They gave a pretty good shove. Is that why we turned them through in the first place. Interesting thought.

My initial bet is that if we knew the history, there were a few incidences where the ground crew bent a rod muscling it through, or it was thought they did. From a military standpoint of standardization, the obvious way to standardize a proceedure to prevent re-occurance, no matter how remote, is to use the starter. Military proceedures are all about standardization - with the starter, you know exactly what you are getting as opposed to a crew which may be inexperienced. that's my guess anyway.

I'm still planning on using my starter as well, but these topics always benefit from recurring introspection.

best
rt

[bdk]

DO NOT pull an R1820-86 by hand unless you have a very good feel for what you are doing. What most people fail to understand is the different -#'s all have different geared ratios. With a .666 to 1 on the T-28 1820's, yes a person can easily bend a rod.

I know just a little more than nothing about R-1820s or T-28s, but with the prop reduction you LOSE torque when turning the engine through by hand. With any geared engine the torque you could apply to the crankshaft by pushing on the prop would be LESS than if the engine were direct drive with the same diameter prop.

I wonder what the SBD or B-17 manual says about this compared to the T-28 manual? Certainly by the jet age in the 1970s a lot of piston engine aptitude (tribal knowledge) had gone missing from the military.

[skymstr02]

When pulling the props thru by hand, and you determine that a cylinder has a hydraulic lock, what do you do?
A) Continue pulling to push the oil out?
B) Back up the prop to suck the oil out?
C) Remove a spark plug to drain the cylinder?

If you opted for A, you may already have bent a rod. If you opted for option B, where does the oil go? Now you've got that amount of liquid in the induction system ready to go into the cylinder again. The only correct answer is C, not to mention that you also have an oil fouled plug to clean now.

With the mechanical advantage of leverage on the prop, you could bend a rod and not realize it by pulling the prop thru by hand.

[C118FE]

When pulling the props thru by hand, and you determine that a cylinder has a hydraulic lock, what do you do?
A) Continue pulling to push the oil out?
B) Back up the prop to suck the oil out?
C) Remove a spark plug to drain the cylinder?

If you opted for A, you may already have bent a rod. If you opted for option B, where does the oil go? Now you've got that amount of liquid in the induction system ready to go into the cylinder again. The only correct answer is C, not to mention that you also have an oil fouled plug to clean now.

With the mechanical advantage of leverage on the prop, you could bend a rod and not realize it by pulling the prop thru by hand.

If you had leaking valve guides as on the R2000 and R2800 it would solve the oil in lower cyl problem.Starter should hang when lock is present.9 revs on the blades if 3 bladed prop.