Damaging an engine by turning the prop backwards

This forum has been developed to discuss aviation related topics.

Moderators: sky's the limit, sepia, Sulako, lilfssister, North Shore, I WAS Birddog

corethatthermal
Rank 5
Rank 5
Posts: 391
Joined: Tue Feb 12, 2019 7:27 pm

Re: Damaging an engine by turning the prop backwards

Post by corethatthermal »

Another thing to be concerned about is lack of spin-back on the large continental starter adapters. Putting a newer geared starter or having an old non-geared but hard(er) to turn starter motor will not allow the adapter spring to fully release and the starter motor will be engaged during your flight !
---------- ADS -----------
 
User avatar
PilotDAR
Rank 11
Rank 11
Posts: 4053
Joined: Sun Sep 30, 2012 6:46 pm
Location: Near CNJ4 Orillia, Ontario

Re: Damaging an engine by turning the prop backwards

Post by PilotDAR »

Putting a newer geared starter or having an old non-geared but hard(er) to turn starter motor will not allow the adapter spring to fully release and the starter motor will be engaged during your flight !
Though not associated with turning the prop backwards, this is certainly a very important aspect. Do not use geared starters on starter adapters. The drive tang of the starter motor should move freely enough that you can turn it either way with your thumb and fingers (not a wrench). If it's too stiff for this, have the motor serviced. The starter motor must turn backward about a quarter turn for the starter adapter clutch spring to release for the shaft gear. Otherwise, it'll get really hot during your flight! (And costly after you land).
---------- ADS -----------
 
bodyflyer2
Rank 1
Rank 1
Posts: 26
Joined: Mon Dec 05, 2016 4:05 pm

Re: Damaging an engine by turning the prop backwards

Post by bodyflyer2 »

For another very engine-specific case:
Shouldn't turn a Rotax 912 etc prop backwards, well, not more than 1 turn they say.
Don't know the details but something about air getting ingested into the valve train -- have to keep oil filling the hydraulic valve tappets

One ref I found online:
SB-912-036 R1 SB-914-022 R1
Cited in Compliance 1.5 – “engines which have had the prop spun for more than 1 turn in reverse direction allowing air to be ingested into the valve train.”
---------- ADS -----------
 
Jungle Jim
Rank 6
Rank 6
Posts: 436
Joined: Wed May 26, 2004 6:29 pm

Re: Damaging an engine by turning the prop backwards

Post by Jungle Jim »

Guys,

I pull my prop through in the forward direction. I also do mag checks, so I know I won't have a live mag. My logic in this is that it is better to have the oil pump gears pushing oil into the engine in the normal direction as opposed to having the oil sucked out, like it would if the prop were turned backwards.

Jim
---------- ADS -----------
 
User avatar
PilotDAR
Rank 11
Rank 11
Posts: 4053
Joined: Sun Sep 30, 2012 6:46 pm
Location: Near CNJ4 Orillia, Ontario

Re: Damaging an engine by turning the prop backwards

Post by PilotDAR »

The effect of turning the prop backwards relative to the operation of the oil pump is minor. The important film of oil [hopefully] remaining between all the moving parts when you turn the engine over will be there whichever direction the engine is turned. Yes, if you turned the engine over forward by hand a lot, you would move some oil into the engine. Conversely, the oil pump could not create suction so as to remove oil from all the passages. Of course, we want a good oil film where it should be in the engine, the best way to get that is to assure that the oil is warmed prior to a cold start, then get the engine running, and confirm oil pressure is present. There are pre-oil systems available, but they're not common.

Live mag checks are really important. I once hand propped a friend's 150. I called "mags off" he repeated "mags off" and I pulled it through. It started and ran first pull. I stood glaring at him through the prop disc. He held up the keys for me to see. Always treat mags as though they are live.
---------- ADS -----------
 
User avatar
Panama Jack
Rank 11
Rank 11
Posts: 3255
Joined: Fri Feb 20, 2004 8:10 am
Location: Back here

Re: Damaging an engine by turning the prop backwards

Post by Panama Jack »

With a lot of small aircraft now being powered by Rotax 9 series engines (912, 914, 915), I think it is important to point out that the manufacturer specifically states that its engines should not turned opposite direction.
---------- ADS -----------
 
“If it moves, tax it. If it keeps moving, regulate it. If it stops moving, subsidize it.”
-President Ronald Reagan
corethatthermal
Rank 5
Rank 5
Posts: 391
Joined: Tue Feb 12, 2019 7:27 pm

Re: Damaging an engine by turning the prop backwards

Post by corethatthermal »

I pull my prop through in the forward direction. I also do mag checks, so I know I won't have a live mag
Yesterday. I swore the mag check worked, today im in the hospital LOL I always treat the engine as live and do prop starts from behind!
---------- ADS -----------
 
pelmet
Top Poster
Top Poster
Posts: 7138
Joined: Tue Jun 14, 2005 2:48 pm

Re: Damaging an engine by turning the prop backwards

Post by pelmet »

Panama Jack wrote: Thu Jun 13, 2019 7:52 am With a lot of small aircraft now being powered by Rotax 9 series engines (912, 914, 915), I think it is important to point out that the manufacturer specifically states that its engines should not turned opposite direction.
Thanks. From the point of view of preventing an accidental start, it won't happen anyways when pulling it through in the forward direction at normal or even more than normal speed(unless you really pull it through super fast). Thank goodness as this is standard for every pre-flight when 'burping' the engine. The worst one I had to deal with require more than a hundred pulls to get a gurgle. Not fun on a hot day and a bit embarrassing too with restaurant people wondering what you are doing.
---------- ADS -----------
 
User avatar
AirFrame
Rank 10
Rank 10
Posts: 2610
Joined: Sun Oct 11, 2009 10:27 pm
Location: Sidney, BC
Contact:

Re: Damaging an engine by turning the prop backwards

Post by AirFrame »

Jungle Jim wrote: Thu Jun 13, 2019 6:09 amMy logic in this is that it is better to have the oil pump gears pushing oil into the engine in the normal direction as opposed to having the oil sucked out, like it would if the prop were turned backwards.
You can't generate enough suction in your oil pump, turning it a few blades in either direction by hand, to move a noticeable amount of oil.
---------- ADS -----------
 
trey kule
Rank 11
Rank 11
Posts: 4762
Joined: Fri Aug 19, 2005 7:09 pm

Re: Damaging an engine by turning the prop backwards

Post by trey kule »

Free turbines spin the prop the wrong way all the time on windy day.....
There is no lubrication going on at that point. As someone else mentioned it is not a good thing.

When you typically start a free turbine, you will almost immediately get oil pressure...before introducing fuel and starting...it is why we check to see we are getting oil pressure before moving the condition lever to low.

It is also why there are prop locks ( the stringy kind) that stop the windmilling. As used regularly by professional pilots.
---------- ADS -----------
 
Accident speculation:
Those that post don’t know. Those that know don’t post
goingnowherefast
Rank (9)
Rank (9)
Posts: 1948
Joined: Wed Mar 13, 2013 9:24 am

Re: Damaging an engine by turning the prop backwards

Post by goingnowherefast »

How do you stop the prop from wind milling between removing the tie and hitting the starter? Wind milling (backwards) for 5 or 10 minutes while boarding won't hurt a PT6 or PW100 series. 15 hours of day long neglect isn't good.
---------- ADS -----------
 
trey kule
Rank 11
Rank 11
Posts: 4762
Joined: Fri Aug 19, 2005 7:09 pm

Re: Damaging an engine by turning the prop backwards

Post by trey kule »

Gosh...seems to me , if wind is an issue, you could take them off right after the pax are on board while they are getting seated . It is not a common problem.
I even seem to recall some crews doing this.
---------- ADS -----------
 
Accident speculation:
Those that post don’t know. Those that know don’t post
goingnowherefast
Rank (9)
Rank (9)
Posts: 1948
Joined: Wed Mar 13, 2013 9:24 am

Re: Damaging an engine by turning the prop backwards

Post by goingnowherefast »

I'll let the Encore crew know next time I see them at the airport on a windy day and #2 is wind milling for 15 minutes.

Point being, don't get your knickers in a knot for short durations, it'll be fine.
---------- ADS -----------
 
Rowdy
Top Poster
Top Poster
Posts: 5165
Joined: Thu Jun 09, 2005 12:26 pm
Location: On Borrowed Wings

Re: Damaging an engine by turning the prop backwards

Post by Rowdy »

How come we only tie the left prop on the Dash and Q400?.. One word and it starts with P.

There is enough oil sitting in the gearbox for ample lubrication of everything while it slowly turns at a couple of revolutions per minute if left untied.

Interesting how a question posted about piston engines being turned backwards turns into a rant about PT6's and PW's. The joys of Avcanada I guess...
---------- ADS -----------
 
User avatar
Panama Jack
Rank 11
Rank 11
Posts: 3255
Joined: Fri Feb 20, 2004 8:10 am
Location: Back here

Re: Damaging an engine by turning the prop backwards

Post by Panama Jack »

pelmet wrote: Fri Jun 21, 2019 6:20 am
Panama Jack wrote: Thu Jun 13, 2019 7:52 am With a lot of small aircraft now being powered by Rotax 9 series engines (912, 914, 915), I think it is important to point out that the manufacturer specifically states that its engines should not turned opposite direction.
Thanks. From the point of view of preventing an accidental start, it won't happen anyways when pulling it through in the forward direction at normal or even more than normal speed(unless you really pull it through super fast). Thank goodness as this is standard for every pre-flight when 'burping' the engine. The worst one I had to deal with require more than a hundred pulls to get a gurgle. Not fun on a hot day and a bit embarrassing too with restaurant people wondering what you are doing.

Thanks Pelmet. Recently viewed this interesting video which debunked something I had heard earlier about it not being possible to prop a Rotax 912.

https://youtu.be/-JUBrHYsh4E


He makes it clear that the 912 mags don’t have impulse coupling like your garden variety Continentals and Lycomings and from a safety aspect that is probably a good thing, especially since burping the engine is a standard procedure for checking the oil level.
---------- ADS -----------
 
“If it moves, tax it. If it keeps moving, regulate it. If it stops moving, subsidize it.”
-President Ronald Reagan
pelmet
Top Poster
Top Poster
Posts: 7138
Joined: Tue Jun 14, 2005 2:48 pm

Re: Damaging an engine by turning the prop backwards

Post by pelmet »

Panama Jack wrote: Sat Sep 07, 2019 12:30 am
pelmet wrote: Fri Jun 21, 2019 6:20 am
Panama Jack wrote: Thu Jun 13, 2019 7:52 am With a lot of small aircraft now being powered by Rotax 9 series engines (912, 914, 915), I think it is important to point out that the manufacturer specifically states that its engines should not turned opposite direction.
Thanks. From the point of view of preventing an accidental start, it won't happen anyways when pulling it through in the forward direction at normal or even more than normal speed(unless you really pull it through super fast). Thank goodness as this is standard for every pre-flight when 'burping' the engine. The worst one I had to deal with require more than a hundred pulls to get a gurgle. Not fun on a hot day and a bit embarrassing too with restaurant people wondering what you are doing.

Thanks Pelmet. Recently viewed this interesting video which debunked something I had heard earlier about it not being possible to prop a Rotax 912.

https://youtu.be/-JUBrHYsh4E


He makes it clear that the 912 mags don’t have impulse coupling like your garden variety Continentals and Lycomings and from a safety aspect that is probably a good thing, especially since burping the engine is a standard procedure for checking the oil level.
They are interesting engines and quite different so I made extensive personal notes for myself taking bits of information from a variety of websites.
You mention about mags but it is important to understand that the Rotax 4 stroke mags are different than the mags we are used to.....

From my notes(and therefore subject to possible error)….

"Most ignition systems used in piston aircraft are inductive discharge ignition (IDI) systems. IDI systems rely solely on the electric inductance at the coil to produce high-voltage electricity to the spark plugs as the magnetic field collapses when the current to the primary coil winding is disconnected (a disruptive discharge). This is the traditional magneto.

The Rotax 912 engine has a dual electronic ignition manufactured by Ducati which is a contactless solid-state capacitor discharge ignition system. While these ignition systems are referred to as magnetos, they are different than the traditional magneto. In a CDI(Capacitor Discharge Ignition) system, a charging circuit charges a high voltage capacitor, and at the instant of ignition the system stops charging the capacitor, allowing the capacitor to discharge its output to the ignition coil before reaching the spark plug.

Each of the two ignition systems is powered by independent, stationary charging(or generating) coils located on the ignition housing at the back of the engine. Magnets are rotated on a wheel on the crankshaft and induce current in two coils on the perimeter on left and right sides of the rear of the engine. These induced currents are fed to two capacitors that increase the potential and discharge a high voltage through the sparking plugs. The crankshaft-mounted flywheel rotates around the ignition housing. The permanent magnets mounted in the flywheel rotate about the 8 fixed generating coils(one for each spark plug). As they pass the coils, each magnet induces a voltage in the coil as its magnetic field cuts through the coil.

Aside from the flywheel, which is mounted directly to the crankshaft, there are no moving parts to wear out in this ignition system: no gears, belts, seals, or bearings. The lack of moving parts is far more reliable and efficient. "
---------- ADS -----------
 
co-joe
Rank 11
Rank 11
Posts: 4562
Joined: Mon Feb 16, 2004 2:33 am
Location: YYC 230 degree radial at about 10 DME

Re: Damaging an engine by turning the prop backwards

Post by co-joe »

Rowdy wrote: Sat Jun 22, 2019 7:12 pm How come we only tie the left prop on the Dash and Q400?.. One word and it starts with P.

...
Piss Poor Performance? :lol:

Couldn't resist.

I was told by an AMA that the issue with turning the prop the wrong way on PT6's, was on the old style prop heat, the brushes could be damaged, but that with the newer style there's no problem.
---------- ADS -----------
 
Rowdy
Top Poster
Top Poster
Posts: 5165
Joined: Thu Jun 09, 2005 12:26 pm
Location: On Borrowed Wings

Re: Damaging an engine by turning the prop backwards

Post by Rowdy »

co-joe wrote: Mon Sep 09, 2019 8:37 am
Rowdy wrote: Sat Jun 22, 2019 7:12 pm How come we only tie the left prop on the Dash and Q400?.. One word and it starts with P.

...
Piss Poor Performance? :lol:

Couldn't resist.

I was told by an AMA that the issue with turning the prop the wrong way on PT6's, was on the old style prop heat, the brushes could be damaged, but that with the newer style there's no problem.
:lol: Passengers!
---------- ADS -----------
 
co-joe
Rank 11
Rank 11
Posts: 4562
Joined: Mon Feb 16, 2004 2:33 am
Location: YYC 230 degree radial at about 10 DME

Re: Damaging an engine by turning the prop backwards

Post by co-joe »

Oh those? Yeah I forgot about them. :lol:
---------- ADS -----------
 
Post Reply

Return to “General Comments”