Mounting Position OF The Prop In Relation To TDC

Geico266

Geico266

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Does it make a difference what position the prop is bolted on to the flange in relation to TDC?

RV-3, 0-235, Wooden Sterba Prop
 
Yes. Acheiving proper prop position relative to the crankshaft is called "indexing the prop". For reasons I don't understand, it is said to make a huge difference on certain engine/prop combinations.

-Skip
 
Geico266 said:
Does it make a difference what position the prop is bolted on to the flange in relation to TDC?

RV-3, 0-235, Wooden Sterba Prop
Click to expand...

Put the prop on in any position, start the engine, shut the engine down. remount the prop in the 10:00 <-> 4:00 position. yer good to go. Wooden props do not carry the residence that metal props do. (They flex too much)
 
NC19143 said:
Put the prop on in any position, start the engine, shut the engine down. remount the prop in the 10:00 <-> 4:00 position. yer good to go. Wooden props do not carry the residence that metal props do. (They flex too much)
Click to expand...


What's a "residence"?
 
Skip Miller said:
Yes. Acheiving proper prop position relative to the crankshaft is called "indexing the prop". For reasons I don't understand, it is said to make a huge difference on certain engine/prop combinations.

-Skip
Click to expand...

Thanks Skip, makes sense to me.
 
Geico266 said:
Does it make a difference what position the prop is bolted on to the flange in relation to TDC?

RV-3, 0-235, Wooden Sterba Prop
Click to expand...

With the #1 cylinder at TDC, install the prop at the 2:00 - 8:00 position. This makes it most safe and convenient if hand-propping becomes necessary. The impulse mag will fire as the blade passes through the 8:00 position. Any other position becomes awkward and therefore dangerous.

Dan
 
I just had the Sterba prop repitched a little to increase performance of the 0-235. I went from 68" x 66" pitch to 64" pitch. Looks like I'll get it bolted on this afternoon for a test fly. It's always a good day why you can fly.


Thanks for the responses guys, I appreciate it.
 
Dan Thomas said:
With the #1 cylinder at TDC, install the prop at the 2:00 - 8:00 position. This makes it most safe and convenient if hand-propping becomes necessary. The impulse mag will fire as the blade passes through the 8:00 position. Any other position becomes awkward and therefore dangerous.

Dan
Click to expand...
2:00 and 8:00 from the cockpit reference or facing the engine?
 
Dan Thomas said:
With the #1 cylinder at TDC, install the prop at the 2:00 - 8:00 position. This makes it most safe and convenient if hand-propping becomes necessary. The impulse mag will fire as the blade passes through the 8:00 position. Any other position becomes awkward and therefore dangerous.

Dan
Click to expand...

Starting and stopping the engine does the same thing only you don't have to un cowl to pull the plug and find TDC on #1. A 4 cylinder engine will only stop in 2 positions. both result in a blade in the 10:00 position.
 
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NC19143 said:
Wooden props do not carry the resonance that metal props do. (They flex too much)
Click to expand...
ok now that we cleared up what Tom's mystery word was I have a question.

Each object will carry it's own natural resonance. Regardless of the material it is made up of there is a resonant frequency. That is the frequency the system will oscillate at it's maximum and can actually increase. I did a lot of work on large space structures in the 1980's looking at structural resonances and seen this happen. It can be a lot of fun to watch!!

I can understand that wooden props have a different resonant point over metal ones. I can understand that the wood tends to have less of a rotational mass than metal and thus cause less system vibrations at the system frequencies. But I don't understand what you mean by "carry" resonance.

Help me understand what it is you are observing. I just want to know more about the difference between the two materials for props and why one would be chosen over the other. I am not trying to start a jihad of questions like we are seeing on other threads these past couple of weeks. I think this is a semantics issue more than anything else.
 
NC19143 said:
Starting and stopping the engine does the same thing only you don't have to un cowl to pull the plug and find TDC on #1. A 4 cylinder engine will only stop in 2 positions. both result in a blade in the 10:00 position.
Click to expand...

He has an O-235, which has the TDC marked on the starter ring gear and the index on the starter housing. Easy to find. A Continental would be a little harder.

Dan
 
Dan Thomas said:
He has an O-235, which has the TDC marked on the starter ring gear and the index on the starter housing. Easy to find. A Continental would be a little harder.

Dan
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Do it your way, It will end up the same, but my way is quicker. = $$ saved for your customer.
 
For those who think tracking a wooden prop is the thing to do, should see how much they flex when under power. its a waist of time.

My 80 inch Sensenich will pull forward 8-10" at max power, it's like pulling a long bow.
 
Dan Thomas said:
He has an O-235, which has the TDC marked on the starter ring gear and the index on the starter housing. Easy to find. A Continental would be a little harder.
Click to expand...
My O-200 has TDC, as well as 22-32 degrees BTDC, marked on the prop flange.
 
NC19143 said:
For those who think tracking a wooden prop is the thing to do, should see how much they flex when under power. its a waist of time.

My 80 inch Sensenich will pull forward 8-10" at max power, it's like pulling a long bow.
Click to expand...

For those who know nothing about track and balance, here is some information:

If blades are in a track initially they will flex at the same rate maintaining a relative track. I have done lots of dynamic prop balances (both metal and wood) and have found blades with as much as 1/4" track differential. Moved over a bolt hole or two, brought track much closer and noticeable vibration (using Aces 2020 ProBalancer) reduced. :rolleyes:
 
smigaldi said:
Each object will carry it's own natural resonance. Regardless of the material it is made up of there is a resonant frequency. That is the frequency the system will oscillate at it's maximum and can actually increase. I did a lot of work on large space structures in the 1980's looking at structural resonances and seen this happen. It can be a lot of fun to watch!!
Click to expand...

That it is. Here's perhaps the most famous example of resonance causing destruction:

http://www.youtube.com/watch?v=3mclp9QmCGs

And, of course, the classic example:
http://www.youtube.com/watch?v=17tqXgvCN0E
 
Rotor&Wing said:
If blades are in a track initially they will flex at the same rate maintaining a relative track.
Click to expand...

I agree. It makes no sense not to "track the prop" before final toque of the prop bolts. A few paper shims and you can get it pretty close. I mounted the Sterba prop and got it to about 1/32". Close enough for government work.

BTW, I had Sterba take 4" of pitch out of the prop, but I can't feel or see (RPM's) where it made much difference. Maybe due to the cold temps now, but the good news is the RV-3 is airworthy again, AND I need to fly it more for more test data! Even with an 0-235 she is a hoot (and cheap) to fly. :thumbsup:
 
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jmaynard said:
My O-200 has TDC, as well as 22-32 degrees BTDC, marked on the prop flange.
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If you place those marks at the TDC alined with the bottom case seam, which cylinder are you aligned with?

or does it matter?
 
NC19143 said:
If you place those marks at the TDC alined with the bottom case seam, which cylinder are you aligned with?

or does it matter?
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You know, that's a good question. I'll have to see next time I've got the spark plugs out.
 
Rotor&Wing said:
It's always good to check the track of the blades after installing the prop. Proper track will cut down on vibration.
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Do you check the track visually or is there an instrument? Is tracking valuable for 3 blade props as well as 2 blades?
 
Dave Krall CFII said:
Do you check the track visually or is there an instrument? Is tracking valuable for 3 blade props as well as 2 blades?
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It's simple. place something like a block just behind the blade so the back of the first blade is just barely touching the block. Bring the next blade around and it should be in the same position. If not measure the difference. If you have a 3rd or 4th blade do the same.

Sometimes the fix is as simple as moving the prop a bolt hole left or right one, or even reinstalling the prop 180 degrees from previous. If it's way out some other things need to be looked at.
 
Geico266 said:
Maybe due to the cold temps now, but the good news is the RV-3 is airworthy again, AND I need to fly it more for more test data! Even with an 0-235 she is a hoot (and cheap) to fly. :thumbsup:
Click to expand...
Good deal, let me know when you get sick of flying it, I can help out :)
 
flyingcheesehead said:
That it is. Here's perhaps the most famous example of resonance causing destruction:
Click to expand...


Here's what happens when a helicopter goes into ground resonance:

watch


http://www.youtube.com/watch?v=0GEj69NANc8
 
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Rotor&Wing said:
It's simple. place something like a block just behind the blade so the back of the first blade is just barely touching the block. Bring the next blade around and it should be in the same position. If not measure the difference. If you have a 3rd or 4th blade do the same.

Sometimes the fix is as simple as moving the prop a bolt hole left or right one, or even reinstalling the prop 180 degrees from previous. If it's way out some other things need to be looked at.
Click to expand...

Yes that would be easy enough. I was envisioning checking the track while under full power to check for balanced prop flex. I guess for that super slow motion video might show it.
 
jmaynard said:
You know, that's a good question. I'll have to see next time I've got the spark plugs out.
Click to expand...

Don't bother. On a four-banger the firing order is 1-3-2-4, so the TDC mark will line up with the case seam on both 1 and 2. The prop will be at the 8:00 - 2:00 position in either case. You don't need #1 at TDC, just the TDC mark at its index whether it's the case seam on a small Continental or the starter dimple on the Lyc. The only time you need to know whether #1 is at TDC (or more correctly, at the firing position ahead of TDC) is when you're installing or timing a mag.

Dan
 
Dave Krall CFII said:
Yes that would be easy enough. I was envisioning checking the track while under full power to check for balanced prop flex. I guess for that super slow motion video might show it.
Click to expand...

There are strobe setups available for checking propeller and helicopter rotor blade tracking while at RPM. Expensive and not necessary for most props. They use different coloured reflector tape on each blade so they can determine which blade is running high or low (or forward or back).

Dan
 
Dave Krall CFII said:
Yes that would be easy enough. I was envisioning checking the track while under full power to check for balanced prop flex. I guess for that super slow motion video might show it.
Click to expand...

I can do that with the Aces2020 Probalancer, but it's really not necessary. Just a static track and you're good to go.
 
Dan Thomas said:
There are strobe setups available for checking propeller and helicopter rotor blade tracking while at RPM. Expensive and not necessary for most props. They use different coloured reflector tape on each blade so they can determine which blade is running high or low (or forward or back).

Dan
Click to expand...

You don't need any fancy equipment to see the tracking on a prop.

Place a red reflective tape on one blade, and white on the other, start the engine and shine a flash light on it. You see pink its in track, you see 2 lines one red, and one white, it is not tracking.

add throttle see the lines move forward and back

its best done in the dark.
 
NC19143 said:
You don't need any fancy equipment to see the tracking on a prop.

Place a red reflective tape on one blade, and white on the other, start the engine and shine a flash light on it. You see pink its in track, you see 2 lines one red, and one white, it is not tracking.

add throttle see the lines move forward and back

its best done in the dark.
Click to expand...

That's cool & easy, how would you handle a 3 blade prop?
 
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