Van's Air Force
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Lyc Wet Dog Shake
- Thread starter Jim P
- Start date
gmcjetpilot
Well Known Member
Depends
Sorry there was a thread where someone posted a deflection, could not find it. But it depends on engine, prop and brand/type engine vibration isolators. The deflection depends on where you measure it. I think most of the movement is rotational. If you are looking for gap between baffles and cowl, follow the plans. I think there are some clearances in there.
Sorry there was a thread where someone posted a deflection, could not find it. But it depends on engine, prop and brand/type engine vibration isolators. The deflection depends on where you measure it. I think most of the movement is rotational. If you are looking for gap between baffles and cowl, follow the plans. I think there are some clearances in there.
cytoxin
Well Known Member
looks like
http://www.youtube.com/watch?v=yoX4KEXVuFo watch at 6.23
about 2 inches total (1up and 1down) could be more probally less. this is my concern for the fuel pump to flow meter hose.. that hose is suppose to be flexible but its not so flexible as to not wiggle the gascolator/fuel flow assy. remember the baffles are only 3/8 from the cowl so it cant be as much as the video shows..i hope.
http://www.youtube.com/watch?v=yoX4KEXVuFo watch at 6.23
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cytoxin
Well Known Member
look again
full screen the video if you did not and you will see the more than obvious relative motion. it moves, and a good bit at that.just as you hear the implulse coupling click. however i dont know what type of mounts he's using. vip v/s lords ??
edit : the best ground run video ive seen yet and perfect timing BTW for my concerns...like he read my mind.
full screen the video if you did not and you will see the more than obvious relative motion. it moves, and a good bit at that.just as you hear the implulse coupling click. however i dont know what type of mounts he's using. vip v/s lords ??
edit : the best ground run video ive seen yet and perfect timing BTW for my concerns...like he read my mind.
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AlexPeterson
Well Known Member
The majority of motion on my engine seems to be rotational during startup or shutdown. I have an O360 C/S prop, with non-aerobatic mounts. I would estimate that the valve covers, during this rotational motion, move up and down maybe 1/4 to 3/8" from their rest position. Certainly no more. My baffles have 1/2" clearance, and there is no sign that they've hit the cowl. The center of the engine, just behind the prop, moves up and down perhaps 1/8".
RVAddict
Well Known Member
Seriously off topic guys, and I apoligize, but can anyone identify the pickup truck in that video? I can't tell what it is. PM me if you know so the thread does not get hijacked.
Thanks
Josh
L.Adamson
Well Known Member
Initially, I, along with another builder, was concerned about the clearance between the two horizontal fiberglass baffles attached to the bottom side of the top cowling & the vertical aluminum baffle pieces that are on each side of the starter gear ring. We wanted to know if we needed a larger gap, along with the rubber seal.
Numerous aircraft that we looked at, only had an 1/8" gap or slightly more/less, and little signs of wear on the fiberglass, which proves it is much more rotational; and almost nothing with side to side motion, considering it's far forward of the mounts.
L.Adamson -- RV6A
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az_gila
Well Known Member
Rotational
On my Tiger (O-360 engine, similar mounts...) I installed an indicator on the bottom right engine mount bolt - well, not quite, but the aftermarket PowerFlow exhaust system has a rod that passes through the cowling about 10-12 inches below the mount. This rod is fixed to the engine mount bolt and the exhaust - it moves with the engine.
The cowling hole had to be opened up to allow for the "wet dog shake", and is about 3 inches wide (rotational shake) and less than 1 inch fore and aft (up/down shake).
The rod can be seen in this picture....
Based on this, I would say the biggest movement is rotational, and the biggest physical movement would be an up/down movement at the cylinder heads.
gil A
On my Tiger (O-360 engine, similar mounts...) I installed an indicator on the bottom right engine mount bolt - well, not quite, but the aftermarket PowerFlow exhaust system has a rod that passes through the cowling about 10-12 inches below the mount. This rod is fixed to the engine mount bolt and the exhaust - it moves with the engine.
The cowling hole had to be opened up to allow for the "wet dog shake", and is about 3 inches wide (rotational shake) and less than 1 inch fore and aft (up/down shake).
The rod can be seen in this picture....
Based on this, I would say the biggest movement is rotational, and the biggest physical movement would be an up/down movement at the cylinder heads.
gil A
G
Geoff
First start video
Here's a link to my first start video: http://home.comcast.net/~n70ge/start.wmv. It's a 1-minute, 3.4 meg video. You can see the rotational movement at startup and shutdown. The engine starts and runs beautifully until it runs out of gas because the idiot in the cockpit (me) forgot to turn on the fuel selector valve -- even after he was reminded to do so.
-Geoff
Here's a link to my first start video: http://home.comcast.net/~n70ge/start.wmv. It's a 1-minute, 3.4 meg video. You can see the rotational movement at startup and shutdown. The engine starts and runs beautifully until it runs out of gas because the idiot in the cockpit (me) forgot to turn on the fuel selector valve -- even after he was reminded to do so.
-Geoff
strahler13
Well Known Member
Josh, If I had to guess, it may be a Ford Explorer Sport Track.
Mark
Mark
Jim P
Well Known Member
Here's the reason for asking this question (which might fall under "stupid builder tricks"):
Just when I thought I had a pretty good location for the fuel sensor (the topic of another heated thread), I looked at this and thought, with a little rotational shaking, that fuel line downstream of the sensor might be an issue.
I'm thinking I have two fixes: (1) raise the sensor and open the baffle hole to give teh baffle more room to move, as well as changing the forces on the line, from a pull to more of a up-down. Option (2) might be to just mount the sensor on the back of the right baffle and solve all relative movement problems, but I'm not sure how the sensor is going to stand up to that shaking.
Just when I thought I had a pretty good location for the fuel sensor (the topic of another heated thread), I looked at this and thought, with a little rotational shaking, that fuel line downstream of the sensor might be an issue.
I'm thinking I have two fixes: (1) raise the sensor and open the baffle hole to give teh baffle more room to move, as well as changing the forces on the line, from a pull to more of a up-down. Option (2) might be to just mount the sensor on the back of the right baffle and solve all relative movement problems, but I'm not sure how the sensor is going to stand up to that shaking.
gmcjetpilot
Well Known Member
Well it might rub or.....
May be the worst will be the fire sleeve rubbing ever so slightly on the the plastic dip stick tube? It's that or the AN fitting will fail.
(I'm kidding but only partly)
You're violating one golden rule of hose runs, you must have service slack or dip. Hoses need a droop or slack between two ridged supports, especially when vibrating. You also have a very short segment. Its almost like a strut between the engine and airframe. To be extremely paranoid, I'd worry slightly about the angle AN fitting being bent as the hose wiggles with engine vibration. This could cause bending fatigue across the AN fittings threads due to vibration. The fuel line/fire sleeve may be pretty flexable? I can't tell from the picture.
The hose bends and prys on the AN fitting, it could fatigue the fitting, in theory. It's a far stretch may be? Fittings have failed this way before. You want some service loop / slack to allow the hose to be flexable before you nail it down to a fitting or support. The idea is make the hose take all the movement, not the fittings.
An example of this is when the FAA issued an AD for prop Gov lines/fittings on Lycs about 15 years ago. The AD changed aluminum AN fittings and aluminum ridged tube to steel AN fittings & stainless steel ridged tube (optional flex hose). It was not really a design or material problem. The issue was good for 30 years, but over the years maintence folks did not re-install proper supporting clamps on the ridged line. The vibration caused fatigue failures of the AN fittings and tube. Even with 30 years of service on countless planes with no problem, the FAA demanded a switch to steel. You just don't want to pry on an AN fitting. May be replacing the aluminum AN on the engine side of the FF sensor with a steel one might be better?
Any thing you can do to alleviate or lessen to strain on the AN fitting (if there is any) would be good. It would be expensive to make new hoses, but you could open up the hole in the baffle, where the fuel line passes. It will leak a little air, but the gap would allow the hose to float free (and not vibrate with the engine as much).
When it comes to fuel lines, no bending or tugging on the AN fittings is my rule. The fuel line is one item I do get paranoid about.
If the hoses or cables are too tight, don't have the service slack, they can and do transfer vibrations to the airframe. This set up might also cause you to feel more vibration in the plane.
May be the worst will be the fire sleeve rubbing ever so slightly on the the plastic dip stick tube? It's that or the AN fitting will fail.
(I'm kidding but only partly)You're violating one golden rule of hose runs, you must have service slack or dip. Hoses need a droop or slack between two ridged supports, especially when vibrating. You also have a very short segment. Its almost like a strut between the engine and airframe. To be extremely paranoid, I'd worry slightly about the angle AN fitting being bent as the hose wiggles with engine vibration. This could cause bending fatigue across the AN fittings threads due to vibration. The fuel line/fire sleeve may be pretty flexable? I can't tell from the picture.
The hose bends and prys on the AN fitting, it could fatigue the fitting, in theory. It's a far stretch may be? Fittings have failed this way before. You want some service loop / slack to allow the hose to be flexable before you nail it down to a fitting or support. The idea is make the hose take all the movement, not the fittings.
An example of this is when the FAA issued an AD for prop Gov lines/fittings on Lycs about 15 years ago. The AD changed aluminum AN fittings and aluminum ridged tube to steel AN fittings & stainless steel ridged tube (optional flex hose). It was not really a design or material problem. The issue was good for 30 years, but over the years maintence folks did not re-install proper supporting clamps on the ridged line. The vibration caused fatigue failures of the AN fittings and tube. Even with 30 years of service on countless planes with no problem, the FAA demanded a switch to steel. You just don't want to pry on an AN fitting. May be replacing the aluminum AN on the engine side of the FF sensor with a steel one might be better?
Any thing you can do to alleviate or lessen to strain on the AN fitting (if there is any) would be good. It would be expensive to make new hoses, but you could open up the hole in the baffle, where the fuel line passes. It will leak a little air, but the gap would allow the hose to float free (and not vibrate with the engine as much).
When it comes to fuel lines, no bending or tugging on the AN fittings is my rule. The fuel line is one item I do get paranoid about.
If the hoses or cables are too tight, don't have the service slack, they can and do transfer vibrations to the airframe. This set up might also cause you to feel more vibration in the plane.
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cytoxin
Well Known Member
i feel your pain
good luck. it is hard to do this particular job by the book. that shake down makes the wheels in my head turn. i know there are plenty out there but what kind of hours are we talking about. in my own words, all to often said to customers "nothing lasts forever" i can honestly say that on a fi model i would put it on the the floor just down stream of the boost pump and live with the error. lucky you.
good luck. it is hard to do this particular job by the book. that shake down makes the wheels in my head turn. i know there are plenty out there but what kind of hours are we talking about. in my own words, all to often said to customers "nothing lasts forever"
i can honestly say that on a fi model i would put it on the the floor just down stream of the boost pump and live with the error. lucky you.
Jim P
Well Known Member
May be the worst will be the fire sleeve rubbing ever so slightly on the the plastic dip stick tube? It's that or the AN fitting will fail.
There's actually a lot of room between between the dipstick and the line as well as some slack on the other side of the baffle, but some mods are going to be made..
az_gila
Well Known Member
On top of engine...
Jim... IIRC, the new C-182s have their fuel sensor (looks like a FloScan) on top of the engine. It is completely wrapped in a fire sleeve cover though...
The back baffle should be similar for heat and temperature....
gil A
Jim... IIRC, the new C-182s have their fuel sensor (looks like a FloScan) on top of the engine. It is completely wrapped in a fire sleeve cover though...
The back baffle should be similar for heat and temperature....
gil A
