[RVG8tor]

I know the engine moves but how much? In hooking up hoses and cables they will come close to the supports for the engine mount, and in my case the RV-8A it is basically a spider web of supports.

In the shot below I have a proposed location for the anchor the the throttle cable, to the left of the picture is one of the mount supports, part of it is off frame. This is where the anchor needs to be for the required travel of the throttle arm, but this puts the cable sheath 1/2" from the mount support.

So this brings up my question, since the engine will move up down under "G" and side to side with power change would me by guess. What is a good guide line on minimum distance between cables and hoses and proximity to things that don't move, like the engine mount structure?

The -8A exhaust goes through a small opening in the gear mount and there is no way to get much clearance all around, since I think air loads will tend to lift the pipes my plan is to leave most of the clearance between the pipe and the exhaust ramp.

So if I reason correctly the pipe movement and the space is less than 1/2" then will this work for cables and hoses. For you DARs out there what do you look for with this kind of thing. I will have a similar proximity issue with my mixture cable, I am also having to send the AFP unit back to have the rotation of the mixture made CCW, the exhaust pipe gets in the way otherwise.

I don't think there are many flying with this set up as I did not find much in my searchs. AFP FI / RV-8A /vertical induction, the combination of engine mount supports and exhaust pipe positioning make hooking up the mixture a real puzzle.

Cheers

This shot shows the exhaust on the throttle side but you can see the issue would be the same on the left side, also you can just make out the throttle anchor.

 

[swisseagle]

Wrong tube routing!?

Hello Eliot

I have nearly the same setup, but I think you have the exhaust tubes on the wrong place, they should be mounted outside of the noswheel triangle motormount tubes! Your tubes have to hang down into the breeze and should not end up so close to the floorskin, this will create otherwise a lot of vibrations and maybe skin cracks.

Check also the placement of the exhaust hangers, they also come into the way and are not freely placeable.

SORRY! I saw right now that you have an RV-8A, so there it is maybe like this. I was talking about an RV-7A. So not much more help from my side possible. The RV-7A has a straight bottom and not an recress like the RV-8.


Regards Dominik

 

[RVG8tor]

DAR help

OK I have Googled, word searched AC43 and I can't find any guidance. What should one use when hooking up control cables and other stuff connected to the engine. I would think there is some rules of thumb on this issue, like nothing closer than XX inches unless it is item "Z".

If you're inspecting an airplane and you see something attached to the engine close to an aircraft structure, how close is it before you become concerned?

Thanks, why didn't I build with the stock engine and fuel control, oh yeah it experimental.

 

[DanH]

This is where the anchor needs to be for the required travel of the throttle arm, but this puts the cable sheath 1/2" from the mount support.

Nemo, there is no one firm answer. The engine rotates around the crank axis in reaction to accel/decel of the rotating mass (crank and prop). The angular displacement of the engine is thus a function of oscillating gas pressure (throttle) and mass moment of inertia (heavy or light propeller). Combine an open throttle, rough hot start with a metal prop and you get a lot of engine rotation. What do you have?

You need to be sure that throttle bracket can never take a hit.

The -8A exhaust goes through a small opening in the gear mount and there is no way to get much clearance all around...

Well, if the pipes don't fit get some made that do.

...why didn't I build with the stock engine and fuel control, oh yeah it's experimental.

Bit o' philosophy sir, if I may........the decision to experiment doesn't excuse lack of quality. It means designing and fabricating parts equal to or better than the bolt-on stock arrangement is the builder's responsibility. If it takes special parts, so be it, but compromise because there is no off-the-shelf solution is not acceptable.

 

[RVG8tor]

Thank you for the input

@DanH,

I am not sure where you got the idea that I was doing less than quality work from my statement. I am here asking questions because I want to find a good quality solution to my problem. This forum is usually a wealth of information on numerous subjects, I guess just not this one. I plan to tackle this one like the others I have encountered in my build. I research all the information I can find on a given subject, filter through what I think is good and bad, what I think will work, run by an idea or two and then with all due diligence and consideration make the best quality product I can.

I am no expert, this is my first build and I love the process, I also appreciate anyone willing to help someone going down this path for the first time. I think my build is taking as long as it is because I strive for perfection. You may note that I did not charge ahead with my cables and brackets, I saw the potential for interference with things and asked for some help and guidance for at least a place to start. As you say it seems there is no strong opinion in this regard. For the record I am using quality components; AFP FI and a Vertterman exhaust, how to actuate those quality parts with a quality solution is where I am at right now.

Again thanks for your input, I will use them along with any others that come along.

Cheers

 

[Walt]

If you're inspecting an airplane and you see something attached to the engine close to an aircraft structure, how close is it before you become concerned?

It can get very crowded FWF and things do get close or in some case cross or come into contact with other items. The important thing is that you leave enough slack in hoses and cables to allow for things to move around without straining them. Where things contact each other it's generally acceptable as long as you provide some means to prevent chafing from movement (clamps, protective sleeving, etc.) As far as fuel lines, there should be a minimum of 2 inches from any exhaust tube and heat deflectors (fire sleeved lines of course) used anywhere less than about 3 inches exists. Radiant heat is the enemy of cables and fuel lines so do everything possible to prevent it.

No hard and fast rules here, just lots of good sound judgement. Sounds like you're not very familiar with FWF stuff so plan your systems and then try to get someone to look at it with you.

 

[PaigeHoffart]

Mike,

I think if you rotate the exhaust pipes, you'll find you have a lot more clearance.

As for the cable clearance I'd get as many eyes as I could on the actual area of interest. Photo's aren't always the best for coming up with solutions to three dimensional problems. Worst case, you could always come up with a small bell crank arrangement to get more clearance.

Paige

 

[Tom Martin]

A fore/aft picture of your cables would be helpful. While it is desirable to have the cables directly inline with the "work" there is an allowance for side to side movement. The cable manufacturer should publish the allowed angle of movement' and this might help you to get more clearance. I would like to see more then 1/2" in this location. The engine can rock back and forth a lot at start up and shut down. With that in mind I have some reservations regarding your exhaust system. I just can not see how they can safely go through that location with enough clearance. The farther you get from the crankshaft the greater the the rotational movement mentioned before.
Send this picture to Larry Vetterman, he is the guy and there is no one here as qualified as he is to address your concerns and to come up with a different solution if it is required.

 

[RVG8tor]

Proven Exhaust

A fore/aft picture of your cables would be helpful. While it is desirable to have the cables directly in line with the "work" there is an allowance for side to side movement. The cable manufacturer should publish the allowed angle of movement' and this might help you to get more clearance. I would like to see more then 1/2" in this location. The engine can rock back and forth a lot at start up and shut down. With that in mind I have some reservations regarding your exhaust system. I just can not see how they can safely go through that location with enough clearance. The farther you get from the crankshaft the greater the the rotational movement mentioned before.
Send this picture to Larry Vetterman, he is the guy and there is no one here as qualified as he is to address your concerns and to come up with a different solution if it is required.

Although the -8A has its challenges with the tight fit on the exhaust, many have flown with the same Vetterman exhaust. I have already shown this picture to Larry and he told me to work on the rotation of the pipes so it angles more down the opening in the mount.

I may not be explaining my question well; the tight fit of the exhaust and having to make my own throttle and mixture brackets brought up the question in my mind of how close can you get things to the non-moving parts of the aircraft structure.

I figured a DAR would be looking for clearances of cables from the airframe during and inspection, what is the distance before the inspector goes, "we have a problem"?

As far as the pictured throttle cable location (1st post). A frontal picture would show a 1/2" from the side of the cable sheath. This is in line with the motor mounts and it does not seem as though there could be very much movement here but could there be a 1/2 inch?

I have received some PM that has given me some guidance. I may do some testing and with straps try to pull the engine to see how much movement I can get in various directions to come up with my own number.

As for the pictured throttle linkage, I can move the bracket in and gain another 1/4" clearance so I will go that route.

This is thread is starting to generate the discussion I had hopped. I have re-read my Tony B. books and nothing there, though there is mention of hoses and proximity to hot exhaust. I have Googled hoping to get some excerpt from an Airframe and Power plant text on this issue but so far no luck. I think I will try to make a visit to the local Technical Collage.

Cheers

 

[Jerry Cochran]

Eyeballs

Hi Mike,

Like someone said, hard to get a 3D look from 2D images... Best if you get a couple experienced builders to eyeball it, and I bet there are simple solutions.

if none close to Oly, I am 40 min away by RV, so if needed I would be happy to fly up and take a look for you.

My email is [email protected] and 503 702 2663 cel

 

[Andrew M]

Ideas

Mike,
It looks like what is driving the location of your bracket is how much deflection from straight on that rod end will give you.
Make a tapered block that will bolt on you F.I. arm thought the second hole, and have a countersink screw to hold the rod end on. The C/S screws face will be buried under or between the tapered block and FI arm. Put what taper you want to give the clearance you think you need.
Remake your attach bracket by cutting out a slot on the angle face that you show cleco clamped. This will give you a little more room to move those locknuts inboard, or remake what that attaches to.
I think your judgment is sound concerning where to put existing clearance for the exhaust, and others here with direct experience may have some better ideas on how to get more clearance. Unfortunately the only real answer I can offer is "more is better and less is bad" Clearance issues are a top item to continually inspect for, so with that in mind, do what you can, then fire it up and see what it does. I personally will not pronounce something as good until I have seen it run.

 

[sf3543]

Mike
You can always look to 4313.1b for guidance on installing anything on your airframe.
In my experience, I have seen that the engine can move around about 1/2 inch during start or shut down, especially if it kicks back during a hot start. I don't think you would be able to duplicate that movement by using straps since the mounts are very stout and it takes a lot of torque to move them very much. My rule of thumb, on baffles, is to be able to put a finger between the baffle and cowl, which is about 1/2 inch.
Movement closer to the engine and mounts would be less, but still, hoses or cables routing close to the mount need to be contained so that they do not chafe. (Mostly from vibration.) You can do this by strapping them together using adel clamps or tie wraps or protecting them with some kind of tubing, or both.
Since the engine is moving, relative to the stationary airframe, you must allow some slack. That's why you sometimes see a round loop in copper or aluminum tubing going from the firewall to the engine, to allow for this movement. Flexible hoses don't need so much slack but enough not to put them in a strain.
So, how close is too close? If you can deflect the hose or cable so it touches any adjacent fixture, hose or cable, I would secure them somehow. If you can not deflect them to touch something else, they are probably ok.
As for your exhaust, I would go with Vetterman's advice or that of other successful builders. I have used a different exhaust mounting method from Larry's which works better for me. I can send pictures via iphone if you like but they are not nosewheel mounts.
Good luck.

 

[RVG8tor]

Some good inputs

The last day of posts have been very helpful. I leave today to do my real job but will mull over everything posted and come up with a plan of action. Getting away from the project is usually very helpful in this regard. It gives me time to think about ideas and even sketch some out.

I will post some pictures of what I come up with although it might be a couple weeks from now. I am working most of the days between now and the 12th.

Thank you all for your inputs, you can't believe how helpful this can be to get one going in the right direction, or at least a direction.

Busy all last night watching a pregnant mare, she had a colt this morning at 5 am, and he is huge! He is as big as a foal born a month ago, although she was small for a new foal. My wife appreciated my help with the all night mare watch, and he was so big we had to give a little external help pulling to clear those big shoulders.

Cheers