Help - Spinner rubbed on cowl during landing

[TheNewGuy]

Had some not so great landings as I learned to fly the RV8 with my instructor, who is also an RV8 guy. He mentioned they can take this sort of abuse although I'm getting the hang of things. After some harding 3-point landings and go arounds, I noticed the spinner had rubbed up against the cowl. I sent some photos to my RV8 CFI, who happens to be a well known RV builder and A&P. He said it looks normal but I want to pull the cowl today as I am on a transient XC flight home.

Looking to get some opinions here before I head to the airport today to pull the cowl and inspect. I have a rough idea but what should I look for under the cowl and does this look like a simple quick Lord Mount compression after a during a hard landing? Thanks

 

[D-Dubya]

The spinner rubbing against the cowling is "normal"? While it looks like a very tight gap between the two, I would think that an inspection of the engine mounts is in order. If they look pregnant, you may have an issue that requires replacement. The good mounts aren't cheap, either.

 

[fixnflyguy]

I'd pull the upper cowl and take a look-see...Odd to have that on the upper half. It looks like its a fairly close fitting cowl to start with, but hard landings would tend to swing the engine downward. With upper cowl off, grasp couple blades of the prop close to the hub and lift up and down.

 

[TheNewGuy]

Today’s plan is to look at the mounts, firewall, and tubes for any anomalies. Plane is currently at Sporty’s so hopefully there is a mechanic on field who can assist should I find something

 

[BoydBirchler]

I've seen this on aerobatic planes quite often, caused by doing snap rolls. The engine isolators should be tight against the metal spools. If the engine is too loose, in the rubber isolators, I have shortened the spool an 1/8"or made a new one out of 4130 tubing an 1/8" shorter to get more compression.

Conversely, If there are no spacer washers under/ between the isolators and the engine; adding them might give you an extra 1/8", which you clearly could use.

The 1/8" clearance you have is simply too close.

 

[TheNewGuy]

I've seen this on aerobatic planes quite often, caused by doing snap rolls. The engine isolators should be tight against the metal spools. If the engine is too loose, in the rubber isolators, I have shortened the spool an 1/8"or made a new one out of 4130 tubing an 1/8" shorter to get more compression.

Conversely, If there are spacer washers under/ between the mount and the engine; removing them might give you an extra 1/8", which you clearly could use.

The 1/8" clearance you have is simply too close.

Thanks. We did do around 5 aileron rolls back to back towards the end of my transition training. Didn’t notice any rubbing after but I’ll look for the spacers if any

 

[RNB]

Ian, are you the builder? If not, how old is the plane?

 

[blaplante]

Thanks. We did do around 5 snap rolls back to back towards the end of my transition training. Didn’t notice any rubbing after but I’ll look for the spacers if any

Thought I remember from somewhere that snap rolls were not part of the aerobatics set that Van designed for. At least on the 6. Maybe the 8 is different.

 

[Carl Froehlich]

As already discussed, your spinner to cowl clearance is too tight. I also note you have minor engine sag. Assuming your engine mounts are in good shape, both issues can be addressed with large washers placed between the engine mounts and the engine.

Here perhaps a single washer under each of the two top mounts and two washers under each of the two bottom mounts. Most likely this will require slightly longer engine mount bolts.

Carl

 

[TheNewGuy]

Thanks guys. My mistake, we did aileron rolls not snap rolls. They were snappy but smooth. I am not a builder but come from a background working on cars. This is my first experimental

 

[blaplante]

As already discussed, your spinner to cowl clearance is too tight. I also note you have minor engine sag. Assuming your engine mounts are in good shape, both issues can be addressed with large washers placed between the engine mounts and the engine.

Here perhaps a single washer under each of the two top mounts and two washers under each of the two bottom mounts. Most likely this will require slightly longer engine mount bolts.

Carl

Don't underestimate the magnitude of this job. In a car, putting some washers under the engine mounts will be a quick job.
The Lycoming dynafocal mount angles will fight you. Not a one person job. Voice of experience here. I'm sure someone will chime in and say they had no problems doing it but that's not par for the course for a first timer.

 

[TheNewGuy]

Don't underestimate the magnitude of this job. In a car, putting some washers under the engine mounts will be a quick job.
The Lycoming dynafocal mount angles will fight you. Not a one person job. Voice of experience here. I'm sure someone will chime in and say they had no problems doing it but that's not par for the course for a first timer.

I’ll be enlisting a knowledgeable A&P to learn more about the RVs and slowly wade myself into work when I deem fit. I plan on building down the road when my schedule and space allows

 

[TheNewGuy]

Met with the local mechanic today. He noted that the cowl has a little “slop” when a good force is applied. I’m not sure how normal that is on an RV-8, so I’ll give Van’s a call to confirm. He also mentioned that the spinner-to-cowl clearance is very tight. All four engine mounts do have shims installed, but he suggested leaving them in place for now because the exhaust is already lightly rubbing the lower cowl and removing shims would lower the engine further and make that contact worse.

Is there another way to increase the spinner-to-cowl gap with a Catto Propeller? The prop does sit slightly off-center, but it looks like it’s always been that way

Firewall, mount structure, and engine mount frames all appeared normal to both me and the mechanic. The two standout issues were the cowl movement and the tight spinner clearance.

 

[blaplante]

Met with the local mechanic today. He noted that the cowl has a little “slop” when a good force is applied. I’m not sure how normal that is on an RV-8, so I’ll give Van’s a call to confirm. He also mentioned that the spinner-to-cowl clearance is very tight. All four engine mounts do have shims installed, but he suggested leaving them in place for now because the exhaust is already lightly rubbing the lower cowl and removing shims would lower the engine further and make that contact worse.

Is there another way to increase the spinner-to-cowl gap with a Catto Propeller? The prop does sit slightly off-center, but it looks like it’s always been that way

Firewall, mount structure, and engine mount frames all appeared normal to both me and the mechanic. The two standout issues were the cowl movement and the tight spinner clearance.

Typical Vetterman exhaust is adjustable. Do you have two exhaust pipes?

 

[TheNewGuy]

Typical Vetterman exhaust is adjustable. Do you have two exhaust pipes?

yes

 

[D-Dubya]

Why is the cowl moving? Are any of the fasteners or pins missing / sloppy?

As far as that gap spacing goes, the gap is built in when the cowling is fitted to the firewall. Some builders like a very tight gap as it may have lower drag. Other builders open it up a little to allow for wiggle room and to make removing the lower cowling easier. Not sure what you can do about that at this point without doing some fiberglass work or installing a different prop. It's doable, but not in the middle of a cross-country flight. There are spacers made for prop flanges, but not sure if you could get one that would be only 1/4" thick; and again, it won't be quick and easy.

You might have your mechanic watch the prop from the side while you do a run-up and maybe he can see if the gap closes up with power changes. If not, you're probably good to go home. If it's moving around, though, that's an issue. It's possible it only rubbed on one particularly firm landing. But now that you've got THAT out of the way...

 

[TheNewGuy]

The Skybolt holes might be worn through slightly. It takes quite a bit of force to get it to move up and down when bolted in. I’ll see if the mechanic will come out again to have a look at the gap when adding power before I depart this week. It looked fine when it turned the prop by hand. He’s the only mechanic on the field but doesn’t know much about experimentals

His suggestion was to color the scuffs in with a marker and see if I notice any fresh ones after the flight home

 

[mburch]

As far as that gap spacing goes, the gap is built in when the cowling is fitted to the firewall.

Definitely true. But - the gap can change if you swap props. Maybe the prop/spinner that are on it now are not what the cowl was originally built to fit?

 

[blaplante]

yes

Vetterman exhaust has some supports that fit into sections of rubber hose (for isolation). Loosen the hose clamp and adjust the pipe up as needed.

You've just run into the issue with A&P help... 99% have never worked on an RV. Keep that in mind as you go along!

 

[BoydBirchler]

I’ll be enlisting a knowledgeable A&P to learn more about the RVs and slowly wade myself into work when I deem fit. I plan on building down the road when my schedule and space allows

What I said about the spacers ( see edit) was backwards: you need to add spacers to move the engine forward. PS, aileron rolls usually do not case enough gyroscopic forces to move the engine much. Also you might check to see if the engine isolators are installed correctly. the one in back on the top ( the harder durometer of the pair) should be the one in front on the bottom.

 

[TheNewGuy]

What I said about the spacers ( see edit) was backwards: you need to add spacers to move the engine forward. PS, aileron rolls usually do not case enough gyroscopic forces to move the engine much. Also you might check to see if the engine isolators are installed correctly. the one in back on the top ( the harder durometer of the pair) should be the one in front on the bottom.

Thanks. I’ll have a look tomorrow. Spoke with Saber so I’ll get a spacer if all else looks good. No new rubbing today although I didn’t have any hard landings. Handles a lot differently without 240lbs in the backseat