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Cowl Inlet Ramps - needed?

pilotkms

Well Known Member
I saw an RV that did NOT have the fibreglass cowl inlet ramps installed on the underside of the upper cowl. So wondering what their purpose is and if others have left them out? I am at the point to install them but do i really need to ? Maybe i wait til after flying and only consider installing them if i have heat issues - CHTs ? If this has been discussed please refer me to the right search term.
Thanx
 
I saw an RV that did NOT have the fibreglass cowl inlet ramps installed on the underside of the upper cowl. So wondering what their purpose is and if others have left them out? I am at the point to install them but do i really need to ? Maybe i wait til after flying and only consider installing them if i have heat issues - CHTs ? If this has been discussed please refer me to the right search term.
Thanx

The short simple answer is they are very important... the reason the are supplied in the kit.
 
Yes, they are necessary!

And for a slightly longer answer. These ramps smooth the airflow coming into the cowling. Without them, especially in a climb configuration, the incoming air becomes turbulent and will not cool the engine properly.
 
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Van's includes very little that isn't necessary.

Van's didn't include an engine or propellor in my kit, so I left them out. Maybe that's why my plane is so light...









:D Sorry, one of those days, couldn't help myself <ducks for cover...>
 
I have to agree with Scott. Mine are not closed off and they work great.
 
OK.

I'm putting them in. I'll probably seal the ends (sides?) just to be redundant, if they are that important.
Thanx Mel for the more technical (and requested) answer.
Thanx Lars - i appreciate your humor.
Keith
 
Mike,
That is not needed and is actually redundant if the Van's supplied baffle system and associated seals are installed as intended.

Yes but I think there is a minority that achieves the "as intended" especially around the nose section. For them, sealing will provide a cooling improvement.
 
Yes but I think there is a minority that achieves the "as intended" especially around the nose section. For them, sealing will provide a cooling improvement.

That might have been the case years ago, but i don't think it is any more.

Regardless, plugging the inlet ramp to prevent plenum air flow through them is applying a bandaid to the problem. It may help, but there will still likely be baffle and seal issues that will cause poorer cooling performance than if it was done right.
 
Sorry Scott but I dont accept that the new baffle kits will work as desired without adding custom fiberglass work to the ramps in order to provide a surface for the seal strips to ride on. On the -M1B application there will be a couple of inch gap on each side of the nose where the seal comes off the inlet ramp and jumps to the cowl surface. I have seen plenty of installations that have not dealt with this problem. That gap needs to be fixed or the ramps need to be sealed (As a less effective bandaid)
 
I dunno about new baffle kits, but I have observed that the average builder does a sorry job of sealing both the inboard and outboard sides of each inlet.

Extending the ends of each glued-in upper ramp may provide a better surface for seal fabrication. Simply closing the ends of the ramps is probably a waste of time.

While on the subject, I think the cowl as supplied should be trimmed as seen below before installing the ramps. Too many get the ramps glued in too far rearward. The resulting pinch, in particular over #1, may reduce available static pressure. The preferred cross section is a smooth expansion.

Inlet%20Pinch.JPG
 
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Sorry Scott but I dont accept that the new baffle kits will work as desired without adding custom fiberglass work to the ramps in order to provide a surface for the seal strips to ride on. On the -M1B application there will be a couple of inch gap on each side of the nose where the seal comes off the inlet ramp and jumps to the cowl surface. I have seen plenty of installations that have not dealt with this problem. That gap needs to be fixed or the ramps need to be sealed (As a less effective bandaid)
I'm not sure if the ramp design has changed lately, but on my new(ish) -9A the inboard edges come pretty close to the baffling, so the "elephant ear" seals have a nice surface to plaster to, without any extension/modification whatsoever. The curvature of the ramps makes the seals lay down real nice.
 
I dunno about new baffle kits, but I have observed that the average builder does a sorry job of sealing both the inboard and outboard sides of each inlet.

Extending the ends of each glued-in upper ramp may provide a better surface for seal fabrication. Simply closing the ends of the ramps is probably a waste of time.

While on the subject, I think the cowl as supplied should be trimmed as seen below before installing the ramps. Too many get the ramps glued in too far rearward. The resulting pinch, in particular over #1, may reduce available static pressure. The preferred cross section is a smooth expansion.


I'm just about to this point and need to examine the cowl/baffle relationship at the inlets. I'm assuming I will need to trim either the inside of the inlet as depicted on your sketch or the front baffle to allow the removal and re-install of the lower cowl. You bring up a good point that leaving the cowl inlet more or less untrimmed moves the ramp rearward and would affect the airflow thru this area. The million dollar question is where the cowl inlet and baffle meet. Anyone have a data point for the approximate horizontal measurement they used at the inlet?

Another opportunity for education I guess :cool:
 
I'm having a really difficult time picturing any of this. I don't recall any instruction to seal the sides of the baffles.

You know what would be helpful in explaining some of this? A picture or two.
 
I dunno about new baffle kits, but I have observed that the average builder does a sorry job of sealing both the inboard and outboard sides of each inlet.

Extending the ends of each glued-in upper ramp may provide a better surface for seal fabrication. Simply closing the ends of the ramps is probably a waste of time.

While on the subject, I think the cowl as supplied should be trimmed as seen below before installing the ramps. Too many get the ramps glued in too far rearward. The resulting pinch, in particular over #1, may reduce available static pressure. The preferred cross section is a smooth expansion.


I have thought about that geometry issue. On my -M1B installation the snorkel definitely forces the aluminum lower ramp to be in the trimmed configuration. Not true for carbureted. It could be anywhere.
I think you are right that if the inlets were trimmed very short, then the curved ramps could be far enough forward that the ramp meets the cowl ahead of the nose baffle. While I did trim mine, I did not trim them that short, so I had to build some side ramps for the baffle seal to sit on.
Since my CHTs are great, and well balanced, I don't think I have the ramps far enough back to be a choke point problem.

16721977964dc74d47e78e3.jpg
 
With all due respect to Dan, who is obviously one of the smarter guys on this site, I'm not sure I'm buying into that whole shorter nostril trimming makes the airflow more efficient thing. On it's face, sure, looks good, but isn't the intake volume pretty much dependent on the size and efficiency of the cowl outlets? Don't air plenums restrict the intake in the same way? Maybe more so? Just wonderin......
 
Don't air plenums restrict the intake in the same way? Maybe more so? Just wonderin......

They can, but they don't have too! It all depends on the design.
I know of RV's that cooled better once the builder designed plenum was removed and switch to traditional baffling.
 
With all due respect to Dan, who is obviously one of the smarter guys on this site, I'm not sure I'm buying into that whole shorter nostril trimming makes the airflow more efficient thing. On it's face, sure, looks good, but isn't the intake volume pretty much dependent on the size and efficiency of the cowl outlets? Don't air plenums restrict the intake in the same way? Maybe more so? Just wonderin......

You're mixing issues. A plenum, by itself, does not restrict airflow. It hopefully reduces or eliminates the air leakage which occurs around typical baffle installations.

That said, IF your plenum eliminates wasting of (say) 10% of your cooling air compared to stock baffles, you can make the inlets and outlet 10% smaller without losing cooling capacity, and will have a lower drag cooling setup.
 
[/QUOTE]

What kind of clearance between the #1 cylinder and the inlet ramp (at the "pinch" point, measuring from the cylinder head or barrel) is good to have? What do some of you have on yours? My #1 and #3 both run a little hotter and I don't have that much space there.
 
Hey Mike,
A lot of folks suggest that you should be able to get your fist between the leading cylinder and inlet ramp. In stock form, the left side ramp was just about perfect, but I cut and re-glassed the right side (left in picture), moving it forward to approximately match the cylinder stagger.

Temps are quite even now in cruise, though #1 is a little hot still in climb. I've cut the air dam in front of it a little more, and will see if that helps on my next flight.

 
As a data point, the ramp to #1 cylinder space on mine is about a fist. The ramp to #2 cylinder space is several inches larger. #1 and 3 cht's are evenly cooler than #2 and 4 cht temps.which are evenly hotter by about 20 degrees. In retrospect, I probably should have installed the ramps to better reflect the stagger of the cylinders.
 
... the incoming air becomes turbulent and will not cool the engine properly.

I have always wondered about this assumption since I read an article where John Thorp was quoted as saying "The optimum airflow over the engine is opposite to what you want over the outside of the airplane. You want it as turbulent as you can make it so you don't have any stagnation. What you want is the air to mix to give maximum heat exchange."

It is certainly counter-intuitive and I wonder if there is any science to support either stance. NACA papers perhaps?

How I remember this stuff I don't know - the interview was published in the winter edition of "Air Racing" 1973.
 
I have always wondered about this assumption since I read an article where John Thorp was quoted as saying "The optimum airflow over the engine is opposite to what you want over the outside of the airplane. You want it as turbulent as you can make it so you don't have any stagnation. What you want is the air to mix to give maximum heat exchange."

It is certainly counter-intuitive and I wonder if there is any science to support either stance. NACA papers perhaps?

How I remember this stuff I don't know - the interview was published in the winter edition of "Air Racing" 1973.

Thorp is correct when reffering to the air in immediate proximity to the cylinder fins. Between the fins I mean. Turbulent flow is better for local heat transfer. Same could be said for the oil inside the oil cooler. Turbulent is better.

HOWEVER, this should NOT be construed as "turbulent is better at the cowl entrance". Totally different physical process at the inlet. Laminar is better for turning velocity into pressure.
 
IF not installing all Vans parts is bad I guess I am in trouble. I didn't install the little fillets in the front outside corners of the baffle. The seals on the front of the cowl fill this area very well. I found that it would make the air filter removal on the left side difficult. I may put a finger sized fillet of RTV in the corners just to fill in the last little bit. Anybody else leave them off?
 
IF not installing all Vans parts is bad I guess I am in trouble. I didn't install the little fillets in the front outside corners of the baffle. The seals on the front of the cowl fill this area very well. I found that it would make the air filter removal on the left side difficult. I may put a finger sized fillet of RTV in the corners just to fill in the last little bit. Anybody else leave them off?

You talking about here on a horizontal injection cowl Jeff?

I don't think the plans call for it next to the filter. Its a bit fiddly to get one mounted. I was not sure this "mod" would stick. It has.
FYI the upside down flush rivet does not go through the filter mount. It only goes through the "L" bracket directly below so the side panel is loose when the 3 screws are removed for filter maintenance.

5551769464dacf97635567.jpg
 
Hey Mike,
A lot of folks suggest that you should be able to get your fist between the leading cylinder and inlet ramp. In stock form, the left side ramp was just about perfect, but I cut and re-glassed the right side (left in picture), moving it forward to approximately match the cylinder stagger.

Temps are quite even now in cruise, though #1 is a little hot still in climb. I've cut the air dam in front of it a little more, and will see if that helps on my next flight.


Thanks, Doug. Good picture. My RH ramp is about the same size as your old one. I'll probably open that up as you did.
 
Hey Mike,
A lot of folks suggest that you should be able to get your fist between the leading cylinder and inlet ramp. In stock form, the left side ramp was just about perfect, but I cut and re-glassed the right side (left in picture), moving it forward to approximately match the cylinder stagger.

Temps are quite even now in cruise, though #1 is a little hot still in climb. I've cut the air dam in front of it a little more, and will see if that helps on my next flight.


Doug,

When you modified the #1/3 ramp, did you have to install a new baffle seal in that area to close up the gap or was the existing seal able to conform? My plane is flying, but I would like to even things up, like you did, for better cooling. Just wondering if I'll need to re-do seal material in that area.

Thanks,

Larry
 
Mike,
That is not needed and is actually redundant if the Van's supplied baffle system and associated seals are installed as intended.

Scott,
The RV10 has the prop governor sitting into a cutout in the left ramp. It would seem that a lot of air will enter into the governor cutout and out the sides of the ramp if they are left open?? That air will be lost for cooling and reduce upper plenum pressure I would think.
No such problem on the right I believe because ramp surface is intact.
Is your statement true for the RV10 installation?
Thanks.
Johan
 
Scott,
The RV10 has the prop governor sitting into a cutout in the left ramp. It would seem that a lot of air will enter into the governor cutout and out the sides of the ramp if they are left open?? That air will be lost for cooling and reduce upper plenum pressure I would think. No such problem on the right I believe because ramp surface is intact. Is your statement true for the RV10 installation?

If an installation requires a cutout in the upper ramp, it can be sealed with flexible foam, or a solid recess can be built in to mirror the governor. Either way, there is no reason for a leak.
 
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Hi Larry,

The existing baffle seal worked just fine with the relocated ramp. I was prepared to cut some new seal pieces, but when I stuck my hand inside the inlet and pushed against the seals, they made nice contact on the ramp. Of course, it might vary depending on how your seals are cut.

Here's what mine look like. I went with a pretty decent overlap.

 
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Scott,
The RV10 has the prop governor sitting into a cutout in the left ramp. It would seem that a lot of air will enter into the governor cutout and out the sides of the ramp if they are left open?? That air will be lost for cooling and reduce upper plenum pressure I would think.
No such problem on the right I believe because ramp surface is intact.
Is your statement true for the RV10 installation?
Thanks.
Johan

No, that statement doesn't apply to an installation that has a fwd gov. (there were generalized comments implying it should be done in all circumstances... the reason for my comment). When a fwd gov. is involved, just closing off both ends of the inlet ramp does not seal the leakage path.

I think the RV-10 inlet ramp seals the outboard end so only the inboard end needs to be dealt with.

I cut a piece of soft foam to shape that can be glued inside the ramp, with an ~ half circle piece removed so that it conforms to the top side of the gov. body. It gets positioned laterally so that it aligns with where the upper baffle seal meets the inlet ramp
 
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Thanks Bill. I figured someone would show me just exactly how to add a new item to my list of thing to complete to get my plane in the air.
 
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