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RV-4 Cowl Differences - Exhaust Bulges

C

CATPart

Well Known Member
Some cowls have exhaust bulges at the bottom (Style 1) and some have a smooth bottom (Style 2). Did these come with the cowl from Vans? Are these added or removed by different builders as an option? Did Vans remove these from the design at some certain year, if so when? Just curious because I see less RV4s with Style 1, which leads me to believe they are the older kits.
Thanks!

P.S. These are random pictures I borrowed from google, so thank you if one of these RV4s are yours. :)

RV4_Cowl_Styles.JPG
 
Our RV that was built in 1989 has the bulges in the cowling. The cowling on the new RV-4 in process doesnt.
 
Bulges

The cowls as far as i know all come without bulges. Until you fit your exhaust you don't know if there is enough clearance in the cowl. You can go several ways with the exhaust so builders generally customise the cowl to fit the exhaust.
 
Mine was built in 89 as well but has no buldges. Im about fourth in the line of owners so it may have been replaced along the way, or maybe 89 is the year Vans changed it, or as stated above it may be spmething the builder would have had to do or not do.
 
Mine was finished in '97 (the kit was bought in '88) and has the bulges. As stated above, I am about the 4th owner so I don't know if it came that way or not.
 
Could it be that the cowl with the "bulges" is for the 12" spinner, and the "no-bulge" cowl is for the 13" spinner?

Was there ever a 12" spinner? Just musing out loud.........
 
May depend on the FAB

My cowl is an old polyester gelcoat and has the bulges. Looking carefully at the pictures, it looks like the flat-bottom cowls have the FAB scoop mod. Depending on how you fiberglass this on, you may end up with no or smaller bulges. I have the 360 FAB scoop but kept my bulges since they accommodate the 4-pipe Vetterman exhaust perfectly.
 
More info on this.

Hi All,

I have now been informed by someone in the know that there were various incarnations of the cowl that have been supplied by Vans, some with exhaust bulges, some flat, as the cowl was developed.

So, I guess the correct answer to the question is that some cowls were made with bulges by Vans some were not, while others like mine have been modified by the builder.
 
Two styles of cowl....old,new

Two different styles of cowls there......Notice the two on the left have a much smaller spinner, thats the old style cowl. Cowls did not come with the bumps on them, that would have been a builder mod.
 
Cowls

Bottom left picture if I'm not mistaken is from G-BULG and this was a new cowling supplied by Vans about 4 years ago, not the "Constant Speed" cowl but similar to the original with a prop extension. Google the reg and you will see the original cowl.

Happy Flying
Rob
 
Well I guess we have some conflicting opinions thus far. Wam120rv thinks the bulges came from vans, Marc D. thinks they did not come from vans. I am not sure if rv8or is saying whether or not the bulges came from vans, but I do agree it is the aircraft he identified.

rvator51 did you build your 1989 rv4, therefore you know first hand that the bulges came with the cowl or not?

Thanks for the responses so far.
 
Mine is an '85 kit registered in '87. It looked like the upper left when I got it. I added the fab and glassed on a scoop I got off a wrecked cowling. Also included with the sale was an "untouched" old style cowl that didn't have accomidation for a fab but both cowlings have the exhaust bumps. These were made this way.
 
I've built/owned 5 RV 4's, the older ones all had the exhaust outlet 'bumps' and the air inlet snorkels were squared off at the top. The newer cowls had the smooth lower cowl with the rounded air inlet snorkels. If you are looking for the year I don't have it.

The point I think the OP did want to know is that the builders did NOT add the bumps for the exhaust on those airplanes.....Vans aircraft put them there.

BTW, the RV cowl in the top right of your photo was one of my RV4's :D. That poor airplane doesn't have 50 hours on it since I sold it 5 or 6 years ago :confused:.

Here's a better pic:




CATPart said:
Well I guess we have some conflicting opinions thus far. Wam120rv thinks the bulges came from vans, Marc D. thinks they did not come from vans. I am not sure if rv8or is saying whether or not the bulges came from vans, but I do agree it is the aircraft he identified.

rvator51 did you build your 1989 rv4, therefore you know first hand that the bulges came with the cowl or not?

Thanks for the responses so far.
Click to expand...
 
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I was waiting for you to chime in Rick. Yes I wanted to know if Vans put the bumps there, as a device for me to judge the age of the kit should the owner not know. I am more fond of the smooth bottom cowl, but in my seemingly eternal search for an RV4, I will buy what comes first. Rick you know I'm pretty crazy about the details...now go secure a deal on that 50 hour plane for me :)
 
The Long and Short of it...

Easy to spot an older cowl, just look for angled air intakes. When I purchased my RV4 finish kit in 95' Van's offered two cowls, constant speed and fixed pitch. Though both were the white vinylester the differences were in the front. Neither had bumps, at least in 95'.

The FP cowl had the nose extension for the spinner 4" forward of the air intakes to supplement a 4" prop shaft extension. The air intakes are angled slightly forward. The C/S cowl was squared off even with the air intakes. When Van switched to the pre-preg cowls in 97' they eliminated the "long nose" cowls and all are squared off even with the air intakes.

V/R
Smokey


Constant Speed Cowl (now standard)



Fixed Pitch Vinylester Cowl (pre-97')
 
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Cowls

I have given some bum information.
The cowls on G-Bulg were repaired after a small mishap, I thought they were replaced so these cowls are the original cowls from the build modified on a change to the aircleaner.

Happy flying
 
Thanks Smokey. I had not yet picked up on that difference. This leads me to one slightly off topic question for the long vs short fixed pitch cowls. Will a newer fp rv4 have no prop extension and therefore be 4 inches shorter from firewall to prop when compared to an older one? I assume the engine mounts hold the engine in identical locations.
 
Cowl length

I don't believe the current -4 cowl is a full 4" shorter than the old FP cowl. Instead, I believe a ~2 1/2" extension is used for fixed pitch props to approximate the installed length of a constant speed prop.

Aside from the exhaust bulges, length variations, and intake configurations, I believe the RV4 cowl was changed from a 12" diameter spinner ring to a 13" somewhere along the line. Others can confirm.

To throw in some more variables, the Sam James RV4 cowl has a 13" diameter spinner ring, a length suited to a 2 1/2" extension FP (or no extension with CS), and an intake too small to fit a filter. Most folks hack off the SJ air intake and replace it with a larger one to accommodate the FAB or other intake system.

m
 
pre peg cowl 2 1/4 extension

the yellow -4 bottom right was one of if not the first pre peg cowl and the fit was terrible. still is. I believe my extension is 2.25 in. and the spinner back plate is 13 inches. I think I bought the finish kit in 99 or 2000.

CM
 
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