Van's Air Force
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RV-4 cowling question.
- Thread starter AX-O
- Start date
randylervold
moderator
No problem, just use the FAB-360.
gmcjetpilot
Well Known Member
Same same
There is a difference in 320/360 scoop, in that the 360 scoop is a little larger/deeper to accommodate the bigger taller carb.
It has less to do with lateral alignment from sump offset and more to do with depth from the larger 360 carb and air box.
In the old days Van left the scoop off and the builder had to bond on the scoop 320/360 scoop. There was some discussion about offsetting the the scoop but center line is where I put mine. The air box can be angled to make alignment.
Later Van supplied cowls with the scoop pre-installed onto the cowl and thus a 320 or 360 cowls. There where also long and short cowls but all became short cowls. If using a constant speed prop you will want the short cowl. If you have fixed it does not matter, as you can buy a compatable prop extension to match the cowl (ie long or short).
When you install the air box you angle it to match up with the cowl scoop inlet regardless of the sump you have. The scoop postion is nominally on the center line. You will not know about alignment of air box and cowl until you install the cowl.
There are different 320 Lycoming sumps, with different offsets. Again I would make that compensation with a centered scoop.
Worst case scenario is you cut the old scoop off and bond and glass on a new 320 scoop. However that is what you may want to do anyway, not for alignment but because it's smaller and has less depth. The difference in drag between a 320/360 scoop is small, but the 320 nicer looking being less bulky from the side view.
It sounds like a lot of work to put a new scoop on but its not too bad. I did one on a RV-4. Replacement scoops are avaiable from Van. I put mine on the center line and angled the air box slightly to make the alignment. You really don't want the scoop offset too much because it looks weird. That is what I recall the old builder plans called for, but you can deviate from that. Later Van put the scoops on all cowls for all engine sumps.
http://www.vansaircraft.com/cgi-bin...-256-279&browse=engines&product=cowl-airscoop
Of course you want a 320 FAB (filtered air box), but if you stick with the 360 scoop you might be able to mix and match and use the larger 360 air filter. The filter is bigger in the 360 FAB and it may fit the 360 scoop better. The larger filter element of the 360 on a 320 will not add performance or HP but will does have more area. This means it will not get as dirty as fast, so maintenance periods will be longer. (larger filter is not more flow just more area to get dirty.)
http://www.vansaircraft.com/cgi-bin...6-256-279&browse=engines&product=fab-vertical
You may want to consider selling your old cowl and buying a Sam James cowl and plenum, if you have some spare cash (lots of spare cash). You can expect up to 7 mph increase in cruise and the cowl pins will not be under as much stress. The Sam James cowl is designed to use a pressure plenum, not relying on the cowl to hold upper cooling air pressure.
If you have a I0-360 angle valve 200HP you would have to mod the cowl to make it fit, because the 200HP engine is wider and the fwd induction.
same same one size fits all.................. (well kind of sort a)
There is a difference in 320/360 scoop, in that the 360 scoop is a little larger/deeper to accommodate the bigger taller carb.
It has less to do with lateral alignment from sump offset and more to do with depth from the larger 360 carb and air box.
In the old days Van left the scoop off and the builder had to bond on the scoop 320/360 scoop. There was some discussion about offsetting the the scoop but center line is where I put mine. The air box can be angled to make alignment.
Later Van supplied cowls with the scoop pre-installed onto the cowl and thus a 320 or 360 cowls. There where also long and short cowls but all became short cowls. If using a constant speed prop you will want the short cowl. If you have fixed it does not matter, as you can buy a compatable prop extension to match the cowl (ie long or short).
When you install the air box you angle it to match up with the cowl scoop inlet regardless of the sump you have. The scoop postion is nominally on the center line. You will not know about alignment of air box and cowl until you install the cowl.
There are different 320 Lycoming sumps, with different offsets. Again I would make that compensation with a centered scoop.
Worst case scenario is you cut the old scoop off and bond and glass on a new 320 scoop. However that is what you may want to do anyway, not for alignment but because it's smaller and has less depth. The difference in drag between a 320/360 scoop is small, but the 320 nicer looking being less bulky from the side view.
It sounds like a lot of work to put a new scoop on but its not too bad. I did one on a RV-4. Replacement scoops are avaiable from Van. I put mine on the center line and angled the air box slightly to make the alignment. You really don't want the scoop offset too much because it looks weird. That is what I recall the old builder plans called for, but you can deviate from that. Later Van put the scoops on all cowls for all engine sumps.
http://www.vansaircraft.com/cgi-bin...-256-279&browse=engines&product=cowl-airscoop
Of course you want a 320 FAB (filtered air box), but if you stick with the 360 scoop you might be able to mix and match and use the larger 360 air filter. The filter is bigger in the 360 FAB and it may fit the 360 scoop better. The larger filter element of the 360 on a 320 will not add performance or HP but will does have more area. This means it will not get as dirty as fast, so maintenance periods will be longer. (larger filter is not more flow just more area to get dirty.)
http://www.vansaircraft.com/cgi-bin...6-256-279&browse=engines&product=fab-vertical
You may want to consider selling your old cowl and buying a Sam James cowl and plenum, if you have some spare cash (lots of spare cash). You can expect up to 7 mph increase in cruise and the cowl pins will not be under as much stress. The Sam James cowl is designed to use a pressure plenum, not relying on the cowl to hold upper cooling air pressure.
If you have a I0-360 angle valve 200HP you would have to mod the cowl to make it fit, because the 200HP engine is wider and the fwd induction.
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