Two RV-7 cowls, but different size of the inlets. Any ideas to why?

I discovered something strange today: the cowl-inlet on my newest RV-7 is actually alittle bit SMALLER than the inlet on my oldest -7....

Here's a couple of pics of the oldest cowl:






The height of the inboard edge is about 10 cm, and the height of the outboard edge is about 8 cm.






Here's a couple of pics of the newest cowl:





The height of the inboard edge is about 9 cm and the height of the outboard edge is about 7 cm.





When you look at both cowls at the same time, you can see the difference:








The oldest finish-kit was bought from Vans early in 2007 and the newest was bought late in 2010.

Does anyone have any idea as to why the cowl openings got smaller? Better cooling? Less drag?


Both -7's have fine engine temps etc, so I'm just courious if anyone knows anything about this?

The newer cowl looks wider than the older cowl. Maybe it's the same cross-sectional area, just shaped a little differently?

Are the two spinners the same size?

If they are different, it is understandable.

Spinners and width

Good point about the width of the inlet! I'll check tomorrow and report back.

Spinners: I don't know for sure: the blue one is a spinner from M/T, bought together with the M/T prop.

The green one is a spinner from WW, bought together with the RV200 prop.

I'll measure both spinners tomorrow and report back.

It looks like the green cowl might have been trimmed more at the center joining line.

Check the bottom edge of the cowl "spinner flat". It looks like there may be more of that "flat" exposed on the blue one.

Trimming could certainly account for at least 1 cm in a vertical direction.

Perhaps one cowl is for a 0360 the other a 0320.

Reason found...

I measured the opening width today and both cowls had the same horizontal size: 21 cm (measured from the inboard corner to where the ruler touched the FG)






Then, it was only one more measurement to do; the circumference. That gave me the sollution... Bill and Gill sure had it nailed: the green spinner (WW) has 6-7 cm smaller circumference than the blue (M/T) one....

Voila: reason found...

The size of the spinner has nothing to do with the fact that the opening is smaller. I measured an RV6 cowling with a hartzell CS speed 16 years old vs mine which was finished 2013 which is considerably smaller like your green one. Perhaps this also explains why his temps are lower than mine when we climb together. There are a couple square inch differences.
Jack

Smilin' Jack said:

The size of the spinner has nothing to do with the fact that the opening is smaller.

Click to expand...

It sure does... and big time. Trimming the cowl down for a good spinner fit will change the size of the inlet.