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Old 11-08-2022, 02:46 PM
penguin penguin is offline
Join Date: Jan 2005
Location: England
Posts: 1,170

Thanks for all of your thoughts
Originally Posted by hgerhardt View Post
Question: (maybe too late now, but) why didn't you start with a -7 cowl for an angle-valver? You shouldn't have to do any fiberglass mods that way. The -6 and -7 share the same firewall dimensions.
When starting out on a project like this there are always a few goals, mine were
- Save weight (goal is 70lb lighter) allows sensible fuel load at aero weight and some baggage when my wife is along.
- Save drag & go faster or further
- Repair the cowl and make it much easier to remove and refit

The cowl (an old non-honeycomb item that had been adjusted to accommodate the angle valve motor) was rather tired and every year at the annual need some repair. Plus it was not at all easy to remove and refit. I was offered a just delivered RV-6 lower cowl for a very good price. Remember that shipping anything from Van’s to England is really expensive, when shipping a cowling the price of the shipping approaches that of the part. So that made the decision to change the cowl as part of this process. At the time I wasn’t aware that the 7 IO cowl is wider than the 6 cowl. Once I had the cowl the die was cast.
Originally Posted by rvbuilder2002 View Post
I hate to be the bearer of bad news, but I think you should be prepared for some engine operational issues because of the shape of your modified snorkel. The 200 series fuel servo is very sensitive regarding clean inlet airflow. …
That very sharp turn that your snorkel shape takes as it changes to go aft into the fuel servo is likely going to cause problems.
I have already found that out! The original installation had an AFP extended inlet with a diverter valve. When I bought the aircraft I was instructed to select alternate air on the ground and ram air in flight. At low throttle settings, such as just after start up, the engine really struggled to run and needed constant large throttle movements to stop it quitting. Yellow arrow in picture below shows where the air enters in Alt Air.
Eventually I figured out that the FM 200 was getting very turbulent air. Selecting ram air on the ground made the engine run much more smoothly. The radius on the left hand lip of the snorkel is as large as I could make it (after reading some Dan Horton comments). It is substantially reshaped from the original profile. I hope it is large enough but am aware of the risk. Exactly what to do if it does not run smoothly is tomorrow’s problem!!

Talking to the original builder the cowl was intended to be the first iteration of an ongoing development, except he was having too much fun flying to move on to stage two! The scoop I cut off won’t really fit – needs to be higher up – I might have to rip off the scoop from an Extra cowl.
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