Oh no don't do that, please
kevinsky18 said:
The Sam James and the Show Plane Cowl installation instructions call for a prop extension.
You don't need extensions any more with the SJ cowl. He now has a no extension cowl as I understand it.
"A shorter length, carburetor version of the RV-6, 7, & 9 is available for use without a prop extension."
http://www.jamesaircraft.com/Our_Products.html
James aircraft have been solid laminate cowls but I think he is now working on honeycomb cowls like Vans new epoxy cowls (which have been in production for many years). The honeycomb cowls are stiffer and lighter, emphasis on lighter. Nothing wrong with solid laminate, just weight and local stiffness. I think he also uses polyester resin not epoxy. Epoxy is more stable and shrinks less with age, but don't quote me on that, ask Jame's aircraft.
Show Plane does need a extended prop.
http://www.showplanes.com/index_1024.htm
If one knows a head of time that they are going to be using one of these cowls can you modify your engine mount to have the engine a few more inches forward to avoid the need for the prop extension? or does the cowl actually require the engine to sit further back to get the cowl to fit right?
Oh golly! Don't think about extending engines and changing mounts. Keep It Simple Stupid - KISS is what I tell my self. Besides you only will run the engine alternator, starter, flywheel into the cowl. A PROP extension does not = moving the engine forward, trust me. The idea is move the blades fwd of the engine, not the engine further from the firewall. Two different things.
Also what are the key differences between the Sam James and Show Plane Cowl? In short which is better and why?
The Show Plane is for RV-8 only, has honeycomb core epoxy construction (like the new stock Van cowl). Sam James latest and greatest I believe may now be honeycomb (as opposed to solid laminate like Van use to make his cowls). However I think he still uses polyester resin? Ask the manufacture. The Vans and Show Plane cowls are epoxy (lighter).
The show plane is set up to use vans stock Fwd Air box, with the filter in the left cowl inlet, aka no scoop. If you go with vertical induction you need to modify the cowl with a scoop.
With SJ's cowl and fwd induction you end up with a little scoop in the fwd part of the cowl. With vertical induction he can supply the scoop attached already I believe in some models. Read the site.
Here is the big advice: IT ALL HAS TO WORK TOGETHER. You have to start with what engine, induction and prop you are going to use. Now you could choose a engine, induction or prop to match the cowl of choice but that is backwards. You can make choices that will make your life miserable. Pick a combo that is worked out and has bolt up parts. Other wise you will need to invent solutions that will either take 100's of hours or 1000's of extra dollars with little gain.
Keep in mind forcing yourself into an extended prop situation is no big deal with a fixed prop, however with constant speed it becomes troublesome and expensive. The best constant speed prop for the money and with out equal in performance is the Hartzell BA prop. It does not come in an extend version. There is a Lancair prop out there or a extended version for the 320 that will fit the extend cowl but they cost more and are not ideal for the RV, at least compared to the BA (blended airfoil prop).
Next is induction, vertical and horizontal. If you go with a short cowl you run into issues with fwd facing induction. I have not TURN ON for fwd induction. It actually makes it hard to install and airbox. However Van's HORZ-FAB is very nice but will only work with the short Show Plane cowl. Not sure you can use it with the James aircraft cowl. If you don't mind a lower scoop, than the Sams Aircraft is set up for that. Show Plane has only one induction option. Make sense.
Cart > Horse > order. Pick engine, induction and prop. James aircraft has more options, however if you are going to pick a IO360 (200hp), MT prop and vans airbox, than the Show Plane will work well. Bad news is if you use a MT prop, you may give up 8 mph from the faster Hartzell BA, which cuts into the gain of using a custom cowl? Not hostile about the MT but its not a "speed prop" its a unique (very expensive to buy and maintain) wood/fiberglass German prop. I understand the appeal I want to buy a german 911 for really no good reason. However the American made Hartzell BA is specifically made for the RV and shown to be much faster than any other prop. (Here is vans test, click, the BA prop is second from top, in yellow.)