What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Sam James Cowl and Prop Extensions

kevinsky18

Well Known Member
Sam James / Show Plane Cowl and Prop Extensions

The Sam James and the Show Plane Cowl installation instructions call for a prop extension.

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?

Also what are the key differences between the Sam James and Show Plane Cowl? In short which is better and why?
 
Last edited:
Partial answer

kevinsky18 said:
The Sam James and the Show Plane Cowl installation instructions call for a prop extension.

If one knows a head of time that they are going to be using one of these cowls can you modify you 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?

Also what are the key differences between the Sam James and Show Plane Cowl? In short which is better and why?
I am not familiar with Show Plane.

With respect to the SJ cowl (and don't forget the plenum) the idea of moving the engine forward 1.5 inches would have significant effects on W&B and maybe on engineered strength. I also don't think it would fit the same. You would maybe have problems with the forward top of the plenum hitting the cowl.Best advice is to ask Will James about that.
 
The idea is generally to put more distance between the prop and the cylinder heads. So in answer to your first question, engine position doesn't preclude the need for an extension.
 
If you were able to move the engine forward safely the long James cowl would no longer fit. You already have a very tight tolerance on the upper forward portion of the plenum to the cowl and minimum clearance between the alternator pulley and the side of the cowl. Additionally you would greatly complicate the intake system as it is already tight between the carb (or servo if FI) and the front of the cowl and you must have room for the air fliter and connectors.

Hope this helps.

db
 
A couple more reasons.

The extension gives more room for the translation from round inlet to rectangular opening at the plenium. And allows a more streamlined cowl.

Mike
 
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.)

 
Last edited:
Just to add to what George said, the extended hub C/S props are not generally approved for acro.
 
No but

a compact hub and a 2.625" extension is not the same thing as an extended hub prop...Huh?...Well the compact hub prop don't care what its bolted to and according to Mahlon the extension will be fine on a C/S Lyc crank doing RV type acro....I.d normal, not high gyro load stuff like a Pitts or Extra will do.

Put it this way, I've gone to +5 and -1.5 and it hasn't fallen off yet...:)

Frank
 
I too had the same questions as I intend to use the Sam James Cowl. When I contacted them, I was told to tell MT ( the prop I was intending to use) and they would make the prop hub assembly accordingly. I also think that someone told me that the various engine builders could modify the engines to make up the difference. ( but don't quote me on that) The best thing to do would be to contact James Cowls. Hope this helps point you in the right direction.
Mike
 
Hartzell does make a extended hub blended airfoil prop for the James cowl, the part number is M2YR-1BF/F7497 and it is available for order thru Van's.
Contact John Popel at Hartzell for technical information.

John Popel
Technical Representative
Hartzell Propeller Inc.
Product Support
Phone: 937.778.4379
Fax: 937.778.4391
Email: [email protected]
 
George is usually very correct, but in the case of extended hub Hartzell's, both the "M" and the "E" extended hubs are available with the "BA" blades. Both the preferred "7497" and the earlier "7496" BA blades are available.

I believe the preferred CS prop for the James cowls is the M hub (2.56" extension) with the 7497 blades.

Check

Vans will order the prop for you for a price adder over the standard "C" hub BA.

Deene Ogden
EAA Tech Counselor/Flight Advisor
 
There is another option ...

kevinsky18 said:
The Sam James and the Show Plane Cowl installation instructions call for a prop extension.

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?

Also what are the key differences between the Sam James and Show Plane Cowl? In short which is better and why?
Think of another option as the **Will** James Cowl ...

It is dimensionally compatible with Van's STANDARD cowl.

It works with the standard, Lycoming carbureted O-360 with the standard Hartzell (or pick your favorite) propeller.

It works with the Sam James plenum.

No extensions on the prop.

James
{ I worked with Will James (Sam's son) to "get 'er done". }
 
I bought the plenum with the aluminum rings and the ram air induction from James. I am going to modify my stock Vans cowl to the round air intakes. I'll post some pictures when I get started on it. Don
 
AFAIK, there are no aftermarket cowls for the -8 that do not require an extension (both the James and Showplanes cowls DO require extensions for the -8).

Aerocomposites told me that they can make the prop with whatever hub is needed, and that there are no restrictions on its use:
"We machine our hubs for both standard and Sam James cowl installations on the RV-8 so you don't need any separate extension. There is no extra cost for the perfect fit hub. There are no restrictions placed on the hub."

Thomas
 
Ooops! My Oversight ...

TShort said:
AFAIK, there are no aftermarket cowls for the -8 that do not require an extension (both the James and Showplanes cowls DO require extensions for the -8).

Aerocomposites told me that they can make the prop with whatever hub is needed, and that there are no restrictions on its use:
"We machine our hubs for both standard and Sam James cowl installations on the RV-8 so you don't need any separate extension. There is no extra cost for the perfect fit hub. There are no restrictions placed on the hub."

Thomas
I missed the fact (in his signature) that he is doing an RV8. My comments apply to the side-by-side RV6/7/9 (A)s.

James
 
Last edited:
My Engine is an:

AeroSport IO-360-M2 (Parallel-Valve) ECI components
Horizontal Facing Induction.

Fixed pitch Catto 3 blade ( though I'm thinking I may change the prop as Craig is just not very responsive. I've sent two e-mails in two weeks and nothing. I've also heard he's really backlogged.)

I'm trying to keep this set up fix pitched.

Do you still get the ram air effect with the Show Planes cowl vs the Sam James with the small scope on the bottom?

Also Show Planes doesn't have a Plenum for their cowl. I'm thinking the Sam James Plenum probably won't fit. Would I be correct in that assumption?
 
Last edited:
Maybe

kevinsky18 said:
My Engine is an:

AeroSport IO-360-M2 (Parallel-Valve) ECI components
Horizontal Facing Induction.

Fixed pitch Catto 3 blade ( though I'm thinking I may change the prop as Craig is just not very responsive. I've sent two e-mails in two weeks and nothing. I've also heard he's really backlogged.)

I'm trying to keep this set up fix pitched.

Do you still get the ram air effect with the Show Planes cowl vs the Sam James with the small scope on the bottom?

Also Show Planes doesn't have a Plenum for their cowl. I'm thinking the Sam James Plenum probably won't fit. Would I be correct in that assumption?
If you install the SJ plenum low enough, as intended, I can't see why another cowl would not fit. The minimum height is a function of the prop spinner's diameter and then a line back to the top of the firewall. I don't know about the intake scoops, but the SJ cowl uses a neoprene cylinder to connect the plenum to the cowl, so there is room for small adjustments. The issue might be the location of the two intakes on the horizontal dimension. The vertical center is the same as the prop.

I feel that the SJ cowl with the scoop is giving me a ram effect. My GRT EFIS said 80% at 10,000 density altitude today. The intake path for the combustion air is very straight and goes through a K&N filter, but turns vertical at the throttle body in the airbox that comes with the cowl/plenum. With your horizontal induction you would want to talk to Will James about which configurations you could use.

I don't know how to compare props, but you might want to check out Prince props. See my website for link.
 
The question of doing aerobatics with a prop extension or extended hub has nothing to do with the extension or hub itself. It has to do with the increased stress it puts on the crankshaft and main bearing due to the weight of the prop being farther out from the bearing. This increases the moment on the crank and it is a question as to whether this could cause a failure of the crank or bearing. I don't think there has been a definative study of the issue and the numbers that are bandied about as to how many Gs you can do with an extension are probably just CYA guesses. Personally, I'm not going to worry about it with any maneuvers that I could potentially do. My Aerocomposites prop has a hub made to match the Sam James cowl. I think the lower weight of the prop may offset the extension to some extent with respect to the stress on the crank. Someone who is better at math than I am could calculate the loads on the crank with different prop weights and extension lengths.
 
Good to know thanks

deene said:
George is usually very correct, but in the case of extended hub Hartzell's, both the "M" and the "E" extended hubs are available with the "BA" blades. Both the preferred "7497" and the earlier "7496" BA blades are available.

I believe the preferred CS prop for the James cowls is the M hub (2.56" extension) with the 7497 blades. Check

Vans will order the prop for you for a price adder over the standard "C" hub BA. Deene Ogden EAA Tech Counselor/Flight Advisor
Thanks, good to know, but they do cost more Money right.
 
Last time I checked

And this was while ago, the M hub was about $800 more than the C hub...The Sabre extension will still cost $360 or so but for me the fact that somebody could change back to the Vans cowl made the extension the way to go.

As to the load on the Front bearing one only has to look at the unlimited aerobatics videos to see how many Lycoming have the end of the crank fall of.

Now this is not an engineeering study but there is no way I'm ever going to be doing a Kirby Chamblis in my 7a...I've barely gotten courage to fly the thing upside down for more than 5 seconds so far...:)

Frank 7a, SJ cowl, Chub + extension
 
Back
Top