"G" Limits w/ 4" Spacer (& Sam James Cowling)?

A friend informed me that he read of some potential "G" limitations when using a Sensenich FP prop with the 4" spacer required for the sam james cowl. The Sam James FAQs list some reference to a 3.5g limit, but it sounds very unclear. Does anyone have more information on this?

Also, I was told this might be negated with an aerobatic "A" version of the 0-360 with beefier bearings. Do Mattituck and others sell the "A" version of the 0-360 in new clone form?

Any help is appreciated. I already have the prop and spacer, and the cowl is on order.

Thansk,
Scott
7A Wings
www.scottsrv7a.com

You are the test pilot

You are in experimental land and this configuration is untested. You are hanging an experimental prop on an engine with an experimental extension. I am sure the people who sell the extension or the cowl might say no problem, but from an engineering stand point that is shoot from the hip. Call Lycoming and tell them what you want to do.

Common sense would say aerobatics or G's would or should be limited to well below 6 G's. The Hartzell with extended hub reduces the G's to 3.6(?).

I took the stock cowl and did the NACA/Lopresti mod using the Dave Anders aluminum rings (Like a Sam James cowl).

Cheers George

tx_jayhawk said:

A friend informed me that he read of some potential "G" limitations when using a Sensenich FP prop with the 4" spacer required for the sam james cowl. The Sam James FAQs list some reference to a 3.5g limit, but it sounds very unclear. Does anyone have more information on this?

Also, I was told this might be negated with an aerobatic "A" version of the 0-360 with beefier bearings. Do Mattituck and others sell the "A" version of the 0-360 in new clone form?

Any help is appreciated. I already have the prop and spacer, and the cowl is on order.

Thansk,
Scott
7A Wings
www.scottsrv7a.com

Click to expand...

Scott,

Why don't you get the cowl that does NOT require the extension?

Looks like you have the carbureted O-360 and if so, give Will James a call. He has a cowl now that should be the same "dimensions" as Van's.

James

Scott,

Vans should know the answer for sure. They're selling the spacer and it was for their "old style" cowls that were longer than the new ones. Does it mean that all old RVs that used this combo had this limitation?

I'd contact them and check up on it. Please do let us know what they say. I'm interested, as I'm planning on same prop/cowl..

Thanks!

I think you have been mislead about aerobatic versions of O-360s having larger bearings - I believe the only change is in the oil system (and mostly extenal to the engine). O-320s are a different matter entirely. Mahlon at Mattituck might be able to help you by phone?

A Hartzell prop is significantly heavier than a Sensenich - my O-320 Sensenich weighs 40lb with bolts & spinner, I believe a Hartzell is approaching 60lb. So mounting a 40lb prop 1 1/2 inches further out may not exceed the loading imposed by the heavier prop? If no one else can offer any advice you may have to do the math and decide what risks you are willing to take.

Pete

sam james cowl?

woud some one tell me what a sam james cowl is. Thanks

Sam James Cowl

Try this link http://www.jamesaircraft.com/

What is Sam James

Here is his web site:
http://www.jamesaircraft.com/

Sam Makes the Holly cowl (w/ circular inlets), pressure plenum along with wheel pants. The cowl is longer than Vans current stock cowl by about 1.75".

If you are using fixed pitch a Sam James cowl needs a 4" extension. If you want constant speed prop you need the extended hub type Hartzell: F2YL-1F/7663-4 prop or F2YR-1F. These props are limited to 3.8g's and are equiv to 4" extension on a fixed pitch prop. These props weigh 57lbs.

Fixed pitch props back in the day where usually very light wood props. Now one of the best fixed pitch prop choices are the metal Sensenich, which I am told it about 40lbs. If the Hartzell with the extended hub

So what is the G limit with a 40-lb Sensenich? (well a little engineering ratio)
If a 57lb prop on a 4" extension is certified to 3.8g than a 40lb prop:
3.8g x 57lb/40lb = 5.4g

This is not scientific and the strength of the fixed prop hub extension is unknown, but check with the manufacture to see what they say.

George

(Van's A/C used fixed pitch and constant speed props many years ago. The fixed pitch was equiv. to Sam James cowl and the shorter cowl was for constant speed props. Van standardized all airplanes (fixed and c/s) to the short cowl which works with the common Hartzell HC-2YK c/s prop, which is equiv to a 2.25" prop extension on a fixed pitch prop, so the 4" extension fell out of use. Read Van's online catalog for more info.)