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  #1  
Old 12-08-2022, 12:49 PM
flyin_jibbs's Avatar
flyin_jibbs flyin_jibbs is offline
 
Join Date: Jun 2022
Location: South Lake Tahoe
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Default -7 Prop Choices/Confusion!

Hi all,

Just to get it out of the way, I am NEW to Vans and planes altogether! Im a 15 year career helicopter guy buying my first plane. Ok, so self disclaimer out of the way.

Now, I am looking for a new prop for a -7 I have just bought. I would like to go composite, 2 blade. The current prop is the older alum version that is also well out of its 6 year overhaul spec.

So I have made a few phone calls to both Vans and Hartzell, as well as still waiting to get somebody on the phone at WW.

Vans doesn't list/won't sell a 72" Comp C/S prop because they never (for unknown reasons to them) vibrationally tested the 72" version, and dont plan to. They do however list the 74" but it isn't "recommended" for the -7, only the 6A, 7A and 8/8A, and 14A....

The rep did tell me however hes sold numerous 74" to -7 owners. And of course there is a few out there on -14's, but I assume that one sits higher? Even though its still not on the recommended list from Vans. Lookin at you Steve (FlightChops) haha

So whats the deal? Is the 74" too close for comfort on clearance? Lack of in depth knowledge question here but what makes the -8 any different/better than the -7 or -14 for that matter?

Im still likely leaning towards a WW if I could ever get them to answer/call back/provide info but Im just so confused on the Hartzell/Vans deal...

Any insight greatly appreciated by this newb!
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  #2  
Old 12-08-2022, 12:57 PM
BobTurner BobTurner is online now
 
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Location: Livermore, CA
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Default

Something you didn’t mention: take a look at your weight and balance. Putting a lighter prop on the nose will move the cg aft, maybe too much?
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  #3  
Old 12-08-2022, 01:32 PM
Desert Rat Desert Rat is offline
 
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Location: Wichita KS
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Default

I think Vans recommendation on prop diameters is based on certified airplanes. It's in the FAR's somewhere (pt. 23?) that a trike needs 7" of ground clearance and a tailwheel needs 9" in takeoff or taxi attitude, whichever is less.
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  #4  
Old 12-08-2022, 01:37 PM
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sahrens sahrens is offline
 
Join Date: Jan 2007
Location: Battle Ground WA
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Default 74 not recommended

The 74” prop is not recommended for the RV-7 due to clearance. If you over rotate forward on a firm landing the prop can contact the runway surface. I don’t know how many, but there have some incidents. I have the aluminum blend airfoil and even with the weight my baggage compartment is restricted to 80 lbs due to CG.
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  #5  
Old 12-08-2022, 01:49 PM
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Mark33 Mark33 is offline
 
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True, you can run a 72” or a 74” on your -7, but as you said, it’s not “recommended”. It’s certainly your decision, but for the money and performance, it’s hard to beat the 72” Hartzell BA aluminum prop for your -7. The -7 tends to be a little on the tail heavy side, so you may want to think twice about loosing any weight on nose which you’ll get with a composite prop.
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  #6  
Old 12-08-2022, 02:43 PM
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flyin_jibbs flyin_jibbs is offline
 
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Quote:
Originally Posted by BobTurner View Post
Something you didn’t mention: take a look at your weight and balance. Putting a lighter prop on the nose will move the cg aft, maybe too much?
Quote:
Originally Posted by Mark33 View Post
True, you can run a 72” or a 74” on your -7, but as you said, it’s not “recommended”. It’s certainly your decision, but for the money and performance, it’s hard to beat the 72” Hartzell BA aluminum prop for your -7. The -7 tends to be a little on the tail heavy side, so you may want to think twice about loosing any weight on nose which you’ll get with a composite prop.
Thanks gents! I ran 4 different bar napkin (not really, I typed it on my mac note pad) configurations for an extreme circumstance regarding the weight change. I penciled it with a 20lb weight loss (Ive read the WW's are about 18lbs difference from the Hartzell BA). And the 4 configs are my most common would be scenarios: Full & low fuel + me + 75lb baggage and Full & low fuel + two 200lbs pilots and no baggage.

All calculations came out within CG range as well as within MGW for non-acro flight. So just for bar napkins sake, it looks as though should this particular airframe lose 20lbs it should be ok.

FWIW, it does have a Garmin G3X IFR suite up front, so maybe that helps with a little weight up front? I also could be completely off but I used all of Vans posted stations along with the W&B data pulled from most recent update in the log books and adjusted Empty CG accordingly which may not be 10000% precise but should be very close..? But it appears to have the range for the weight loss unless Im really blowing it here

Last edited by flyin_jibbs : 12-08-2022 at 02:48 PM.
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  #7  
Old 12-08-2022, 03:01 PM
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Untainted123 Untainted123 is online now
 
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Location: Azle, TX
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Default

Quote:
Originally Posted by flyin_jibbs View Post
I would like to go composite, 2 blade.
I won't question someones tastes, so if you are doing this because you like the looks/sound/etc then go for it, but...

Quote:
Originally Posted by flyin_jibbs View Post
The current prop is the older alum version that is also well out of its 6 year overhaul spec.
There is another (actually a couple) prop thread that just popped up yesterday discussing prop overhauls. I got my Hartzell "older alum version" prop that hadn't been overhauled in 12 years IRAN'ed and repainted to shiny new (the blades were still in good condition) for about $1100. I am guessing that is way cheaper and faster than getting a new prop from Van's/Hartzell or WW.
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  #8  
Old 12-09-2022, 09:43 AM
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Jpm757 Jpm757 is offline
 
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Don't rule out the MT option.
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  #9  
Old 12-09-2022, 10:26 AM
Taltruda Taltruda is offline
 
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Quote:
Originally Posted by Jpm757 View Post
Don't rule out the MT option.
MT would be my LAST choice.. every MT prop ove seen gets these cracks in the finish. They say it’s not structural, but boy are they ugly. Also perhaps it’s just a coincidence, but MT props seem slower than other planes. I really like the new stuff coming from WW..
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Last edited by Taltruda : 12-09-2022 at 10:31 AM.
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  #10  
Old 12-09-2022, 11:13 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by flyin_jibbs View Post
TAnd the 4 configs are my most common would be scenarios: Full & low fuel + me + 75lb baggage and Full & low fuel + two 200lbs pilots and no baggage.
Are you sure you are OK with 2 passengers with 0 allotment for baggage? Would seem to be a large hit to the plane's utility. I added a 20# crush plate to my 6A. DOn't like what it does to handling, but was unwilling to settle on 15-20#'s of baggage with a passenger.

Larry
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Last edited by lr172 : 12-09-2022 at 11:15 AM.
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