What's new
Van's Air Force

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

-7 Prop Choices/Confusion!

flyin_jibbs

Member
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 :D;)

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!
 
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?
 
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.
 
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.
 
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.
 
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?

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 :D
 
Last edited:
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...

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.
 
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..
 
Last edited:
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
 
Last edited:
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..

Speed "depends". I picked the BA 2 blade for my Rocket because its the "fastest" according to The Man himself. And at 2700 RPM I handily outpull the MT 3 blade on my buddy's (very fast) F-1. THAT SAID, he crushes me at 2300 RPM, and thats where I spend 90% of my flying time.

Im not a fan of the MT shipping, overhaul ritual and cost to own, but if I had to do it over, I'd probably go that way because on MY AIRPLANE, the MT would provide better performance overall than my Hartzell.

And for the record, I dont give a lot of thought about how a propeller "looks".
 
Kitplanes article WW vs. everyone else

Bang for the buck is probably a two blade Hartzell blended airfoil prop. They can be found used and IRAN'd for a reasonable price.

Whirlwind seems to have a slight edge on performance according to the Kitplanes article on the subject here https://www.kitplanes.com/whirl-wind-300/ but it comes at an increased cost.

Weight and balance can easily be adjusted by adding useful things like a vacuum drive back up alternator if you don't already have one, a second battery up front for your G3X panel back up, or a remote oil cooler bracket/mount which add up quick in weight to compensate for the lighter propeller if you indeed need some ballast up front.

If you're going from a fixed pitch propeller to a composite prop the weight issue is in reverse as in the CS props are almost always heavier than the FP it replaced. Definitely easy to add weight vs. removing it.

Best of luck and let us know which direction you go. It is a bit disconcerning that WW isn't getting back to you in a timely manner, lets hope everything is going well over there.:)
 
If you can overhaul your prop that by far is the least expensive option and probably the fastest. I had a prop strike at Airventure this year and my Hartzell BA prop was toast ( Dug a trench with it). Looked at ordering a new Hartzell BA but the wait time was truly excessive (7 plus months at least) with a price over $17.5K.

Explored other options and decided the MT three blade with the heavy duty hub,in my case, was an excellent option. Several people I know have the prop and were satisfied. The advantages over a WW were the lack of annual maintenance requirements and a 2,500 hour overhaul versus 500 hours for the WW. Also, MT doesn’t impose any rpm restrictions for EI systems as Hartzell does and I’m converting to dual PMags with the tear down/rebuild. Availability through MacFarland was immediate and at a lesser price than the Hartzell.

I’m told the three blade MT9 that I’m getting will be smoother, quieter and lighter than my Hartzell. Since my RV7A is a bit of a porker (1,187 lbs) a few pound weight reduction is not a bad thing. Performance, I’m told, is better in climb and cruise but top speed will likely be a few knots lower. Since I don’t fly near Vne that shouldn’t be an issue. We’ll see pretty soon.
 
Last edited:
Speed "depends". I picked the BA 2 blade for my Rocket because its the "fastest" according to The Man himself. And at 2700 RPM I handily outpull the MT 3 blade on my buddy's (very fast) F-1. THAT SAID, he crushes me at 2300 RPM, and thats where I spend 90% of my flying time.

Im not a fan of the MT shipping, overhaul ritual and cost to own, but if I had to do it over, I'd probably go that way because on MY AIRPLANE, the MT would provide better performance overall than my Hartzell.

And for the record, I dont give a lot of thought about how a propeller "looks".

I’ll second the fact that the MT prop doesn’t seem to lose speed at lower RPMs.. I delivered a -7 and it was the same speed at 2700 as it was at 2100 rpm. It didn’t seem to care.
 
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

Larry, thanks for brining that up! You're right! I hadn't done those configurations because for me that flight scenario is very last/most unlikely on my list of use cases. However, after reading your thoughts, I definitely needed to run those numbers on 4 more configurations, and you're right.

Whether its me and a 200lb buddy or the wife and I, with full fuel and 75lbs in back i barely keep it inside and of course as fuel starts getting down there it works its way out of CG.

(Conversely if its Me and 200lb buddy or the wife and I and 0 baggage, Full and Low fuel, it stays in CG in all 4 of those configurations)

Again for my use case, these scenarios would be the least used, if ever, configuration. The only person id really ever travel with along with alot of baggage would be the wife, and Im pretty confident that will never happen (a: she's not a fan of flying and b: when we travel together for anything overnight we have to take the SD Tremor along with our two 110lb Rotties, (also no kids) they're too much to leave in the hands of other people).

And when/if I go out to camp or fish with my buds, well, they have their own rides ;)

My use case will be primarily travel for work while having alot of fun doing it!! Of course along with joy riding and lunch runs etc. But after 15 years of commercial travel im over TSA and all their silliness, layovers, lost bags, cancelations, weirdos sleeping on you etc hah!

Now Im finding myself stuck on the 2 vs 3 blade dilemma which again will further inhibit the 2 people + bags envelope (1lb difference from my weight with these aforementioned calcs).

So overall, you're right it does inhibit the utility a bit, but nothing that will take away from my user experience. And if that time comes when its important, well, maybe I can convince the wife I need another plane :D

Sorry for the long winded response but making this thread was actually very helpful so thanks!
 
Last edited:
I’ll second the fact that the MT prop doesn’t seem to lose speed at lower RPMs.. I delivered a -7 and it was the same speed at 2700 as it was at 2100 rpm. It didn’t seem to care.

You should not assume any propeller has a linear efficiency curve over a range of RPMs.

For MPG, I found my two bladed, 74” Hartzell BA to have best cruise efficiency at 2480 RPM. This drops off (slowly) at both higher and lower RPM settings. Best to do careful data runs to determine your own sweet spot as there are many variables at play.

My new cruise sweet spot is 2480 and 9K’ (RV-8, IO-360M1B with AFP FM-150C).

Carl
 
Back
Top