|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

08-10-2017, 08:20 PM
|
|
|
|
Join Date: Nov 2015
Location: Osage, IA
Posts: 142
|
|
72" versus 74" inch Prop
Looking to buy a used prop for my -7 QB kit and see it is 74". Vans recommends a 72" prop for the 7. Is the extra prop length that big of a deal? If that one inch creates a significant prop strike risk I prob shouldn't be building an airplane. Opinions anybody?
Thanks,
Dave
__________________
RV7 QB started 1/17
Working on FWF
2020 dues sent
|

08-10-2017, 08:44 PM
|
|
|
|
Join Date: May 2017
Location: Madrid, Spain
Posts: 32
|
|
Interested as well
I'd like to know the answer to this also. I remember reading somewhere that the longer 74" was ok for a tailwheel, but 72" should go with a nosewheel. Then I was browsing props on the mothership website and one company (I believe Hartzell) had just the opposite, where they recommended a 74" for nosewheel and the shorter for a tailwheel, which defies the logical (to me) reason for one vs the other regarding prop strike potential. I'll be following.
|

08-10-2017, 09:27 PM
|
|
|
|
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
|
|
There are some rotary powered -6's & -7's (both nose & tail wheel) flying with 74" & 76" props. Given a choice, I'd pick the 74" over the 72". No downside on top speed, and better mass flow on the low end for improved climb performance.
Charlie
|

08-11-2017, 04:27 AM
|
 |
|
|
Join Date: Aug 2014
Location: Bowie MD
Posts: 886
|
|
Quote:
Originally Posted by rv7charlie
There are some rotary powered -6's & -7's (both nose & tail wheel) flying with 74" & 76" props. Given a choice, I'd pick the 74" over the 72". No downside on top speed, and better mass flow on the low end for improved climb performance.
Charlie
|
I could go either way on the M2, but I bought a 74 over a 72. I was told and also read that there is no difference in performance as the hub in the shorter prop has its course stop set slightly higher so that it takes a bigger bite of the air than the longer prop - engine speed wont change in any regime because the hub is set up to compensate appropriately. So the only reason I went with the 74 is it was available when I had cash ready and it gives me a small margin of rework over its life - the 72 is at its min size already. Price was the same. I also have bigger tires on the front than the standard 5x5s. Maybe consider what your prop clearance will be with one flat tire.
FWIW, my hub came off a Mooney w/72" blades. Also makes sense to me that in general a 3wheeler would have a shorter prop than a taildragger.
__________________
Mani
Busby MustangII (FoldingWing) Pending DAR.
Don't be a hater; I'm a cousin with thin wings! 
N251Y (res)
Last edited by maniago : 08-11-2017 at 04:46 AM.
|

08-11-2017, 04:43 AM
|
 |
|
|
Join Date: Mar 2006
Location: Gilbert, AZ
Posts: 1,628
|
|
Bigger is better!
My Hartzell is 78-inches. I have no issues with ground clearance. I have flown RV-8s with 80 inch props. Those with a nosewheel may have issues with a larger prop.

__________________
Ron Schreck
IAC National Judge
RV-8, "Miss Izzy", 2250 Hours - Sold
VAF 2021 Donor
|

08-11-2017, 06:13 AM
|
|
|
|
Join Date: Jun 2010
Location: Easley, SC
Posts: 40
|
|
Prop Length 72 vs longer
There is very little difference in performance. If your mission is aerobatics then the longer blades will give a bit of improvement in those instances. BUT, there is a large difference in noise. The longer the prop the greater the tip speed at a given RPM. As the tip gets closer to transsonic speed the noise and vibration increases a lot. If you want to sound like a Bonanza on take off roll then go with the longer one but be prepared for an earlier prop overhaul.
Tyler
A&P, EAA tech
|

08-11-2017, 07:35 AM
|
|
|
|
Join Date: Nov 2015
Location: Osage, IA
Posts: 142
|
|
Longer prop
Thanks for all the input guys. Love this site for stuff/questions like this.
Dave
__________________
RV7 QB started 1/17
Working on FWF
2020 dues sent
|

08-11-2017, 08:29 AM
|
|
|
|
Join Date: Nov 2013
Location: Harwinton, CT
Posts: 68
|
|
I have a 74" whirlwind on my 7A, still have over 9" ground clearance. No issues.
__________________
Charlie Luke
Connecticut, EAA Chapter 324
RV-7A
|
| Thread Tools |
Search this Thread |
|
|
|
| Display Modes |
Linear Mode
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 12:23 AM.
|