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74 inch verse 72 inch

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rv7a.builder(at)yahoo.com
Guest

Posted: Thu Apr 19, 2007 12:04 pm Post subject: 74 inch verse 72 inch

Hello Group,



  I am about to order the engine and prop for my

RV-7A. The Hartzell constant speed prop comes either

72" or 74". Ken at Van's could not give me a

compelling reason to go either way with a nose wheel

plane. Does the group have any thoughts?. Thanks. JR



__________________________________________________

klwerner(at)comcast.net
Guest

Posted: Thu Apr 19, 2007 12:10 pm Post subject: 74 inch verse 72 inch

I'd go 74"

 [quote]   ---

tylerii(at)infoave.net
Guest

Posted: Fri Apr 20, 2007 6:21 am Post subject: 74 inch verse 72 inch

74 is more noise a lot more...maybe a little better climb....less groung

clearance....no real cruise improvement.... I went with 72 inch on a RV7A

with IO360/180 w/LS PII

TANGOBRAVO



--

klwerner(at)comcast.net
Guest

Posted: Fri Apr 20, 2007 6:50 am Post subject: 74 inch verse 72 inch

Good points, the ground clearance is  1" less on the 74", but I believe (don't hold me to it) the service limit is 72"  on these props, so if you ever would damage the 72" with a need to cut it down a  bit, you are already there!!!  The 74" has an inch on each blade that you  could work with. It should also have a little bit more  thrust (theoretically) then the 72".  It is your choice,   and do not archive

  

 [quote]   ---

rv7a.builder(at)yahoo.com
Guest

Posted: Fri Apr 20, 2007 7:36 am Post subject: 74 inch verse 72 inch

Given all the considerations, noise would be a factor

to consider when all other performance data is

virtually undetectable? I just wonder why a

manufacturer would go to the expense of having another

model of prop, in this case the 74", without some

advantage? If there was not an advantage then everyone

would be using the 72"? Thoughts?  JR

--- "Konrad L. Werner" <klwerner(at)comcast.net> wrote:



[quote] Good points, the ground clearance is 1" less on the

 74", but I believe (don't hold me to it) the service

 limit is 72" on these props, so if you ever would

 damage the 72" with a need to cut it down a bit, you

 are already there!!!  The 74" has an inch on each

 blade that you could work with. It should also have

 a little bit more thrust (theoretically) then the

 72".  It is your choice,  and do not archive

  

   ---

tylerii(at)infoave.net
Guest

Posted: Fri Apr 20, 2007 8:17 am Post subject: 74 inch verse 72 inch

Just a bit of marketing to us experimenters. Plus some of the RV8 Rocket

gollywhoppers.. gotta have more performance.. need more thrust.. more HP etc

guys want the biggest and best. So the manufacturers fill that niche. Same

reason Superior offers IO400 and LYCO offers IO390.....MORE POWER.....



At the end of the day you must ask...will the 180 HP engine with the 72 inch

CS prop carry a RV7A at 200 MPH true cruise at 8000 feet.....you bet it

will....and still get about 25 MPG

TangoBravo



--

dan(at)rvproject.com
Guest

Posted: Fri Apr 20, 2007 8:33 am Post subject: 74 inch verse 72 inch

The party line on this is...if you go with the longer blade, you have one 

more inch on each tip that can be REMOVED in the event you need a repair. 

Some would consider this cheap insurance since I believe the price is the 

same.



Ok, so that's all well and good, but let's take a poll.  How many people out 

there have (or know somebody who has) had a prop strike where the prop was 

salvageable with a simple 1" repair?  Sound of crickets chirping...  Maybe 

I'm wrong, but the "advantage" of having that extra inch is questionable 

imho.



Personally, I'd evaluate the difference between 72" and 74" props, otherwise 

identical, on the basis of:



- ground clearance

- cruise performance

- climb performance



(the order may vary depending on your mission & landing gear)



Maybe you want to send an email to Les Doud or one of the other terrific 

engineers over at Hartzell.



I have a 72" on my RV-7 taildragger.  If I were buying a prop for my setup 

today it would be the 72" BA Hartzell.  Known good.



)_( Dan

RV-7 N714D (1253)

www.rvproject.com / www.weathermeister.com



---

rv7a.builder(at)yahoo.com
Guest

Posted: Fri Apr 20, 2007 10:09 am Post subject: 74 inch verse 72 inch

I just talked to a service center guy at Hartzell and

he agreed that the longer the prop the more noise but

it may be negligible with this small difference. He

recommended the 74" but without much conviction. I

guess I should of talked to an engineer over there

instead of a service center guy? Anyway Dan, this is

John Robinson, have not talked with you in a couple of

years since I have been out of the flying business for

that long. I did order my engine and prop today(74").

My next bit of business is to get on a hangar waiting

list. JR

--- Dan Checkoway <dan(at)rvproject.com> wrote:



[quote] 

 <dan(at)rvproject.com>

 

 The party line on this is...if you go with the

 longer blade, you have one 

 more inch on each tip that can be REMOVED in the

 event you need a repair. 

 Some would consider this cheap insurance since I

 believe the price is the 

 same.

 

 Ok, so that's all well and good, but let's take a

 poll.  How many people out 

 there have (or know somebody who has) had a prop

 strike where the prop was 

 salvageable with a simple 1" repair?  Sound of

 crickets chirping...  Maybe 

 I'm wrong, but the "advantage" of having that extra

 inch is questionable 

 imho.

 

 Personally, I'd evaluate the difference between 72"

 and 74" props, otherwise 

 identical, on the basis of:

 

 - ground clearance

 - cruise performance

 - climb performance

 

 (the order may vary depending on your mission &

 landing gear)

 

 Maybe you want to send an email to Les Doud or one

 of the other terrific 

 engineers over at Hartzell.

 

 I have a 72" on my RV-7 taildragger.  If I were

 buying a prop for my setup 

 today it would be the 72" BA Hartzell.  Known good.

 

 )_( Dan

 RV-7 N714D (1253)

 www.rvproject.com / www.weathermeister.com

 

 ---

dpharker(at)worldnet.att.
Guest

Posted: Fri Apr 20, 2007 2:56 pm Post subject: 74 inch verse 72 inch

Hartzel told me the minimum usable is 72" so if you ding it your done.



I went with the 74"

Don Harker



RV-7A Finish Kit

rikvincent(at)aol.com
Guest

Posted: Fri Apr 20, 2007 3:28 pm Post subject: 74 inch verse 72 inch

It sounds to me that if you had a prop strike that only took 1" to repair, may not of hit the ground if it was 1" shorter.

    

  

 --

gmcjetpilot

Joined: 04 Nov 2006
Posts: 170

Posted: Sat Apr 21, 2007 11:00 am Post subject: 74 inch verse 72 inch

72" WILL give higher top speed, so if you like flying at full power and 

RPM than this is the clear winner.

   

  74" WILL give slightly better climb (low speed).

   

  That is a fact. Now how much? A mph or two or three, a few dozen fpm.

   

  Yes the service limit may be 72" but if WACK you prop, 72 or 74 it will 

likely be damaged beyond repair.

   

  Nose gear planes can easily strike prop, you are not immune; it takes 

an uneven surface and/or gear deflection and/or botched landing, whack, 

whack, whack.

   

  My suggestion is for the average flyer get the 74". You can always cut it 

down later if you want to race it at full RPM. Prop Dia makes a diff but a 

small one. Since most don't run around at 2,600-2,700 RPM the larger 

dia will be fine.

  

 



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