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RV-4 Prop questions.

MRA

Member
Hi Folks!
I have a few (actually quite a few..) questions I need some more or less qualified inputs on before I make some descisions. I have searched on the forum and have found some answers, but not all... Hope some of You out there with experience can help a rookie from Norway out a little...:)

The almost ready to fly RV-4 I bought a few months back, has the short landing gear and a 72" Hartzell c/s two blade prop (HC-C2YK-1BF/F7666-A-4) in front of a Lyc. (I)O-360-A1AD (Bendix fuel injection refitted) with dual Lightspeed ignition.I'm planning to operate about half the time on a 400m/1200ft grass RWY that is not always as a pooltable, actually hardly ever...
I guess 60% will be CC flying, the rest aerobatics and formation.

Case 1:In the two-point position, my ground clearance is about 17cm or 6,69".

To me that seems to be a little less than I would desire, but am I wrong?
Do anyone have experience with the short gear and 72" prop?

I see the "standard" propdiameter now is 72", but for comparison, can anyone tell me what is the groundclearance two-point with the long (now standard?) legs?
Do anyone have any thoughts about my groundclearance?
Do I have a propstrike just waiting to happen, or will I be fine?
Does anyone still fly with the short legs, or is changing to the long legs done easily?

Case 2:The prop was overhauled/0-timed in 1995, inspected in 2001, run for a few hours between then and 2005, and has not been used after that.
When sent in for inspection again two weeks ago, the Prop-shop said it had to be overhauled/0-timed again and the hub needed to be NDI'd every 100hours because it was of a old type. Besides, the combination of blades and hub was not approved by Hartzell to be used on RV-4's. They also said the blades had been cut to it's minimum length and the internal vibrations could be unfavorable due to the relatively thick blade.

The prize for the OH and a new hub was, at least for my wallet, substantial, (approx $7270,- pluss taxes and shipping). Then I will have a prop with a new hub and old blades that still may be too long, and I am now considering spending a few $$ more and get a prop that is more suited for the RV-4 and my type of operation.
Fixed pitch is not an option!

I guess some of the following questions will strongly be influenced by the answers to case 1, nevertheless...
I assume that I am keeping the short legs and have to go for a shorter diameter prop.

What diameter should I go for, ie. what will be sufficient groundclearance?
Should I go for a 2 or 3 blade prop, and what would be the benefit/sacrifice going for one or the other?
Will a shorter diameter be compensated by adding another blade?

I have received an offer for an MT MTV-12-B/175-59b 3 blade prop with spinner at $10225,- plus tax and shipping.
Is that a reasonable prize?

Any other suggestions ot thoughts?:confused:

Thanks for any advise or comments!

Morten Raustein
Norway
 
My old short legged RV-4 has had a 72? prop atleast since 1989 when the big engine was fitted, an MTV 15 B 183-33. I have even flown 50 hours or so with a 74? MT three blade prop wile my prop was in the shop. I believe my Dad?s new ground adjustable WW prop is 72? on his short legged RV-4 also. I don?t know if your strip is rough or the grass is just long, I don?t land on rough strips but the length of the grass has never been an issue and is sometimes fairly long at places I visit. I can?t speak to your current prop or the price of your options but 72? is not a problem. YMMV
 
Morten, I am in a long gear -4 so I wont address prop size.

I fly behind an MTV11. For price see here. So $10.2K looks too much. Ask MT also.

My thoughts on 2 & 3 blades are here.
 
No weapon too short for a brave man...

Morten,
My rule of thumb on RV4 props (having tested five on my short gear RV4) was 69" maximum length for short gear, 72" for the long gear. A friend had a 72" Hartzell and 180HP on his short gear 4. I flew it primarily flying off my turf strip and several gravel runways. I noticed over time the Hartzell getting "greener" at the tips. This was after extended grass operations and I also noticed small chips in the leading edge from gravel at the annual. I was very careful not to run it up stationary over gravel greater than 1200 RPM and used backcountry techniques for takeoff, landings and run ups. This isn't a show stopper but it is important to note. If you fly primarily off prepared surfaces, you shouldn't have any problems. You do need to be aware of the tip clearance in 2 point attitude as you mentioned.

I'm not by any means condemning the use of the 72" on short gear, just be advised. I wouldn't shorten an existing prop, and Van's agrees with that logic in the RV4 builders manual. I would sell it and buy a new one if you are concerned. Personally the MT 2 blade C/S propeller Steve has on his blog above is hard to beat for weight and smoothness. Martin Albrecht at MT is a good guy and performs excellent engineering on a case by case basis. Send him an email, you might like what he has to say. I have had very positive success with MT FP props myself. The MT your friend has is a decent price for a 3 blade, Van's has the 2 blade MT on their site for $8250 delivered, MT might work something out since Norway is closer...:)

Smokey

[email protected]
 
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Performance with shorter diameter prop?

Thanks for the replies!

I would assume, theoretically at least, the 69" would give less performance than a 72", but how much?

Smokey (or anybody else as well of course!):
In Your experience comparing the efficiency and performance, was there a great difference?
Any noticeable difference in 2 or 3 blades vs. diameter?

I understand all newer RV's have the long legs, so there must be some disadvantage with the short ones..or??
How much higher are the long legs, ie. what is the groundclearance?

I must admit I'm tempted by getting a new prop, but the downside is 10 weeks deliverytime.. I would like to start flying NOW!!
Then of course it's the extra 3k$..

As for selling the Hartzell: Probably not going to happen.. If I buy a new prop, it will still have the old hub and need an overhaul. Nobody will touch it I'm afraid, and if so, the money I will get for it will be minimal.. :-(

Decision must be made this week...

Morten
 
Daddy long legs...

Morten, my 4 had short legs but I flew many 4s with long legs and my HR2 (really long)I liked the over the nose visibility with the short legs, otherwise the long legs are far superior. I found flying many different 4s that 2 bladed models were faster but the 3 blades climbed better.69 inch props work well with the 0-320. With your HP, a three blade would be a nice compromise for ground clearance, climb and efficiency. If you do change props, keep your old prop, never know when you might need it. :)

Smokey
 
Hard decision...

Smokey, I tried e-mailing Martin at MT, but he was out of office for a while.. No help there at the moment..

Like my Hartzell is now, it's not airworthy unless I get it overhauled and change the hub. That will cost a bundle, but not as much as getting a new one. I can't afford both, so either the Hartzell gets to live, or it ends up on a hangar wall with a clock pasted to the hub...

How much would be a cofortable groundclearance when operating regularly on dirt/grass?

Thanks!

Morten
 
Clearance Clarence

Morten, I think you could safely handle your current prop on any surface. Personally, I would go composite. Check Barnstormers and I'll look as well. Maybe Jim Ayers can help!

Smokey
 
MTV-12-b/175-59b propeller

Hi Morten,

The list price in the USA for the MTV-12-B/175-59b is $11,740. Using the "standard discount" with full payment to place the order, this would be $10,800. Plus tax, crating and shipping from the factory in Germany.

From theoretical performance data, the 175 cm diameter propeller will have a slightly lower climb rate than a 183 cm diameter.
From my own flight testing on another manufacturers propeller, the smaller diameter should give a slight increase in maximum speed.
For your application, these are both likely to be bearly noticeable differences in the performance of your RV-4.

What will be noticeable with the MT Propeler is the initial accelration for take off. Whatever RPM matches the throttle position is the RPM you have now.
The inertia of the heavier aluminum blades in the Hartzell prop creates a noticeable lag in the engine RPM for take off.

Again, Martn Albrscht is your preferred source of information. Also, the Sales Director, Eric Greindl. [email protected]

If I can help in any way, you can contact me at [email protected]

Jim Ayers
 
Thanks again!

Great info Jim!

I know there are'nt any RPM restriction issues on the MT 3 blade props, but are there on the MT (or other composite types) 2 blade props?

I'll try Eric too..

Anyone: I would still like to know what groundclearance the long legs give on a -4 with 72" prop..;)

BRGDS

Morten
 
How about the Whirlwind 151? 69" 3 blade...

I was going to ask the same question, just wondering if it has to be a certified prop in his country. I switched from a Hartzell to the RV-200 and the difference was dramatic with a O-360. It made the airplane much more balanced and the added performance was a great plus.
 
I considered the Whirlwind, because I've seen a lot of good reviews on it.
If I would have been able to get in on the discount deal some time ago, that would have been a really strong contender.
The problem is that as far as I know, there are none that will overhaul or repair a whirlwind in Europe, much less in Norway, so there would come considerable freight and extra time to ship it across the Atlantic a few times for that.
If I'm wrong, please let me know!

We don't need certified propellers, but they need to be maintained according to the manufacturers reccomendation. I don't have the knowledge to repair or OH a prop, so for all practical purposes, I will have to send it to one of the very few prop-shops on this side of the pond.. And they will only touch the ones they know...

But thanks for good suggestions!

BRGDS
Morten
 
Aeromatic.com

Check the web site. The Aeromatic may be a good choice for some RV's.

The Aeromatic prop is a certified propeller, not an experimental propeller.

I called Van's Aircraft today and offered to loan them a prop for evaluation. I asked the chap if he knew what an Aeromatic prop was and he said that he did. So I offered him one to play with.

His reply, "We are not in the propeller testing business up here".
 
And the descission is...

..Some may be interested to know that I finally ended up with a 70" MT, 3 blade propeller...
It certainly wasn't an easy descission, but for my needs and wishes, it gave me the best combination of several factors. Some of them quantitative, others just plain gut feelings...

Thanks to all for all the excellent inputs I have received! They've been extremely valuable and have confirmed some beliefs as well as crushed others. Very educative!

Best regards,

Morten
 
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