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View Full Version : Whirl Wind 70" versus 75"



herman pahls
10-07-2016, 12:33 PM
I am shopping for a new prop more out of curiosity than need.
Model 4 Kitfox (700#'s) , 912 RotaxULS (100hp), 29" ABW's.
The Warp Drive 70" taper tip with leading edge protection performs well both short field and cruise (100-115 mph above 10,000msl).
It is starting to show the abuse from a steady diet of sand and gravel bars.
I would not mind going to a prop with less mass moment of inertia (MMofI).

Whirl Wind (WW) suggested their 75" fits my flying style but I will lose some cruise.
The WW 75" will have more MMofI than the 70" but less than the current Warp.
McDeans say they sell mostly 70" WW for the 912's (100hp) and 75" to the 914's.

Questions.
1. Any experience out there with the WW 75" with 912ULS?
2. WW says their blades fit the Warp Drive hub 80% of the time.
Has anyone tried WW blades on a Warp hub?
3. Any experience switching from a WW 70" to a WW 75"?

I am considering a big bore kit in the future.

I do not want to make a mistake thinking bigger is better.
Apparently most of the Air Master users are using WW 70" blades with 100HP.

Thanks
Herman

Dave S
10-07-2016, 01:29 PM
Herman,

Not an answer to your question; but, your question inspired a question I have (also running the same warp drive prop/engine combo you have).

With your thinking that the Warp is close to needing help from wear and tear, I am curious how many hours of service you have been able to get out of it so far?

Mine has 310 hours on it and is a ways away from needing attention...but we don't have a lot of gravel strips out here either.

Another option is Warp apparently can take a well worn prop and redo it to new condition including new nickle edges....not sure what the price is but it is less than a new prop and if the hub is fine there is no need to replace that.

WWhunter
10-07-2016, 05:24 PM
I have both but have used them on a RANS S7. My engine is a 105hp Zippered ( originally an 80 HP) engine. I think either one would serve well. Only reason I changed was due to wanting to have the 'latest and greatest'. Plus, the 70" was developing severe cracks in the outer finish that I wasn't sure was safe. Whirlwind said it was only cosmetic... I say BS!

The 75" pulls a little harder but I never really put enough time on the 70" to give you an honest comparison.

herman pahls
10-08-2016, 10:06 PM
Dave S
Of the 600 hours on this Warp, I have only flown 150 of them.
I was not aware that Warp Drives could be reconditioned.
Even with a few small chips and dings in the leading edge protection it still performs great and smooth.

Whunter
Thanks for letting me know your experience between the Whirl wind 70" and 75".
I ordered the 75" thinking it would be appropriate when or if I go with the 115 hp big bore kit.
I really wanted to try the Prince 78 or 80" but was concerned about not enough ground clearance even though I am on 29" ABW's and standard Model 4 Grove gear.
I am not ready to spend $2500 for extended Grove or Cub Style gear so I spent $1900 on a prop when the existing prop works very well and I really want to try a Prince.
Why did I do that???

Wish list.
115 Hp big bore kit $5000.
Extended gear $2500.
Prince Prop $2300

herman pahls
10-25-2016, 02:53 PM
I recently installed a 75" Whirl Wind (WW) prop that was replacing a 70" Warp Drive on a model 4 Kitfox with 100 hp Rotax 912.
The Warp gave me excellent all around performance.
I do most of my flying near sea level but was looking for better short take off and climb when I go to the Backcountry of Idaho or Nevada (Nevada has some strips at 9000').
I did a pull test before removing the Warp to get a baseline.
I am using a 550 pound scale that looks like a large fish scale that I purchased on Amazon.
The Warp pulled 400 pounds at 5360 RPM.
The Whirl wind pulled 480 pounds at 5300 RPM at 15.7 degrees pitch.
Who knows how accurate my scale is but the seat of the pants method told me the WW definitely pulled harder than the Warp.
With the Warp I could easily hold a full power run up with the brakes, with the WW the brakes can no longer hold the additional thrust.
I was told by WW that their 75" prop was well with in the Mass Moment of Inertia (MMI) that is recommended by Rotax.
I was also told that the Warp I took off was borderline or exceeded the Rotax recommended MMI.
I have not done the MMI tests so I have to go by what I have been told.
I was disappointed that the complete 75" WW including their 10" spinner weighed 11 pounds- 4 ounces which is 2 ounces more than the Warp.
The only explanation as to why the 70" Warp has a higher MMI than a 75"WW when it weighs 2 ounces less is that the Warp blades must be heavier at the tips than the WW.
My 100 HP rotax does not have the soft start that the newer 912 ignition modules have so it takes a cold start up procedure to prevent kick back.
The WW blades seem to start easier so that may be an indication of less MMI than the Warp.
I knew that I would lose cruise speed and I have probably lost about 10 mph at the current 15.7 degree pitch angle.
With the Warp I often get 110 to 115 mph above 10,000' with 29" ABW's burning 5.5 GPH with out a HACman.
I have noticed on the fuel flow, that at low altitudes the 75" burns more fuel.
This is a beautiful prop to look at but I am not sure it would be the best all around performance prop.
I would think the 70" WW would be best all around in the WW lineup.
For my local gravel bar bashing I am pleased with the prop but may need to go back to the Warp for long distance flights.
I am sure this would be an excellent prop for floats.
Herman

av8rps
10-25-2016, 05:12 PM
Over the years I have found the 68 to 70 inch 3 blade props to provide the best overall performance on the 912 series engines on airframes like the Kitfox. I know the longer blades like the 75 inch do better in the hard STOL environments, but they suffer immensely in cruise due to having too much drag. As an example, I have a 70 inch 2 blade Sensenich carbon fibre prop on my 912S powered Highlander, and it is a very impressive performer. It will climb solo at 1800 fpm and yet cruise at 108 mph at 5400 rpm. And that is with large diameter 8.50 tires and an open tube gear. For a Highlander that is not only a great cruise but also a great climb.

For comparison I tried a 72 inch 3 blade Warp with tapered blades with nickel leading edges and lost more than 20% in climb and 10% in cruise. I have a Sensenich 3 blade 69" (aka 70") I will be trying one day as I suspect that will be the best overall prop on my Highlander. Of course I'm not pushing my Highlander on mountain tops like you are. But even with my current 70 inch 2 blade prop I can outperform pretty much any Supercub. So I'm happy.

I think the 912 gear reduction providing such a low prop speed changes a lot of what we thought about propellor and engine efficiencies. That's the only logical explanation I can come up with.

Try to find someone in your area that will lend you a shorter blade to try to see if what I'm saying applies to your plane like it does on mine. That 75 inch WW is a VERY NICE prop, but I'd be surprised if a 70 or 72 inch prop wouldn't be more to your liking.

herman pahls
10-31-2016, 03:35 PM
Hi Paul
Thanks for reporting your experience with props.
I did not realize that Sensenich was providing props for our type airplanes.
Seems like the majority of 912 powered Back country airplanes use GSC, IVO, Warp or WW props.
I had good all around performance with a Warp 70" taper tip nickel leading edge.
To hear that your 70" 2 blade Sensenich was a significant all around improvement over the 72" Warp makes me want to check it out .
Now I am curious what the performance difference is between the 70 and 72" Warps?
I wonder if there is a significant "sweet spot" difference with 2 less inches since my 70" Warp did quite well?
I agree the shorter WW would give better all around performance.
If you want to try a 75" WW with 2 hours on it, I will try your Sensenich.
Herman

av8rps
11-02-2016, 07:53 PM
I sure hope I'm not getting you off course with my comments. I still believe firmly the longer diameter blades ( like your 75 WW) will provide the best overall STOL performance. But, for an overall prop I have found a 70 inch blade provides a good cruise as well as a good climb. So it works best for overall performance. So it is more about bow you want your plane to perform.

For the record, I really like Warp Drive blades as water doesnt affect them. But I feel the Sensenich or WW will perform better. Just look at the airfoiled blade shape compared tbe the warp. The Sensenich is a much more advanced blade design if you compare it to others.

I wouldn't mind trading props for a while, but that would render my plane inoperative. So i really don't want to do that. Thats why I suggested finding someone closer to you.

av8rps
01-07-2017, 09:18 AM
Herman,

I was just re-reading this thread and thinking about your situation, and wanted to further comment. If you do go to a big bore kit on your 912uls I'd be willing to bet you will love that 75 inch Whirl Wind you bought.

Many of the Highlander guys run the 75 inch Kiev and love it. And while it works well overall on the 912uls, it really works well on the 914, having just that little extra power. Oh, and fwiw, the WW and the Sensenich blades look almost identical to the Kiev, so I think you have a great prop in that WW.

With all that said, let's stay in touch on this subject. If you get really frustrated with that 75 WW I would consider a swap on one of my 70 inch props, even just as a test. I do fly floats mainly, so a longer prop is always better for getting off the water. But like you I want good takeoff and good cruise, and on the 912uls I feel the shorter 70 inch blades work better. But with more hp the longer prop really is the hot ticket. So if you really want to go to the big bore kit, you probably want to keep that beautiful 75" Whirl Wind.

herman pahls
01-09-2017, 12:08 AM
Paul, good to hear from you and thanks your comments.

I purchased the 75" WW with the intention that it would be a great fit with a high compression big bore kit in the future.
Yes, near sea level where I do most of my flying, I lost some cruise speed and the fuel burn went up at the same RPM's that I flew the 70" warp.
I also gained 20 percent more thrust at the same full throttle static rpm which is very noticeable seat of the pants.
Plus the WW is more interesting to look at.
It is hard to justify a big bore kit when this Model 4 performs as well as it does.
Since most of my flying consists of finding new gravel bars, cruise speed and fuel burn are not an issue.
The Kitfox has been a great way to live out my dreams of owning a Super Cub at a reduced cost.
Herman

av8rps
01-09-2017, 01:39 PM
I'm glad to hear that you are enjoying that new prop. I think that extra pull that gives you better acceleration is probably better than going faster, and is more fun especially since you like the back country flying so much.

Oh, and for the record, I think you would probably find that Supercub boring compared to your super high performing 100 hp Model 4. My buddy just passed on an even up trade for a Smith 180 hp Supercub for his Highlander. He was pretty excited about the deal until he flew it. He said it flew at essentially the same cruise speeds or less, carried the same weight or less, but burned twice or more as much fuel, and it had nowhere to put anything. And his wife said she didn't like sitting behind him when traveling (same thing my wife says).

But I wasn't surprised as I fly my Kitfox amphib regularly with some friends that fly Supercub and Husky amphibs, and while I really like their airplanes, for the money they have invested, I like my Kitfox more. It does most everything theirs do for a lot, lot less money. And I do that on only 80 hp. Imagine if I Zippered mine and had a 35% increase in power. They might not be able to keep up with me at all then. :cool: