Prop Choice

[Dick B in KY]

Question for the general population - How/Why did you choose the prop you have for your Kitfox? I am building a SS7 with Rotax 912ULS and am interested in the selection process folks used to get their prop - Mfg, dia, type of flying, etc.etc.

Thanks,
Dick B

[jiott]

Ditto, I am in the same boat and am very interested in the replies.

Jim

[jamesmil]

we are going to use the kive prop on our ss7.

[HighWing]

I just went through this process and took delivery recently of a Warp 68" taper tip. I am going to be flying a Model IV with the Rotax 80hp. I considered the IVO and the Kiev. A couple of guys I regularly flew with had Power Fin props and they were poor performers relative to the Warp, so didn't consider Power Fin.

I put 900 hours on a Warp with my first Model IV with no issues and the guys I most frequently flew with favored the Warp. I found while flying with some IVO guys that inflight pitch issues would occasionally occur requiring unscheduled stops to do field maintenance (two in one flight - both of the IVO equipped airplanes). The Kiev has great reports, but being fairly new, I decided to go with what I was familiar with.

Our flying group has flown all over the Western US - Parts of Washington, Oregon, Montana, Wyoming, Arizona, Utah and most of Idaho, Nevada and California. Terrain has included Mountain, high Desert and the coast.
Lowell

[DanB]

I just went through this process and took delivery recently of a Warp 68" taper tip. I am going to be flying a Model IV with the Rotax 80hp. I considered the IVO and the Kiev. A couple of guys I regularly flew with had Power Fin props and they were poor performers relative to the Warp, so didn't consider Power Fin.

I put 900 hours on a Warp with my first Model IV with no issues and the guys I most frequently flew with favored the Warp. I found while flying with some IVO guys that inflight pitch issues would occasionally occur requiring unscheduled stops to do field maintenance (two in one flight - both of the IVO equipped airplanes). The Kiev has great reports, but being fairly new, I decided to go with what I was familiar with.

Our flying group has flown all over the Western US - Parts of Washington, Oregon, Montana, Wyoming, Arizona, Utah and most of Idaho, Nevada and California. Terrain has included Mountain, high Desert and the coast.
Lowell

Thanks for posting this one Lowell. As I am somewhat of a rookie Kitfoxer having been around for only about 6 years, this is one observation I have noted as well. Many of the guys that fly with the IFA IVO Prop experience trouble (such as shorts and getting stuck in one position). This is not to say anything negative about the performance of this composite, but it is troubling to know the IFA system is not solid. Now to be fair, I have heard there are some differences in design between the light prop system and the Medium set-up. I was told at some point the Medium IVO had a "beefier" IFA designed into it but I don't know the specifics. Can someone take this and explain the differences and or, your experience? Thanks

[catz631]

I removed my Warp taper tip and installed the Kiev. It was a dramatic difference ! It is much smoother,quieter,better looking, and easy on the gearbox.I have had it for about a year and still love it. It took awhile to get the pitch correct but it is there now. My prior posts will give you more info on the selection.
This is one area where everyone has a different opinion and it kind of depends on the area of the country you are in as to which is most popular.

Jeez Lowell, I have my old Warp taper tip hanging on the wall and could have sold it to you cheap !

Dick Maddux
Fox 4,912UL
Milton,Fl

[DanB]

Thanks for posting this one Lowell. As I am somewhat of a rookie Kitfoxer having been around for only about 6 years, this is one observation I have noted as well. Many of the guys that fly with the IFA IVO Prop experience trouble (such as shorts and getting stuck in one position). This is not to say anything negative about the performance of this composite, but it is troubling to know the IFA system is not solid. Now to be fair, I have heard there are some differences in design between the light prop system and the Medium set-up. I was told at some point the Medium IVO had a "beefier" IFA designed into it but I don't know the specifics. Can someone take this and explain the differences and or, your experience? Thanks

Still waiting for someone to tell me about their experience with the IVO, IFA.
Medium vs. Light? I know there are a bunch of you out there...do I intend to start a debate about props? Yes, I think I do. Time to step up and defend the IVO IFA system. Is it lacking? Can it be better? Has anyone determined what can be done to make it more of a solid platform? Has anyone developed a fix the rest of us would be interested in?
All you ole timers...throw us youngsters a bone :cool:

[kitfox2009]

I suppose the main criteria would be whether rules that the a/c is operated under allow IFA props. If they do, then I would definitely choose IFA.
I have a Vixen (912UL) and switched to an IVO ultra light 70" about 120 hours ago. This change made my 97 mph a/c into a 117 mph a/c and allows for 1000fpm climb-outs. Pretty happy with that for 80HP!
At about 100 hours the pinion on the carrier stripped requiring replacement. I replaced this myself although I had never opened up the planetary assembly before. The job was quite a simple (about 2 hours) procedure and next time would very straight forward.
I am not sure if 100 hours is the "operating life" of these parts or whether I might have over used the IFA feature because it was a brand new fun thing to play around with. I am finding now that I probably do not play around with it much as when it was a new novelty. For example, if I am just doing circuits I now leave the prop at climb out pitch.
I just cannot understand how ANY propeller that has a fixed in flight pitch would be able to match the performance of a properly operated IFA. (Especially on these smaller horsepower engines)
I am sticking with my IVO!! Even if I need $20 parts every 100 hours!
Cheers
Don

[av8rps]

I have an 80 hp 912ul on a Kitfox IV on aerocet amphibs with a 3 blade IVO UL blade and love it. I have around 400 hours on my IVO and the only issues I've had with it was the protective leading edge tape coming loose. I'd be willing to bet that is the biggest issue most other IVO users suffer with as well. The mechanical system of the IVO UL blade is simple and reliable in my opinion. BUT, I do think there are IVO owners out there that might be having problems due to not following IVO's very specific set up and installation directions. And I think that is critical with the IVO IFA. If you don't you are likely to add additional stress to the motor and gears. Mine is set up exact to what IVO said to do, and as soon as my motor gets to the end of its travel limit my breaker pops, which I believe saves my motor and gears from being overstressed.

All that said, I unfortunately cannot tell you about the Medium blade IVO IFA as even though I have friends using the IVO medium on their Highlanders (and love the prop), they are the ground adjustable versions.

I will say if I had a 912uls rather than the 912ul I would use the medium. BUT, if any of you guys have seen the 912uls Highlander perform in the DEADSTICK TAKEOFF video (trailer is on you tube or at www.deadsticktakeoff.com (http://www.deadsticktakeoff.com) ), in the video he is using a IVO IFA ultralight blade. He (Steve) says the UL "Patriot" blade works ok on the 100 hp 912, but it does cavitate a bit on initial power application. But hey, if you watch the video you will see one super performing back country airplane doing some pretty wild things that many wouldn't even think possible. So the IVO UL IFA must still work pretty well, even on the 100 hp engine.

I will post in a separate reply info I did on another forum recently where I shared specific performance numbers from my IVO compared to a ground adjustable version. In that I give some pretty hard numbers, along with some pretty upfront and honest opinions about the IVO. Maybe that will help answer more of your questions.

[av8rps]

And here's some IVO IFA info I had posted on another forum that you may find interesting;

Last night while flying my Kitfox amphib in really nice calm skies I did a test to see what the real gain is for top speed using my IVO in flight adjustable prop verses if it were a ground adjustable version (to do the comparison I just moved the prop switch to change the pitch, "pretending" as if I had adjusted the prop on the ground with a wrench and a prop angle gauge).

Here are my results;

Flying straight and level with wide open throttle (912ul - all 81 ponies)

- At 5800 max rpm I was able to go 119 mph.

- Leaving the prop set for a max rpm of 5800, I pulled the throttle back to 5500 rpm (max continuous power for a 912) and my top speed was now 114 mph.

- Putting the throttle back to wide open again, I increased the pitch so I could only get 5500 rpm, which provided the highest speed tested...124 mph.

- Moving the electric prop to maximum pitch while keeping the throttle still wide open, giving me 5275 rpm my top speed dropped to 116 mph.

So, I proved to myself last night that the inflight adjustable prop does in fact make my Kitfox faster. BUT, if I set a ground adjustable version to a max of 5500 rpm, it would fly just as fast (assuming the blade style and dimensions were the same for both props). Of course, then I would lose some takeoff and climb performance, so a better setting for water ops or STOL work might be a max rpm setting of 5800 rpm straight and level. So I could expect to lose around 10 mph in top speed when comparing the IFA to a ground adjust version.

In addition to the improved top speed, takeoff, and climb, another thing I really like to do with mine is to fly around at 4,000 rpm at 80-85 mph with a lot of pitch. It makes for a really quiet and smooth pleasure flight that doesn't burn much fuel.

So for now, I'll be keeping my IFA prop. I shared this information so I could let everyone know what the real gains are with an IFA prop.

[jtpitkin06]

Dick B,
I think that’s a great question. We can all learn the thought process of how and why a particular prop was installed. It’s a much better question than one that simply provokes unsubstantiated opinions like, “What do you think of the Buzzbat vs. the Zoom-master prop.”

The question promotes learning from actual experience. Thanks for your query.

My aircraft has not flown so I wasn’t sure if my reply would be much help without actual Kitfox performance numbers. However, I decided the question is really more about the decision process than actual performance.

I wrote this two days ago and sat on it before posting. At first, I was reluctant to reply, knowing the popularity of three blades and how some builders are fanatical about them. But these are decisions I made for my airplane, not anyone else. Perhaps the process will help someone.

Everyone makes the “which prop?” decision at some point in their build. Usually long before it will take flight. You have to start somewhere.

For my engine, a 100 hp Corvair six cylinder, I chose a 66 inch Warp Drive non-taper two blade propeller.


Why two blade?

There are dozens of articles published on two-blade vs. three-blade props. .. the latest is in this month’s Aviation Consumer. All of them pretty much agree that, barring ground clearance, a three blade prop is largely cosmetic. Face it, the guys with slide rules got it right decades ago when designing props. Since then it’s been just a few tweaks and twists but the performance is about the same as it was in the 60s. A correctly sized two blade prop will perform just as well as a three blade.

Other reasons are:

A two blade generally has less drag than a three blade prop. A reduction in drag can translate into higher thrust.
A two blade prop costs less.
and;
A two blade prop weighs less.

My selection is but a starting point. The only way to get reliable data on prop performance is to do scores of tests with different pitch settings using multiple props. That is a lengthy process the average builder is not willing spend the time and money researching.

I built my engine under the guidance of William Wynne who has dyno tested more Corvair flight engines than anyone on the planet. He has hung not one or two; but many props on the front of these engines. He has hundreds of engine runs on his dyno test stand. William was quite helpful in choosing a prop for my aircraft based on similar airframes within the same speed range.

The reason for the wide blade is also a result of flight and dyno testing. The wide blade Warp Drive absorbs more of the engine power and produces more thrust than the taper tip when loaded to the same RPM.

Of course, nothing is as good as actual in-flight testing, so I can’t report on that yet. I have promised to publish all the figures, including weights and speeds when I get the aircraft flying. I’m starting to cover the aircraft now, so it won’t be too much longer.

That’s pretty much my thought process of choosing a prop to mount on the Corvair / Kitfox combination. Because the vast majority of builders have a Rotax engine they may have a different choice. However, my selection process demonstrates I did not simply grab a prop off the shelf because that’s what everyone else is using. It was carefully thought out and evaluated using the best test data I could find.


Let's hope it flies as well as predicted.


Regards,

John Pitkin
Greenville, TX

[HighWing]

John,
It looks like you have done your homework. I can't fault your choice because it is a fairly uncommon engine prop combination and who knows for sure. With the Rotax, however, there is a short history of guys trying two blade props and the typical complaint is that there is more vibration than with three blades. Most guys then go back to the three despite the practical evidence that the two blade prop is more efficient. I suppose the smoother operation could be considered one of the cosmetic benefits.
Lowell

[jtpitkin06]

Most guys then go back to the three despite the practical evidence that the two blade prop is more efficient. I suppose the smoother operation could be considered one of the cosmetic benefits.
Lowell

Lowell,

I agree... on almost all aircraft, there is a perceived reduction in noise with a three blade although noise meters can tell a different story, and a perceived reduction in vibration possibly due to the higher frequency of prop pulses. I did some testing on my Cardinal RG with a two blade and another one with a three blade. Otherwise the aircraft are identical. I wanted to know how much quieter the 3 blade prop would measure. We were surprised to find the 3 blade measured louder by 3 dB. The meter used measured both A and C weightings. It was a real shocker... I still think my friend's aircraft is quieter and he agrees mine is faster.

I'm not educated in the effects of the gearbox and prop combination on the Rotax vibration. Harmonics is really out of my area of study.

JP

[MotReklaw]

Just curious John, what is the RPM range of the 100hp Corvair?
Thanks,



Dick B,

For my engine, a 100 hp Corvair six cylinder, I chose a 66 inch Warp Drive non-taper two blade propeller.

Regards,

John Pitkin
Greenville, TX

[jtpitkin06]

Just curious John, what is the RPM range of the 100hp Corvair?
Thanks,

Idle at 650. Max 3150 RPM for the 164 cid 2700 cc engine at 100 hp.
3200 PRM for the 190 cid 3100 cc engine at 120 hp.

Direct drive, no gearbox or psru.

[sturdee]

In flight adjustable WOODCOMP VARIA 170-2-R

SMOOTH TWO BLADE CARBON FIBRE PROP

FULLY FINE 5750 rpm for t/o
crank handle 25" MAP 5000 RPM GIVES 90 KTS

MK 4 1050LB 912 80 HP ROTAX

mine originated from the czech republic

see it G-FOXF

[MotReklaw]

Thanks for your reply John.

I'm thinking your engine is similar to mine (O200) except Max RPM is 2750.

What was your reason for choosing a 66" prop as opposed to a longer prop?

Thanks,


Idle at 650. Max 3150 RPM for the 164 cid 2700 cc engine at 100 hp.
3200 PRM for the 190 cid 3100 cc engine at 120 hp.

Direct drive, no gearbox or psru.

[jtpitkin06]

Thanks for your reply John.

I'm thinking your engine is similar to mine (O200) except Max RPM is 2750.

What was your reason for choosing a 66" prop as opposed to a longer prop?

Thanks,

My max RPM is higher than the o-200. With the higher RPM the 66 inch diameter prop will not have excessive tip speeds.

Dyno testing has shown the Warp Drive 66 inch to be the best balance of power, thrust and rpm for the Corvair when used on airframes similar to the Kitfox. I'll be using a starting point of 8.5 degrees.

JP

[SWeidemann]

As you can see, I'm bringing up the old question again about what prop to use.

My recently acquired Vixen 912ULS with about 1600 hours on it apparently needs a new prop and I'm looking for testimonials about what and why I should put on a specifically good prop. My run out one is a long three blade IVO which gives great performance but I would like to get one that will accept a nice looking medium size spinner too. Present front runners are: Whirlwind (OEM on Kitfox SLSA), Warp Drive, Sensenich, Kiev and maybe another Ivo (with a little spinner). My primary goal is reliable performance (don't want any trouble away from home) and fast cruise without overloading the engine. Takeoff performance is important however the Kitfox does such a good job at relatively short takeoff anyway so a few more feet and a slightly diminished climb rate is a small price to pay, keeping in mind the Light Sport gross weights are less than the design loads of the airplane.

Any specific experience, facts or opinions you may want to share would be much appreciated.

Skot
Kitfox Vixen
912ULS N24V



Question for the general population - How/Why did you choose the prop you have for your Kitfox? I am building a SS7 with Rotax 912ULS and am interested in the selection process folks used to get their prop - Mfg, dia, type of flying, etc.etc.

Thanks,
Dick B

[Steves142]

I'd like to share my limited experience and hopefully get some advice as well. I recently finished a 2002 KF Classic 4 with a 912uls.Thinking I might want to put floats on it some day I went with an IVO medium 70" 3 blade ground adjustable. At the same time a friend finished an earlier classic 4, same engine with an IVO UL 72" 3 blade GA. He has a little cavitation when he throttles up, but no other issues. I had no cavitation but some what major vibration issues when descending or decelerating. Start up and shut down also seemed a little on the violent side. Carb balancing helped the vibration by 20%. I bought the blocks and changed to a 2 blade, which took 3 lbs off, and now it seems like 80% of the problem is solved. I lost a little in climb but the change gave me another 3-5 mph at the top. I love the looks and performance of the 70" 2 blade but I'm thinking that it may still be a little too heavy for the gear box.

IVO Specs
IVO UL 3 blade = 8 lbs
IVO Medium 3 blade = 14.2 lbs
IVO Medium 2 blade = 11.2 lbs

[kitfox2009]

Hi Steves
A friend of mine recently installed an IFA IVO Medium on his gyro and then took it for balancing. He ended up putting quite a few grams of weight on before it was balanced properly. This may be something to look at.

I fly a Vixen with 912UL and 72" IVO IFA UL and find it made a whole new a/c out of it. I now get full 5800 on climb out and much better cruise,
The only issue I have had is the small pinion in the center of the planetary carrier wears out quite frequently if you "adjust" too much. Big improvement over the GSC it replaced.
Cheers
Don

[DesertFox4]

I like the UL or Patriot Ivo for the 912uls. Mediums have been used with success. Yes the UL's prop in-flight pitch drive motor is a little under designed if used frequently on every take off and landing. I've killed a couple motors over the years and usually it's the cluster gears that go first. My current prop has been stuck in cruise mode for 1.5 years now but flying in southern Arizona I haven't had to do many really high density take offs where I'd need the flat pitch and full power or short runways with obstructions. I can still cruise at 120 -125 mph and it tops out at 132 mph in this setting. Static run ups yield about 5050 to 5100 rpms.

The Rotax 912uls will induce some cavitation with the UL Ivo if you advance the throttle extra quick from a complete stop. It only lasts a second or maybe two before the prop bites fully. The UL Ivo seems to be pretty much maxed out at 100 hp.

No cavitation with the Med. though. The Medium 3 blade is on the verge of being heavy for the gearbox. A good dynamic balancing may help a great deal with some of your vibration issue regardless.

** During shut down if you will try this little procedure you may greatly reduce gearbox stress and avoid the violent compression stop from just shutting off the ignitions.

It takes a few times to get the timing just right so give it a chance.

When ready to shut down, set rpms to about 2,000 or 2,200 but keep your hand on the throttle. At the same time you are quickly shutting off both ignitions be pulling the throttle to idle stop. The prop should slow down smoothly like a Lycoming or Continental with no abrupt compression stop. Again it takes a little practice and I still mess it up once in a while but even then the stop is much smoother. Give it a go next shut down.

[Slyfox]

I first had the patriot prop inflight adjust on my 912ul. It was a good prop, but the motor always blew out the gears. When I went to the Uls motor I used the same prop. yes it did cavitate if I put too much power to it. I went and bought the medium prop, wow what a difference. no more cavitation and no more problems with the gears. just pure enjoyment. if you have the money, get the right prop for the uls.

[Steves142]

Thanks guys for the suggestions.
Does this make any sense? An IVO medium 3 blade @ 14.2 lbs is on the verge of being heavy, changing it to a two blade @ 11.2 lbs shouldn't be a problem for the gear box and any vibration problems could most likely be a balance issue.
I have access to a ul 3 blade so I could make the change if necessary but like I said, I really like the performance of the med 2 blade. That and the blades on the ul remind me of the strings on a weed wacker.
I just don't want any problems with the gear box down the road.
I'll try your shut down method D.F. before I do anything and see if that helps.
Thanks again

[Slyfox]

Yes I did balance my prop, I own a dynovibe. It did take a little bit to get it balanced. My answer to the vibration on shut down is to back off my idle screws about 1/2 turn, this makes the idle about 500rpm. I don't run it there, it's mainly for those real short approach to landing I so much love. and when shutting down I pull the throttle all the way off and kill the mags at the same time, nice smooth shut down. I use the inflight adjustments on my prop all the time, makes for a nice leap off the runway and a predictable landing. many times on landing I will pull the throttle all the way off(see my rpm above) combined low rpm and flat prop, wow, nice short landing without using flaps. down in about 300ft. the way I have my airplane set up, I couldn't emagine anything different.

[jrevens]

Slyfox,

Do you have the small "cap" spinner on your Ivo, & if so how do you add weights for balancing?

[Slyfox]

I actually put the fiberglass spinner on mine. I went and used auto weights for balancing with the stick um on the back(first put them on the ouside). after balancing I put the weight on the inside and than used pop rivets to secure them. I would use aluminum rivets and the small washers on the inside, keeps the rivet from pulling through the weight. I've had mine on for almost 3 years and about 400hrs. still like I just put them on. but like any weight you put it as one of your precheck on the aircraft to make sure they stay in place.