Kitfox-4-1200 : 2180 VW power Performance Data Available !!!!!

[rogerh12]

Howdy all;

Ok, I finally was able to get the performance numbers off a flying Kitfox-4-1200 with a 2180 Great Plains VW motor installed, it‘s the one in St. Louis, currently listed on Barnstormers.

The great thing about this plane is it’s a known quantity. As VW aero engines can be anything from a 1600 cc 45HP engines to a 2300cc 100+ HP monsters (with water cooled heads), this engine has been identified as a 76 HP Great Plains 2180 cc engine turning a Sterba 62x32 prop at 3000 rpm in cruise. This engine requires Avgas at this HP rating and develops peak power at about 3500-3600 rpm, but typically cruises at 3200 rpm, which is close to where the peak torque is created.

Here are the specs, I would be interested in any comments:

N53RJ KitFox IV Speedster

Weights:
Basic Empty Weight = 700lbs
Max Weight = 1200lbs
Usefull Load = 500lbs
Fuel Capacity = 27 Gallons
Wing span = 28.8 ft.
Fuel Burn = 4 - 4.5 Gallons an hour
Cruise speed (economy setting) = 90 to 95 mph at 1500 feet (3000 rpm).
Cruise speed (high setting ) = 110 mph at 7500 msl.
Max speed (At full power) = 115 mph at 7500 msl.
Rate of Climb (two people) = 700 fpm
Rate of Climb (One ) = 1000 fpm
Take off roll at Gross Wt = 300 feet
Landing roll at Gross Wt = 300 feet
Stall speed (with vortex) = 37 mph
Approach speed = 60 mph

Ok, well let me know what you think.

Roger

[szicree]

This is only my opinion, but I feel some skepticism when I see an empty weight of exactly 700 lbs. Too many round numbers for me to trust their accuracy, especially when it's a plane for sale.

[jtpitkin06]

Roger,
I applaud you for exploring alternative engines for the Kitfox in the spirit of experimental aviation.
The Kitfox has undergone a metamorphosis with engine changes over the years. From the diminutive two-cylinder two-stroke to the Rotec radial. If no one had the courage to try a different engine, all Kitfox aircraft would have that wonderful ring-ding-ding two stroke exhaust note.

Many engine combinations are flying… some good, some not.

Your inquiry into the VW engine is not without merit. On the positive side it is significantly lower in cost than a Rotax. It can be purchased completely assembled. You can get an off-the-shelf motor mount to fit the Kitfox. Parts are cheap and many are available at your local auto parts store.

On the negative side is additional weight and a slight reduction in available power for a reduced level of performance. However, the performance of a Kitfox is so sprightly; you might give up a little without putting the aircraft into the flying dog category.

If the cost difference between the Rotax and the VW is the make or break point on being able to afford the airplane, I’d say go for the VW. That’s better than no airplane at all.

For example, there are Champs and Cubs flying with 65 hp engines and some versions flying with 180 HP. To be sure, the higher HP versions have great performance; but, that doesn’t make the lower performers any less fun.

So it is with the Kitfox. I don’t think any Model 1 or 2 owner will say his aircraft is worthless because it doesn’t perform as well as a Model IV with a Rotax 100 hp. To the contrary… I only hear of how much fun they are having flying. If you decide to put in a VW it should be a great flying airplane and who cares if it isn’t the superstar of performance. You can buy a lot of gas for the $10,000 saving in engine acquisition.

I don’t think reliability is an issue. The VW runs and lasts just fine. It’s been flying in airplanes for over 50 years. When you look at most engine failures, you’ll find they are usually fuel system related with few mechanical failures. I wouldn’t hesitate to fly behind a VW from Great Planes.

I first looked at the Kitfox in the early 80’s then 90’s and 00’s. When the Rotax 912 80hp first hit the scene, lots of naysayers touted it was too big and too heavy. How things have changed.

One factor has popped up of which you may not be aware. The Kitfox factory is phasing out the Model IV. It is currently special order only and it is not public how much longer they will produce the airframe. Unless you buy a used Model IV to do an engine swap, you are probably looking at a Super Sport for a new Kitfox.

That may change your engine specification window due to the heavier airframe. Certainly the days of 65 hp engines in a new Kitfox are over. And perhaps the days of 76 hp engines are over, too.

This should give you a lot to chew on.
Enjoy your quest.

John Pitkin
Greenville, TX

[rogerh12]

John;

Thank you for your well thought out remarks, it's nice to see others understand that without lower cost engine options for the Kitfox in these tough times, fewer Kitfoxs airframes will be sold and fewer people will get to enjoy this wonderful airframe.

I am painfully aware that the Kitfox model 4 is being phased out, and I have told the Kitfox owners that I think it is a big mistake !!! They risk locking the company into producing an airframe that can only be powered by a an expensive European engine. What will happen to their airframe sales when that Rotax 912 engine starts selling for $39,000 ??? Don’t laugh, it will a happen !!! It used to be a $9000 engine, then a $19,000 engine and I think we all know it’s going to be a $29,000 engine soon enough, with the state of the US dollar / Euro exchange.

$39,000 Rotax 912 engines will become a reality; it’s just a matter of when !!!!

The Kitfox-4 is different; it CAN use cheaper American made alternate Engines like the VW. Yes, some of the new parts come from Brazil, but we aren’t loosing that $$ exchange race. Most of the Aircraft VW parts are made in the good old USA, the crank, the Cam and other major parts.

If Kitfox wants to keep selling airframes, even in tougher times, they need to offer the Model -4 as it will remain the aircraft that can STILL be powered economically, with smaller engines like the VW and others.

My three cents worth.

Roger

[GDN]

Do you think it's possible to install an engine as so heavy then a Rotax 100 HP on a kitfox 2 or not ?

[Av8r3400]

Actually, Roger, the model 5 and up can use "regular" aircraft engines - Continental and Lycoming. They were designed for the additional weight. The model IV was designed for a 80# Rotax 582 two-stroke.

These motors can be had for much less than your VW conversion kit (as can a 912) if you know how to look for them.

[rogerh12]

Howdy all;

The question was "Do you think it's possible to install an engine as so heavy, then a Rotax 100 HP on a kitfox 2 or not ?"

I had the Kitfox 2 with a 582, and I think that that is really the limit on weight and HP on his model (though some have used heavier engines) It just didn't have a lot of structure to support anything more than that in my opinion, and was very limed on the tail feathers Also, even with the lighter 582 it flew terrible. Slow with the old wing design, and the worse adverse yaw imaginable, in my opinion. Also, on the ground it was very tippy due to the narrow gear, but climbed good.

I would not consider any Kitfox before the Model 3 anymore, and even the model 3 should have model 4 upgrades installed. But that is only my opinion, and is directed at the "average" pilot.
The model 3 can handle the VW, but upgrading the lift struts is recommended, (both main wing and tail struts) as well as the rudder peddles, landing gear and perhaps also raising the tail and increasing the elevator size.

Final note, a "light weight" VW engine variant is available, it uses aluminum cylinders and single magneto ignition with a Posa or Aerovee carb. Total install weight is something like 15 lbs less than typical VW installed weight.

Hope this helps

Roger

[Newkid]

I was just going to say that if you don't mind going used you can have a very cheap airplane. For the last few years I helped my dad build a Model IV that we had a little more than $20,000 in. We found a kit in California, that hadn't been started, for $6,000. Bought a 912S with 300 hrs. on it for $9,000. Bought extended landing gear for a grand. Got a prop on a trade, painted it ourselves, and bought a firewall forward from Kitfox. It had a new Garmin SL40 and a P.S. Engineering intercom. I know you can't always find a 912S for $9,000, but there are 80hp 912s out there for even less that you can hop up to 95hp or so. I know a guy that is converting a 912UL to a 914 for less than $10,000 motor and all.
So for twenty grand we had a Model IV that would take off in 90ft. solo, climb at 1500 fpm. and cruise at 108 mph. Not bad

[DBVZ]

The actual W/B spreadsheet for this aircraft says 695. Perhaps 5 pounds allowance for loose stuff.

[rogerh12]

Dweight;

Ya my Zenith 601 HDS with the same engine weighed in at about 650 lbs. It was built to a 9 G spec, and is made of all aluminum with lots of structure in the wings, and had steel landing gear to boot. I find it hard to believe a kitfox -4-1200 could weight much more with the same engine myself....

Roger

[akflyer]

I have lots of hours in a model I and II. I cant see how one could possibly say they flew terrible. I think it is one of the more enjoyable planes I have flown to date! Yes it has some adverse yaw but nothing close to terrible. If all you have ever flown was a spam can with rudder / aileron interconnects, then I can see it being an issue to transition, but a few hours and all should be sorted out.

Floats wheels and skis I think the early model Avids and kitfoxes are about as much fun as you can have with your clothes on.

[DBVZ]

Funny what people will do with a Kitfox IV-1200 though. In my shopping I recently inquired about one with a Subaru 100 HP engine, and the seller reported the empty weight as 817. I asked him to check that since he was not the builder (estate sale I think), but he seemed sure that was it. Someone bought it since.

[rogerh12]

The original builder of my Zenith had a Subaru engine on it, with the redrive. It was fast all right, but weighted a solid 100 lbs more than the VW 2180 he later installed. It was a simple installation, true, but 100 lbs of extra wight over an already heavey engine was kind of crazy. However, he did the engine swap, not because of the Subaru weight or perfomance problems, but becuase he could not sit and watch the tac turning 5000 rpm all day, it just made him nervious.

Roger

[Av8r3400]

Link (http://www.kitplanes.com/issues/28_4/builder_spotlight/Wayne_Clagg_Zenith_CH701_9498-1.phtml)




As for the VW engine it covers, he’s still testing a fat-fin modification he hopes will solve its hotheadedness and keep him flying until he saves up enough for a Rotax 912S.

“The VW has its place in aviation; the Sonex and other planes prove that,” Clagg said. “But based on my experience, the 701 isn’t one of them.” Keeping the engine cool is one problem, and weight is the other. His CH 701 weighs 742 pounds empty. The engine, complete with baffling, alternator, vacuum pump, Ellison injector and dual ignition (12-volt and Slick mag), weighs 223 pounds.


Drawing on his past VW racing experience, Clagg had hoped to develop a cheap, reliable powerplant with mass appeal. With a local source of high-performance parts, he wouldn’t have to pay freight, and he believed he could overcome any problems. Putting 90 hours on it in less than two years, he has overcome problems for the most part, but, “Sometimes, you know, you’re just not too smart,” he said.





From the mouth of a 701-VW owner and builder.


Problems he has:


Lack of power
Inability to keep CHT down
Lack of performance
Lack of reliability
Excessive weight

All of these will apply in a Kitfox as well. Why reinvent the wheel? I don't understand.

[rogerh12]

I agree, the VW is not good for the Zenith 70, I have heard that from my 701 builder buddy as well, and he is on the 701 group forum. The problem is these guys are nunts !!! The climb out is at something like 20+ degrees noise up, and they hold it only moving along at like 45-50 mph.
In fact, I think the top speed on this plane is only 75-80, even with a 80 HP rotax.

The 2180 75+ HP VW needs at least, well based on my experience over 5 years, 75 mph on the 601 to get proper cooling in a steep climb. At 85 mph and with an outside temperature of 80 degrees or less, I could climb at full power until I ran out of sport pilot ceiling. It would never get too hot, oil or cylinder heads.

I think the 701 guy must have installed a redrive on the front of the VW. Did it have a 3-bladed prop, or a composite or metal prop?

233 lbs is more than even a Corvair installation, I could carry my VW engine across my garage (without intake or exhaust), and I am no body builder. I would estimate my engine to weight about 155-165 lbs, based on the load on my back !!!! The redrive adds weight, but it depends on which one, so I don’t know how much.

The VW conversion is very popular here around Kansas City, both Aero vee and Great Plains VW are only about 3 hours away, and you can drive up and get engine parts same day, if needed !!!
As a result, we have 4 Sonex’s at my local airport, all of them have the VW conversion (3 are areo Vee) and they tell me their heads run on the cools side. Of course, that’s a true 130 mph plane, but the air intakes look awful small to me.

It seems to me, that basically if a kitfox can climb well in the 75-85 mph range, then it will not overheat the heads or oil at any temperature below 80, even at full power. I say this as the kitfox has at least as big an air opening (with the round cowling) as my 601 did. However, something besides the stock top mount oil cooler may be needed for higher air temperatures. I say this because when I found that I could not run full power in a climb endlessly at air temperatures over 80 degrees with the 2180 VW, that was because I was still using the stock top-mounted oil cooler, and not the under engine one like use on the Revmaster and Aero Vee engines. I would recommend only installing the larger bottom mount oil cooler on a Kitfox.

Note: This winter, I saw 4 Revmasters listed on Barnstomers, used, but otherwise all listed as “complete and ready to install” for between $3000 and $4000 (though I bet they would have sold for less). The Revmaster 2100D makes 70 HP. Now that’s cheap power !!!!!!
Roger

[szicree]

I mean no offense and don't wish to hijack this thread, but it seems that price is the major knock against the Rotax. I've not seen it mentioned that when it comes time to sell you might actually come out ahead with the Rotax. I sold a VERY nearly done RV-4 with a Superior 360 and got my money back quite easily, with multiple cash offers the day I listed it. Meanwhile I've seen a lot of similar projects with Subarus and such languish unsold for months. Whenever I have doubts about the cash outlay for this project I just remind myself that I can always get my money back out as long as I build to suit the typical buyer. That means mainstream engine and panel, conservative paint job, and good workmanship.

[rogerh12]

Howdy All;

This is off Great Plains VW web site, and outlines the engine weight. This spec is very similar to what Revmaster and AeroVee state as well.

ENGINE DISPLACEMENTS: TYPE 1 - AIR COOLED (The big boy ) 2276cc

Take off HP, 3600 RPM (MAX)........... 80
HP @ 3400 RPM .................................76
Displacement, in CC ........................ 2276
Compression Ratio ........................ 8.0:1
Minimum Fuel Octane ................... 96
Weight in Pounds ......................... 165

Note: The above weights are for engines that include the Diehl Accessory Case package and Generator, intake manifold, Single Slick ignition system and oil cooler. (I think the Battery, exhaust, fuel system and secondary ignition would add another 20-25 lbs, but using a light weight wood prop would help the installed weight). Aluminum cylinders aid in cooling, and reduce engine weight by about 10 lbs.

Reducing Compression to 7.5:1 allows the use of Car gas, but decreases horse power by about 4 HP.
I would expect a total firewall forward kit to add less than 200 lbs to a bare Kitfox Airframe (bare with cowling attached). This would be the total installed weight, with oil, prop and ready to fly. Using Aluminum cylinders would give you an installed weight 10 lbs less than that, and a light weight ATPs UltraStart-Red battery will save another 5-7 lbs (this battery worked with my old VW install, it was a lower compression engine). Probably yielding a true installed weight of about 185 lbs, ready to fly.

Anyone know how much the Rotax 912 80HP version adds to an airframe, with fluids prop and battery (ready to fly)?

Hope this helps

Roger

[whitewulfe]

On a somewhat related note, do they mention how that octane is measured? I ask because I find it somewhat odd an American company would use a RON octane rating when in North America we use AKI ((RON+MON)/2) ratings (which would put such as 91-92 octane fuel in North America, if such is the case)

[rogerh12]

I have not seen it listed definitively, but I think the 96 octane is with respect to 100LL.

I tried to cut my Avgas, on my high compression engine, with 92 car gas. It would run at full power the same, but the exhaust temps went through the roof (cloud cover :) ). The 7.5:1 compression for car gas is determined by experience I think. In the winter, you can just run 87, but in the summer 91+ would be in order (oh so I have heard). Around here, we have 92 octane with no Alcohol, so this what I will setup my engine for. Right now, I have two guys wanting to sell me there used factory VW conversion, but no prices set yet (am hoping to pay about $2500 on a used one, then spend another $500-$1000 and have it rebuilt to my specifications)

Note: On the VW, if your compression is still a bit too high, cylinder or head shims can be added to adjust it down, for your particular fuel requirements (Like the new 94LL ), it’s not a problem.

Hope this helps
Roger

[JRLAMB]

what i would like to know...

a. did you use the belt reduction put out by great plains...


b. what is your dry weight when you mounted the vw... not counting the engine mount...


thanks for the moment.... a kitfox iv... about 90% done...

[rogerh12]

a. did you use the belt reduction put out by great plains...?????
NOPE, JUST DIRECT DRIVE.

b. what is your dry weight when you mounted the vw... not counting the engine mount...??????????????? THE TOTAL PLANE WEIGHT WITH OIL WAS 654 LBS, THAT IS THE ONLY TIME I ACTUALLY WEIGHED THE AIRCRAFT.

thanks for the moment.... a kitfox iv... about 90% done...

[rogerh12]

Hey Guys;

I am looking at a couple of good used VW's for the kitfox, and got my first pricing. I thought I would pass it along for reference to a used Rotax 100 HP. This engine is a Great Plains 2300 cc engine, direct drive with less than 50 hours on it (nicely broken in). Here it is:

Basically a running 2300 cc, dual plug engine with all the extra stuff like oil cooling, baffling, remote oil filter, super HD oil pump, remote oil drain, and some engine instruments. Also, intake, exhaust, and Ellison Injector carb, but no motor mount, prop, spinner. $6000.

Well, would still need an engine mount, cowling and prop to finish the Kitfox-4-1200 with the 75 HP VW aero engine, (shimmed out to run on car gas). which would set me back another $1500 or so. So for about $7500, I have an "almost new" FWF package ($8000 will be budgeted) that can run on car gas.

This is fairly cheap, for comparison my buddy put in a factory rebuild 0-time rotax 100 HP for about $17,000 (minus the cowling) , but of course he gets an extra 25 HP and less weight. Still, I would save almost $10,000 bucks over that, and the real saver is the rebuild cost of the VW. It’s only about $500 in parts and I can do it myself, if needed.

Anyone know what Rotax charge for a rebuild?

Hope this helps.

Roger

[Av8r3400]

$8k for a converted auto motor with very questionable reliability and performance in an airframe like a Kitfox.

My good friend, Dave, just bought a complete, running 912UL (80 hp at a usable prop RPM) for $6500, 150 hours TT and a fresh tear-down inspection from LEAF. (The motor was involved in a crash - fuel exhaustion, no sudden stop.) Combine this with known performance & reliability and a supported FWF package with cowling from Kitfox. This would make for maybe $10k total FWF.

Personally, I would gladly pay a $2k premium for a motor that I would be totally comfortable trusting my own and my passenger's life with.

Roger, you are obviously sold on the VW conversions. At one time, I was too. I hope your plans work out for you. But, just stop and think for a moment, if this experiment does not perform (and I truly don't believe it will), you will have, at best, a plane that needs to be re-powered, at worst a wreck (that hopefully has not injured you or a passenger). Either way you are back to square one.

One man's opinion and my last input on the subject. Good luck to you.

[rogerh12]

Wow, 10K for a Rotax 80HP FWF is great deal !!!!. My pricing of 8K for a used VW FWF is conservative or course as it includes 6K for the engine (it's only his asking price). I am sure there are folks out there that will point out that I should expect to pay 1/2 that for a used VW Aero Engine, but these numbers are REAL and can be used for a direct comparison, and that's what I was shooting for.

Of course, I too would prefer the Rotax, but for a person like myself that buys and sells aircraft and engines occasionally for the past 10 years, I have never been offered such a smoking Rotax deal myself. However, I do run across smoking VW deals on a regular basis (I saw 4 over the winter on Barnstormers for cheap) and that means it’s possible to “low ball” and get your engine for even less (low ball a Rotax 912? Good luck !!!).

VW reliability questions aside (this is a factory build VW aero conversion, not one from "Bob’s airboat emporium") , we do now know the real performance of a VW powered aircraft, which is what started this thread:


N53RJ KitFox IV Speedster

Weights:
Basic Empty Weight = 700lbs
Max Weight = 1200lbs
Usefull Load = 500lbs
Fuel Capacity = 27 Gallons
Wing span = 28.8 ft.
Fuel Burn = 4 - 4.5 Gallons an hour
Cruise speed (economy setting) = 90 to 95 mph at 1500 feet (3000 rpm).
Cruise speed (high setting ) = 110 mph at 7500 msl.
Max speed (At full power) = 115 mph at 7500 msl.
Rate of Climb (two people) = 700 fpm
Rate of Climb (One ) = 1000 fpm
Take off roll at Gross Wt = 300 feet
Landing roll at Gross Wt = 300 feet
Stall speed (with vortex) = 37 mph
Approach speed = 60 mph

I personally call these figures "good" for a small low cost aircraft, beter than the Ercoupe I use to fly, that's for sure !!!!

Roger

[cainbird]

This past winter I bought a used early 912 with about 150 hours tt. It was involved in a crash caused by fuel starvation and no damage to the engine. I found it on Barnstormers and paid 6k delivered. I may have spent 1k bringing it up to snuff. I am not trying to discurrage you from your project, just saying the deals are out there, you just have to be patient and persistant. I hate to see someone spend tons of time and money on a project that turns out to be a dissapointment! If you can pull it off, buy a 912 and you will never regret it. Your resale will be about 10k better too!

Best of Luck~Cain B

[DBVZ]

I went for a demo flight Sunday in the Speedster on Barnstormer's that is in St. Louis. It has the Great Planes VW conversion. For what is it worth, the engine ran well, and operated like an aircraft engine. The carb and throttle body are the same as used on some small Lycoming engines; with a conventional mixture control and carb heat. We were unable to get up high for a speed test leaned out because of weather, but in the flat flying we were doing at full throttle the airspeed indicated 95-100 mph that his equipment translated to about 110mph TAS at the DA we had. We did not have a GPS we could use to check that against a GPS ground speed. He was still running full rich, so some better numbers at higher altitude seemed at least reasonable to expect. With the 62" X 32 pitch prop, he was turning 2900 at WOT running ROP with an oil cooler in use. Up higher with leaning it seems like 3000 or even 3100 should be possible, even though the engine power rating and the length and pitch of the prop seems to say it should not turn that fast.

Still, the resale issue is important. If the consensus of Kitfox builder believe the 912 is the right engine, and the VW conversions are not, it has got to limit the number of buyers that will even consider a VW powered Kitfox, and that ought to force down resale prices. But from the asking prices I see, the engine choice has some effect on the price; but not as much as other factors. I saw prices that range from about $20,000 to $40,000, and while the engine choice was one factor it did not command a $10,000 premium, nor did a VW conversion get a $10,000 penalty relative to aircraft near being equal otherwise. Things like the equipment in the panel, paint scheme, workmanship of the builder, TW or tri-gear, range and endurance, speed, care since finished, hours since finished, empty and gross weight, 2-cycle or 4-cycle etc, all contribute to setting the relative value of a specific plane. And then, some sellers have highly inflated expectations, and set the asking price that way,

[Geowitz]

Not trying to knock anyone's ability to make their own decision for an engine, but I simply don't believe the important number - Rate of climb. This is by far the biggest difference in a Kitfox between an auto conversion and the rotax. Also, in my opinion, besides reliability, rate of climb has the greatest affect on safety. 1000 fpm is a great rate of climb, but I just don't believe it's a true sustainable number for the VW. I think the "VW 1000 fpm climb" youtube video is misleading. When you build up your speed and get 1000fpm for 30 seconds it doesn't mean your true sustainable rate of climb is 1000 fpm. I want true pulling power and a VW with a 62 inch prop just doesn't have it. Sure, I researched the VW, but there were too many perfomance compromises that added up.

[rogerh12]

I agree, rate of climb is probably the biggest fudge factor you will see on airplane specs. Of course, it depends on many factors, such as prop, outside air temps, humidity and even thermal updrafts in the area.

As you saw, one of us got a ride in the VW powered Kitfox on barnstormers. Here is what he found (see below). This flight was made with two in the plane, but no total take off weight was noted. Also, it was done this summer, and it’s hot in the Midwest this time of year, so performance in the winter work be at least 10% better I would think.

Climb was 700 fpm with both of us in it. He did not use the flap handle at all for Take off or landing. We were on pavement, though a grass strip was available he thought it was too wet after recent rains. He did not work at a short field take off or landing, but roll was less than 500 feet for each, lift off was around 50 mph.

700 fpm is in line with my expectations, based on VW experience and performance specs for a similar (rotax equipped) plane. Less performance to be sure, but I will rate it as “pretty good”, and certainly better than a Cessna 150 with two in it.

Roger

[rogerh12]

2300 cc VW engine conversions are now available. Running avgas, 85 HP may be possible from this engine and it still wieghts in at about 165 lbs.

Roger

[SkyPirate]

I'll have to disagree with your statement about the model 11 flying terribly Roger,..my model 11 was a dream to fly,..she did everything I asked of her ,..yes it had the 582 in it ,..but then I have flown everything from ultralights to jets ( no not bragging ,..but it does help a great deal addapting to the "feel" of any aircraft in flight),..,..in any plane it's a matter of the pilot mastering the planes capability,..with co ordination

[Av8r3400]

At what RPM requiring the use of what diameter prop?

That is the entire argument against these motors' performance in a Kitfox. Low speed thrust works most efficiently with a large diameter prop.

[rogerh12]

Though props from different makers are measured different, and things like blade width and how the trailing edge of the prop tapers down effects the effective pitch, in general the props that seem to work best on the VW (with aircraft having large frontal areas like the kitfox) have 60-62 inch diameters, with a pitch somewhere between 28-34 inches, depending on engine HP and desired cruise rpm and projected cruise speed. Of course, your mileage may vary !!!!
The main problem in figuring pitch is that you need to factor in prop slip, or not. In some props its as much as 10-12%, on others it’s zero (or maybe even less than zero). Once you have the pitch selected, you can size the diameter (or you can just guess) Prop selection is a black art, but I do have software that lets me take an existing prop, enter it’s size and full power rpm and it will tell me how changes in diameter and pitch will affect it’s performance (fairly accurately). So if my existing prop needs to pickup 200 rpm, it will tell me how much to cut off the diameter, or flatten out the pitch to get those 200 rpm.
Hope this helps
Roger

Roger
Oh, I think I didn’t answer the question. Cruise speed on the VW is not set by rpm, but by manifold pressure. 22-25 inches is the cruise range, and this can correspond in a prop rpm between 2800-3400, depending on pitch and diameter of the prop. I like to size my prop to cruise at 3300 @ 25 inches myself (in my zodiac, which as a large frontal area), as this gives me a max power setting at 29 inches of about 3500 rpm (3400-3600 is peak power in most VW conversions, but peak torque is around 3000 and gives the best economy cruise compromise with speed). 22 inches will get me back down around 3000 rpm in the cruise, which slows the plane down a bit (but mostly reduces the fuel bill a lot)
Hope this helps
Roger

[akflyer]

I think you missed Larrys point. VW conversions have been done on the KF and Avids before. Bottom line is, if you want to retain the STOL performance you need to swing a big prop.

You say your a modeler. Look at the electric planes and how far they have come. Take a speed 400 motor. Direct drive you use a 6" prop and the plane will go fast but it wont climb for crap. The same speed 400 geared will swing a 12" prop and give you TONS more thrust for climb. None of the electrics really gained popularity because until the advent of a reliable gear box all that little prop did was make lots of noise but would not really pull the planes around.

One last test for ya on the modeling thing. Take any old tired worn out .25 engine you have and put your 8X7 or 9X5 prop on it. Use a digital scale used for weighing fish and get an actual thrust measurement. Now put a 10X 3 1/2 on it and take another measurement. I know for certain which one will produce the most thrust. Granted the plane wont be as fast top end, but it will go straight up, spool up quicker etc. That is why APC came out with the line of "fun fly" props that were weird diameters and pitch (like the 12 1/4 X 3 3/4) to use on a .40-46 size engine instead of a 10X6.

[HighWing]

Roger,
One sincere request please. I think the topic of this thread speaks volumns about your project. It has been done before many times and very little actual data about the performance. Is there only one of these guys willing to talk about it? Please, after you are finished and flying, post the numbers. What I think we would all like to see is empty weight. Prop pitch and diameter. Anything that had to be done to manage W/B. Take off distance, Climb solo and at gross. Cruise at 75% and max comfort level. Also, of course fairings etc. that can greatly affect certain of the performance numbers. Let's have at least two detailed reports of VWs in Kitfoxes. What we need is data. If it is great, people need to know of a real viable engine option. If it is not so great, in fairness, people need to know that too.

Historically, what we typically have in these situations is lots of thought and research. Lots of discussion. Great anticipation, then the 40 hours begins and lots of silence. It would be great if history proves all of the skeptics wrong.
Lowell

[rogerh12]

Hi-wing;

I would be happy to provide the requested data, but it’s going to be a while !!!!

What I can provide is data from the flying kitfox 4 in St. Louis , as outlined below, and of course my own personal experience with the Zenith 601HDS flying behind a VW. Though you might think it not a good analogy to the kitfox, in some ways it is. The cowling used on my 601 was the BIG one used with Subaru engines having Re-drives, so it was way bigger than needed and had significant frontal area. Also, though this plane is a taper wing, the wings themselves are very thick, crazy thick really and had a lot of drag. The landing gear used round tubes and also had a lot of drag.

What is my point? Well the 601 flew well with the 2180 cc 75HP version of the VW, and climb was better than the ercoupe I trained in, even with it’s short tapered 23 foot wing span, so I think that in the kitfox the climb would be better and cruise speed about the same (which is what the recorded numbers showed below).

Certainly the Rotax 912S is better for the kitfox all the way around, but the VW does appear to provide a fun and flyable compromise on performance at significant cost savings (I saw a brand new 2180cc VW aero long block on Trade-a-plane for just 3000 bucks !!!!) and with rebuild cost of around $500 bucks in parts, continual cost savings. Could the VW provide the kitfox with stall performance? Not like a rotax, but a flatter pitch prop would give a better static thrust for STAL flying, but this thrust will certainly drop off quick as the airspeed builds and not give much of a cross country cruise speed, if that’s what you are looking for too. I personally don’t need to get off the ground quick in Kansas, as that’s what we have lots of around here, ground, -flat long- ground.

Hope this helps
Roger

[rogerh12]

FYI:
This was the original post, and since then one of the members of our forum flew in it a few months back and thought these performance numbers were basically correct with respect to rate of climb and cruise speed (though he didn't weight it). Note: it does have the speed wing mods and vortex generators, it is also a tri-gear with spring gear, so my plane will be setup almost exactly the same as this one as mine has already been converted to Tri-gear (but will run the larger 2300cc engine on car gas)
Here is the post:
Ok, I finally was able to get the performance numbers off a flying Kitfox-4-1200 with a 2180 Great Plains VW motor installed, it‘s the one in St. Louis, currently listed on Barnstormers.
The great thing about this plane is it’s a known quantity. As VW aero engines can be anything from a 1600 cc 45HP engines to a 2300cc 100+ HP monsters (with water cooled heads), this engine has been identified as a 76 HP Great Plains 2180 cc engine turning a Sterba 62x32 prop at 3000 rpm in cruise. This engine requires Avgas at this HP rating and develops peak power at about 3500-3600 rpm, but typically cruises at 3200 rpm, which is close to where the peak torque is created.

N53RJ KitFox IV Speedster

Weights:
Basic Empty Weight = 700lbs
Max Weight = 1200lbs
Usefull Load = 500lbs
Fuel Capacity = 27 Gallons
Wing span = 28.8 ft.
Fuel Burn = 4 - 4.5 Gallons an hour
Cruise speed (economy setting) = 90 to 95 mph at 1500 feet (3000 rpm).
Cruise speed (high setting ) = 110 mph at 7500 msl.
Max speed (At full power) = 115 mph at 7500 msl.
Rate of Climb (two people) = 700 fpm
Rate of Climb (One ) = 1000 fpm
Take off roll at Gross Wt = 300 feet
Landing roll at Gross Wt = 300 feet
Stall speed (with vortex) = 37 mph
Approach speed = 60 mph

Final note, I think the cruise speed could be improved with a prop diameter 2 inches smaller, though the rate of climb maybe negatively affected (or not). I would call the rate of climb good for a small cheap plane, better than the cessna 152 I flew at gross weight !!!!

Roger

[rogerh12]

FYI;

Looks like another VW powered Kifox is on Barnstormers.
Too bad it has not flown yet, I would like to get the performance data from it. Judging by the large frontal area, it has the larger VW cowling.
Roger