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AK 670 Powered Kitfox on Barnstormers

72 posts in this topic

Posted

There's a Rotax Rick 670 powered Kitfox in Fairbanks for sale on Barnstormers right now. Any of you guys familiar with the plane? I'm still trying to figure out if this engine is a viable option or not. I'm hearing a lot about it but I've yet to see or hear from anyone that is out flying behind one troublefree on a regular basis. I spoke on the phone with someone who has quite a bit of experience behind one and who I consider an expert and he said that the fun factor on an insane climbout is only good for the first 45 seconds but all the headache does not even come close to making it worth it if your looking to cruise for hours on end on multi state cross countries like I do.

 

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Posted

Did he give a list of what these headaches were.

I have one that's going on my mod 4 when its finished.

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Posted

Bob is sounds like most of the issues people are having is tuning related, having to wire the Rave Valves into a fixed position, and getting the exhaust system set up. A friend of Larry's had a couple of engine outs using one trying to get it tuned. Could just be a lack of 2 smoke set up knowledge who knows. I'll be really curious to see what starts popping up after time.I am going to need to make a decision on rebuild or trying something else with mine probably next winter. I would love to be able to climb out hanging on the prop but it's not worth it if it takes a 100 hrs of screwing with it to get it reliable and a bunch of work modding my plane to bolt it in. Keep us in the loop on your install.

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Posted

I may still do this in the future. More power is great and all but 4.5gph cruise is what I need! My 582 burns way too much fuel

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Posted

Bob is sounds like most of the issues people are having is tuning related, having to wire the Rave Valves into a fixed position, and getting the exhaust system set up. A friend of Larry's had a couple of engine outs using one trying to get it tuned. Could just be a lack of 2 smoke set up knowledge who knows. I'll be really curious to see what starts popping up after time.I am going to need to make a decision on rebuild or trying something else with mine probably next winter. I would love to be able to climb out hanging on the prop but it's not worth it if it takes a 100 hrs of screwing with it to get it reliable and a bunch of work modding my plane to bolt it in. Keep us in the loop on your install.

Joey,

Sounds like you need to take your fall vacation and shack-up at Soldotna, and help Leni get that 800 going!

EDMO

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Posted

Is he running the 670 in an avid where its upside down or right side up

in a fox? In an Avid the exhaust valves will carbon up. 

I have the 670 exhaust for a Fox and it fits inside the round cowl

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Posted

I may still do this in the future. More power is great and all but 4.5gph cruise is what I need! My 582 burns way too much fuel

The guy I spoke with who has a lot of experience with 670's and 583's told me this about fuel burn. He said ya it'll burn 3.5 gph if you keep it at 5000 rpm but that's like having a muscle car with a 505 big block in it and never going above 2000 rpm between shifts. If you put a hot rod motor in your plane your going to want to use the power! Even Rotax Rick will tell you that if you run a 670 hard it'll burn up some fuel...A LOT of it! With the exhaust and carb set up people have developed the power is a lot more linear than it used to be but keep in mind that engine was never designed to run at 5000-5500 continously like you would if you were on a long range cruise. I am sure the 670 is happy as a clam at 7000 rpm making tons of power and burning up tons of gas hence my comment about the WOW factor on takeoff but after that you basically have 582 power again. We all want more power but at what cost? 

 

How much gas are you burning in your 582? I flight plan for 5 an hour at 70 kts and that is conservative most of the time. A fuel computer is an invaluable tool. I found that with my set up I was burning 5.5 gph running it at 5800 rpm and cruising at 85 mph. By just backing the power off to 5600 the fuel burn went down to well under 5 gph and I only lost a couple of mph. Every plane has that sweet spot where it takes a lot more power and fuel to overcome the drag and pick up just a few mph. I discovered this concept in my truck too. I installed an Scangauge II to watch diagnostics while pulling my 6500 lb trailer and find the best speed to run to get the best mileage.

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Posted

At 1000' I burn 5.3 gph at 6000 indicating 95 on the dreamometer asi... Gives me 75-80 mph ground speed on floats and 1150 on the egts with the 582.

Ed, I got a picture a couple days ago of the almost completed adapter plate for the 800. As soon as Dave completes that and gets the fly wheel machined, I can start the engine mount and exhaust mods... It's gonna be a fun machine when I get that stuffed in the nose!

:BC:

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Posted (edited)

I called the man in Fairbanks about his plane w/670 motor. He only has 5 hours on the motor, gray head before.

He said takeoff and clime is great. Fitting the exhaust was the biggest problem because the maker turned

one elbow 180 out, mine is the same way and will have to be cut and rewelded.

We are only talking about 88 more CC's and one step up on jets. The motor, I believe was mint to follow

the 582 because of the drilled and threaded holes for the gearbox on the early models. I haven't found anyone

to verify this but there is no other reason for Rotax to fit the gearbox to a 670. Then about the same time

they brought out the 912 and the holes were no longer drilled on the 670.

Just guessing here.

Your exactly right about adding power. I have a Ford Ranger with a 289 V8 w/about 400 horse and is real

hard to not use it at every red light.

 

 

 

post-2-0-66073200-1375897083_thumb.jpg

Edited by akflyer

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Posted (edited)

I'm currently burning 6GPH at 6,000 RPM with barely an 80mph cruise on a Kitfox IV in a clean configuration

 

On takeoff I burn 6.5GPH at 6,500 RPM

 

If I back the power off below 6,000RPM my speed drops significantly.  (sub 75mph)

 

I am using a fuel totalizer and flow meter at all times.

 

I had a long conversation with Rotax Rick.  He explained to me that the 670 and the 582 work very much the same except for the RAVE valve.  At the same RPM's the two engines make the exact same power, even with his custom "tuned" exhaust.  The difference is the 670 can be cranked up to 6,900RPMs and the RAVE valve opens giving you more power for climbing.  That extra 400RPMS is what gives you the additional 25 HP).  At full throttle (6,900) the 670 will burn between 6.5 and 7 GPH in a Kitfox IV.  When you level off you throttle back between 5,800-6,000RPM.  You WILL NOT cruise any faster with this engine but you will climb alot more.  He explained that it takes alot of effort for the 582 to maintain 6,000RPMs hence the high fuel burn, with the 670 it just kind of chugs along at this RPM sipping about 4 or 4.5 GPH.  He recommended NOT running this engine above 6,000RPM other then for climbing, it will significantly reduce the life of the engine just like running the 582 at 6,500 all day long would not be good.

 

For someone like me that only has 15 Gallons of usable fuel it would make a world of difference reducing my fuel burn that much.  I would go from a 2 hour 15 minute endurance to almost 3 hours and 15 minutes.  That is a HUGE difference, I could actually take a fun trip instead of being stuck in the local area.

Edited by RMendler

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Posted

I think John Knapp was running a 670 when he refurbished his A-model Avid, and was running the 583 before that. If he could be reached he would probably have alot of input. I don't think he spends much time on forums, but I think he was on the yahoo site at one time. He also has a Micro Mong biplane on floats.

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Posted

The general aviation airplanes I have flown from 150's to Bonanza's, it seems Lycomings and Continentals burn about 5-6 gallons/100 horsepower.

I am sure the 2 strokes will also burn according to power output with no magical fuel savings with a certain engines including the 670.

Inflight Adjust Props and mixture control are the only way I have found to maximize take off, cruise performance and fuel burn on 2 strokes.

I want 100 MPH at 5 GPH on 29 inch ABW in my Kitfox which probably is not possible with a 2 stroke.

If money and weight and balance were not a problem, we would all be flying 912's for maximum power/fuel burn/weight.

Herman

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Posted (edited)

I have the 618. So far so good. Im still trying to get some clean numbers for fuel burn and speed. Right now she seems thirsty and slow! Slow I dont mind, but thirsty I do.

What fuel flow systems are you guys using? Yes, I'm sure a watch and a gas can back at the hangar should work fine....

I've got my prop set to 15deg, and I'm running 5800-6000 at cruise, 1100egt. My static is 6200 and wide open cruise is 6500. According to Rick, at 6000, I shouldn't be opening the rave valves. They really don't come into play until its screaming wide open which isnt what we do with these birds. For that reason, he did float the idea of wanting to secure the valves closed.

Today I need to give my cooling system a good once over. Doesn't help that its 97 today. But last night, after shutdown, my coolant was spewing out of the overflow bottle. I'm going to increase my water ratio to my coolant, check the cap gaskets, and make sure the overflow bottle has minimum fluid when cold.

Edited by Deejayel

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Posted (edited)

From what I understand the rave valve opens just at or over 6,500 rpm.

The mixture control (HACMan) does NOT work with the 670, has something to do with the RAVE valve.

Greensky and Rotax Rick confirmed this for me

I am using the NavMan 2100 as a fuel totalizer/flow gauge. It gives me total fuel, fuel burned per trip, total fuel burned and a very accurate flow rate. It also allowed me to install 2 external warning led's. One comes on in the event of a fuel line blockage and the other tells me when to turn my fuel pump on when my wing tank is almost empty. It works quite well.

My idling fuel burn used to be 1.5 GPH at 3,000RPM. I recently installed an AirTech RK400 clutch and my fuel burn dropped to 0.2 GPH at 1,500RPM. That's a big difference if your stuck behind some traffic on departure.

If I do not switch to the rotax 670 then I am going to add another wing tank and eliminate the tanks behind the seat. My airplane simply does not have the endurance to take me anywhere right now. With 15 gallons of usable fuel and 6gph fuel burn your options are limited

Or I can throttle back and deal with a 70-75 MPH cruise

Edited by RMendler

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Posted

John "Snaps" Knapp the famous Avid guy from Oshkosh is who I mentioned in my above posts about the WOW factor of a 670 vs a practical, reliable engine. He has been there and done that. I believe he holds a record for the shortest takeoff on floats in an Avid. There's a video on Youtube of him going side by side against a challenger on floats and he's about 300ft in the air before the Challenger gets off the water. Rmendler try adding a a degree or two of pitch into your prop. I found that 6000 on take off made it a cruise prop and 6500 made it a climb prop. I have a hard time grasping that my airplane will out cruise a Kitfox IV. I run 80 all day long at 5600-5800 rpm. That was with a 70" 2 blade tapered tip Warp. Still gathering data on my 72" 3 blade IFA Ivo. Thanks for confirming the Hacman rumor with the 670 also. That alone made up my mind. The Hacman is absolutely awesome when your up above 6000ft. I would also be adding the extra tank if I was you. No reason you can't go on longer trips in a Kitfox. I'm running 28 gallons of fuel. My longest leg I ever flew was right around 300NM in 4hrs and 15 minutes. I could barely walk when I got out and bee lined it for the back of the hangar when I landed but that's besides the point :flush:

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Posted (edited)

I just installed my 72" ivo ifa. I'm hoping my cruise will come up. I also removed most of my panel which let me take that Venturi off the side, that must give me 3mph or so.

I wish I was the builder, adding a tank would be a lot easier and much cheaper. A$P's and IA's charge a lot!

I could also kick the person who took the Hacman control off my 582. It's in the logbook as being installed in 2008 but its not there now ! I even have all the manuals with it! God would that help me some.

Edited by RMendler

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Posted

You don't need to be the builder to add a tank!

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Posted

Isn't it a major modification? Removing the wing, fabric and all?

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Posted

14 CFR 21.93 is pretty broad as far as a major mod. It includes things such as a different type of engine, new wings all together, ect. People rebuild their wrecked airplanes from the ground up and as long as it's basically the same plane that the Airworthiness cert was issued for originally it's totally legal. The biggie is the conditional inspection. As you probably already know if you are not the builder an A&P must sign it off. Doesn't even have to be an IA. Hope this helps.

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Posted

Awesome didn't know that. My local ia would argue with some of those points but whatever, I've modified this thing alot already.

A Rans S9 Chaos is on barnstormers with a Rotax 670. Apparently it is a fairly famous airplane

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Posted

Now that seems like a good match for a 670. WFO over the top of a runway doing aerobatics. I bet that would be a blast. It would be like flying a miniture Extra 300. If your looking at that guy check out the S-9 that has his ass saved by a BRS last summer when his wing departed the airplane!

Awesome didn't know that. My local ia would argue with some of those points but whatever, I've modified this thing alot already.

A Rans S9 Chaos is on barnstormers with a Rotax 670. Apparently it is a fairly famous airplane

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Posted

He was doing a negative pushover. Typically not recommended by Rans, haha. I would say we have a very high number of the chaos's here in North Carolina. I have seen 5 or so in the last year. Neat airplanes.

Why would one wire shut the rave valve? In all my talks with greensky and rotax Rick this has not been mentioned. Wouldn't it negate most of the power increase?

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Posted

The valve doesn't move until the very last part of the power band like above 6500 rpm.

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Posted

I bet if you wired that valve shut then the hacman kit would work! My understanding Is the valve opens, changing the intake pressure and preventing the hacman from leaning the mixture. Wire the valve shut and I would think the problem is solved.

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Posted (edited)

Please don't quote this to the FAA or your IA: Experimentals don't come under the same rules as certified - A certified would probably require you to buy an STC, or if in Alaska, and NOT in Missouri, you might get a field approval for a certified mod. AND, it would require a form 337 signed by an IA and approved by the FAA.

The best rule I have ever heard is: "It never happened if you don't report it". !!!!

You will need to do new W&B for your bird, but you can do that anytime you want to without any major changes - You don't need an IA at all - Just an A&P for conditional inspections every 12 months. And, you can remove wings, repair fabric, other maintenance, repair, rebuild, recover...etc.

ED

Edited by Ed In Missouri

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