Being in the "vented tank" camp, I really do not want to bring us back to an old debate, but FWIW my old KF2 (with a big "header tank" LOL) would get an airlock in the feed line from the wing tank to the main "header" tank. I would draw the main tank down to about half then turn the wing feed on (in the air). Air would then rise up (mostly due to more pressure in the main due to a main tank cap tube that produced pressure better) and that higher pressure would push air (in the half empty tank) up into the feed line to the wing and "lock" out the flow. I'd have to land and blow air into the wing cap tube to restart flow. So, possibly like the OP here, I was in a situation with unusable fuel in a wing (due to more pressure in one tank than the other). Here's a possible scenario that would be like what I experienced: If his right tank pressurized better, then it may have fed better and went empty sooner. Then, when empty, the pressure tube on the right continued to push across to his feeder / header (assuming no vent from header to left tank). The pressure from the right may have had nowhere to go except up the fuel line to the left, stopping flow similarly to what I experienced. If you think about it, it would be possible, (on the ground without header tank venting) to pressurize one empty tank enough to even reverse flow or blow air bubbles across to the other tank (if it were empty enough without a lot of head pressure), and that is why I am in the camp of header tank venting. But, admittedly, this scenario I purpose only arises in the air with a significant pressure differential (uncommon) and low head pressure (low quantity in other tank). Kind of a rare scenario, and that is probably why systems without vents work just fine for people most all of the time.
OK. The basic frame of the mount is all done and ready for the pro welder. It'll come back built enough to hang the motor and figure in addnl stucture and accessory mount points before it goes back for final welding and powder coat. Also note that in building my mount using the firewall as my jig (and not a proper jig), I used oversize tube (3/4") at the FW mount points and am using brass bushings with an offset hole (not in middle of bushing) to allow for the small amount of warp that I anticipated the mount would undergo in welding. So far that plan has worked well and I only had about a third of an inch warp in the main weld-up of the mount. Next will be some slow going while planning out and ordering all the little hardware and connections for oil and cooling systems.
The fella in ND is William Langford. He has made up some FWF components for the Yamaha that fit the KF 4-7 and has offered to help with custom engine mounts. Problem there for you obviously is about 1000 miles! But dont be too intimidated with making your own custom mount. I had not done it before and (with some help and a lot of time) was able to tackle it: http://www.avidfoxflyers.com/index.php?/topic/5345-yamaha-genesis-rx-1-install-in-kitfox-5/&page=2
Glad you had a good landing option in that field! Nice job getting your plane down safe!! I think your big question is why you couldn't use the fuel in that left tank. The guys here will have better ideas on that than I do, but my first thought is the same as "wypaul", whether or not you are equipped with a header tank. The other thing I've seen is a failure to get ram air pressure in a tank (clogged fuel cap pressure tube / bad fuel cap gasket / fuel cap backwards) In hopes of having a warning if a fuel feed problem arises, I installed a low fuel warning above my 1.5 gall header tank. This is the system Kitfox sells as an "add on" low fuel warning. Designed to give 10-15 min warning if fuel stops flowing (empty tank - clogged finger strainer - vapor lock - etc.) In theory a system like that should warn in a situation like you describe.
A while back there was a post about low fuel warning where I said I would post up the kit Kitfox is currently selling once I got mine from them. Nicely done kit indeed. Every last little washer, tube clamp, ect is included. Simple one page instructions. $185 Basically you tie into the fuel vent line and add a small tank which is mounted just above the header tank. Small tank has a float switch. In theory if fuel in wing tanks is empty or otherwise unavailable, the small added tank will go empty before the header tank and the float switch will activate a panel light. I plan to use the flashing and buzzing type light because the one kitfox sent was a small sinlge led type which I probably would not notice.
An update due here since Teal has now finished extensive ground testing (over the past few months) with this gearbox and now has it off to Steve Henry for flight testing. Teal is also accepting deposits on gearboxes and I'll remind him to come in here and post up the details.
Not a sales pitch here, but the Yamaha comes in at about 30- 40 lbs less than a Soob... with 130-150 HP. Lotta work to do a custom install, but one fella out there provides a semi complete FWF package for Kitfox. With a motor and all costs taliied up you'd be looking at right about $10k.
Yeah the internal tube has smoother transitions than what you see on the outside. And ideally that would be more of one piece formed tubes like you see when they do big production runs on something like motorcycle headers. But I suppose for a "one off" this is about as good as one can expect.
CUSTOM HEADER: I had a great experience with an outfit here in MN helping me build headers for the Yamaha! I first looked at trying to rework some auto / motorcycle headers but quickly learned that for a unique "one off" application that has to precisely fit under a cowl, you really have to go custom. So then you have two options: 1. DIY using auto parts fittings or 2. Go with the GP mock up kit which allows the following advantages: 1. A totally custom header design. With the mock up kit you have virtually unlimited options as to the routing, design, and output of the header. The guys at the header shop have a lot more options than you can find at NAPA! 2. Professional fabrication. This guy does this exclusively... all day and every day. Top notch materials, processes, and weld quality will pay off down the road and is definitely worth a few extra bucks IMO. 3. Your choice of material. From mild steel, 304 sst, and 321 sst. Price estimates were approx $900 USD for mild steel, $1200 for 304 stainless and $1800 for 321. My build was out of 304 and came to $1240 (with everything included). Below I will post up some pics of my build with the GP mock up kit. Pic 1 is of my pvc mock up with the GP kit. It only took a few hours to make! Pic 2 is the one piece CNC cut flange that GP made up for the 4 cyl Yamaha motors (note that it is made for the mock up kit with internally threaded stubs and obviously not the one used for final fabrication) Pic 3-5 are the finished product. https://www.gpheaders.com/products/custom-headers/
Had a great experience with an outfit here in MN helping me build headers for the Yamaha and thought I'd post it for anyone else that might have a need to do something like this. I first looked at trying to rework some auto / motorcycle headers but quickly learned that for a unique "one off" application that has to precisely fit under a cowl, you really have to go custom. So then you have two options: 1. DIY using auto parts fittings or 2. Go with the GP mock up kit which allows the following advantages: 1. A totally custom header design. With the mock up kit you have virtually unlimited options as to the routing, design, and output of the header. The guys at the header shop have a lot more options than you can find at NAPA! 2. Professional fabrication. This guy does this exclusively... all day and every day. Top notch materials, processes, and weld quality will pay off down the road and is definitely worth a few extra bucks IMO. 3. Your choice of material. From mild steel, 304 sst, and 321 sst. Price estimates were approx $900 USD for mild steel, $1200 for 304 stainless and $1800 for 321. My build was out of 304 and came to $1240 (with everything included). Below I will post up some pics of my build with the GP mock up kit. Pic 1 is of my pvc mock up with the GP kit. It only took a few hours to make! Pic 2 is the one piece CNC cut flange that GP made up for the 4 cyl Yamaha motors (note that it is made for the mock up kit with internally threaded stubs and obviously not the one used for final fabrication) Pic 3-5 are the finished product. https://www.gpheaders.com/products/custom-headers/
Good idea. Thanks for checking it over! Yes and as I was talking with a buddy here today, I think I will get it back from the welder, mount up the motor and fit all the accessories (airbox, oil tank, coolant system, ect). Then I'll mark off where I can add in some extra tube. In studying other examples it looks like I should be doing exactly what you suggest, essentially running two braces from every firewall mount location, making a triangle of support from each.
R-1 AIRBOX OPTION for APEX / RX-1 CONVERSIONS I ended up going with an 04-06 R1 motorcycle airbox. It is a nice small box that is available for about $35. (I need to credit "Yooper Ed" for finding and proving out this airbox... Thanks Ed!) The small problem with this airbox is that the 4 holes are spaced a little narrow, so I came up with a plan: I'm gonna use the snowmo airbox carb boots and sleeve 2" pvc into them and then into r1 airbox. I'll need to use 2" CTS (copper tube size) PVC which has an OD of 2.1", which should be a nice snug fit in the carb boots. Standard 2" PVC has an OD of 2.37 and will not fit. A little spin and flex of the carb boots should get the pvc lined up to slip in the airbox. Below are some pics and videos of my R1 airbox. (The second pic shows a comparison between the snowmo box (in front) and the R1 box I used.
Video #2 of my airbox, now complete with Frogzskin hydrophobic mesh prefilter:
OK, I've got a couple updates here that I'll copy over from the Facebook group.
First I'll post up some conversion tips I have learned from those who have built and flown the Yamaha, then I'll post up my (slow) progress in my build.
CONVERSION AND TUNING TIPS, Yamaha RX-1 engines ---- Airbox considerations: The snowmobile airbox is large and difficult to fit under a cowl, but when it is used, the RX-1 jetting (135 mains) and setup is fairly close to final tune. Typically, smaller custom airboxes are made and, generally speaking they tend to run leaner... requiring larger jetting (up to about 180 sized) to achieve the correct air to fuel ratio. An airbox is generally needed to buffer under cowl turbulence and allow for consistent pressure across the carb rack (RX-1). Individual filters on the carbs have been reported as highly problematic, especially at higher speeds / cowl pressures. Carburetor venting (float bowl) needs to match internal airbox pressure and not the under cowl pressure. This is typically done by running venting inside the airbox. (See note below) Also the crankcase breather is vented into the airbox. It should be noted that when rerouting the float bowl vent lines into the airbox that you should have a way to allow for fuel overflow to exit the bottom of the airbox. I have seen a stuck float in sleds where quite a bit of overflow comes out of those vent lines and you would want a way to evacuate that excess from the airbox and route it to a safe exit point. This airbox exit will also serve as a oil exit if any were to "burp" through the crankcase vent line in the airbox. I ended up going with an airbox off of the Yamaha R1 motorcylce (same engine block as the RX-1) and will make a seperate post on that. ----- Header construction: I chose a custom header from a pvc mock up kit that I will do another post on below. (Pic of my mock up below) Header primary tubes (prior to collector) need to be as long as practical (24"+ ideally) and as equal length as possible. A 4 to1 collector is common in the R1 motorcycle header, snowmobile exhaust (which is later split to dual exhaust) and aircraft fabrication. 4-2-1 designs have also worked very well. The primary tube ID on the RX-1 is 1.28 and 1.38 on the R1 (which uses an EXUP type valve in the collector to "choke" at lower rpms). So there is a 1-3/8 size that is ideally used (It can also be found as a 35mm metric size). It comes out to a 1.37 OD and about 1.32 ID. Keeping proper tube dia, long (and equal) primary length, and smooth inner tube transitions will help throttle response. If you try to deviate from those things too much your run quality will likely suffer. - Modding headers from other vehicles: Using a pre fabricated header off another vehicle can work well for non-cowled applications. For planes with a cowl, I found that the rework on any of these options outweighed a full custom fabrication. Some people have successfully used motorcylce headers such as from the R-1 motorcycle and 07-08 gsxr 1000. The motorcycle headers run about $50 on ebay but are sometimes made of titanium, so modifying them can be problematic. The 1990's Honda Civic headers have identical port spacing and are avail for $60 in steel and stainless steel but the tube diameter is a smidge on the large side which makes the "step up" transition from the snowmo flex flange output a bit problematic and there can be a little bit of throttle lag / hesitation when using tubes that are too large. Suzuki samurai headers have also been used and line up well with the head, but like the civic header they do not bolt right up, so you have to cut them and weld in a flange adapters. If I were working with the civic or samurai header I definitely would buy the one piece header flange (with stubs) for the yamaha 4 cyl from GP Headers to save a ton of time and frustration getting these headers matched up to the head. www.gpheaders.com - As far as mufflers, I am using a 2012-14 gsxr 1000 muff For those of you that have the yamaha three cylinder you can use the yamaha yxz 1000 side by side header pipe . Same engine nice long sweep headers that curve down. (See pic below) --- Tuning with the AFR guage: Some guys here know a ton more about the afr guage than I do, and which one is best to buy. I'll leave it to them to post up their opinions. But generally speaking, my notea show that we should be looking for Air to Fuel Ratios of about 18:1 at idle, 13.5 for cruise, and a little richer for WOT.. about 12.5 to 13.0 Teals note: I have ran a few RX1 aircraft and noticed that a leaner idle (17-19) seems to work really well. I have found that if i set the AFR at 13-14) at idle it will have a little rough spot around 4500-5500 rpm. --- RX-1 Jetting Ok. The RX-1 uses altitude compensating Constant Velocity (CV) carburetors. I'll let an expert explain how they work via the vacuum slides (yamaha calls them "piston valves") in front of the throttle butterfly, but generally speaking the vacuum slides have a spring that can be changed for tuning purposes, the main jets can be changed or drilled out to enlarge, the needle position (in the vaccum slides) can be raised and lowered, and the idle mixture adjustment made via a fuel screw. Alternate vacuum slide springs and main jets are available from Holtzman (Steve Henry's setup uses the blue colored Holtzman slide springs) NOTE THAT IF YOU CONTACT HOLTZMAN, TELL THEM YOU ARE TUNING A "SNOWMOBILE"! They don't understand experimental rules and are a little nervous about supplying parts for aero use. http://www.holtzmaneng.com/carburetion-products - As far as drilling main jets, If you have a full drill index you can open your jets up. A 135 main jet is 1.35 mm in diameter or .051" - Teals note: These carbs have 3 jets. A idle jet thatvis normally a 17.5 (.175 mm) a main jet (stock is around 135) and a starter jet (choke or enficher circuit). The idle jet is used up to about 1/4 throttle then the the needle positioning inside the the needle jet sets mixture. As the slide rises and the needle rises out of the needle jet (needle is tapered so the more it is pulled out the more fuel can pass) the more the main jet controls mixture. The main jet controls mixture mainly at 1/2 throttle and above. More so at 3/4 to wot. The needles have 5 positions just like most other carbs. Needle position is used for midrange tuning. There is also a screw on the bottom of the carb that sets air fuel ratio at idle and just above idle. One other thing ive noticed on a number of RX1 carbs ifs that idle jet is opened up. Im not sure if by normal cleaning or drilled. The hole in the idle or pilot jet is tiny at 17.5 (1.75 mm or .007" in diameter). One way to tell is to measure the cleaning wire with a caliper and see how it fits in the jet. Ive found that running these engines with opened up pilot jets causes a slightly rougher transition to the midrange and doesnr idle as smooth. Also this jet doesnt have anything to do with what airbox your using because at what throttle position that these jets are being used at the slides are causing the correct back pressure. Unlike when the slides are opened up at higher throttle settings and there is a lot of air flow through the airbox.
Yep been there too. Part of this game we play. No fun when it is "our turn at bat" and we strike out.... but the good part is that everyone else on your team understands and is there to pat you on the back.
That's right Buddy! We all have you in mind and prayer! You were the first to welcome me when I started in here... you stuck with me even when I became a traitor and switched away from "The Sooby", and then again as I became the self righteous know-it-all egomaniac that everyone now just rolls their eyes at! If you stick with me after all that then you're a hell of a guy! Get off that mind numbing juice quick so we can have ya back!
For anyone who might be following, I did an update 2 posts up on the c box that had a problem. And here's a pic of what was meant by "improperly assembled". Absolutely amazing that the gears and gearbox held up to 140 hp for 200+ hours with the gears barely even meshing like that!!
Teal contacted me today with a report that a pinion shaft bearing began to fail on a (appox 200 hr) Skytrax RX-1 running an RK-400 centrifugal clutch. This event is noteable because it is very similar to one other case where the same problem was encountered (also a Skytrax RX-1 w/ RK400, but with approx 110 hrs). Other noteable facts include: - Both failures suffered NO powerloss. The bearing began to give out but the rigidity of the RK-400 clutch (mounted on the PTO) helped keep the clutch drum and pinion shaft centered and the gears remained "meshed" and running. It appears likely that at least one of these two gearboxes ran for a number of hours in the partially failed bearing condition. The problem (in both cases) was detected during a subsequent preflight by noting some side to side play in the clutch drum. - Also noteable is that there are many other setups nearly identical to this one (centrifugal clutch with similar hrs of use) which have had NO problems, and also there have been no reported problems while running the rubber flex drive ("hardy disc"). ******UPDATE**** Analysis is back from the Rotax service center on these two gearboxes. It was determined that the latest gearbox was assembled incorrectly during a gear set change (see pic 2 posts down), and that both gearboxes had the pinion bolt come loose during operation. (that bolt in the center of the pinion shaft, bolt head located in gearbox, going out through to the coupling that connects to the clutch drum / hary disk) When that bolt came loose, the pinion shaft apparently "rode up" the gear teeth and rammed against the outer pinion bearing (in outer case), loading it axially which in time caused the bearing to fail. Also the gear wear pattern on the second (improperly assembled) gearbox had the large gear scraping the case cover and the pinion bearing race. Wear marks showed that the two gears in that one only had about 50% tooth alignment. So it looks like the problems here have been isolated to improper assembly and also more noteably from the pinion bolt coming loose, so a couple unofficial recommendations are suggested from the shop to users of the c gearbox: The pinion shaft bolt should be cleaned thoroughly and red loctite used during final assembly. (torque is 212 in-lbs) When you have the gearbox apart to that point, the axial clearance of the pinion shaft should be checked. This clearance is critical to bearing life and gear engagement. In the post below I'll reference the service manual excerpt on how to make this check. Additionally anyone running the Rotax gearbox can also make an easy preflight check to determine that the pinion bearings are in good condition. This is a simple procedure where you reach in the access / cooling hole and physically push on the drum / hardy disk. There should be no detectable side to side movement.