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.
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/
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.