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|04-30-2012, 10:03 PM||#1 (permalink)|
Join Date: Apr 2004
Location: Lake Mary, FL
Interview - Designing the Whiplash Gas Helicopter - Chris Lund - April 2012
Todays interview is with Chris Lund of Flyco which is the parent company of Miniature Aircraft USA.
As you know Miniature is building the Whiplash line of XCell helicopters. Since this forum is about gas helicopters we're going to focus on the Whiplash Gas version and Chris Lund was the designer for it
GPT:You're a pretty busy guy these days, thanks very much for taking the time for this interview. Lets start off by finding out a little about yourself, background, where you are now, where you from originally, education, family, pets, etc?
CL: I was born and grew up in Rapid City SD. I started flying R/C models when I was 13, and have been addicted ever since. I attended college at Montana State University in Bozeman Montana, and graduated with a bachelors of science degree in mechanical engineering. After graduation I took a job at a large machine shop near Bozeman where I programmed, setup, and ran large machine tools manufacturing parts for several industrial industries. I then moved to Billings MT and started Big Sky CNC with FlyCo. My family is my wife and two daughters, ages 2 and 5. I grew up owning dogs but no pets currently.
GPT: You seem to hold several jobs with Flyco, can you elaborate?so are you effectively a design consultant to Miniature Aircraft?
CL: Primarily I’m the general manager of Big Sky CNC. I also work as an engineer for the Miniature Aircraft brand of helicopters.
GPT: So are you effectively a design consultant to Miniature Aircraft? Thats pretty typical of the industry today.
CL: I wouldn’t really call myself a consultant as I’m a FlyCo employee. We do consult with many people in the industry that are not employed by FlyCo.
GPT: Did you design most or all of the Elevated R/C products? and make them too?
CL: All of the Elevated R/C products are designed within FlyCo. Most of them are manufactured by Big Sky CNC.
GPT: What helicopters do you fly personally? I already know you fly a lot of gas powered models.
CL: Since early last year I’ve been flying the Whiplash Gas prototype. Previous to that I was flying an MA Stratus. The Stratus was the last glow powered model I owned. I’m now glow free! I fly some smaller electrics in the winter, but WG primarily. All the planks I fly are gas or electric as well.
GPT: So you designed the XCell Whiplash, I wanna focus on the gas version since thats the way we roll here. What were your original design goals for it?
CL: Our biggest goal with Whiplash is creating models for guys that want to fly, and fly a lot. We’ve designed them to be rugged, easy to build and fix, and have top level performance and quality without top level pricing. We set out to make the gas machine more user friendly than previous gassers on the market.
GPT: WG will be only the second production ready for gas model to use the RC format of Zenoah motors (vario was the first). What was the driver for using this motor?
CL: The cooling system and lower vibration levels were the driving factors. The cooling system on previous XCell machines needed updating for today’s flying. The Zenoah cooling system meets the requirement, so why reinvent the wheel? The RC engines also seem to run smoother in stock form, which is specifically important for the current FBL trend.
GPT: A common argument about the RC motor is that its heavier than the PUH version. Its clearly bigger. whats your position on that?
CL: We found that the different in weight is fairly small when a cooling system is added to the PUH engine. I believe the smoothness and user friendliness is worth the small weight penalty.
GPT: Did WG start with a blank sheet of paper or does it incorporate parts or ideas from other XCell models?
CL: Almost. The Fury55 and Furion6/450 were the first big step away from the Fury/Stratus design. We’ve taken that one step further with the Whiplash machines, but we have incorporated ideas and parts from those models.
GPT: How do you come up with dimensions for something like this?
CL: We start by laying components out, and filling in the gaps like a big 3D puzzle. The final part dimensions are set by the assembly.
GPT: what design tools do you use?
CL: We model everything in SolidWorks.
GPT: Was the entire model built in 3D before any parts were made?
CL: Yes. Everything is “virtually” assembled before we start cutting parts.
GPT: Was WG your first complete helicopter design? if not what was?
CL: I had some input on the Fury55 and Furion6, but the Whiplash is the first model I’ve been involved with from start to finish.
GPT: WG is available with three gear ratios, how did you go about deciding to make exactly three and which three?
CL: I looked at what engines are available and what the recommended rpm ranges were. Comparing that to the head speed range set the required ratios. I calculated a range of roughly 6.5:1 to 7.3:1 that would accommodate the current engines on the market. In keeping things simple, we decided to adjust the ratio by changing pinions and keep the same main gear for all the Whiplash models.
GPT: You chose graphite for frames. some mfgrs use GRP or FRP for vibration resistance. can you comment about why you went with graphite?
CL: We’re using graphite for its low weight and high strength. The WG frame is big so the weight penalty of using fiberglass is noticeable.
GPT: you and bobby watts are the whiplash designers. Did you both work on all of them equally or did you sort of divide them up by platform?
CL: We started with a combined effort on the nitro frame, head, and tail sections. From there Bobby took on the majority of the electric and I took on the gasser.
GPT: Was one of them designed first or did they all happen in parallel?
CL: The head, tail, and nitro were first. The electric and gasser were somewhat parallel.
GPT: What do you think is the most unique feature on WG?
CL: The clutch stack is probably the biggest departure from traditional heli design.
GPT: WG does seem to have a rather unique clutch system for a model helicopter, tell me more about it
CL: We’re using the Zenoah swing shoe clutch. It’s heavy duty, inexpensive, and works really well. We’ve retained a 6mm start shaft for the guys that want to spin start or run a generator. The start shaft also helps with rigidity up top. There’s no second gear or crown gear so the auto sprag is in the clutch bell.
GPT: So the model can be both pull started or top started with a spin starter. Probably takes a pretty good spin starter to work eh?
CL: I’ve found any starter capable of spinning a .90-.120 slimer will start typical gas engine.
GPT: The fuel tank is in the front of this model. thats less common today can you talk about how that came to be?
CL: It’s mainly due to the way the cooling system works on the RC engine. Cooling air is pulled up from the bottom of the engine and exits on the muffler side. Mounting the engine with the cylinder to the front would require removing about half the canopy on the muffler side. Otherwise the engine would be exhausting hot air inside the canopy. Electronics don’t like hot air blowing on them. If the tank was in the back accessing the park plug and balancing the model would be difficult.
GPT: How much does the model weigh RTF? Is that heavier, lighter or about the same as other models on the market?
CL: It depends a lot on how it’s setup. It’ll come in anywhere from 12-13lbs depending on equipment used and if it has a flybar or not.
GPT: Touchy subject i suppose, how does the model hold up when it crashes? Are their sacrificial parts? Whats the common break parts? Usually the frame is the most painful part to repair, how does it hold up in crashes?
CL: Despite my best efforts I’ve crashed WG a few times now. Overall the machine is very robust and I haven’t broke a frame. Typical crash parts are the normal suspects: main shaft, spindle, flybar (if you use one), tail boom, torque tube, boom supports, etc. The canopy is mounted on sacrificial break away tabs that help keep the frame and canopy intact.
GPT: So how does this compare to the earlier Spectra-G in terms of build complexity?
CL: WG has a lot less parts which makes is faster to build. Other than that the biggest thing Spectra owners seem to struggle with is engine/fan alignment. Once everything is in place the Spectra drive train works great, but getting there is a little tedious. WG is more “bolt it up and go.”
GPT: How does the model perform as compared to other gas helicopters on the market?
CL: It flies better than any other gasser I’ve flown. It definitely feels like an X-Cell.
GPT: It looks really easy to change gear ratios, how does that work on WG?
CL: Changing ratios is just a matter of changing pinions and moving the engine. The engine mount and start shaft block have 3 sets of holes. Each set of holes corresponds to a pinion size so the stack is always aligned by the frame.
GPT: Where is the fore/aft CG on the model with and without fuel?
CL: The tank sits forward in the frame so it’s slightly tail heavy dry, and slightly nose heavy full. Some muffler options are offset back more than others so that has some effect but overall it flies very neutral.
GPT: What about the vertical CG, the RC motor certainly looks big, where is the chassis CG relative to the tail boom or rotor head?
CL: The vertical cg point is very close to the centerline of the tail boom allowing it to roll very axially.
GPT: The spectra allows the motor to be installed in different directions, WG is fixed with the motor facing backwards. what was the consideration for that?
CL: The engine is mounted backwards due to the cooling system, cg and spark plug access set the location for everything else.
GPT: What parts are different/the same between WG and WN/WE? Do you expect to see conversion kits?
CL: The complete head assembly, tail assembly, canopy, landing gear, main gear, main gear hub, main shaft bearing blocks, servo mounts, radio tray, and gyro tray are common. Many of the frame spacers and tray mounts are common also. There will likely be conversion kits.
GPT: Any likelihood of offering a PUH version or conversion?
CL: Not unless there becomes a large demand for it. If someone comes out with a 14HP PUH engine I will be converting mine instantly!
GPT: At the time of this interview, WG is near production, are you planning an R2 version for the future yet or did you get most of what you wanted in this one?
CL: Any changes we’ve wanted to make are in the R1 version
GPT: What motors have you tested in WG so far? any preferences?
CL: WG has been tested with both stock and modified engines. Alan at TRM Power has been supplying us with performance modified engines for the 3D demonstrations. TRM has a long history of working with and supporting MA. He’s been great to work with!
GPT: whats your take on the larger (slower, more torque) vs smaller (faster, more HP) engine argument?
CL: I think there are many ways to skin a weed whacker! I don’t have much to contribute to that argument as I’m not an expert on the inner workings of 2 stroke engines. If an engine is generating the performance I’m looking for, I’m not too picky about how it does it.
GPT: So back to your original design goals for WG, do you think you hit them?
CL:I believe so. WG is far and away the best model I’ve owned. It’s allowed me to be "done" with glow power and I have no desire to go back.
GPT: So what do you think is next for gas helicopters? whats the next evolution?
CL: Currently the gasser market seems to be focused on the 700 class of helicopter. I think we’ll see that broaden both bigger and smaller.
GPT: Do you see any revolutionary changes coming, you know a game changer?
CL: A ground up heli specific gas engine would be the most likely thing. There are new gas engines constantly releasing to the plank market. As gas helicopters become more popular, engine manufacturers will take note.
GPT: What do you think will cause more pilots to adopt gas power as a plaform?
CL: I think it’ll be mostly driven by the costs of flying electric and glo. The performance of gas helicopters has gotten to the point where they appeal to the guys wanting to up their flying skills. Current gas models are capable of any maneuver in the book. They’re a little heavier and slower than glo and electric however they’re perfect practice machines.
Thanks very much for your time Chris and your dedication to Gas powered helicopters! Looks like you've really kicked it up a notch for Whiplash Gas! I know a lot of people are anxiously awaiting its delivery!