Long Neglected Mosi Motorglider Project is Going Electric!!

For those of you having shown interest in my Mosi project, please excuse my neglect of it and the feeble level of progress seen over the last few years..
My workload has been very heavy, and I loaded myself with other projects, like the SWIFT ultralight glider.. which I just sold, by the way... it was an awesome wing, but my 61-year-old body foot-launching a 140-pound glider on a regular basis proved to be impractical, and there was no well-sorted-out power package available, and there were no suitable ultralight towplanes in this area.
So the SWIFT turned into yet another non-flying project that was yet another drain on my spare time & scant resources.
It seemed like a better plan to liquidate the SWIFT and refocus efforts & funds on the Mosi project.

On the Moni powerplant front, the long-since out-of-production KFM-108 engine had its day.. people are steadily migrating away from it.. due in no small part to the lack of factory support.
Other 2-stroke engines (Rotax-447 etc.) have been successfully used, but they are now out-of-production as well .. it's only a matter of time before support for them are gone too.
And my hope to build a 4A032-based 4-stroke power plant for the Mosi .. while certainly plausible .. began to loom large as time & money pit .. far too life-consuming for a one-off aircraft effort, and also with diminishing parts & tech. support..

In the the last few years, a lot has changed .. particularly improvements in electric propulsion technology.
It is suddenly is looking a lot more promising for the Mosi and similar aircraft!
Model aircraft have undergone a rapid electric revolution in a big way.
Instant power availability, low vibration, no exhaust disposal or fuel storage/delivery issues, CG flexibility, etc.. certainly, there are drawbacks too, such as low duration/range, and high up-front costs, but it's getting better very quickly.

So, I've decided to go ELECTRIC !!  no more gasoline!
But YIKES!! Now I have to learn about a whole new world of rapidly changing technology.
You all probably know of Randall Fishman's admirable electric power adaptation of the Moni a few years ago, under his Electraflyer moniker.
http://www.electraflyer.com/electraflyerc.php
I've talked with Randall, and he has a lot of impressive experience & knowledge about it.
He's making a commercial go of it, trying to sell his flight-proven batteries, controllers, chargers, motors & airframes.
His prices are kind of steep, but not that bad if you consider life-cycle costs.
Do-it-yourselfers on a tight budget are scared off.. and some are trying to adapt RC hardware to do the job .. with mixed results... cheap stuff usually works, but not for long, and the life-cycle cost of Giant-scale RC hardware probably ends up being worse than quality Electraflyer components in most cases .. but I have very little data to go on.. and new products & suppliers are coming & going almost daily.. impossible to keep up.

So, I'm going to bury myself in studying about motors, batteries controllers, chargers.. etc. etc. for a while, then go buy some hardware and start testing it.

As always, your comments and advice are welcome!

2013: A New Beginning

Well, yet another year has flown by.. a year filled with long workdays, peppered with a series of looming deadlines, and not NEARLY enough time to spend on my Mosi project!...  I often fly hang gliders when I can tear myself away from work .. I've got a UP Predator 158 and a Saturn 167.  And to make matters worse (or better, from another perspective), I picked up another motorglider project last year, which has absorbed almost all of my building time.. It's a Bright Star SWIFT .. an ultralight sailplane or a joystick-controlled rigid wing hang glider, if you prefer.. I fixed it up and flew it in 2012.  YouTube video link of my first flight in it:  http://www.youtube.com/watch?v=NYtA4Tush44

The Mosi project came to a halt as I devoted almost all my spare time to getting the SWIFT flying.  Right now, I'm in the midst of adapting a small 4-stroke power unit to the SWIFT undercarriage.  The engine I have selected is based on the single cylinder 212cc "Predator" engine.. you can buy one from Harbor Freight for $100.  It's "Made in China", and while that usually means dicey quality, this is actually a solid-built engine.  I've stripped it, added some performance parts, replaced gaskets, and am now planning to mill the heads and bore/replace the carb... I'm hoping to get 14 hp @ 5,000 RPM out of it.  Dan Batchelor has done a lot with this engine and he's been very helpful and encouraging.  He reports on his continuing progress on the "Egg Motor" Yahoo group site, so check it out if you're interested.. it's primarily a place for 4-stroke direct-drive paramotor "egg-sperimenters".. ;)  http://uk.groups.yahoo.com/group/eggmotor/

But I have NOT abandoned the Mosi project!!  ... just temporarily neglected it.  I have gone back and forth on Mosi engine and landing gear options until I'm dizzy, but I'm committed now to the original plan of using the 4A032 engine.  The more powerful 2A042 turned out to be just a bit too heavy and wide.. sticking out of the cowling several inches on each side.. which is kind of ugly for my taste, and is a significant drag increase that would erode power-off soaring performance... the 4A032 just fits inside the cowling.  Also contributing to my re-reversal of engine selection are some encouraging reports of performance upgrades that others have successfully made to 4A032 engines.  In fact, there's reportedly a MiniMax ultralight out there powered by a souped-up 4A032 that has "hundreds of hours" on it and still running strong and smooth.  Upgrades typically include a larger carb and milled heads for higher compression.  I may install an electronic fuel injection system and new ignition from Ecotrons.. expensive, but more reliable, easier starting, automatically altitude-compensating, and free of carb icing problems.

The Mosi landing gear will be taildragger style, like I had originally envisioned.. it looks cooler than tricycle gear, plus has lower drag and is easier to connect up with existing hardware.  I obtained Grover spring aluminum legs for the mains.. this has a fairly low drag profile, and provides an extra 3 inches of prop clearance compared to the stock monowheel configuration.  That'll be perfect for the 40-inch diameter prop that is matched to the 4A032.

So, during 2011-2012, I admittedly didn't accomplish much on the Mosi project... guilty as charged.
However, in the last couple of months, the project has started moving again. The molds for the wing tip extensions were cut on my CNC foam cutter out of huge blanks of 3 lb./cu.ft. EPS foam, seen here.  These wings tips add 4 feet to the span on each side and taper from 26.5 to 9.5 inches in chord, not counting ailerons.  Added to that will be non-movable wingtips, shaped similar to "Horner" tips.. That will bring the total wingspan of the Mosi to 34.5 feet.  I also carefully measured wing airfoil co-ordinates for a good fit to the metal wings and found out that the original Moni airfoil section is a very close fit to Wortmann's FX 61-147, contrary to other reports.

Also cut were the foam molds for the Y-tail airfoils.. I decided to go with the old standby tailplane airfoil, NACA 0012.  The Eppler airfoil I had originally planned on using is a laminar section, which is a little trickier to implement, plus the tail surfaces are mostly in turbulent prop wash anyway, so the primary benefit of a laminar flow section is lost.

More updates coming soon.

Dan

Engine Giver

OK, "slight" change of plans. ;)

Here we are in the new year again.. not much has changed.. but on the other hand, a lot has.
I've been rethinking the Mosi power plant, and doing some wing & tail feather work as well.

Bottom line: the 4A032 engine seems a little too small to provide a comfortable climb rate margin at the density altitudes at which I want to fly the Mosi... it'll be operating out of a 5,000 ft. elevation home airfield, hopefully to go up to 15,000 ft. on occasion, in the summer months.. this scarcity of atmospheric oxygen leaves the "world's smallest flat-4" in the "inadequate power" category file... yeah, it would get airborne, but the climb rate would be underwhelming.

So, I've decided to switch to the 2A042 military surplus engine. It's a flat-2 (AKA Opposed twin, AKA Boxer twin) with 42 cubic inch total displacement, 21 cubic inches per cylinder.. 3.00 inch stroke, 3.00 inch bore. See 2A042 Yahoo Group for more details: http://groups.yahoo.com/group/2A042/

Empty weight should come in at around 80#.. the final number depends on many details.. (ignition, starter, battery, carburetor, engine mount, oil pan mods, etc.) . So, with the somewhat heavier engine hanging on the nose, reducing tail weight is not as big of an issue.. getting the CG right looks easier (on the other hand, nothing is as easy as it seems). The stock Moni cowling will have to be modified, as the 2A042 is too wide to fit in as is, but a couple of side bulges might look kinda cool anyway, so no worries !! ;) The engine I'll be using will be here in a week or so, and I'll post pictures ASAP. The right-size propeller looks to be around 40-42 inches in diameter, with 32-36 inches of pitch.

I'm still planning to go with tricycle gear, Y-tail, and wing span extension panels. .. more to come!

With the New Year Comes Renewed Commitment

It's 2010... HIP HIP HOORAH !!! (oh, crap!)

Along with the new year's celebration comes the realization that I made far too little progress on the Mosi project in 2009. One of my new year's resolutions is to complete the Mosi by the end of the year! A tall order, to be sure.

Also, I pledge to update this blog on a monthly basis.. at a minimum. I haven't even visited this blog site for months and I noticed a couple of comment postings from a last summer that I hadn't even seen before. Sorry, gents! That is shamefully irresponsible of me, and I vow to do much better... I shouldn't use the crushingly heavy workload in my "day job," my elbow surgery, or the cold weather as excuses. Anyone can at least commit to a few minutes a month.

Mosi status:

The fuselage has been stripped of it's old landing gear, and it's sitting up on sawhorses, waiting for me to finish the 4A032 engine mount, Y tail, and landing gear... all of which are still in the drawing stage.

I have decided to keep the original plan to make it a conventional tail-dragger for simplicity and better looks. Also, I decided to make the Y-tail and wing extension sandwich panels out of Carbon fiber/epoxy skins over PVC foam core. This should be much stiffer & stronger without the worries over styrofoam outgassing & delamination.

Pictures and further updates to follow in about a week. May the new year bring health, happiness and fulfillment to us all!

Gear in the Headlights

The long pause in my postings is due to an unusually heavy workload at Compositex... (what is this "recession" people keep talking about?) I'm not ready for retirement, and the incredible shrinking 401K does not help matters. But I can't complain.. the only thing worse than working is NOT working. Anyway, I will hopefully be less busy with the "day job" so I can devote more time to the Mosi project by the end of May.

I've been going back & forth on my landing gear choices, and this decision impacts the planned Y-tail and engine modifications. I've been stuck on this indecision loop for too long already, and am itching to move ahead. Here's some background on it:

The original Moni monowheel gear (one fixed main wheel near CG, two fixed wingtip wheels, one steerable tailwheel) is OK for the small 33" prop, but I need more ground clearance for the 40" prop, and a taller monowheel leg would drive the need for taller tailwheel and tipwheel legs too... it gets a bit ugly. The monowheel Moni ground handling and tipping forward/prop striking tendency has never received rave reviews from pilots to begin with, and putting it on stilts is bound to make it even worse. My plan for the last few months had been to convert it to a taildragger configuration (fixed dual main wheels ahead of CG with steerable tailwheel), which I still think is the coolest looking and simplest option... but there are drawbacks. Taildragger cons as I see them:

• Higher likelihood of prop strike
• Greater difficulty on ground handling
• Greater tendency to "ground loop"
  
• Less visibility of runway on takeoff roll
  
• Longer takeoff roll
• Greater difficulty with takeoffs & landings in cross winds
• Higher likelihood of damage to tail surfaces from runway rocks
• "Ballooning" back up after initial landing touchdown
  

So, I'm now leaning towards conventional trigear (dual mains behind CG with nosewheel). The original Moni had trigear as an option, but I haven't found much info. on this yet. Final decisions are yet to be made on brakes, steering and gear leg structure. Solid aluminum spring gear legs mounted on the fuselage is one possible answer, but this is a bit heavy and draggy and requires "gun drilling" to get the brake lines through. A streamlined hollow-molded composite spring gear of equivalent strength is certainly a viable option, and is probably what I'll end up doing. Another option is spring loaded gear legs mounted off the main wing spar and not attached to the fuselage at all. This would create less drag due to a smaller exposed frontal area and being located completely out of the propwash, but this option requires tearing into the wing skin. If I was building the wings from scratch, I'd probably do it that way, but I'm not.. so I won't. Even better would be retractable gear... but that's opening an even messier can of worms.

I'm thinking a steerable nosewheel with symmetrical main wheel braking is a much better option than castoring nosewheel and differential braking of main wheels, mostly because of how the brakes need to be adjusted and controlled. Direct coupled nosewheel steering needs to be designed at some rudder-to-wheel steering ratio TBD.. I need to learn more about that to do it right. In any case, changing to trigear on the Mosi increases the labor hours even more, but I think the result will be better overall. -- Change one thing, change EVERYTHING!!

As always, your comments are welcomed.

How You Can -- More or Less -- Get More with Less

Many people are irritated by my claim that the climb rate and cruise performance of a KFM107-powered Moni (supposedly 25 hp) can be matched with a 4A032-powered Mosi (supposedly 16 hp). Until the Mosi is flying and generating test data, opinions and beliefs are likely to remain unchanged... hell, even I won't believe it 'til I see it .. but for now I can at least estimate, calculate and predict, so here's a plot of my performance predictions for these two aircraft. The data for this plot is from my spreadsheet-based performance model, reported in pounds of thrust or drag as a function of TAS (true airspeed) reported in miles per hour assuming a 5,000 ft. elevation, which is about what most of the airfields are around here (Salt Lake City area).

Total drag force (see solid lines on the plot) is the sum of induced drag and parasitic drag, and each vary greatly with airspeed. Basically, induced drag is dominant at low speed, while parasitic drag is dominant at high speed. Note that at the lower end of the speed range, the Mosi's greater wing span of 33 feet results in significantly lower induced drag than the Moni's 27.5 ft. wing span. This drag advantage diminishes with increasing airspeed, and above 105 mph, where parasitic drag is greater than induced drag, the Moni's overall drag is lower due to its slightly smaller wing area (75 vs. 84 sq.ft.).

The Moni's thrust was calculated for a standard Moni propeller (33" diameter, 18" pitch) spinning at 6,000 RPM, while Mosi's thrust was figured at 3,600 RPM with a 40" diam., 30" pitch prop. Note that the Moni's thrust is indeed higher over the entire speed range (see large dashes on plot)... but before you jump to conclusions, note that maximum climb rate is determined by thrust minus drag (T-D) at the best climb airspeed. After taking-off and clearing the runway, you attain your maximum climb rate at about the same airspeed used for engine-off minimum sink gliding flight... which is also the same airspeed for maximum endurance or minimum required power to maintain level flight.. they're all the same. Because the Mosi has slightly larger wing area and wing span, it has a best climb airspeed of 48 mph, while the Moni's best climb airspeed is 55 mph. Comparing the T-D curves (see small dashes on plot) of the Moni vs. the Mosi ... note that the Mosi T-D peaks at 48 pounds, while the Moni T-D reaches a maximum of 45 pounds. The result is that the maximum climb rate of the Mosi should be at least as high as the maximum climb rate of the Moni in its standard configuration... That's an encouraging result!

Not shown on the plot is the power delivered by both engines at this best-climb condition.. it's 17.2 bhp for the 4A032 and 19.8 bhp for the KFM107... you see? Getting more with less... more or less...and if you assume the 4A032 can only crank out 16hp max.. using the same 40x30 prop, the Mosi has a maximum T-D of 45 pounds, exactly the same as the KFM107-Moni.

The performance model also predicts maximum airspeed (where T-D equals zero). The KFM107-Moni is shown to reach a top speed of 99 mph with an engine power output of 13.1 bhp, while the 4A032-Mosi is expected to top out at 94 mph, needing 10.4 bhp from the engine... but wait... let's review the assumption of constant propeller RPM. At increasing airspeeds, propellers naturally unload the engine and loose thrust because the angle of attack on the spinning blade airfoils is decreasing. If you keep increasing airspeed without increasing the RPM, the prop will eventually provide zero and then negative thrust as it starts to "pinwheel" while your aircraft goes into a steepening dive. If you want to get to higher airspeed in level flight, it becomes necessary to increase the pitch of the propeller and/or increase the propeller RPMs. The problem is that the Moni's propeller blade tip speed is already at the sonic limit of Mach 0.80 due to the 33" diam. direct-drive prop on the KFM107 engine spinning at a nominal 6,000 RPM. It's generally considered good practice to have propeller blade tip speed at Mach 0.75 or less. Beyond Mach 0.8 tip speed, higher RPMs will result in little or no increase in thrust, but it will result in rapidly increasing fuel consumption and prop noise decibel levels, so there's no good reason for it.

In contrast, the Mosi's 40" diameter prop at 3,600 RPM has a blade tip speed of only Mach 0.59 at 100 mph forward airspeed.. consequently, it should be very quiet. You would have to spin a 40" prop at 5,000 RPM to reach the Mach 0.8 limit. If the 4A032 engine with a 40x30 fixed-pitch prop is spun up from 3,600 to 4,000 RPM, as it should be able to do with a low load on the prop, the Mosi can attain a maximum level speed of 105 mph, which is 6 mph faster than the Moni... This will require 14.1 bhp from the engine and will maintain the blade tip speed at a benign Mach 0.65 .. and with a higher pitched prop, CRUISE EFFICIENCY CAN GET EVEN BETTER!!

But you usually aren't flying around with the prop at maximum RPM. After getting to a desired altitude, you probably want to level off and get somewhere as efficiently as possible. It would be typical to cruise at 60-80 mph to increase your range and fuel economy. To do that on the Mosi requires throttling the engine down to perhaps 2,400-3,200 RPM. Fortunately, 4-stroke engines generally have a wide RPM range for smooth operation, but 2-stroke engines have been known to run rough when they are throttled down below their relatively narrow power band (ironically, 2-stroke engine guys call it "4-stroking" when their engines run rough at lower RPMs). But ignoring that, and just comparing engine power requirements in level cruise at 60-80 mph, the 4A032-powered Mosi requires 5.2 to 8.0 bhp, while the KFM107-powered Moni needs 7.1 to 8.9 bhp.

Therefore, it is expected that with its more efficient wings and propeller, and the flexibility of being able to vary RPM over a broad range without exceeding engine or tip speed Mach number limitations, the 4A032-powered Mosi should be able to match or exceed the climb rate and cruise performance of the KFM107-powered Moni in spite of engine maximum horsepower ratings that would suggest otherwise.

But what about fuel consumption? The 4-stroke 4A032 is expected sip fuel at about one-third to one-half the rate of the KFM107 2-stroke at normal cruise power settings. That ought to keep Al Gore & his cronies off my back.. And what about pollution levels? Not even in the same league! 2-stroke engine exhaust is notoriously dirty, as your sense of smell can easily confirm. With all the increasing emphasis on environmental issues nowadays, it just makes sense to use a quieter, cleaner and more fuel efficient power source... why irritate your friends & neighbors?... it's best to keep them on your side!

I've studied this alternative engine option pretty thoroughly and am satisfied with the engine & propeller plans I've made for the Mosi, at least, so far. But watch out.. if it can go wrong, it will go wrong!.. Murphy and his gremlins are always ready to spoil your best laid plans without warning. If it turns out that in static tests the 4A032 doesn't crank out nearly as much power as I thought ... I'll have to decide whether it's worth it to keep tweaking the engine to squeeze more power out of it, or shift to a different 4-stroke engine option... in any case, I ain't goin' back to no stinkin' 2-stroke!


As always, your comments are welcome.

Painting the Outside of an Airplane from the Inside

Here are pictures of a couple of the many dozens of test panels I've made of fiberglass/foam sandwich construction. The S-glass/epoxy composite face sheets are about 0.005" thick, with a 0.25" thick sheet of HighLoad 60 Styrofoam in between. I've been trying to get the best combination of surface preparation for the foam and exterior painted surface finish for the Y-tail and wing tip airfoils, and some of the results have been promising. The picture of the panel on the right shows a mirror-like glossy finish obtained only with run-of-mill aerosol-can white spray lacquer from the hardware store. This was done by applying release agent to a Mylar caul sheet, followed by spray painting it and letting it dry for a few days... then I hand-laminated the sandwich panel with a wet-layup technique, applying the painted side of the caul sheet against the epoxy. After vacuum-bag curing, I peeled off the release-coated caul sheet, leaving a very glossy exterior finish with the paint layer adhering very well to the S-glass/epoxy composite skin. A similar panel that was painted after vacuum-bag curing has much rougher and uglier finish, as seen in the comparison photo on the left (pardon my feeble photography skills). About the only way I could figure out how to capture the finish of these panels was to snap a picture of the reflection from the 4-light bulb fixture in my office.

Composite molders do a similar thing by "gel-coating" the mold before laying up, but by using a glossy caul sheet on the mold side, I can have a not-so-smooth mold surface, and still get a glossy exterior finish... and not just for looks either... you get improved laminar air flow. All in all, it seems clear to me that painting the outside from the inside is the way to go!!! This allows an unskilled painter like me to hide roughness and surface imperfections underneath the paint layer, not on top.

These featherweight panels are amazingly strong and stiff, as the flexural tests are proving now !!... quantitative results will be published here as soon as we have declared victory on achieving our "exit criterion" in the panel design's delivered strength & stiffness. As engineers should know, but sometimes forget, a project's progress can come to a grinding halt in the pursuit of the "optimum".. for example: a directive from your boss and/or customer saying something must be "as light as possible" or some such vague nonsense.. so how do you know when you're done making it lighter?... Remember: nothing is perfect, therefore you can ALWAYS make ANYTHING better... be it stronger, lighter, faster, shinier, more efficient, etc. To exit the endless merry-go-round of incrementally improving your design, you need a finish line.. an exit strategy... a success criterion clearly defined as meeting a pre-established requirement... then you MOVE ON! As one pithy Russian general said it best: 'Better' is the enemy of 'good enough'

As a related side note from my personal experience circa 1999: At Beal Aerospace -- which is now nothing more than a case study on how NOT to run a private space launch company -- we used to joke that the technical requirements were far less important than our wealthy owner's ever-shifting "desirements." He wants the rocket to be bigger one day, simpler the next.. then he would get on a make-it-cheap-like-a-hillbilly-would kick, followed by orders to make it prettier, quicker, tested more, tested less, able to handle even bigger payloads, etc. We were getting good at redesigning & rescheduling, but not building & flying.. Well, the joke was on us.. after burning through untold millions of his money, he laid us all off, shut the place down, and our giant rocketship never flew... lesson learned.