So I set about choosing a stronger engine and a lighter weight quad airframe. I bought one from Skycruiser.com. From there, I've been going over and optimizing all of the details in an effort to come up with a highly reliable PPG quad rig for my flying purposes. From my own perspective, many things needed modifications; This page offers details of the modifications I've made as well as tuning tips, information sources, and parts options & sources.
While doing my research, I came across James Weibe's excellent review of the POLINI THOR 250 engine, his installation in his BELITE ULTRA CUB, and the story of his cross-country flight from Kansas to Oshkosh, Wisconsin and back with only a couple of minor issues. (The link to this review is at the bottom of this page. )
With a power rating of up to 36.5 HP in a high reliability water cooled light weight engine, I decided I'd found the engine I was looking for.
Polini THOR 250 DUAL SPARK engine has many more advanced solutions, including:
- The cylinder is die-cast in light alloy, it ensures a better thermal stability.
- The piston, gravity cast at high silicon content light alloy, reduces thermal expansion and the coupling slack. The design of the piston top is specific to optimize the compression ratio.
- It is provided with a balancing countershaft; this feature cancels the vibrations and guarantees such a driving comfort never felt during a flight and a longer life for the engine itself. The counter-rotating rollers decrease greatly the upsetting torque-steer for an extra comfort in flight.
- The centrifugal clutch is in oil bath with helicoid mechanical reduction.
- The electric starting is standard but to offer the maximum safety the engine is also equipped with manual starter with easy system thanks to the flash starter device that speeds up and simplifies the movements.
- It is equipped with the comfortable closed-circuit system for the recovery of fuel during transportation and the 12 V output for any use.
Small and compact THOR 250 DUAL SPARK engine has an extraordinary power to weight ratio.
Advanced technology and high performance of the new THOR 250 DUAL SPARK allow a better feeling of driving performance, making the flight more dynamic, responsive and sensitive, besides ensuring even greater stability.
The new THOR 250 DUAL SPARK engine adapts to different types of applications including one or two-seat trikes, powered hang gliders, one-seat small three-axis ultralight aircraft, and ULM motor-gliders
Polini THOR 250 DUAL SPARK is a 100% Made in Italy product.
Technical data Polini THOR 250
Engine: 2 stroke monocylinder, Liquid cooled
Displacement: 244 cc , Bore for stroke: 72 x 60
Power: 36 HP at 7500 R.P.M.
Cylinder: Aluminum with Gilnisil coating
Compression ratio: 11,5:1
Piston: Two chromium plated rings 1mm
Intake: Reed valve in the crankcase
Carburetor: PWK 28
Air filter: Air box
Ignition: Magneto and Electronic ignitions included on Dual Spark version
Battery charger included; Output power 80 W at 5500 RPM
Spark plug hood 5k Ohm resistance
Fuel type: Lead free petrol with 2% synthetic oil minimum ; 50:1 typically used after break-in
Gear reduction unit: Helical teeth in oil bath with 2,8 reduction ratio
Starting: (Electric starter optional) Pull start with self winding cable FLASH STARTER
Clutch: Centrifugal in oil bath
Muffler Expansion with oval silencer
Engine weight 18 Kg (19kg with electric starter) without radiator: =43# without radiator, ~54# complete installation
Propeller rotation: Clockwise.
Cylinder Head Temp 130 to 185 F; Max 194F
EGT Operating Range Centigrade: 500c to 620c ; Max 650c
EGT Operating Range Farenheight: 932F to1148F ; Max 1202F
Best Efficiency EGT Operating Range: 1075F to1148F
Operating RPM Range ~1700 to 2200 RPM Idle, to 7500 Peak Power ; Red Line 8000 RPM
Fuel Efficiency ~3 litres/hr @ 5300 RPM ; ~8 litres/hr @ 7500 RPM (When jetted for sea level operation)
On June 7th, 201 I flew a flight of 2 hours and 1 minute, covering 65.9 miles. I started from my launch area at about 9800 feet. I flew north & west, crossing Georgia Pass, flew north to pass over Swan Mountain just south of Lake Dillon, then flew back south over Hoosier Pass to return to land at my launch site. During this flight, I flew up to a maximum altitude of 12,905 feet ASL . After landing, I measured the fuel used Engine RPM was up to 7450 RPMduring most of the climb, crossing over the continental divide twice on this cross-country flight. EGT stayed within the peak efficiency range. I used about 3.5 gallons of fuel on this flight.
Update JUNE 2018: I'm flying the Mac Para Charger reflex wing; I have a #122 main jet installed. At full power & high RPM while climbing, I may use from 1.75 up to 2.0 gallons of fuel per hour. (Cruising at reduced RPM uses substantially less fuel.)
Polini Watercooled 250
Also Available in Lowboy
Now Using the Polini THOR 250 Engine which is water cooled for great durability
Light Weight and Powerful
Complete units starting at $7,800.00
FEATURES:Chrome-moly steel tubing used for the main Quad frame with an aluminum prop guard cage. Powder Coated ; 1" Solid Fiberglass Axles, fold down seat. Bare Quad weighs in at 58# before adding cage and motor installation. Low Attachment Points for easy inflation, good ground handling stability.
The good news: Belite now offers the Thermostat on their parts page- see the links at the bottom of this page. I've also recommended that Leon at Skycruiser Manufacturing add this item to their THOR 250 parts page. The link to their website / parts page is also listed at the bottom of this page.
With the thermostat installed, once the water temperature is up & the thermostat is working, the water temp reading is holding at ~156 degrees F at full throttle on around test on a ~62 degree morning.
08-16 UPDATE: My THOR 250 setup NOW uses a Powerfin two blade propeller set with a 57-3/4" diameter. This is a ground-adjustable pitch propeller and each blade is adjusted individually. Pitch is adjusted to limit the THOR 250 engine's top end RPM to a maximum of 7500 engine RPM; I'm presently adjusted for ~7350 RPM max in flight.
When previously using the 56" diameter 3 blade GSC prop which Leon had supplied with this quad, I had to reduce the pitch on the three blade set to 9.1 degrees of pitch at the 75% of blade radius point, in order to get the engine top end RPM up to 7500. (I am using a digital angle gauge purchased from Harbor Freight for $30. Blade pitch is referenced to the center flat surface of the prop hub; that means that you set the gauge to zero against the face of the prop hub, then measure the angle of each blade at 25% in from the tip on the blade's back surface.) This pitch setting allows the THOR 250 to run at 7500 RPM at full throttle at 9940 ASL, but it was not really generating the thrust and speed that I need at this setting.
I've now switched to a two blade propeller setup using two of these blades in a different mid-part / hub; blade pitch setting will be steeper on the two blade setup. I'm now flying it at 12.5 degrees pitch, which does generate better thrust and airspeed. Presently for flying form ~10,000 feet ASL flying site: main jet is #118; Pilot Jet is #35 ; Air Screw is set to 7/8 to 1 turn out from bottom; Jet needle now has the clip in the second to the top slot of 5 for a leaner lower mid-range run. I'm running a 50:1 gas-oil mix, using 91 octane gasoline and Quicksilver synthetic mix oil.
TECH NOTE: GSC BLADE PITCH ADJUSTING: My technique for getting fine changes in blade pitch while making the adjustments: with all bolts loosened to no tension on the prop center hub and both pairs of prop blade mounting bolts, I'll simultaneously rock each blade forward and back within the prop hub while exerting the twisting force. A fine index mark on the base of each blade where it enters the prop hub helps me to see the slight changes in pitch angle while doing these adjustments. Once I have both blades at the identical angle, I snug down the hub bolts lightly, and push both blades fully FORWARD. The idea with this is to get the tracking of both prop blade tips as close to identical as possible (- within 1/16"). I'll do some final tweaking until they match as closely as possible. I use a measuring stick from the side cage frame tube to insure that both blade tips are tracking the same distance from that frame tube as I rotate the prop, recheck the pitch angle once more on all blades, and then tighten all bolts to the 100 foot-pound torque recommended by GSC.
On the left, I mount my Garmin GPS; it has topo maps loaded as well as offering an ongoing readout of altitude and relative ground speed. The PPG meter offers a readout of EGT, CHT, Engine RPM, Fuel Level, current flight duration,and hour meter. It stores minimum and maximum readings for later display. The EGT readout is especially helpful in establishing the optimum jetting for full throttle running.
[10-2017 UPDATE NOTE: I now use a newer Garmin GPSmap64s.]
On the right is the ignition control box for this Dual Ignition Polini engine. The top toggle switch is the master on/off switch; the green LED at the top right glows when this switch is turned on. The bottom center switch is the electric start push button momentary switch. The two red push button switches are used to test the ignitions by disabling each of them temporarily and separately. The right is for the magneto ignition; this normally OPEN switch is pushed to short that ignition to engine ground, thereby killing that ignition spark. The left red push button switch is a normally CLOSED push button switch; when it is pushed, the secondary electronic ignition is opened, isolated from it's 12V power source, killing that ignition spark. The engine will run on either ignition separately. It runs very smoothly and reliably with both ignitions active- especially noticeable when doing test runs at the full 7500 RPM.
To kill the engine in a conventional aircraft installation, the top master toggle switch is toggled to the left, killing both ignitions. However, when flying a PPG, we typically have our hands full of the control line / brake toggles while landing, so reaching for the toggle switch without disturbing the canopy isn't reasonable- it's simply not safe. So there needs to be a way to kill the engine with a kill switch on the throttle handle while making a landing approach, or whenever the pilot wants to immediately shut down the engine.
I accessed the engine control box's wiring harness connections for the magneto ignition [pale blue wire in the photo below= hot & black = ground], located back near the engine, to add in the wires for the kill switch connections (coming from the Normally Open contact section of the DPDT Momentary push button switch which I added into the throttle's handle.)
To do the kill switch wiring for the secondary electronic ignition, it's necessary to interrupt the 12 volt supply to that ignition. That 12 volt supply comes into the ignition wiring unit on the violet wire with the black stripe shown in this photo below. The heavier pair of Red & Black wires runs inside the sleeving over the throttle cable down to the second Normally Closed set of contacts of the momentary push button switch in the end of the throttle grip.
The CHT thermocouple that comes with the Fly Henry PPG Meter is the type that has a ring mount that goes in under the spark plug- it's easy to install.
I was a bit challenged with the sensor lead lengths being short from the PPG Meter on the control panel back to the Engine's location on this PPG Quad installation- the EGT probe wire just barely made it! Their web site says that the leads have since been extended another 6", which will be handy for trike / quad setups.
Since then, I'm quite fond of rigging a low hang point setup where the wing's trimmers are clear BELOW the riser guide rings. That makes them more accessible for possible in-flight trimming adjustments, while also keeping them where they can not hang up on the upper frame guide rings.
Also shown in this photo are the extension loops I fabricated for extending the bridles from my APCO Mayday 18 Bi reserve parachute. An identical pair of 24" long extensions were sewn up from 18.5 kN (4047#) 1" tubular climbing webbing, with a center stitched section where three layers overlap for 4". (Stitching also extends beyond this center overlapped section.) I machine sew these with a heavy black bonded polyester thread that's specified for this application- it's really strong thread that's also very UV exposure stable.
The main jet is accessible through the larger aluminum bottom cap. A 126 main jet was supplied in this carb when the engine came from Polini, which is appropriate for sea level & low altitude operation. In spring of 2018, when flying over Colorado's central Rockies and flying from an airfield at close to 10,000 feet ASL, I'm now using a #122 main jet.
[NOTE 06-2018: for flying at 1100 feet ASL in AZ earlier this year, I had to go up to a #132 main jet to get the EGT down into the optimum range.]
The prop you have and it's pitch determine how it loads this powerful motor. (With too much prop pitch, the engine can not run up to full RPM, regardless of the mixture.) The main idea is to prop a motor so that, at wide open throttle, the prop load limits the maximum RPM of the THOR 250 engine to 7500 RPM after the engine is broken in. More pitch can be used on an adjustable pitch prop at lower altitudes, where the engine can produce more power in the denser air.
UPDATED INFO: The stock pilot jet that came installed was a #45; the idle & low end mixture was richer than I wanted at my higher altitude. I next tried a #40 pilot jet, then a #35. I Tried a #32 for quite a while, but it acted lean on cold morning starts, so I have switched back to the #35. This should be ideal for running at 10,000 feet & above. I've also moved the jet needle's clip to the 2nd from the top of 5 slots, for a leaner run & quicker pickup coming up off idle. Air screw is set from 7/7 to 1 full turn out from bottom.
TECH NOTE: The throttle cable must travel to move the slide up 28mm in order to open the slide completely on a 28mm throat carburetor - to give you maximum air/fuel flow for correct top end tuning and maximum power output from this motor. When I received my SKYMAX quad, the throttle cable setup was only opening the slide about 23 to 24 mm- not what was needed. The photo below shows the modification I made to the AVID throttle handle /housing / cable adjustment locking device to get maximum travel from fully closed to fully open.
Finding a listing for a replacement rubber part online for this Polini engine was elusive; while getting a new rubber boot would take time, I decided to do a reinforcing repair to the original one. (This is my already proven technique; I've used it before on similar parts on my Hirth F33 engine, which have since been in service for a long time.)
I had been told in the past by the owner of an auto parts store that the Permatex BLACK silicone adhesive / sealant was the strongest and most oil and fuel-resistant product to use on a molded rubber part like this. It's shown in it's package. The other tool you see in the photo above is a fly tier's bobbin loaded with a spool of kevlar fly tying thread. This is incredibly strong, tough thread; if you tried to break it by hand bare-handed, you would cut into your hands before ever breaking this thread- it's that tough. (You can find it on Ebay in an assortment of colors, or buy it at a store that sells fly tying materials & tools. The bobbin makes handling the thread far easier than it would be to work with the spool of thread alone.
The first step is to remove all traces of the 2 stroke mix oil from all surfaces and any cracks in the rubber connecting boot. For this job, I use an automotive spray 'Brake and Electrical Parts Cleaner'. All traces of oil must be eliminated so that the black silicone adhesive can bond strongly to the rubber. Once it's clean and dry, the first application of the adhesive is worked thoroughly into any checks and cracks to fill them completely, and then a coating is applied to the outer surface in the stressed area.
Next, while the adhesive is freshly applied and wet, the kevlar thread is wrapped around the entire stressed rubber area, criss-crossing back and forth to create a weave that crosses all of the stressed area and adding the desired strength. This is the area where the clamp will be reinstalled later. Once the thread has been wrapped on adequately, more of the Permatex black silicone is applied over it to end up with the thread being completely wetted and covered with a thin smooth layer of the adhesive. Make sure the inner surface is smooth- wipe away excess, then set the part aside in a warm place to let the silicone cure out for about 24 hours.
The resulting reinforcing repair is what you see in the photo above; all cracks filled & bonded with a layer of kevlar thread which results in the part being stronger than the original un-treated rubber part. It's ready for re-assembly in one day.
[You can see in the photo that I had installed a rubber tube stand-off and cable tie support from the upper front edge of the air box to the PPG frame to minimize movement & secure the assembly forward well clear of the prop, but more modification in the carb / airbox mounting was needed.]
My approach was to remove this rubber part, thoroughly clean it, and add the Permatex black adhesive sealant and the reinforcing thread wrap to the outside where the stress affects were found.
Taking the weight off this rubber mount part was my next project. I decided to simply add the stainless steel wire support link shown in this photo between the carburetor's top cover mounting screw and one of the mounting screws form the electronic ignition module's mounting plate. I used two electrical ring connectors on each end of the wire to provide the mounting rings which the screws pass through, then adjusted the length so that the rubber carb mounting boot was no longer being asked to carry the weight of the carburetor and air box / silencer. The result, as seen in the photo above, is effective- the SS wire is adequate to handle the task with a minimum of added weight, and easily removable / replaceable for normal carb servicing.
You'll also note in the photo that the throttle cable boot at the top of the PWK 28 carburetor was already cracking and failing after only ~5 months; I've temporarily wrapped it with some tape, but plan to do the kevlar thread & silicone sealant treatment to this part to when I next pull the carburetor top cover.
So Polini may need to improve the quality of their rubber carburetor mounting parts. Maybe they are already in the process of doing so- I hope so. But now I know to keep watching these areas during my pre-flight inspections.
My Strobe Light can be quickly mounted just above the radiator, using nylon tie wraps. I use an independent Lithium-Ion Battery to power mine; it can optionally be wired into the 12V system. Operation with a strobe visible from 3 miles allows extended flight operations 1/2 hour before sunrise and 1/2 hour after sunset. It also makes this PPG more visible to low flying aircraft.
I have now installed a full set of replacement 15x6.50-6 smooth ribbed tires (similar to the tire shown below). These are a tougher 4-ply garden tire, weighing only 5.5 pounds each. They should be more 'cactus-resistant' than the light 13" Lawnpro tires.
I then cut down the upper cage support members to the required length, did the saddle notch, drilled the pass-through holes for the stainless steel clamps, and re-assembled the support arms and cage. The photo below shows the result of this modification. Now the tips of the prop on the upper part if it's travel are well clear of the support frame members. (Unfortunately, the tips of the blades actually travel below the bottom of the quad's frame under the fuel tank, leaving them very vulnerable to damage form ground debris and rocks kicked up by re wheels; even the shorter 56" blades on the GSC prop set took some significant damage from rock strikes during ground running tests.)
I set the initial pitch at 12.5 degrees (measured at 75% of prop radius out from the center.) A test run here at 10,290 feet ASL in 59 degree dry air gives a peak RPM of 7400 to 7420 RPM- very close to the ideal of 7500 RPM for max H.P. output.
This propeller is running smoothly and providing good thrust; it's a good match for the THOR 250 engine flying at this altitude.
Adding An Extended Prop & Line Guard Hoop with 7" Stand-Offs To The Prop Guard Cage&
When the device is slid all the way into the throttle housing, the throttle lever is held at close to full throttle position.
As pilots, we do our ongoing maintenance and pre-flight checks to assure ourselves that our equipment is in serviceable condition, ready to perform reliably and continuously. But it also doesn't hurt to be prepared for a possible landing in less than favorable terrain. Being hung in a tree in your gear is a remote possibility; being able to get yourself down safely if you ever are is close to priceless!
 A light weight climber's seat harness and Chest harness and 1 locking carribiener; I built this one from 4000# + 1" tubular climber's webbing and the heavy bonded polyester thread which I use to sew the low hang loops for my Quad. (The adjustable waist belt with the cam buckle to which the main leg loops are sewn just helps keep the leg slings in place; the main leg sling loops carry all of the load when in use. )
 A "Figure Eight" descending / rappelling device
 A 100 foot long length of 6mm quality climber's accessory cord
 A good pair of gloves for rope handling with leather palms
 A 4 foot section of 1" climber's webbing (Or a good quality Cam Buckle strap) & another carribeiner for use in fashioning an anchor point.
 30' of strong 4mm utility cord
To use this gear if hung in a tree, etc., a stranded pilot (transformed then into being a climber) would first carefully get out a shorter section of rope and tie them self and their gear off to the tree- no need for a sudden unscheduled early decent! Next is to put on the climbing seat harness and rig the carribieners and figure eight as shown; the loose end of the rope in the above photo would be the one tied to or looped around a solid branch or part of the tree trunk, or tied to the webbing anchor point. Using the rope run through the figure eight more than once increases friction, and running this 6mm rope through doubled is fairly standard self-belay procedure; the center of the rope is looped over an anchor point attached to the tree so that, once on the ground, the rope can be retrieved from the anchor point for further use. [Mammut's 6mm cord has a breaking strength rateing of 1700 pounds. Sterling Rope's 6mm cord is rated at 1978#]
[A book or website on climbing ropes, rigging, and use and a bit of hands-on practice should further help in an understanding procedures for rappelling using a descender. Professional ski patrol personnel carry a similar kit for self-evacuation from a chair lift if the lift is shut down while they are on it; fire fighters carry similar gear with high temperature-resistant rope. A practice self-belay decent from a very modest height might not be a bad idea for those unfamiliar with rope & self-belay techniques. A Gym with a climbing wall and instructor might be a good place to familiarize yourself with the equipment and techniques; that info is beyond the scope of this web page.]
Above: REI gear. (I changed out to the buckle for my PG kiting use.) The figure eight chest harness helps keep you upright while doing a descent if your technique is less than perfect, and you may like the solider feel of rigging that way. REI sells both- I bought the set from them many years ago. I have used this climber's seat harness a lot for kiting my PG wing. The gear I'm carrying is lighter and more compact.
I fly with the reserve parachute mounted and with these emergency survival and self-rescue kits always along because I'm inclined to fly over high rugged remote areas most days - that's where I live & fly- and I figure it's worth having along this 4.5 pounds of emergency gear. That's my personal approach - a part of prudent PPG flying in this beautiful and rugged part of Colorado's high country!
I carry a Midland GTX1000 GMRS radio which has up to 36 miles of line-of-sight range, while leaving a matching radio with someone back on the ground, and I leave my flight plan with them. If I do have to put down somewhere other than at my launch point, I'm fairly well prepared.
2017 Updates and Modifications
This update section was last updated on October 27th, 2017
Late in 2016, I had Andy McAvin ship me a new MacPara Charger 31 wing. This is a Reflex wing with a higher cruising speed when the trimmers are let out into the full reflex mode. In the thinner air here at altitude, with the ~380# total ready to fly wing loading of the quad and me, I'm cruising at an average speed of 37 MPH. With trimmers pulled in fully for better climb angle, the speed is at 33 MPH. [In comparison, the 31m Muse 3 would cruise at 32 MPH when the trimmers were let out fully.]
Really like the way that this wing launches and flies, and I find the wing tip steering very nice to work with. However, for use on my quad with it's riser guide rings on the upper frame, I had to do some modifications.
With the long travel trimmer adjustment range and the added wing tip steering, the Charger's risers are more complex and far bulkier than those on a simpler wing like the Muse 3 which I had previously been flying. The 2" I.D. riser guide rings provided with the Skymax quad (mounted on the quad's upper frame members to control the hang attitude)& were too tight a fit- the wing tip steering lines were regularly fouled / hung up and unusable, and other parts of the stock risers would also hang up in the guide rings, leading to problems and aborted takeoffs.
First, I fabricated a new set of low hang point loops that positioned the trimmer clamps where they were workable below the riser guide rings. Next, I fabricated a new set of larger 2-9/16" I.D. riser guide rings which offered more adequate clearance for the Charger's risers. I use the 2" guide rings to route the reserve parachute's risers separately, inside the upper frame members, and then down to the main carabiners on the low hang loops, keeping them clear of the wing's risers.
These modifications helped, but all of the extra D-rings and shock cord form the original rigging and routing of the Charger's wing tip steering lines running up through the middle of the riser bundle through the riser guide ring still left the wing tip steering toggles & lines fouled and unusable a large percentage of the time... so I decided next to try to remedy this aggravation.(This situation might not necessarily be an issue for a trike or quad rigged with a high hook-in setup, or for foot launch pilots.)
(The photo below shows the stock Charger risers through the 2 inch I.D. riser guide ring, with the stock wing tip steering line run up through the midst of the bundle.)
The photo below shows the original stock wing tip steering line rigging run through 6 D-rings with a lot of ~1/8" shock cord run back and forth everywhere.... when these risers are used through riser guide rings on a quad or trike setup using low hang point rigging, all the extra D-rings & shock cord result in wing tip steering line fouling and hangups far too often.
My solution: The risers come with two brake line pulleys sewn in place on the risers. On my quad with it's low hang point rigging, I need to use the upper pulley for the brake line. I use the upper brake toggle retaining magnet (the right one in the photo below) to park the brake / control line toggle while in flight. ( I use the wing tip steering all of the time while cruising; I only use the brake control lines during takeoffs and landings.)
This leaves the lower brake line pulleys unused, and so available to be re-positioned and re-purposed in a cleaner wing tip steering line setup. The idea is to end up with the wing tip steering line routed to bypass the riser guide ring completely, eliminating any of the fouling and hangups.
The photo above shows the 2nd lower brake pulley sewn in it's original position, down low and close to the trimmer clamp. I carefully pulled the stitching to remove it with it's webbing loop. Next, as shown in the photo below, I sewed it to the existing upper brake pulley's webbing loop with heavy duty bonded polyester thread; it's solidly in place. I then proceeded to remove all of the 6 un-needed D-rings and shock cord, and the old low eyelet through which the wing tip steering line had once been routed leaving nothing left for lines to hang up on. (I later found that the extra low position brake toggle parking magnet was hanging up in the riser guide ring, so I pulled it's stitching and removed it, too.)
The important thing to keep in mind if someone else decides to clean up their wing tip steering line routing for a quad /trike with riser guide rings and low hang point rigging is to only cut the thread carefully- do NOT damage the risers themselves! A seamstress's 'stitch puller' tool is very handy for this type of careful work.)
The photo below shows the finished result- the wing tip steering line toggle still parked on it's magnet and snap fastener, the line run freely on the outside of the riser bundle up through it's own pulley. It performs flawlessly in flight now.
While flying my early flights with the Charger wing, I found that the torque from the Polini THOR 250's gear drive resulted in a left turn tendency when both trimmers were set to neutral. Since I wanted to be able to fly the full trimmer range during normal flying, I was looking for a way to compensate for this left turn tendency... after all, for long cross country cruising flights, it's really pleasant to have the rig set up for hands-off straight line flight for extended periods of time.
I noted in watching the wing that it only takes about 3" of inward deflection on the wing tip via a modest pressure on the wing tip steering line to compensate for that left turn tendency. On the Charger Riser control line setup, there is a short line which I have come to refer to this 495mm long " stC1 line" as a 'snubber' line connected between the C riser quick link / mallion and the wing tip steering line; by shortening it the right amount, it can also function as a 'torque compensator' device.
I first made up an adjustable parallel line with a 3/4" wide strap and cam buckle- similar to the regular trimmer cam buckle and strap setup. Once in flight, I pulled in the adjustable line until I had a hands-off straight line cruise. After the flight I determined that I needed a 'stC1' line that was 100mm shorter to keep that right wing tip pulled in the required ~3" to result in a straight ahead hands-off cruise.
So I made up a 395mm long line from 220 pound test Spectra line and installed it in place of the original 495mm green line. It's been performing as intended for many long cross country flights since then. You can see the short grey line in the photo below.
[Updated 06-20-2018] I like the electric starter on my POLINI THOR 250 engine... but it does have it's own maintenance requirements. James Weibe, in his BELITE blog, wrote of having to repair a broken internal brush wire; nice to know.& I have had to do the same myself.. I ended up having to solder both brush wires to their terminals; it seems that the spot welding of the fine strand copper braid to the terminals results in a heat-induced fatigue of the copper. Since I did the initial soldering of the brush wires, I'v had to go back in and re-solder them on several occasions over the course of the first 80 hours of flying time. I've emailed Polini directly about this issue, requesting to obtain a replacement set of brushes, brush holders, and the attached pass-through terminal. This is an ongoing maintenance requirement on the THOR 250's electric starter which can be done if the parts are made available. I'll add info to let you know how Polini responds on this issue.
The second starter issue deals with the starter's output shaft... the splined section is a separate piece of metal which is inserted into the starter armature's shaft, and crimped in place. It can work loose in service.... not an ideal design! The photo below shows the splined short shaft sitting inside the engine housing, visible when the starter was removed. The only good news is that it can't escape this area to get deeper inside the engine to cause more extensive damage. The bad news is that once it happens, you get to fix it.
The photo below shows the recess in the end of the starter's armature shaft, and the insert shaft's smooth end laying along side just below to the right.
My solution was to first thoroughly clean both parts with spray 'Brake and Electrical & Parts Cleaner", to remove any oil , etc. I then put some thin CyA glue (super glue) into the armature shaft recess, inserted the smooth end of the splined shaft, and seated it to bottom solidly. Once the glue cured well, the starter has been back in service reliably for many long flights. The photo below shows the reassembled shaft. [06-2018 Update: Shaft staying in place since being glued last year.)
The photo below also shows the brass pass-through terminal for the starter's red positive wire from the starter solenoid; I have had two of these terminals break off at the sharp bend where it comes out the top of the pass-through plastic insulator. To repair this failure, I cut away about .1" of plastic so that a good quality wire could be soldered directly to the remaining brass terminal.
The Polini manual starters are one of the more aggravating features of an otherwise fine performing engine; they really need to improve the design. It's made partially of plastic parts which self-destruct from vibration while the engine is running normally. While the 'pawl set' is relatively inexpensive, it's generally a too-frequent maintenance requirement if you are using only the manual starter. I had started my engine with the pull starter only 2 or 3 times, and left it mounted as a 'backup'.... but when I tested it, it would not engage. So I removed all of the pull starter components, and then glued a protective cover over the magneto flywheel opening where the manual starter had been mounted. This keeps debris from being able to get into the engine's magneto area.
Below: The battery rides in a nice Velcro mounted nylon carrier, isolated from any frame vibration. On my Skymax, the wires would vibrate enough to eventually loosen the screw on one of the battery terminals... not so good a thing to have happen. So I added long cable ties around the battery and it's wires close to each terminal, so that the wires can not move. (I like to use lots of cable ties!)
The photo below shows damage done to one of the PowerFin prop blades by a rock strike during takeoff.. I repaired it, and the blade is back in service.
FLYING IN THE CHALLENGING ENVIRONMENT OF THE HIGH COUNTRY OF COLORADO
The position of these cracks indicate that they may be the result of vibrational down-load stress forces during flight; the axles with their wheels on the outer end must vibrate constantly during flight. Arc welding does induce stress into metals do to the heating being concentrated in a very small area; that's why steel tube built light aircraft frames are built using gas welding techniques, and heat stress relieving is done on welded areas during the build after each weld is completed. Arc welded joints need ongoing inspection and monitoring for the possible development of these stress cracks.
After doing an overlay weld with my wire feed welder as shown in the photo above, I smoothed down the welds and repainted the area. I drilled new horizontally oriented holes for the axle locating bolts well away from the fiberglass axle load stress point at the end of the axle tube. I then chamfered the inner ends of the steel tube to minimize fiberglass surface fiber stress in those areas before installing new black fiberglass axles.
NOTE: I am now buying black 1" diameter round solid fiberglass sections for replacement axles from Max Gain Systems
(The black color may be more resistant to long term U.V. damage of the outer surface resins than light colored axles. I've had fibers raising from the surface of the original off-white axles in the past. I like the looks of the black axles.)
Below: While inspecting the quad, I noticed some deformation on the right end of the front axle carrier tube where it was welded to the upright piece. (This is rather rough ground I fly from, and the takeoff runs are much longer than when flying in denser air at lower elevations. I'm likely close to 380 pounds ready-to-fly weight when I'm rolling at up to 30 MPH across the terrain to get up to flying speed. So for my purposes, I want tough axles under my rig. Being light weight is a lesser consideration, versus a need for structural strength and durability. )
After straightening, I welded on a close to full length piece of reinforcing steel angle iron (3/4" x 3/4" x 1/8" thick.) Added weight is modest, but the added strength is very welcome! I expect long service after this modification.
The photo below shows the rear end of my quad on the trailer with the 15x6.50-6 wheels mounted. I later also mounted two more of these tires on the front end. These larger diameter wider surface rear tires seem to roll up to liftoff speed more quickly than the 13" tires- they handle the short grass prairie irregularities somewhat better. (In the distance is Mount Silverheels at 13,882 ft. MSL.)
The photo below shows how I have my rescue parachute mounted with 3/4" cam buckle straps (from www.strapworks.com ). The blue pack which rides between my knees carries assorted tools and gear. I now use my Garmin GPSmap64s tethered to the pack's outer pocket zipper pull ring where it's easily readable while flying- it's positioned similar to using a knee board.
The PPGmeterI had installed malfunctioned after about 38 hours of service, going into a constant error mesage flashing mode which could not be reset; this made it unusable. So I removed it. I installed a TinyTach to go with my separate H2O temp gauge. I now only temporarily mount an EGT gauge when I'm checking on a change in carburetor jetting. This water cooled engine runs very consistently and reliably, so if the H2O temp is within it's typical operating range of 157 to 161 degrees F, then all is OK.
Below is the DTC T100 Digital EGT Meter which I am now using; it's displaying 50 degrees F on a cool early November Colorado morning. I will only keep this gauge mounted when needed to check a change in carburetor jetting when I fly at lower elevations. It has a quick disconnect wiring connector. This meter has internal calibration and function selection programming capabilities via three internal switches; it's set up for 12V power supply now, and for reading a Type K thermocouple. I'm using the same type K thermocouple probe which I installed from the now defunct PPGmeter.
http://skycruisermfg.com/polini_engine_parts parts are available. (Carb jets are not listed.)
Belite's Polini Engine parts page, with the thermostat offered for ~$45.25 + $8.00 Shipping
CARB JETS : KEIHN PWK28 uses HEX main jets: 126 stock ; [118, 120, 122, 124 & 128 possibly useful on THOR 250]
10 piece pilot jet assortment kit - only $9.99 for all, free shipping from CA