Not to brag or anything... But I got to touch the world famous Variomatic prop when Miro wasn't looking... It was awesome! On another note - It was very fun to watch Miro test the prop and find room for improvement. Being around someone who is innovating, testing, learning, and improving the equipment we use in this sport was very special. Thank you Miro for choosing to fly the Adventure Wingman with Judson, Jesse, and me! I can't wait to fly with you again in the future!
It's been a while since any news on this amazing prop, please keep us updated, so we can keep supporting this genius prop. Can't wait to use one or three.
Miro it was awesome to fly with you and the gang during the challenge. It was fun to pick your brain about the Scout, props, ppg theory and flying in general. This prop is amazing, I can’t wait to get my hands on one
You need a combination of both, spring and centrifugal force, because of the air density the pressure varies, so the spring pressure needs to change on the same rate. If you use just the spring, when you ajust to low autitude it will not work on high altitude and vice versa.
I had this thought when you were developing the prop. As you gain altitude the air gets thinner. The thinner the air gets, the less force it will impart on the blades of the prop and this decreased force causes your transition point to migrate and/or not happen at all. F=M•A. Lower mass in the air means lower force is imparted and therefore more acceleration would be required to match the necessary force. However as someone else stated you would also be dropping in rpm due to the loss in power as a result of the lower oxygen levels. If the design was based on centrifugal force the only hindrance would be the loss in power for the engine. That's virtually unavoidable
You´re the Elon Musk of microlights. Wished you worked on an impossible to tip over nano trike and on a fully electric Scout paramotor. Everything about your company is inspiring.
This is incredibly innovative and inspiring to see the development process. Thank you for sharing it. I'd be interested to see what this could do coupled with a fuel injected Vittorazi motor.
I remember adolescent time when we had variators on our 2 strokes mortorcycles. The belt was moving on a conic shape, increasing in diameter sync with rpm. Same principle of the angle of the prop, but could replace the clutch poulie.
I have a totally different approach for controlling the variable pitch, however I don't have the resources and time to materialize the idea. But if you're interested we could setup a short meeting and discuss the different approach and you'll decide if it's worthy of going further with design validation. If so , just let me know by responding in here , then I'll get you back by emailing to your company e-mail. As for the response for your question, I speculate that prop were not down shifting because of an cumulus of factors, one is that your on the move relative to air mass and this reduces the slippage of the blades, the other one is lower air density resulting on not having enough force to overcome springs, blade slippage is more pronounce at lower air density. The factor between prop leading edge and surface induce drag versus thrust produces by the airfoil becomes less favorable.
Since the moster has a belt drive, and the pulley is offset from the crank, I'm surprised you're not using a collective system that uses a pushrod through the center of the pulley to adjust the pitch. If you use a servo for that you could have manual control of the pitch or run it with a raspberry pi with a barometer that adjusts on the fly based on altitude.
You can make it very simple, forget about electronics and think just about a road that moves axially to increase the pitch to 13 or even 14 degrees. You can make a simple lever that move this push road with a cable that runs with your throttle and adjust it in flight. (If you want something cleaner is better the electronic approach with a servo and to control it, a rc servo tester, it is really simple to wire and use) You should think about it! I’m happy to help if you want
What a great opportunity to learn more about your design. Failure is the best teacher. With a softer spring, can you also add more range at the high end to go above 14 degrees? By all means, please keep going.
This is a tough one RPM drop theories: #1 It could be caused by an imbalance between the center of torsion force the blade applies to the center of thrust force. When I look at the propeller, especially in the "Will this be the best paramotor propeller in the world? Variomatic propeller" video background, it appears slightly swept back compared to the center of rotation. therefore I believe that nearer to the tips will produce a higher torsion force for the amount of thrust created then near the center of the prop. The speed of the air entering the prop would be fairly consistent all round when on the ground. In the air thought, the airspeed will increase entering the propeller towards the outside and the tips of the prop, but would stay lower behind the fuel tank, engine, and pilot. This would cause the propeller to revert to a higher pitch at higher airspeed. On the other hand it could increase load because the air closer to the center remains slower, so the prop is trying to accelerate from a slower speed to an even higher speed. This would be a reasonable explanation as to why it was noticed with the spring tighter, but not when it was lower where it never reached full pitch. If this is the case, it is a non-issue and will be fixed with new springs. #2 The propeller could have been experiencing some slight flutter. As the propeller pulls a vacuum, I believe the air will remain slightly more laminar as it flows behind the fuel tank, pilot, and engine. As the airspeed increases, the air could become more turbulent. This could cause a small drop in force for the blade directly behind the fuel tank and if the RPM matches the resonance with the propeller, a slight flutter could happen at certain rpm ranges. If the prop isn't reaching the stop it might be unchecked. This could also explain why it only appeared with the tighter springs. I doubt this is the case though as you likely would have heard it. If this is the case, it may not be an issue with the new spring. Otherwise you could try thick silicon grease in the bearings like what is used for radio control car differentials to absorb vibration. If that doesn't work, you would need to find some other form of shock absorber.
I have only a hundred hours or so on a fixed wing, single engine, constant speed prop, but I feel like the fact that you don't have a way to adjust the mixture in flight could be a contributing factor. TLDR: As you climb, unless you adjust the mixture you won't be able to take advantage of the high blade angle b/c you won't have enough power. In general, during cruise you want high power and large prop angle (ie: low RPM) for best fuel economy. (I'm writing most of this to explain my thought process/rationale, I realize you already know these things!) If I recall correctly, typically mixture is set on the ground to max power (based on density altitude). You said you were adjusting the carb needles before takeoff so you have that part covered. As you climb to cruise altitude, you lose power due to the mixture getting richer from lower air density. This means fuel is being exhausted, unburnt. Once you get to cruise altitude, you would need to reduce power (throttle) to stop your climb, adjust the mixture by reducing the amount of fuel. You could do this with an EGT readout (maybe a CHT?). Lastly, you would increase the prop angle to slow the prop down. (I realize you're not doing this part b/c there is not an in-flight prop angle control) In effect, the leaning + the slowing of the prop would decrease fuel consumption rate. It seems to me, that without being able to change your fuel mixture, you're unable to produce efficient combustion at altitude. Without spare power trying to turn itself into RPM, the variomatic prop won't increase propeller angle. Hmm, that makes me think of another potential issue you could be running into which I'll put in a different comment...... I probably need to re-watch the variomatic prop videos you've posted, as I'm SURE I'm missing something.
The only thing I can think of is to build or find a test cell where you can replicate being at 6-8,000 feet and test that way. I would love to test one but I don’t ever reach those altitudes. Definitely looking forward to seeing the prop come to market.
Just offer interchangeable springs for different elevations. Might be the simple fix? Also, do you think reverse threaded bolts and nuts for the spring could help from the bolt falling out? Maybe even reversed springs?
I haven't been following the Variomatic too close so I could be misunderstanding how it operates but. Just a thought, Use the aerodynamic twisting moment to determine blade angle for shifting instead of RPM. Aka. more thrust will cause it to decrease pitch. Then configure to shift to high pitch at slightly above cruise thrust. Unfortunately aerodynamic twisting moment increase blade pitch... hmmm. Perhaps a force sensing mechanism in the prop hub that could translate that force into blade angle change. I got an idea on a design but you'd have to completely redesign your prop hub.
How about making sure, that the mechanism easily hits lower degress by allowing it to compress the spring easier when approaching 10 degrees ? Playing with spring angle might help, where angle changes towards 10 degrees Also how about a lever, which compresses the springs fixed ammount ? or a spacer ? So for your altitude/motor/spring you adjust the preload easily.
Lower max RPM in the air vs on the ground: Thinking out loud... When airborne the relative air velocity meeting the prop is reduced > reduced force on variomatic mechanism > keeps 13 degree pitch > motor RPM kept lower due to increased engine load (and the limited force never triggers pitch transition to 10 degrees)?
How strange, the inverse of what we would expect. I can only come up with the notion that a portion of the blade is stalling in static air but fine at flight speed. Besides that, I am boggled :)
It seems like you need to have a measurement of prop angle logged as well. Not sure the best way of measuring that, but it seems like something that should be possible. One way might be a magnet on the prop right next to the mechanism. You could use a hall effect sensor to measure the relative strength of the field every revolution, and calibrate angle vs field strength as a stand in for prop angle. Alternatively, an optical measurement might work. Two dots, on on the prop and one on the aluminum mechanism part. Two sensors, each measuring one of the dots. As the prop rotates to 13 degree or whatever, the spacing between the two dots will change (and hence, the timing delta). From that, you can calculate angle.
Hi Miroslav, About the lower RPM during the flight: If your RPMs on the ground were about 8000 and your take-off site was about 6000ft from sea level usually as you fly higher and higher the oxygen decreases in the air and in naturally aspirated engines that causes decreasing of the power, so the engine RPMs dropping too. Usually, at the seal level, Moster185 can reach 8400RPM but at 3000ft from sea level, it generally can go max up to 8200-8250RPMs.
Perhaps there is an air density threshold? The prop requires a certain amount of air density to achieve the necessary aerodynamic forces across the propeller to change pitch. After a certain decrease in air density (altitude, combined with temperature), maybe there just wasn't enough force to complete the shift? Or, combined with the carb settings, the motor just didn't make the same power, reducing your overall rpm while in the air?
I agree with other comments suggesting you need to add an "altitude corrector" to your prop settings, the way the engine itself ideally would also need to have an altitude corrector to maintain the proper RPM at high altitude. Except for the rare cases when we decide to fly to the high altitudes (I guess every pilot tried this from curiosity maybe just once or twice in their career), we rarely fly too high from the take-off, so this could be an adjustment on the ground for your mean local altitude (/temperature?). I guess at altitude we would need other settings for the prop blades AOA, not 10° and 13°, but, say, 12° and 15°.
From the start the variomatic propeller tries to use aerodynamics force to correct the pitch. But this force depends on altitude/temperature. On the other hand the centrifugal force doesn't depend on air. Maybe use this force to control the pitch? Seems doable.
The lower max RPM could be because of the increased pitch the airflow over the profile stalls on the ground an the propeller spins "empty". In the air the pitch speed is high enough with the oncoming air flow that profile fully "grabs" into the air demanding more power from the motor which then results in a rpm loss. That's something I experienced with my electric motor as well but since it has an fixed rpm setting the current draw in the air was a lot higher than during the ground tests.
Just an idea, but could you test this prop with a motor in a small, custom vacuum chamber (to reduce air density to specific values)? It's probably not all that practical, but maybe one could be constructed relatively inexpensively?
My guess regarding the lower RPM during flight: In flight you air density is lower compared to your take off. So first your engines gets less oxygen = less power. But also your propeller profile produces less lift. So less lift to work against the spring force (=higher angle of attack) + less power in general = reduced RPM.
I wonder if a swash-plate type arrangement would work where the prop assembly is free to move back and forth on a shaft with linkages to a fixed bearing ring… It would be at high pitch when at low rpm, but when throttling up the prop pushes against the engine assembly and flattens the pitch like collective on a helicopter in reverse? I had the idea as a way to stop a wind turbine from overspending, same concept but different application .
I could be totally off here, but you don’t have a prop governor on a paramotor so the engine is basically running at best speed for the throttle input. There’s no way to set a constant RPM or control the manifold pressure or lean the mixture. With that said, you could be extremely rich of peak at altitude which could account for greater fuel consumption, which having a lower manifold pressure due to pressure altitude changes which could lower total RPM production? Does the manifold pressure stay constant with outside pressure? I’m not certain myself. Could it be these are conditions which could lead to high fuel consumption and lower engine performance? Was the spark plug clean? Would the slower RPM at full throttle at altitude explain the lack of shifting the prop to desired pitch? In addition, having an aggressive pitch with an engine that could be behind the power curve, are you sure that the pitch wasn’t actually working as designed but dogging down the motor in a way that limited the RPM by requiring more HP to turn the motor? Maybe an EFI and EGT sensor would be your fix. Short of turbo charging a moster, perhaps leaning out the fuel flow mixture could be just as effective as a pitch change in the prop for fuel consumption. If I’m so far off, it’s not worth a debate… I’ll shut up and learn more. Im just curious about the relation of pressure altitude to Static RPM given a constant fuel mixture.
I wonder if it'd be easier to get data from an electric paramotor such as the OpenPPG SP140? You'd be measuring watts instead of liters of fuel. With the increased pretension I'm thinking the RPM was lower "in the air" than on the ground because it was simply not making as much power and could not overcome the propeller drag as the air got thinner. Electric motors are not affected by altitude so you could separate the effects on the propeller from the effects on the engine. Such a flying adventure may not be the best place for development but obviously is a great place for testing. It's why car companies race.
Armchair/RU-vid Commenter pretending to be an engineer here: I'm wondering if there is some intertwined dynamic between the fact that increasing thrust on a paramotor ends up increasing altitude instead of increasing airspeed. Maybe a slight over generalization, but since paraglider wings fly at a constant speed, any increase in thrust turns into a climb, and decrease in thrust results in decent. At cruising altitude, there is no 'best cruise' power setting like there is in an airplane. Once you're trimmed fully out, there is one *thrust* setting that will maintain level flight. In order to get best fuel economy, you'd want to determine that thrust setting, and back calculate the required propeller RPM and Pitch settings to achieve that amount of thrust. This will be a curve which is a combination of propeller RPM and propeller pitch. IE: Increasing RPM will require reducing Propeller pitch to maintain constant thrust. At any given throttle setting, I think there should be a corresponding RPM/Pitch setting pair; possibly two pairs if the throttle line ends up as a curve? In the end, I'd think you'd be able to create a table which shows what 'tension' to set your prop to for a specific target altitude. Although, that could potentially be a setting which wouldn't allow you to properly climb turning takeoff?
I wonder if the difference is just simply that you are moving through the air. On the ground the test scenario the air is having to be churned against any object and forced past the prop. In the air it is continuously in wind that reduced the load on the engine due to the flow of air. Easier to visualize thinking of a boat against a dock throttling hard and churning the water or one driving across the lake. Cleaner bite and less load.
We need the phone to display data as board computer during flight. It is not just for diagnostics and measurements, it will serve as flight navigation too
#ANSWER - Ground & flight tests results differ because only one of them is moving through the air which changes the relative air flow on the prop which decreases angle of attack thus the spring needs tuning to the flying condition :) #QUESTION - Would adding mass balances to the prop (to power assist the angle of attack change) aid in the tune-ability of set up and help with flexibility of altitude ? ... adjust the mass and or the moment arm against the power of the spring... etc.
Increased density altitude (reduced air density) reduces the maximum output power capability of the motor, and the spinning prop (at the same RPM) moves less air and generates less thrust. Because the air is less dense, there is less air and therefore also less fuel being sucked in during intake, and therefore less power being developed by the motor, over all motor RPM. It is possible for the motor to spin at 8k rpm at altitude but only if there is less load on the motor. Because the air at altitude is less dense, the spinning prop produces less thrust at 8k rpm than it does at sea level. The prop causes less loading of the motor at altitude because it is developing less thrust. GA pilots who fly at high altitude all the time typically go for bigger motors than pilots who fly at sea level all the time, in order to have reasonable performance at altitude. I suspect the original tuning of your variable prop is fine for the motor and prop that you are using. I would argue that at high altitude you tried to use the "wrong" motor and prop. While completely adequate at sea level your motor/prop solution was marginal at high altitude so you needed to run the motor at much higher throttle to maintain level flight and thus the variable control adjusted to 10* as it should have. On the flip side, imagine if you normally flew at high altitude with a bigger motor and prop and had developed your variomatic for those conditions. Now take the same solution and fly it at sea level. I think it will work just fine. It will shift to the higher pitch but you will be able to run with even less throttle as the bigger motor and prop are capable of developing much more thrust. This hypothetical combination might not be optimized at sea level but I would think it would still be better than a fixed pitch prop. I think the variomatic system will need different tuning for different output power motors and different props. 10 and 13 degrees works well for your motor and prop combination but other combinations will probably need two different angles. From what I have read about similar systems for GA each model was tuned for a specific airframe, motor, and prop combination.
The effective angle of attack of the prop decreases with airflow. The site provides less resistance to the prop in flight. So normal props usually rev higher in flight than on the ground. The variomatic behaved the same at the beginning. When I increased the spring pre-load the air provided enough resistance on the ground to overrride the spring. But in the store the resistance was not sufficient and the prop stay ed at high pitch. This is my guess. My propeller expert thought the same
Miro, moc ti drzim palce aby sa finalny produkt vydaril, a dufam budem prvy majitel na SK kto to bude mat a bude hrdo lietat dlhe prelety vdaka tomu 😍😍😍
If you need to change the spring force with altitude, why don't you use air spring? Like air suspension. I don't know if there are some air spring small enough for this. And it would be difficult to calibrate the spring.
interesting idea. but air pistons also change performance due to temperature. the more i think about that idea the less suitable it seems. But surely thank you for the insight.
Hey Miro, I don't mean to discourage you but constant pitch propeller for PPG will be more efficient than a Spring loaded pitch propeller due to constant pitch adjustment, vibrations and tensions in the mechanism etc. All that is energy loss. It doesn't make much sense to put variable pitch propeller on such low speed aircraft.🤞
I mean to think about it the higher you go the more the air thins out so the prop then would have to spin at a higher rate to be able to have the same load/performance as what It dose at sea level even at 13 degrees or 10 degrees As uve got less bite on the prop at high altitude a different spring at higher altutude would be needed because its not loaded as much so won't over come the spring load as well. Now regarding when your at altitude your getting less rpm my opinion is because the prop isn't as loaded an dosent have as much bite on the air this effects the engine loading now on 2strokes when the engine isn't loaded it runs rich. So could it be the prop isn't biting the air at high altitude like it would at sea level because of this the engine isn't loaded like it would be causing it to run rich lowering the rpm.
It had this weird behaviour only when I increased the spring loading. Not before. I reached done 7800 on the ground but a lot less flying over the same ground.
@@SCOUTaviation in theory with how the density of the air up high changes it should take slightly more rpm to reach the 10 degrees at the same rpm as it would down at sea level. Or could it be to the extra preload pulled/bent something on the unit allowing it to change pitch to quickly an not loading up the engine as much creating a rich condition lowering the rpm. I would say when you added more preload and it would play up at altutude but not at low level it's going to fall down to the engine not running right. Or to flips thins up side Down maybe it had to much load on the engine an a high altutude an where normally it would of gone to the 10 degrees its struggling. I'm just putting things out there that maybe you might be able to relate to an think I could check this or check that to find the issue.
Are you afraid of adding a small battery and a servo I can see a wireless variable pitch with a 10 to 30deg pitch range. Can you share some cad files I can think of a much much better way to to the mechanical system
I imagine a servo would weigh more, be more complex and less reliable. I suspect even a manual pitch control would be lighter than servo control. CAD files would be somewhat proprietary (somewhat commercially sensitive) but if you have a "better way", draw it up and share your CAD files :)
@@pimplequeen2 You could make a lightweight in-flight adjustable system using a throwout bearing and a fork, an axial bearing and a lever arm. Cams to change pitch would interface with the axial bearing to change pitch. I trademark it "Dial-a-Pitch".
@@RwP223 Indeed ; sending a push rod through the center of the prop shaft and even using a bicycle hydraulic break leaver cylinder and machining a matching cylinder/actuator for a two position pitch would be simple in "principle"... But that's the issue, thinking it is very easy, drawing is reasonably easy manufacturing it is hard and making it a viable profit maker is a bitch :)
@@pimplequeen2 I can understand why but to me 1lbs is justified If the impact is high enough. I have a Moster 185 on a test stand with a thrust scale so I'm going to take a stab at this from scratch I'm perfectly OK with signing a nda and non compete with scout just to enjoy the project my day job and the 40+ patents have income on lock as is so to me it's just an interesting problem set. Kinda like the custom efi throttle by wire setup on the moster 185 on my test stand. The impact on efficiency from that was massive combined with timing based torque control this might set some eco record's even if it adds 10lbs to total payload that really a minor thing some trikes are running full water cooling on Rotax / continental setups the scout carbon is really nice I have flown a few times I have a maverick atm will might pick up a scout when my divorce is over lol.
Can I suggest that the higher altitude problem boils down to air density, for any given Revolution of the prop the number of molecules and therefore the “force” exerted on the prop is different depending on altitude (air density) temperature (air density) and humidity (air density). I’m sorry, the “remedy” isn’t easy, it involves moving the “actuating arm/s” along/ up or down a helical spring. This implies you have sensors for each variable that are able to input actuator/s to move the arm/s. Keep up the work, I know you want a pure mechanical solution, realise that the “simple, pure” solution era has ended. Put the prop on a Swiss Auto EFI 4 stroke (after any modification for the different torque and rev range) and test it at sea level and altitude again, even go to the extent of testing in a pressure chamber.
Scrap the springs, Scrap the entire design. It's crap. Think about a tail rotor on a helicopter. The tail rotor pitch on a Bell 407 helicopter is controlled by a control tube that links to a control arm that pushes two pitch change linkages from the center hub via a sliding spinning shaft. That is what you need to focus on. Build a cable actuated pitch change linkage that runs through the middle of the hub and can be set manually by the pilot and controlled via a selector setting like a fast slow cable knob on a lawn mower. Set it to fast for takeoff, minimal prop bite then once up at cruise alt you can slide the cable knob back to slow with the little turtle symbol and that would pitch your prop to max bite and you could throttle back to about 3k rpms.
I keep looking for updates on the Quatro, I am assuming it's still out there, but maybe the builder has somewhat run out of steam. I am guessing the crank case volume (too small causing oil breather issues) has taken the wind out of the designer's sails. A real shame, I'm sure they managed to get the weight down to 14kg and it wasn't far off the moster for power output.
