How much power do you need?

In considering low vibrations, high power to weight ratio, and small size, nothing compares with Wankel Rotary Combustion Engine, you had the OS Graupner 5 cc,  less than 1 HP, and the 294 cc, liquid cooled housing, charge cooled rotor 30-50 HP Aixro kart engine, but there are some other Wankel engine producers, references are in the Wankel Engine Wikipedia article. Good luck! + Salut

     http://www.aixro.co.uk/shop/ advertises a liquid cooled housing Wankel engine specially adapted as range extender.

Subaru produces a flat-four, boxer, liquid cooled Diesel, but as stated, in:

'Power Struggle. Why car engines won't fly. Don Sherman; Smithsonian Air & Space magazine; Dec 1996-Jan 1997 issue, p. 71-81. (A detailed discussion on the development history and fate of the V-8 engine in the Lancair Tigress), it's not easy using an engine not designed for aviation in a flying machine, the basic issue may be that airplane engines operate most time at full throttle or close, while automobile engines are rarely requested full output, and if so, just for brief periods, this implies many design features.

Hello,

lots of questions around an interesting topic ;O)

So at first it is to say, that every configuration of UAS has advantages and disadvantages and mostly it is depending on your application, which configuration you will have to choose.

You are speaking about your “small drone”.

 If you talk about “drones”: Do you mean “unmanned aerial systems” as it is normally used or do you mean a “multicopter airframe” as one special configuration of an unmanned aerial system, as some people sometime use this expression?

 In the first case you surely speak about fixed wing platform as for example powered gliders in 4 engine configuration. It would be helpful, to know your platform, especially because it depends on the context whether “small” means 2,5kg or 25kg MTOW.

 Very small engines 0,33 – 15ccm for a long time only have been build as methanol -engines. They consume oil with a little bit methanol. Actually there is a tendency replacing methanol engines with gasoline/petrol engines. Lots of smaller engines where modified by the rc manufactors last years to be able to run with petrol: Then they consume less fuel, meaning, with the same tank-size you will be able to fly longer, or your tank will be smaller saving weight. But these are no more compression ignition engines, but need ignition, ignition battery and so on. Mostly the smallest of them start at 10ccm..

The second advantage of petrol-engines is, that after the flight your airframe will not be as polluted as it will be after using methanol/oil.

Diesel or even cerosin will only be used in turbines and turbo-props engines. In the size of common rc models these kind of power unit will consume lots of fuel and you will not be able to fly long time.

some prfessional airframes use petrol engines with generators (f.I. LUNA). I have never heard about methanol driven generators.

 In europe for the most civilian application electric driven engines have to be used because of restrictions by law. Using motorglider configurations you will be able to fly alsofor a long time and long distances, without the necessity to charge batteries. But also here, the meaning of the expression “long” depends on the context.

So I need more informations about the platform you plan to use and the mission you want to fly, to be able to give more precise hints and suggestions for your power management…

 So my first questions are,

- what UAS configuration do you plan to use

- what kind of mission do you plan to fly (especially endurance, payload and so on)

- should your suggested engine fly onboard (with the drone), or do you think about a cable drone in multicopter configuration tied with a powercable at the ground?

If this engine is staying at the ground, I simple would use a common constant current generator.

Using such an engine onboard as generator, you will have to consider, that all the system will have lots of weight and reducing the performance and endurance of your platform very much. Maybee it would be better to have a very efficient configuration without the necessity of charging while flying.

So, first of all: please give more informations about the platform you plan to use and the mission you want to fly…

With best regards from Munich/Deggendorf in Germany. Patrick

UAV configuration = untethered quadcopter of my own design & construction; mainframe of tubular (welded) titanium alloy; on-board control via a Raspberry Pi with 5 gHz-band bi-directional radio remote link for flight-control / GPS-coordinates / video-link package; total weight (loaded with maximum batteries + payload) = 5.2 kg; total stripped weight (with 4 electric motors, props, computer, servos, antennae, and all control wiring, but no batteries or payload) = 2.3kg Flight times & lifting capacity depends on the type of batteries used and on whether the detachable solar arrays are used. I have designed a very-rapidly-chargeable ultra-light capacitor-power-pack that I use, that outperforms any of the currently available commercially available li-poly battery-packs in terms of power/weight ratio. With these, I don't have any constraints on the amount of power available for lifting heavy equipment packages, but, of course, the heavier the equipment, the more power-packs required ... the shorter the flight-time ... you know the story ... so, currently I am able to get about 20 minutes flight-time fully loaded with high-resolution PTZ camera package, which is NOT enough to safely fly a round-trip mission. 

Mission = archaeological aerial reconnaissance in extremely rugged and inaccessible terrain (steep mountainsides and canyon walls); both horizontal examination of surfaces for rock alignments (e.g., tipi rings & ceremonial or astronomical  alignments) and close-up examination / photography of vertical panels for rock-art ... also, flights INTO the entrances of rock-shelters and cave openings for photography; also, carrying LIDAR and other remote-sensing packages (with similar masses to camera package) on similar missions. The duration of the missions would require flight times of at least 30-minutes at a minimum to be useful in most situations, even those where the "target" mountain and/or canyon is actually in-sight of the operator. In most anticipated cases, however, the UAV will be operated remotely, via GPS coordinate directed flight to target, and directly by operator via video after arriving over target, and will require operational times of a minimum of one hour for roundtrip time to target and return. Maximum flight distance from operator to target is anticipated to be always less than 10km.

Thank you, Patrick, for your interest, and response,

Regards,

Bob

wow! Great! I So I understand: your intention ist to extend flight time and you try to get this integrating a generator...

Did you ever used fixed wing configurations and hav some experiences with it? Flight time is their most advantage. Maybee your difficult flight circumstances could be overcomed using fixed wings with rubberband or catapult takeoff and netlanding?

I will think about the onboard generater and answer again tomorrow.

Great project!!

Dear Patrick,

The last time I used fixed-wing model craft was over 50-years ago! I am sure they would be great for horizontal reconnaissance & photography, but the hovering ability of the quadcopter is essential for the access to vertical canyons, not to mention rockshelters and cavern openings within them.

I suppose it would be best to have BOTH (but even Texans are not ALL wealthy and cannot have everything we wish for)!

Regards,

Bob

;O)

... I mean, concerning efficiency, there is nothing better than only to use your battery, without such an onboard charging system, but we also know that there are restrictions with payload, flight time and so on and it really could be useful to think about it. Maybee there is a possibility to slimm your plattform to extend flight time and range...

 If you did not find the following link bevore, have a look at it. Maybe, it could help:

http://www.sullivanproducts.com/GenesysMainFrame.htm

http://www.sullivanuav.com/home.html

Also in an rc-forum discussion in Australia they linked the side: But I am sure you already could find this. Nevertheless, the link:

http://www.meetup.com/gctechspace/messages/39743222/

 There is also a discussion about the topic in a german rc – forum. There are some interesting ideas, but all in all they are not convinced by the idea: There would be much professional development to do to get an effective system...

http://www.rc-network.de/forum/showthread.php/50148-Anlasser-als-Lichtmaschine

Jetcat has integrated a small generator to charge the systems batterie, but this will not help you if your copter would not be driven using a jet-engine. But maybee here you can find proposals/stimulations for own ideas:

http://www.jetcat.de/jetcatturbinen/helikopterturbinen.htm#00000098f908c8103

In my group we also use rc helicopters, but we never did fly such a long range mission. Also in germany it would not be allowed to fly out of sight. But the mission you describe would be perfect for a petrol or jet driven Helicopter System. It should be possible to fly your mission with such a platform. But you would have to develop and configure such a system especially for such a mission, you also need an excellent pilot and as you mentioned, this also would be an other platform again, spend lots of money and so on…

Mybee you can find some better hints at the links and if you would find a solution, please keep me up-to-date.

With best regards and good luck for your realy interesting mission...

Patrick

Dear Patrick,

Thank you for all the pointers; I followed-up the links and, unfortunately, it looks like there just isn't much specific discussion or help out there on this particular topic. Perhaps I shall just have to do some more experimentation (although slow & expensive, trial-and-error has always seemed to yield my best results in the past). ;)

Thank you for your attention and responses, best regards,

Bob Skiles

How much power do you need?

In considering low vibrations, high power to weight ratio, and small size, nothing compares with Wankel Rotary Combustion Engine, you had the OS Graupner 5 cc,  less than 1 HP, and the 294 cc, liquid cooled housing, charge cooled rotor 30-50 HP Aixro kart engine, but there are some other Wankel engine producers, references are in the Wankel Engine Wikipedia article. Good luck! + Salut

     http://www.aixro.co.uk/shop/ advertises a liquid cooled housing Wankel engine specially adapted as range extender.

Subaru produces a flat-four, boxer, liquid cooled Diesel, but as stated, in:

'Power Struggle. Why car engines won't fly. Don Sherman; Smithsonian Air & Space magazine; Dec 1996-Jan 1997 issue, p. 71-81. (A detailed discussion on the development history and fate of the V-8 engine in the Lancair Tigress), it's not easy using an engine not designed for aviation in a flying machine, the basic issue may be that airplane engines operate most time at full throttle or close, while automobile engines are rarely requested full output, and if so, just for brief periods, this implies many design features.

Thanx, Joe, for the pointer to the Wankel wiki ... I had forgotten all about those great little miniature Wankels! So unfortunate that such a great technology didn't ever catch-on. How much better would the world be now, IF only all those VWs had of been produced with efficient Wankels rather than those atrocious THINGS ... those excuses they called engines ... oh ... I must stop, now, before I have a STROKE!

Thanks, again, Joe!

Best,

Bob

You may have a look at www.rotaryeng.net a site devoted to Wankel Engine use in airplanes, most of it homebuilt ones. Thanks for your kind comment

Hi Bob, I confirm Wankel as ideal motor for drones. If you suspend expensives loads to UAV uoy should take a look here:

http://www.uavenginesltd.co.uk/products/   Electrical motors don't have a good power/battery charging time. You need a powerful and lighter motor with adeguate lift power. Ciao

Www.aixro.com is another Wankel maker. Good luck, + salut

Dear Bruno,

Thank you for the lead. I reviewed the motors available from:

http://www.uavenginesltd.co.uk/products/ 

... these appear to be very suitable motors for larger craft than I build ... the smallest of theirs producing 20BHP ... which is at least 10x more power than I require. However, I noted that their smallest motor, which is touted as being designed for light short-life UAVs (for example, target drones), is rated for only between 10-to-50 hours of operation between maintenance overhauls. This seems to be an extraordinarily SHORT operation life between required rebuilds ... which makes me, now, question just how long the expected life may be for a miniature Wankel (IF I can find one in the

[email protected] Graham McGreish, had some Sachs KM-48 cores for sale, from Nato 'Silent' surplus generators, it's 160 cc per chamber, around 9 HP. Wankel RCEs do work better with 10% alcohol in gaso!ine. 2.2% 2-Stroke synthetic oil is good, you can add 1 cc of LiquiMoly MoS2 additive per liter of oil/gas mix to further reduce friction losses and wear. See www.aaroncake.net forum, 'Reed-Valve controlled...', for some detailsdetas, rotaryeng.net has info about Diesel cycle rotaries, or you can do a Google search about 'Wankel Diesel'. Good luck! + salut

Dear Joe,

Thank you, Joe, for all the great pointers! I once bid on a lot of those surplus NATO generators (because I realized they each had a nice Wankle diesel), but I seriously under-bid (not realizing how many enthusiasts there are looking for such nice little motors) and didn't come-close-to-winning the auction :(

I appreciate your taking the effort to answer my questions, and, I hope your retirement is treating you as beneficently as is mine treating me.

Best regards,

Bob

Ok, How much high must fly the UAV? For how long time? How weight should lift? The load it's a valuable equipement (digital photocamera or valuable home made instrumentation) or a launch and forget type? Let me know please.Ciao

Dear Bruno,

The UAVs I have designed/built/operated (so far) are quad-copters that use four brushless electric motors powered by lithium-poly battery packs. The greatest altitude they would ever need to achieve is around 1000m (this being a rare occurrence, only for getting a general/overall photo of a project area, but usually they are operated well-below 100m ... usually between 20-50m altitude above ambient ground-surface). The heaviest instrument-package they ever lift is a gyro-stabilized PTZ (=pan-tilt-zoom) camera, with a heavy zoom lens, that weighs about 2.5kg (which is the same as the weight of the entire quad-copter, with a full complement of batteries). So, the maximum weight to lift (including the quad-copter vehicle) is always 5kg or less. When carrying a much lighter camera or instrument package (most weigh well-under 1kg), I am able to get adequate flight time (which is a minimum of 30-minutes from take-off, to target with enough time provided for acquisition of photos or collecting sensor data, and return to land safely at launching-point) with all my cameras/instruments (so far) EXCEPT with the heavy (and, yes, VERY expensive) directional/zoom camera package. THAT one is so heavy that it reduces my flight time too much (averaging only 10-15 minutes) for a safe flight/mission at the distances often required (up to a maximum of about 6km from the control-/launch-point). Not to mention that use of the heavy camera package also seems to wear-out the motors and batteries much more rapidly, requiring frequent replacement of these expensive items.

My regards,

Bob

PS - my main aims in transitioning to use of a hydrocarbon fueled motor is: (1) greater power (to make-possible greater range and lifting capacity), (2) obviating the expense of the batteries (expense = time required for re-charging, as well as the actual COST of frequent replacements of the expensive batteries ... which seem to average much reduced lifespans from those advertised, perhaps because I have been charging them too rapidly ... but, THIS advertised ability to rapidly-recharge being the main reason I opted for the li-poly batteries, in the first place), and (30 obviating the need for frequent replacement of the expensive electric motors (so, the time-interval between needed overhauls of the hydrocarbon fueled motor selected needs to be as lengthy as possible ... hopefully more than 1000 hours of flight time).

have you considered a lifting baloon or a dirigible option?  increasing flying time with a safer platform for transported equipement. Additionaly you should recycle your electric motors for propulsion and navigation.

Dear Bruno,

Now that 'dirigible' suggestion of yours may be a genius solution ... perhaps using a helium-filled surplus weather-balloon for the lifting force, and adding remote-controlled battery-powered steering-motors for propulsion. With a small tank of helium and a barometrically-controlled inflator/deflator it might be possible to develop a craft that will hover at any chosen altitude, whilst automatically compensating for changes in the instrument load. That may be the ideal platform ... able to lift-and-hover-in-place with heavy instrument packages, with very little expenditure of energy. The big drawback would be that it could not operate successfully on windy days, but the smaller/ultra-light UAVs I have been using are certainly not immune to the winds, either.

Thanks for your suggestion,

Bob

With ballast system you really don't need helium bottle on board for height control; you should easily control it releasing ballast and or releasing He! With a large low RPm propeller you should control dirigible in windy days! Ciao (here it's 2.44 A.M i go sleep i read you tomorrow!)

Dear Bruno,

Ballasting for altitude adjustment may not be ideal, for a couple of reasons: (1) the lift vessel [balloon] may need to grow to such a large size [diameter] to offset the additional weight of the ballast system [dry sand, a container/hopper for it, and the metering/dumping mechanism], and (2) that may cause it to become difficult to maneuver into the tight-work spaces (inside steep narrow canyons, and near/into/at the entrances to caves and rockshelters) where it will need to operate much of the time.

Nevertheless, having a small ballasting system will be important in making fine-tuned [and rapid] adjustments to altitude that would not be possible to make quickly using only an inflation/deflation altitude control system.

So, I am contemplating using both methods ... trying to rely more upon the inflation level for major adjustments (e.g., initial liftoff and landings) and a ballasting system for fine altitude adjustments.

Thank you for taking the time to consider my question and for your insightful comments and suggestions.

Regards,

Bob

Dear Bruno,

An after-thought ... if not for the consideration of the large size [diameter] that would be necessary [and the maneuverability/access problems that entails], I could consider the use of a hot-air-balloon, instead of the [relatively] expensive helium for a helium-filled balloon. Small cans of propane are ubiquitiously available on the commercial market (for a great variety of cooking purposes) and are SO MUCH LESS expensive (and lighter) than tanks/cannisters of helium.

Best regards,

Bob

Hello Bob,  Don't forget the Hidrogen option for dirigible, cheaper than Helium! What you need its an aereodinamically shaped rigid (or semirigid) shell containing 2 or 3 baloon. A suspended plattform wiht payload and propulsion/directional system. Ballast could be liquid like water releasing could be automatic (barometer uni with a +- altitude and/or radio controlled released. The lifting power of baloon/dirigible is adeguato to all needs. Baloons are the optimal tools for high altitude research, you could esily build one sewing sail canvas or kite tissues. You could recycle old windsurg sails or crahed kites!  I send you a link where you could find other peoples involved in similar projects!                                                                                                          http://skyboat.wikispaces.com/home                                                             Ciao from Italy

You may like having a look at SAE paper 951769, 'Wankel Engine for Hybrid Powertrain', by Angelo Butti and Vincenzo delle Site.

It's $24 dowloading from www.SAE.org no need to be a member

Startup Company Creates Rotary Engine That Weighs Four Pounds

http://www.msn.com/en-us/autos/news/startup-company-creates-rotary-engine-that-weighs-four-pounds/ar-AAh8Oll?ocid=spartandhp