Small Gasoline engines

[kd7ost]

I thought the new Zenoah G20ei was going the right direction for smaller planes and power plants that use a standard 2 cycle gasoline mixture. But look what I just spotted. :D

Dan

http://www.bmeengine.com/html/point90.htm

[macboffin]

Well found Dan! Small gas engines are rarer than hen's teeth! (Good ones that is)
I was asked to evaluate some Italian engines a while back, 10 cc, ie .60 size. The carb was nearly as big as the engine! Very heavy, about as much power as a .40, and all kinds of problems for airplane use ; apparently originally intended for powering a small electric generator. Not recommended! Weston UK Ltd used to market a kit of Hall effect pick-up, little magnet you drilled a hole for and epoxied in place in the prop driver, and battery holder etc. Never heard of anyone trying it. Supposed to be applicable to anything with a big enough prop driver.

[macboffin]

Further to above; just bought an O.S.90 for a project; would have got one of these S.T.s if I had known! That's life!

[kd7ost]

Agreed. My brain hasn’t stopped turning over a twin tail boom design UAV/AP platform to fit around this engine since I found it. It also retains some great RPM and horsepower numbers for its size. It would be a great candidate for the Sullivan Genesys In-Flight power system.

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFV20&P=7

Dan

[dalbert02]

...or possibly:
http://www.cyber-flyer.com/heli/axi_gen_s.jpg

or similar )from Cyber-Flyer.com
-dave

[Blue Sky]

There are also string trimmer and chain saw conversions!
http://www.carrprecision.com/Pages/prod02.htm
Be careful! You are now leaving the realm of model RC aircraft and entering
the realm of experimental aircraft, at least if are planning on flying beyond visual
range.

-Dave

[macboffin]

There are also string trimmer and chain saw conversions!
http://www.carrprecision.com/Pages/prod02.htm
Be careful! You are now leaving the realm of model RC aircraft and entering
the realm of experimental aircraft, at least if are planning on flying beyond visual
range.

-Dave The Super Tigre range of engines, designed specifically for model aircraft use, has been around a few years; strimmer or chain-saw engines they are not! Super Tigre themselves have done quite a bit of work on petrol-fuelled versions of their engines; with the normal carb, but with beefed up crank-pins etc.
As to the comment about "beyond visual range" can I be the first to point out that this section of forum is about UAVs. They are frequently operated beyond visual range.

[mlbco]

I'm a little suspicious about the performance claims for this motor. On the BME web site it is claimed that the fuel consumption is approx 1pound/hour at max power (2.7HP). This gives a brake specific fuel consumption (sfc) of 0.37 lb/(hp-hr) which is better than any gas 4-stroke on the market! I think the HP number is highly exaggerated. Most 2 stroke gasoline engines get an sfc of 1.0 lb/(hp-hr). If you assumethe fuel consumption number is correct, this would put the peak HP at around 1HP which is much more believable. I dyno-tested a Zenoah G-26 at 1.5 HP at 8500 RPM and an sfc of approx 1.0 lb/(hp-hr). I haven't seen any gas 2 strokes perform much better than this. The Zenoah is very reliable, rugged, and can be run backwards for easy integration into a pusher airframe while still using conventional propellers. My engines are stripped down and use electronic ignition for reduced weight. It's still not as light as the Supertigre 0.90, but the reliability is great.

A few years ago I spent some time converting an OS 0.61 heli engine to gasoline with a Walbro carb (see attached photo). It ran well, but after approx. 20 hours the connecting rod failed (no needle bearings). I know the Supertigre is better designed, but I'm still nervous about using any model airplane engine on a UAV that will operate for 100's of hours. Does the Supertigre use a standard size spark plug? The glow plug sized ones (1/4"thread) are not very reliable. If you run this engine as a pusher, cooling may be an issue because of the small fin size. The industrial 2-strokes (Zenoah, etc.) have big fins and can easily run wide open with little airflow and not overheat. A motor using gasoline will run hotter than when fueled with glow fuel, so be prepared to watch the cylinder head temp.

Steve

[wadiprawita]

Dear Steve,

How can I runs a zenoah backwards? Any internal modification I should do?

Thanks

-doni-

[mlbco]

Dear Steve,

How can I runs a zenoah backwards? Any internal modification I should do?

Thanks

-doni-

All you need to do is change the ignition timing, the intake is a piston port-type and does not need to be re-timed. If you install an electronic ignition you'll need to set the timing anyway, so you simply adjust for the proper spark advance in the reverse rotation direction. I have 100's of hours on one of my Zenoah's that's been used exclusively as a pusher, and there have been no problems. I use an APC16x8 (standard) propeller on my UAV.


Steve

[Disciple4123]

KD7ost:

The BME 90 is an airplane engine, but about a year ago the heli guys began to outfit 90 sized heli's with them. They were a bit of a fad, but seemed like fine engines. They stayed in one piece, were comparable to a .70 nitro in power, and were reported to be smooth and efficient. if an airplane engine survives in a heli with limited cooling, I trust it would not be overheating in a plane. I did not have one but read a lot. I contacted BME asking for a 50 sized gasser, it never came to fruition.
Here's a discussion, 410 posts :)
http://www.runryder.com/helicopter/t230036p1/?highlight=bme+90

[kostixx007]

I have emailed BME , asking about fuel consumption and here is the answer : 'Sorry, we have not tested for specific fuel consumption. Most customers tell us that the engine is at least as strong as a .75 and runs about 30 minutes on ten ounces of fuel at mid to full throttle setting.'

[wadiprawita]

Dear Steve,

My knowledge and experience is limited in engine, so is there any website about converting zenoah from puller to pusher engine? Thank's

I also have 3W, the 3W website told me that it can also be converted to pusher, but no further information about this.

Thank's

-doni-

[mlbco]

Dear Steve,

My knowledge and experience is limited in engine, so is there any website about converting zenoah from puller to pusher engine? Thank's

I also have 3W, the 3W website told me that it can also be converted to pusher, but no further information about this.

Thank's

-doni-

Doni,

It's beyond me to explain in detail how to set the engine timing. You should contact the engine manufacturer or dealer and they can tell you how to do it.


Steve

[macboffin]

I can confirm tha Tigre engines don't seem to have a cooling problem; visited Cyprus quite a bit, many Tigre engines used there because no over-heating problems; frequently day temperatures top 100 degrees.Note that Tigre recommend not to use Nitro in fuel "Don't need it" they say; that would help temps of course. Mac

[treehog]

Glow fuel has more onions in it than gas (petrol)and there are lots of issues

first the best size cyclender for gas (petrol) is 200cc to 300cc so thats wy small cars are often 3 cylinders of 300cc instead of four of of 250cc

also the compression ration for glow is higher 9:1 versus gas 8:1 and higher compression makes more power


The conversion kit at $350 will refguire some few hundred hours of use to get your money back compared to glow fuel costs

simple maths will show that the motor will produce 10% often 220% less power than the glow motor

the glow motor is cheap and to sink $350 into a motor that is sub $200 seems brain dead to me

the only reasons to do this is
you intend to get huge duration such as 12 hours plus

you live in a country where glow fuel is banned

you are in the UAV busness and you want to sell a product to rich brain dead users and they want a simple easy start easy fuel system

or you geeky type with lots of money that want to wreck a good cheap glow motor

Reverse running buying a reverse prop is cheaper easier


If I do petrol it would be 50cc and up and probably the CZ MVVS 45cc as that hauls

The mvvs would probably be little bit more heavy but would probably return similar low fuel consumption for the same revs but have more in reserve if I neded it and still be cheaper than this roundabout solution

Honestly I figure the few heli heads that did this petrol convertion are kicking themselfs if they dont use the model every day to get thier money back

Ralf

[macboffin]

Glow fuel has more onions in it than gas (petrol)and there are lots of issues

first the best size cyclender for gas (petrol) is 200cc to 300cc so thats wy small cars are often 3 cylinders of 300cc instead of four of of 250cc

also the compression ration for glow is higher 9:1 versus gas 8:1 and higher compression makes more power


The conversion kit at $350 will refguire some few hundred hours of use to get your money back compared to glow fuel costs

simple maths will show that the motor will produce 10% often 220% less power than the glow motor

The brain dead UAV folks have had problems finding glow motors capable of flying UAVs from 100 to 22,000 lbs weight.Petrol had more BTUs than glow; thats why you use less per horse-power hour. There are serious problems with methanol fuel in quanity, one being that it is hygroscopic, takes up water from the atmosphere very readily.Thats for starters

the glow motor is cheap and to sink $350 into a motor that is sub $200 seems brain dead to me

the only reasons to do this is
you intend to get huge duration such as 12 hours plus

you live in a country where glow fuel is banned

you are in the UAV busness and you want to sell a product to rich brain dead users and they want a simple easy start easy fuel system

or you geeky type with lots of money that want to wreck a good cheap glow motor

Reverse running buying a reverse prop is cheaper easier


If I do petrol it would be 50cc and up and probably the CZ MVVS 45cc as that hauls

The mvvs would probably be little bit more heavy but would probably return similar low fuel consumption for the same revs but have more in reserve if I neded it and still be cheaper than this roundabout solution

Honestly I figure the few heli heads that did this petrol convertion are kicking themselfs if they dont use the model every day to get thier money back

Ralf
The brain-dead UAV users have had problems finding glow motors capable of flying UAVs from 100 up to 22,000 lbs weight.(Last being the "Global Hawk".) Petrol has more BTUs than glow fuel( methanol) and is far less hygroscopic.Thats for starters.

[kd7ost]

Glow fuel has more onions in it than gas (petrol)and there are lots of issues

first the best size cyclender for gas (petrol) is 200cc to 300cc so thats wy small cars are often 3 cylinders of 300cc instead of four of of 250cc

also the compression ration for glow is higher 9:1 versus gas 8:1 and higher compression makes more power


The conversion kit at $350 will refguire some few hundred hours of use to get your money back compared to glow fuel costs

simple maths will show that the motor will produce 10% often 220% less power than the glow motor

the glow motor is cheap and to sink $350 into a motor that is sub $200 seems brain dead to me

the only reasons to do this is
you intend to get huge duration such as 12 hours plus

you live in a country where glow fuel is banned

you are in the UAV busness and you want to sell a product to rich brain dead users and they want a simple easy start easy fuel system

or you geeky type with lots of money that want to wreck a good cheap glow motor

Reverse running buying a reverse prop is cheaper easier


If I do petrol it would be 50cc and up and probably the CZ MVVS 45cc as that hauls

The mvvs would probably be little bit more heavy but would probably return similar low fuel consumption for the same revs but have more in reserve if I neded it and still be cheaper than this roundabout solution

Honestly I figure the few heli heads that did this petrol convertion are kicking themselfs if they dont use the model every day to get thier money back

Ralf

There are many benifits to gasoline/oil mix compared to glow fuel. I use glow fuel engine, electric motors and gas engines btw so speak from experience.

Glow fuel is expensive compared to gasoline.

Glow fuel is messy because the lube doesn't burn off.

An expensive spark plug will long outlast many expensive glow plugs.

Quality gasoline engines have higher reliability than quality glow engines.
(I've only dead stick landed gasoline engines if I ran it out of fuel)

Less fuel is consumed running a gas engine so you can get much longer flight times per ounce of fuel consumed or carry less fuel for similar times.

The higher initial cost of gasoline engines is offset by the fuel and glow plug replacement cost of glow when used for a significant period of time.

Pound for pound, nothing is stronger than a glow engine all other things being equal. But if you need reliability and duration over vertical performance, (Most UAV's fall into this category) then gas is by far a superior fuel.

I can get fuel at any local gas station for ease of continued operation.

I fly glow for fun planes, but gas for work planes.

This is just a start. What are you doing here treehog? :rolleyes: The UAV forum might not be the place you're looking for. Most of us have experience with various power systems and see the good and bad in all of them. To outright bash small gasoline engine conversions makes no sense. I concider a glow engine on a UAV means you can't afford the right parts yet. But if you run it a long time, it will cost you more. An engine out from a failed glow plug at 1 km away will trash all your gear. Now what costs the most?

Dan

[treehog]

@kd7ost
This is just a start. What are you doing here treehog?

you really expect me to reply to that ???



@kd7ost
The UAV forum might not be the place you're looking for.

you really expect me to reply to that???




@kd7ost
Most of us have experience with various power systems and see the good and bad in all of them.

I presume C/L deisel experience dosnt count or small 25cc to 1000 cc petrol motor experience from other fields

To outright bash small gasoline engine conversions makes no sense.

45 years of Historical imperical evedence shows since virualy 1960 which is where the development stoped in petrol versus glow and has remained more or less the case since up to 2007 that the realistic cut off point for glow versus petrol is approx 50cc with the decent to 23cc full of compromises that the RC car 1/5 faterity can tolerate to reduce petrol gas costs

If others want to blaze a trail into what has been a dead end solution where fuel effency V power V weight returns are miserable for the effort then fine but dont expect me to swallow this propaganda and keep quite





@kd7ost

I concider a glow engine on a UAV means you can't afford the right parts yet. But if you run it a long time, it will cost you more. An engine out from a failed glow plug at 1 km away will trash all your gear. Now what costs the most?



Personaly I will probably do my my UAV projects with electric as the probabailty for engine failure is probably the least in small size

in larger size I would opt for 50cc upwards

below that 50cc size such as 90 glow tese are quite cheap reliable motors that do not require high Nitro often no nitro and high quality glow plugs replaced in service regular mode would probably mean that most UAV types who would fly less than 30 hours in a year would be better of to stay with glow mostly cause it is cheap to buy the motor and the fuel costs are not so big for bulk bought glow fuel with no nitro


Motor failure issues at 1 km can happen to any power source so solutions such as second motor electric or glow with on board starting and parachute desend would save most craft that could not glide back


45 years of umteen attempts from umpteen model making companies to get small petrol gas motors into the modeling arena says its flogging a dead horse and a small group of 10 UAV users who fly 200 hours a year is not going to change the reality that exists


Ralf

[treehog]

repeat post mistake

[kd7ost]

[QUOTE=treehog45 years of umteen attempts from umpteen model making companies to get small petrol gas motors into the modeling arena says its flogging a dead horse and a small group of 10 UAV users who fly 200 hours a year is not going to change the reality that exists


Ralf[/QUOTE]

I don't know what else to say to you Ralf. I'm glad you have all your own answers. Many of the rest of us haven't found our stopping point though. ;)

If we continue our discussion of small gasoline engines, it would be nice of you to keep your "idiots" references to yourself. Name calling doesn't serve professional minded people.

Dan

[DiveBombDave]

I'll ask a good question -

Does anyone have any information on the energy density of model diesel fuel compared to gasoline?

The information that is provided by www.davisdieseldevelopment.com seems to imply that a larger glow engine with a converted diesel head would multiply duration several times compared to glow. The conversion process will spin a larger prop slower than the same engine on glow, but supposedly they sip fuel. This "larger prop slower" also seems to fit a maximum duration implementation. One of the large supertiger glow engines could be converted to diesel for the same or less money as a nice gas engine, I'm thinking.

Dave.

[Hovertime]

And diesel does not need a plug glow or spark.
But i guess my choice would be go with either electric or gasoline.
Glow fuel era is rapidly ending IMHO.

[kd7ost]

I don't have an answer for you Dave. But I do know that the Diesel conversions don't run off of DF2. You still have to purchase a special blend, or if you find a recipe you can mix your own. Last I looked, and it was several years ago, the fuel needed was still close to $20.00 a gallon and had to be ordered. Sounds like a question for Clarence Lee.

Dan

[DiveBombDave]

Well, what good are you then? ;) :D

The fuel on the davis site is about $20/gal, if I remember right. But I was thinking that if duration really increased several fold, that would help offset the gap between the $20/gal glow and the $2/gal petrol, when thinking about dollars per mile rather than per ounce. But looking at those numbers it would have to provide 10 times the duration over gasoline to equal it's costs, and that would be impossible I imagine.

I know that a high ether blend of diesel should have more energy density than gasoline, but it couldn't be substantial enough to have to mess with ordering your fuel.

Dave

[kd7ost]

Well, what good are you then? ;) :D Dave


:D :D :D I dunno.

I wasn't speaking for or against it BTW. Just throwing out the little info I had. I do think it would be a boon in some cases to use diesel over gas or glow. I guess when I approach these questions I think about getting support in remote areas as fast as you can. Thats where gasoline really shines just due to ease of purchasing access.

I think going diesel in small glow engines trumps large gasoline or small glow engines. Except that maybe the Super Tiger .90 came along. It's hard to find small engines (sub 1 cid) that are gasoline powered.

Dan

[macboffin]

Well, what good are you then? ;) :D

The fuel on the davis site is about $20/gal, if I remember right. But I was thinking that if duration really increased several fold, that would help offset the gap between the $20/gal glow and the $2/gal petrol, when thinking about dollars per mile rather than per ounce. But looking at those numbers it would have to provide 10 times the duration over gasoline to equal it's costs, and that would be impossible I imagine.

I know that a high ether blend of diesel should have more energy density than gasoline, but it couldn't be substantial enough to have to mess with ordering your fuel.

Dave The ether is just there to ensure ignition, lower flash point. The energy is in the kerosene/paraffin,(depends where you are what you call it!)

[macboffin]

You ever seen a big Mac truck running on petrol or glow?

[macboffin]

Choice of engine/fuel for UAV use?
First points; Total weight of engine, ancilliary equipment, propellor, mounts, fuel, tank/s, ie total power weight for a given mission.
Also relevant, proposed altitude requirements, fuel availabilty in required quality in operational area. Vibration characteristics of engine type and effects on structure and payload. Noise. Infra-red characteristics of engine in a hostile environment. And a few other relevant issues.
(One assumes that since the tax-payer has a bottomless pocket, budgetary considerations are secondary!)
If it is not a serious UAV project, well, whatever grabs you!

[macboffin]

repeat post mistake
Seems to me that ALL your posts are mistakes. Do some homework!

[treehog]

Examples of power cut off points in other modes of power could be that steam is superior to lots of power types for over 600 hp or under 10hp so that is one reason steam cars didn't catch on where 100 hp is the norm and petrol had the slot

Turbine in real aircraft are mostly seen at 600hp and higher and pistons are more normal below 600 hp but there does exist 300hp turbines but they got seriously high fuel consumption for the same 300hp compared to piston of same 300hp

Man whats with the laws of motors that seem pretty self explanatory
petrol works best as a fine spray mist whatever

As you shrink the motor the and the CC of the motor the fuel tends to form droplets more readily and run unevenly and consume more fuel and produce less power and still costs the same as the bigger motors

Changing to alcohol this droplet affect will not happen happen until the motor gets very small but efficiency drops down to less than 5% and as the CC get very small and the air cant get into motor fast enough then introduce nitro methane which supply's extra oxygen to help out

Now a 90 glow turbine motor turning at 24.000 can produce a few HP but if you put a big prop on the same motor the HP will drop
Simple really if the revs drop to say 12,000RPM the intake of fuel is halved and with fuel each cycle make so many watts with each charge of fuel air
double the revs double the fuel intake double the power roughly

Normally to increase revs you get smaller props or turbines and max revs but also the volume of air pushed is less so more power is wasted

Now fuel in the equation is cheap real cheap and until it get to $20 a gal its no generally no big deal so if petrol or gas hit $50 a gallon then everything changes

Similar thing happen for cars
often to recoup the extra cost of a diesel car you have to drive 40K mile a year or fuel has to cost $25 a gallon to get your money back

As for diesel in model planes they have a problem to keep running on low throttle for long periods and can cut out
the are heavy and have lots of vibration
the smaller diesel motors use ether ~30% Parrifin ~30% castor oil ~30% and 1% amyl nitrate from memory in my combat CL days

I do not know of any diesel motors that burn normal diesel

In one club I was in they had for a five teen year period a glow 22cc glider tow plane which served the club very well most every weekend in a good climate well south of in southern europe and most summer nights towing up the gliders
The club bought the fuel in bulk 20 plus gals of alcohol and several gallons of oil and so fuel cost were kept lower

then one day the plane crashed full bore from 200feet into the runway
motor broken

The replacement temporary replacement craft on loan from a club member had a Zenoa petrol motor ~38 cc on a very similar airframe

After several weeks when the club did the sums to see what replacement motor they would get to see them for the next 15 plus years and they ran the numbers of the replacement motor fuel costs both petrol and glow they bought a replacement 22cc glow

When I interrogated them on all the reasons for the decision the main reason glow won was it was found to be cheaper to buy cheaper to run on parts and fuel and would probably remain cheaper as before this accident they had had some other smaller crashes which did not break the motor but would have broken a 4 stroke or complex petrol motor and the fuel cost over time were similar as the petrol had less power and took longer to climb so making it even stevens in terms of fuel count COST per tow flight
The 22 cc glow motor had a petrol option but the extra cost to cover this was unlikely to ever be recovered and performance would be down 20% and fuel cost saving were not expected to be better than some 20% so canceling out benefits

At 50cc petrol the case was pretty clear and that was why the bigger club tow plane was a 80cc petrol plane

As the club had some 200 members some flying models since bang bang RC contributing to the clubs tow planes I think they would reply

They did their years of homework and the club is not a UK club :D

Ralf

[kd7ost]

It's easy to site single instances that weigh one over the other. In fact the crash that broke the gas engine isn't a guarantee. Just bad luck. The crash that didn't break the glow engine isn't a guarantee. Just good luck. I've seen crashes where neither style of engine groke and crashes where both style were broke. An accurate comparison needs to be based on a trend analysis and not a single event. A survival of impact analisys would have to have many different models with exacting replicating impact scenarios to make a fare comparison. Additionaly, crashes are bad on planes at any rate. We design them to fly, not to crash. If you crash it all bets are off.

I fly a 32 cc gasoline engine in my Pegasus1 Ag photography plane. I've used it for over 2 years. My onboard GPS has not had the trip data reset and it has now accumulated over 2,200 miles, (3,540.5 km) with never a shut down or dead stick landing. I can fly for in excess of 1 hour on 32 ounces of gas mix at full throttle. It is cheap and easy to run. Highly reliable, (I've only put a new spark plug in once) and have never had any issues. The engine is as strong now as it ever was.

It's hard to beat tangible results.

Dan

[Hovertime]

Hm. I can not really imagine it would be cheaper to buy alcohol in bulk than gas....
I would choose gas without too much questioning for a work machine.

[copperclad]

hi
i thought you guys might like these pictures of honda's new GX-25 on a bigbee , it's not mine , just saw it posted the other day , honda claims the GX series of engines can be run in any position , looks like a nice little four cycle , dana :)

[Hovertime]

Oh, its gorgeous! :)
One question though - why in the world would they put that cooling fan on the airplane engine ???

[kd7ost]

I can think of two possible reasons.

1. Since it's made by Honda, they could have just used an already manufactured flywheel for some other of their products. It looks like it has a magneto ignition and that's the flywheel with the magnet in there passing the pick up coil. Might as well cast in some cooling fins.

2. In a pusher configuration, especially when on the ground, there is no prop blast over the engine.

Just thinking that's all.

Dan

[dalbert02]

Reference glow vs diesel vs gasoline (petrol) here are some things you may want to consider:

1) An old Colonol I used to work for used to say, "Often times one carefully controlled experiment is often times worth more then a thousand expert opinions."

2) In a Permutations and Combinatorics class I once took, I was taught that nothing can be said statistically without a sample size of at least thirty.

For some insight on the how's and why's of reciprocating engines, I highly recommend reading:
http://www.eaa1000.av.org/technicl/engemp/engemp1.htm

And possibly consider that a super charger / nitro methane is best for:
http://kb-silvolite.com/news.php?action=read&N_id=43

In the boating industry, it is often agreed that over 35'-38' your are better off diesel and less you are better of gasoline.
http://www.yachtsurvey.com/GasDiesel.htm
http://www.yachtsurvey.com/GasNdiesel.htm

So, IMO, no motor or fuel is best as it depends soley on the application and the desired performance parameters (fuel economy, energy density, fuel availability, etc.)

-dave

-dave

[kd7ost]

Sounds good by me.

Also, top speed or vertical performance are not frequently the deciding factors in our UAV type planes. Efficiency doesn't mean massive power. Rather it means endurance and enough power to handle the task at hand without sucking alcohol like a dry drunk.

A big prop turning slow is more effecient than a small prop turning fast.

Dan

[stingrayOZ]

What about newer 2 stroke weedwacker engines. 25-35 cc and extremely cheap. Seem to be reliable and tough. Weight doesn't appear too bad but can be improved.

You can pick them up brand new for ~$50. Cooling could be improved etc. But a dead engine would be quick and easy to replace.

I hear they were very popular before modern glow engines appeared.

[kd7ost]

The problem with those is that they use bearings designed for side loads. When you put a prop on a weedwhacker engine they have lower power and wear out fast. The airplane configurations need to have special crank cases and bearings designed for thrust loads.

Dan

[Hovertime]

I must say that this fan without shroud would not be providing any cooling in either pusher or tractor config.
Its not an airplane engine : http://www.honda-engines.com/engines/gx25.htm

[kd7ost]

I'm not an expert but after we've been taking about this, it seems just as likely, (Or maybe more so) that it not only holds the magnet for the ignition timing but doubles as a heat sink. Maybe those are cooling fins helping transfer heat from the bearings, shaft and out the aluminum fly wheel and built in fins.

You don't find those on gas engines purpose designed for RC. But you do see them on gas engines that have been modified for RC.

Dan

[copperclad]

hi
sorry :o , i didn't get back to this thread till just now , it wasn't my intention to infer that the honda is a purpose built RC engine , but i see from my post that it could be taken that way , my bad :o

the GX-25 is designed as a trimmer - cultivator engine and the interesting feature is that it can be run or stored in any position

the flywheel fan is designed to be used with the original shroud to provide cooling for the engine , and whoever installed it on the bigbee , used a common practice and just stripped the shroud away to allow prop wash and forward motion to cool the engine , they left it in place because the magneto needs the flywheel magnets to operate

i first saw this engine in another forum , a gentleman used it in a conversion for a gasser heli , and hearing the engine run , is what got me interested in it for RC applications

http://www.runryder.com/helicopter/t314487p1/

sorry for any confusion my post caused , dana :)

[kd7ost]

I would imagine in a heli it would work nice. That's side loads on the shaft because the thrust is on the main shaft.

On that flywheel, they have the magnet in there for the pick up coil or hall effect sensor but it's also balanced too. It wouldn't be practical to really remove any of th efins or flywheel. It's pretty well stuck there for balance unless you fabricate a complete replacement.

Dan

[ama1835]

While I was Sr. UAV technician at Advanced Ceramics Research we developed a Honda GX25 and have had very good luck with it installed in the Silver Fox UAV. There have been extensive modificaions to the engine including replacing the magnito with a c&h ignition and a belt driven fuel pump. Flight times are just over 8 hours on 90oz or regular gasoline.
We also use the 3W56i-B2 on the Manta UAV and have a duration of 6 hours on 2-1/2 gallons of fuel with a 50 pound plane.
We also have converted OS91FS to gas and Diesel using a c&h ignition and changing the carb. If anyone wishes more details let me know.
Steve

[dalbert02]

Hi Steve,
Yes please share your details with us!
-dave

[copperclad]

hi
here is a picture of a Honda GX35 converted to electronic ignition , i am thinking the GX25 would be a candidate too , dana

[Dragons_Fire]

I am definately no expert, but i do like playing around with stuff until it works... I turned down the flywheel on a homelite 35cc trimmer engine, stuck a prop on the front, and let it run for a while... its probably only had about 3 hours of run time, but it ran great and never had any problems.. wheni can, i will upload a picture of it. its running upside down, with a copper pipe for the exhaust header, and soup can mufflers out of an old issue of model airplane news.

[Myron]

Hey Guys,

We have just completed our 86" UA project and were now evaluating the power system. Weather is bad so we havnt flown it yet but I dont think the G26 installed in it is going to cut the mustard.. The craft weighs a bit over 16lbs with 24 oz of gas. The G26 is rated at like 2.1hp at MAX RPM but normal running with a 16x8 prop is more like 1.5hp or about 1000Watts.. The motor weighs 3 lbs and another 1.5 with a full tank.. An Eflight power 160 electric motor is rated at 2700 watts and it will put out over 15lbs of thrust.. Thats pretty good for a 2lb motor.. Yeah, I know a huge set of lipos is costly but if your looking for something that flies between 30-60 minutes It seems that a large electric may be the way to go..
Maybe when get this motor going we may be suprised, but our initial impressions are not that great of this motor. Maybe some of you can post a few real world results of a G26 and a 16x8 on about 24oz of fuel..and whatever type of aircraft its on.. I was told at the hobby shop that I needed to prop it up to an 18" to help extend motor life but the booms are too close together for that.. We may have to go to a 3 blade 16x8 pusher.. Looks like we may have to try the reverse running of this thing because 3 blade pushers arent cheap and their not easy to find...

Myron

[clolson]

We have just completed our 86" UA project and were now evaluating the power system ... The craft weighs a bit over 16lbs with 24 oz of gas. The G26 is rated at like 2.1hp at MAX RPM but normal running with a 16x8 prop is more like 1.5hp or about 1000Watts.. The motor weighs 3 lbs and another 1.5 with a full tank ... Maybe when get this motor going we may be suprised, but our initial impressions are not that great of this motor. Maybe some of you can post a few real world results of a G26 and a 16x8 on about 24oz of fuel..and whatever type of aircraft its on.

We have a G26 on the front of a Rascal 110. We are turning an 18x8 prop and get about 7000 rpm on the ground at full throttle. We have done some weight tests and have successfully flown with 5 lbs of balast. The empty weight of the Rascal 110 is about 12-13 lbs if I recall so that put us at close to 17 lbs total weight.

We could have used larger tires since the stock ones wanted to dig into the grass with the extra load.

Otherwise, we got airborn just fine and flew just fine. You could certainly tell the difference between no load and +5 lbs load, but it didn't feel like there were any safety or controllability issues. If we had a hard surface, I bet we could have easily gotten off the ground and flown just fine carrying 10 lbs.

That's just one data point though.

Dan has posted previously that he get's about 2 minutes per ounce with his G26. We haven't paid very close attention to fuel burn on our setup.

Curt.

[Myron]

Thats good info Curt!.. We had some run up and tuning issues at first but we got that fugired out and we got it tuned up quite a bit so taxi test look pretty good with about 3 lbs of ballast in the front.. Turns out we were sucking air because the fuel tubing came off the pickup in the tank.. We need to get a large spinner so it is easer to start.. If the weather clears out we will try to maiden it on Sunday..

Myron

[mlbco]

Myron,

I use the G-26 with electronic ignition and reverse rotation on my Bat 3 UAV products (www.spyplanes.com). We changed to a slightly smaller Walbro carb and we also use a plastic venturi inlet on the carb. Our propeller is an APC 16x8. Our UAV weighs 23.5 lb fully loaded and has a 78" span. Cruising at 35 kts I measured 5.8 hours duration on 3.5 lbs of fuel. This is a real number, the UAV actually flew 5.8 hours, we did not extrapolate to get this. Cruise is around 6000-5500 RPM. We also achieve a rate of climb greater than 1000 fpm at 35kts at sea level using full power. Our dyno test show the G-26 has 1.5 maximum HP and an sfc of approx 1.2 lb/(Hp-hr). I have several G-26 motors with over 300 hours on them and no problems. I use 87 octane fuel mixed with 40:1 oil. This engine has been very reliable for us.


Steve Morris
MLB Co.

[Myron]

Hey Steve,

This is more good info and much appreciated.. Just off the scales, ours weighs 17.5 lbs with about 12 oz of fuel.. If yours flies at 24lbs fully loaded with the same motor and similar wing span, I think we can safely carry 7.5 lbs.. We dont plan on modding the motor at all other than possibly changing rotation just so we have a wider range of prop choices. Our development partner wants 8 hours duration at cruize so I think we can cut back on the payload and stick a 30oz bladder tank in it and get close.

Myron

[kd7ost]

I use this 16x10 three blade pusher from Master Airscrew and it is sold for a reasonable fee at Tower.

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXAPX5&P=ML

I have it on my Fuji BT32A which is a little bigger than the G26 but the HP numbers are pretty comperable. I used the Fuji because it's the smallest gas engine I could find that you can get a spring starter for. It eliminates the massive starter and spinner requirements needed for the G26. The prop was supposed to be a little small for the Fuji but it's just fine. I only detect a small difference between it and the 18x8 two blade pusher. But, it's cheaper and doesn't suck up rocks on take off as bad as the longer prop. It will handle dings a little better than the wood props too.

I flew the Sig Rascal 110 prototype plane at 17 pounds with camera and all other gear and it flew right off the ground. Lots of power. With a 1 qt tank I got 1 hour flying at WOT with the stock carb.

I still have the G26 you guys set up for your prototype twin pusher sitting in the box. I've put no more time on it. In fact you guys are the only ones that ran it. Let me know if you want to purchase it for future planes. My next plane is getting the G45 with starter spring.

Dan

[Airboatflyingshp]

Just an asides but you might want to look at Davis diesel head conversion of a large glow or .....I think Meccoa also do them ?......Much Quieter, Cooler, more economical and slings a bigger prop...............less fire risk..............a good idea in some places these days??

oops Divebomber Dave s done that.............but Ive got an OS FP/FSR40 DDH conversion and even on the stock carb its pretty remarkable does exactly what it says and its a two or three flick start.
Cold weather add a bit more Ether :)

[Myron]

Hey Dan,

Thanks for the info and link.. I have a bunch of 16-18 props of all types and even a few large 3 blades.. I just have to get the rotation reversed on the G26 to take advantage.. I also measured the distance apart on the booms so I can safely run an 18" prop on the 26.. After we got the fuel tank issue resolved, we did some taxi test and she seems to have enough grunt with about 3.5lbs of balast in it and 12 oz of fuel. Tomorrow may be the day for the maiden... Have any of you had issues with a magneto being too close to the RX? I will test fly with pcm g3 so I dont expect there to be any problems...


Myron

[kd7ost]

Hey Dan,

Thanks for the info and link.. I have a bunch of 16-18 props of all types and even a few large 3 blades.. I just have to get the rotation reversed on the G26 to take advantage.. I also measured the distance apart on the booms so I can safely run an 18" prop on the 26.. After we got the fuel tank issue resolved, we did some taxi test and she seems to have enough grunt with about 3.5lbs of balast in it and 12 oz of fuel. Tomorrow may be the day for the maiden... Have any of you had issues with a magneto being too close to the RX? I will test fly with pcm g3 so I dont expect there to be any problems...


Myron

I think I wasn't very clear in my description. The Rascal 110 at 17 pounds flew with the G26. The Fuji is on my 20 pound Pegasus. That Zenoah G26 was a strong engine and was extremely reliable as are all the gas engines I've run. That spark ignition is great. I sold that plane and engine minus radio gear where it serves duty today as a glider tug.

I've never had any issues with the Magneto or spark coils causing me any interference issues. Just for the record, I've flown them all with a Futaba PCM radio system and stock antenna.

I have my receiver way up in the nose of the plane and the engine is in the pusher configuration so there's a lot of real estate between the two units.

I pull the Rx antenna out of the fuselage and run it at an angle out to one of the wings. This keeps the receiver and antenna away from the engine. I'll include a picture. The arrow points at a fuel tubing exit that is strain relieved. The end of the antenna has a number 32 rubber band holding to fairly tight to a small post on the boom. The red line is parallel to the antenna run.

I also have the throttle servo inside the fuel compartment. I use a Du-Bro Laser rod for throttle linkage. They are fairly rigid so you can't bend a tight corner with them. But they are slick as snot and temperature stable so the length doesn't change and affect the trim settings. They aren't conductive either.

The closest wiring to the engine is the servo wiring for the rudders, elevator and ailerons. Since the runs were so long I used some wire and built my own harness. I kept the RF twist in place. Those wires run through the wing about 10 inches from the spark plug but after 2,200 miles of flight I've never had an issue.

Dan

[wadiprawita]

Dear All,

I have lots of problem from the gasoline engine's vibration. Any suggestion?

-doni-

[kd7ost]

Yep, it's almost a school and takes some work.

When you say gasoline what type of engine? Size etc. It's likely a single cylinder? 2 cycle or 4? The two things that have to be managed is frequency and amplitude of vibration induced motion. What are you trying to fly in the plane? Some things tolerate vibration better than others. A camera for taking still’s seems to be the least tolerant.

Here’s a good article to read to start. Pay particular attention to mass and inertia. It’s an easy to read article.

http://www.hicam.com.au/art_vib.htm

Dan

[wadiprawita]

Dear Dan,

I've tried G26, G20, MVVS 26, and DA50. The smoothest from my qualitative judgement is G20. My payload is digital still camera and Black widow system. The engine vibrates most on low RPM (less than 25% throttle) and getting better above that (but still vibrates).

Thank's for the link.

What do you do on your plane?

Thank's

-doni-

[wadiprawita]

Dear Dan,

I also have 3W 28cc and 56cc (twin), but I haven't tried tehm. Are they any better with vibration ?

Thank's

-doni-

[kd7ost]

Engine with opposed cylinders typically do better but still vibrate. Lower RPM does have more vibration because it’s a lower frequency. Super soft engine mounts help a lot at higher RPM but at an idle they walk too much. The vibration is worse at low RPM with real soft mounts.

I use soft mounts that are stiffer. I get them from Estco enterprises. http://www.estcoenterprises.com/display_lines.php?cat_id=9

The ones I use are 5/8th” thick and 1 3/8th” diameter. They use a 5/16 stud. They don’t dampen all the vibration but are still stiff enough to keep low end from going crazy and walking all over the place. This keeps a fair amount of vibration out of the airframe.

Next I soft mount the camera. It takes a special foam. The Hobby Latex foam has good elastomeric propertied and works the best. You can’t leave it loose in the foam mount but you can’t really compress it too much either of it will get stiff. You have to let it move.

After that, the camera was still too light. It still vibrated a bit even though it was getting better. I read that story in the link above and realized I was trying to dampen a sugar cube. I fixed the problem by adding weight to the camera to add mass. The extra weight helps compress the foam and keep the camera from going into motion. You have to capture the camera on all sides. You can also adjust by removing some of the surface area that contacts the foam. Look at it like springs. One is soft and ten are stiff. You can add to or take away from the stiffness by keeping the foam pads fairly small.

The engine vibrates left, right, up and down. Not front to back. So make sure to dampen it in that direction.

Dan

[wadiprawita]

Dear Dan,

Thank's for the info, I will try that.

-doni-

[kd7ost]

No problems.

I should emphasize to keep an idea of where the camera sensor is located. Near the center of the camera. That why it's important to capture the camera body itself on all 8 corners or there abouts. If you just dampen the front or the rear, it will allow the camera to swing by small amounts causing vibration to induce motion to the optical sensor.

Dan

[wadiprawita]

Dear Dan,

Where can I get this Hobby Latex ?

Thank's

-doni-

[kd7ost]

Most of the Hobby Shops in the states have it in stock. Here's a mail order source in case you can't find it. I use the 1/4 inch in my big gasser.

http://www2.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=latex+foam&FVPROFIL=++&search3=Go

[kd7ost]

Here's another option. The prospark ignition to add to glow engines.

Dan

http://www.nelsonhobby.com/prospark.html

The silver Fox UAV from advanced ceramics uses that ignition system on a 4 stroke OS 91.

http://www.acrtucson.com/UAV/silverfox/
http://www.acrtucson.com/UAV/st_helens.htm
http://www.onr.navy.mil/media/article.asp?ID=25

[macboffin]

Just an asides but you might want to look at Davis diesel head conversion of a large glow or .....I think Meccoa also do them ?......Much Quieter, Cooler, more economical and slings a bigger prop...............less fire risk..............a good idea in some places these days??

oops Divebomber Dave s done that.............but Ive got an OS FP/FSR40 DDH conversion and even on the stock carb its pretty remarkable does exactly what it says and its a two or three flick start.
Cold weather add a bit more Ether :) I certainly endorse Davis head conversions, lets you turn a bigger prop, and much endurance on "same size" tank. Davis also supply a fuel concentrate, just add kerosene/lamp oil.