Diesel v Glow

[7severn7]

Can someone give a definitive statement whether or not diesels are more powerful (revs x torque) than glow engines? Are there any companies still making diesels aero or marine? If so, what sizes are they available in?

[max hansen]

The diesel & glow are quite a lot alike . There are sport & racing versions of both . The diesel wins in fuel consumption & maybe in pulling a larger prop for it's size . Several companies make them but most are overseas . Davis Diesel makes heads that fit most any engine , have seen them from Cox .020 to Super Tiger 3000. Look on E-bay , they are always there. Have fun , MAX H. :lol:

[Rustler]

I believe powerwise it comes down to the fuel. Glow fuel burns hotter than diesel, the gases expand more, so you get more power. Diesel fuel contains more calories, so although not so powerful a diesel will run longer/further on an equal amount of fuel. Diesels have a reputation for handling larger props, and generally this is true. The reason is the copmpression ratio of a diesel can be varied to the optimum setting for any prop, using the lever at the top to move the contra-piston. Generally a glow has a fixed compression, set for a typical prop size. If you use a larger prop the compression ratio is "wrong". I'm fairly sure if you optimised the comp. ratio for the glow with the larger prop, it would outperform the diesel.
I do have an engine called a "Hybridni" from the old Czeckoslovakia, which claims to run on diesel or glow, it has a variable contrapiston with a glow plug installed! One day I must run it, it could answer the question.
If you'd like a list of diesel available send me an e-m, <rustler@aero.fslife.co.uk>.

[Frank Klenk]

Here's a link if you wish to buy a diesel. Mr. Carlson has several available.

http://www.carlsonengineimports.com/index.shtml

Frank :)

[7severn7]

Hi Rustler

I'm still trying to get my head around this. Your reply suggests that a glow is more powerful than a diesel; yet a number of the test reports on diesel head conversions suggest an increase in revs on the same prop on the same engine. If my understanding of horsepower is correct (revs x torque) the result suggest the diesel is more powerful.

Is there an expert out who can take time out to explain this better please?

[Dan Mrozek]

Diesels are fun and have there benifits. If you are serious all around flier glow is the show. I keep my model inside and diesel powered in the shed. The diesels will stink your home big time! With a diesel you have one more thing to adjust. As diesel warms up the setting changes. There is good reason that there are many more glow than diesel. Less trouble with glow with contant power.
If you like to tinker then diesels are for you. Some are quite impressive. The fuel takes a little getting use to , but after awhile it is not to bad. You won't belive how many folks think you will need a battery to start it. Another thing to watch is some jerk cranking you diesel to check compression, and it starts up in their hand. If there is fuel in system they can start even after a sitting for awhile. Dan :lol: :shock:

[Rustler]

G'day 7. If a diesel was more powerful, all speed records would be held by diesels. All F1C models would be powered by diesels. Some diesel sellers do hint the conversion is more powerful, personally I doubt it. Ian R.

[topgear]

When i started flying as a young lad in the late seventies, many a days flying was spoiled by a flat battery or burned out plugs. We quickly went off glows & all our early flying was with diesels. As a result i cannot get my head round glows even today, flying control line stunt. Running a glow motor on over rich fuel mixture & expecting it to give full power when some up elevator is applied doesn,t do my nerves too much good either. I suppose the question you have got to ask is how much power, & what sort of power characteristics you need. I recently had a model that was over powered with a .15 glow. The cure was to fit the diesel version of the same motor.

[topgear]

If you want a big un try PAW @ http://www.progress.charitydays.co.uk & MVVS do them upto at least 12cc & in marine versions too. They never had em this big when i were a lad.

[Dan Mrozek]

Putting a diesel in a stunter is asking for trouble. Every one I seen came to a pile of ruble in short order. Diesel conversions included. I solved bad plugs years ago by using TT long RC plugs. As far as flat battery that is poor preparation. I have ni-cad start batteries that lasted years. You do need charge them before hand. I know diesel fans are diehards, but have limited use. I like them too, but not for stunt,speed,combat etc. I have a Elfin 1.5 that powers a 54 inch Powerhouse that climbs vertical under power. :lol: :roll:
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[Jim]

>Putting a diesel in a stunter is asking for trouble.

Really? I haven't flown U/C for decades but back when I did, in the UK .. diesels ran fine in stunt .. and still do.

For instance, check out Gig and Tony Eifflander's prowess over the years in the Gold Trophy at the Nationals there.

I fly similar airplanes in Class A F/F, with equivalent sized diesel and glow powerplants, and have no real preference ... but sometimes it's nice to walk out to the flightline with just a filler bottle and a fuselighter instead of hauling out all the other stuff! As it happens, building a .15 diesel F/F at this time....

[Dan Mrozek]

Jim. I too find diesels great for FF. Thats why my Powerhouse has one. The little Elfin is very good engine. I do not know any serious stunt flier that uses a diesel here in USA. I know nito methane is hard to get on your side of pond, and diesel is easier fuel to get. Maybe you have better understanding of diesel power. :lol:

[topgear]

Some folk obviously forget the hellish lead acid batterries we used many moons ago. No amount of preperation sorts a duff battery, & we often didn,t carry spares cause we cycled (with models) to the flying field. Too young to drive you see . Good thing about the the modern nicads is they are small enough that you can have a toolbox full of spare ones. I always have a spare in my pocket. Incidently i like glows, there are some nice ones like the exellent stalker, but i think most people prefer either diesel or glow and not both. Americans have been influenced by a different enviroment. eg. they invented the glowplug,have difficulty obtaining quality diesel fuel, the great Fred Carter, etc. It is because of our different enviroments that we have variety and choice.

[Jim]

>Some folk obviously forget the hellish lead acid batterries we used many >moons ago. No amount of preperation sorts a duff battery, & we often >didn,t carry spares cause we cycled (with models) to the flying field.

Topgear - sounds as though we both hail from a similar era; where are you in the UK? Those 2v lead acid cells were a pain, especially if they spilled in your bike sadlebag and rotted everything out, Spoiled the butties, too...

I later overcame that problem by mounting and wiring a second 12v battery into the car trunk ( the 'oldfashioned' kind with exposed cell lugs and bridges), tapped terminals into each cell and ran out long leads from each; up to six people could hook on at any one time to start their glows, the battery was always charged - and winter car starting was a snap!

[topgear]

Jim, I get a sense of deja-vu when i read your car battery story. I think the problem with the ripmax orange coloured cell we used was that it was lead acid, & too small. I am sure you will know that lead acid cells should not be discharged exessively, and should be returned to full charge fairly quickly otherwise the plates sulphate & the cell loses capacity. What do we do with a glow cell ? We short it out on a glowplug . Do that several times and it,s nearly flat, & it does,t get charged up on the way home like your car battery either. Time to buy a new cell ? No, not if your resourceful flying friend turns up with a couple of cells sliced off a 12V battery. More than enough capacity for an afternoons flying. (Needed extra long leads though to give a bit of resistance). Mine only died when it burned a hole through my rucksack & dropped on the road. As for the sandwiches, well i was too young, & too busy flying to bother about lunch.

I recently moved from Edinburgh (good control line scene) to Inverness (does anyone fly here?) Are you by any chance an ex-Brit ?

[Jim]

>Are you by any chance an ex-Brit ?

In Canada since '83 .. but still a Brit...

[topgear]

Silly me, should have known you were still British.I remember regularly being told there was no such thing as a Canadian when i lived near Edmonton.

[Jim Thomerson]

I've flown diesels quite a bit in CL stunt, mostly Old Time Stunt. Other than that time the compression lock nut came loose, I have found them to be about as reliable as glow engines. It is a different technology and I'm still learning.

I tried running a K&B 4011 glow on Davis 1/2A diesel fuel. I had to keep the battery connected for maybe 20-30 seconds until it warmed up then it ran fine. That particular engine turns an 11 x 5 APC 9,700 on Sig Champion 10% nitro fuel. On diesel, the needle (ST) turns in about a full turn, and the RPM on the same prop is 9,700.

All very interesting.

Jim

[ffkiwi]

This is a bit of silly question and keeps cropping up! To put it in perspective
what is more powerful-a 200HP Ferrari or a 200HP John Deere tractor?
Next question-which one of these would you want to pull you out of a swamp? Pure BHP is quite misleading taken out of context-you need to know the intended use-propellor size, and a number of other factors.
Diesels, size for size, will always turn a bigger prop that the equivalent displacement glow-and as larger props are more efficient than smaller ones (hence the various geared glow engines and belt drives which have appeared over the years) so a model may well perform better on a diesel turning a larger prop than on the same size glow turning a somewhat smaller one-but this does NOT mean the diesel is more powerful, simply that its torque is better on larger props, and occurs lower in the rpm scale-and that automatically limits the BHP compared with an engine where the maximum torque occurs at a higher rpm. remember BHP is a derived function, not an actual one-all dynamometers (at least in model engine sizes) measure torque, and the torque figures in conjunction with rpm, generate the BHP curbe.
Despite their fixed ignition points, glows can and do rev higher than diesels-assuming their porting allows it-and as a consequence generally produce greater BHP figures for quivalent sizes-which is not necessarily the same as "power"-which tends to be misused by modellers when they should be talking about "thrust" as it directly relates to flying models-not academic BHP figures.
Again even this is a simplistic explanation, since 'power' needs to be defined in context-there are some competition classes in which the engine size is defined, and absolute power is paramount-C/L speed, F1C and pylon come to mind, others where 'power to weight' ratio is a factor-and a lightweight less powerful engine may be a better option than a heavier powerful one.
There is only one event in which the diesel is totally dominant-FAI team racing, and in that the diesel's dominance is due to fuel economy, not absolute power. Fuel economy is the diesel's one true advantage over glow engines-BUT-this can be overstated, since except for team race-and a few vintage events, fuel economy is NOT a factor in most competition classes-and frequently overlooked is the fact that diesel fuel is considerably more expensive than glow fuel, so converting glows to diesel will not necessarily save you anything in fuel costs-especially since the conversions tend to to be fairly expensive to start with. What a diesel conversion of a glow will do is:
(1) potentially allow you to turn a larger prop at the same revs as the glow
(2) allow you to turn a much larger prop than the same size glow at USABLE flying revs
(3) fly for longer on the same size tank OR
(4) fly for the same time on a smaller size tank

Apart from the initial cost of the conversion, and the intrinsically higher fuel costs, there are other hidden pitfalls-the operating stresses of diesels are significantly higher than for glows-and rods and shafts can and do fail.
Others on this forum have already mentioned the smell of diesel which is certainly stronger and more lingering than glow-but failed to mention that diesel exhaust-whilst oily, is less harsh on painted surfaces than glow-but paradoxically, many iron on coverings don't like it.

So rather than asking a question which cannot be directly answered, perhaps you should have defined the parameters better-or asked what advantages disadvantages there are for diesls vs glows
Is the query purely academic? In which case there is no accurate answer
-or if you were considering getting/using some converted glows-what were you planning to use them in?
From my personal 38 years modelling experience and from someone who owns over 300 engines-half of them diesel-the answers would be something along the lines of:
sport F/F- diesel or glow at personal preference
scale-diesel wins hands down for prop size and mild fuel effects
R/c sport-glow operation is easier
fuel alotment events-diesel again
pure HP determined events-racing glow
vintage events-diesel in preference to ignition (where permitted)

There are other factors to be considered as well-diesels rarely throttle as well as glows-and converted glows often create problems-which can often be solved by fitting a SMALLER carb. The fuel is highly flammable and far less widely available than glow fuel-and there is no equivalent component in diesel fuel that can boost power the way nitromethane does in glow fuels.
Diesels in general do not like pressurised fuel systems-which can pose problems in some setups-and particularly important in F/F and limited ER R/C events- do not cut as cleanly as glow engines and tend to run on, resulting in overruns.
So essentially the answer to all this is: define your requirement, and then you can decide whether a diesel is appropriate

[loucrane]

Gents,

I think we lost sight of the original question...

Remember, power is the time RATE of delivering WORK, and WORK is overcoming a resistance over a distance (or equiv).

So, because glow engines use quicker burning fuel, more of it, and at (most often) higher RPM, sheer horsepower will always be easier to get with this kind of ignition.

However...

We (almost none of us, anyway) operate at MAX power the engine can provide. Wear, noise, tricky settings, mismatch of prop diameter with model fuselage size... let me count the ways...

Most sport flying, CL and RC, stay around the TORQUE peak RPM of the engines used -- usually just a bit above that... Here is the most efficient packing of the cylinder, and the most twist out at reasonable noise wear and flight conditions.

Here, a diesel is not so much at a disadvantage. We can prop (and set, and fuel) a diesel to operate just at the natural torque peak RPM. IOW, the engine floats slightly above that RPM in clean cruising flight, and any load added merely pulls us right back to MAX torque.

A high flow capacity glow engine is less efficient at these conditions, and with less energetic fuel (fewer BTU/unit weight) has to pass more fuel through, in comparison, to match the torque output.

So, back to the question... Ultimate horsepower with alcohol based fuel, but when we run at lesser conditions, diesels are more fuel efficient.

[Jim Thomerson]

I think my little K&B 4011 glow/diesel experiment described above supports Lou's last statement.

Jim

[diesel_don]

Nothing definitive, just some observations; Lately the trend has been to try to run bigger props though at lower RPM in F1C hence the megabucks geared configurations now available. Isn't that what the diesel has offered all along? More torque at lower RPM? Take the MP Jet "D" 1cc , almost identical to its glow counterpart; Th "D" peaks in the region of 17-18K and will swing an APS 7X3 in that region.,to make .20 - .21 bhp. The Glow can make similar or even slightly greater hp but the prop is down to 5.7 X 3,and rpm in the mid 20s. Seems conventional wisdom would opt for the the larger "swath" of the 7X3. On the other hand the nitro crowd has the 'silver bullet' "add more nitro", and no such additive is available for the "stinker" afficinados. Cheers;d-d

[dankar04]

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