OS MAX 40FP diesel conversion
 

Hello

Yesterday I tested an OS MAX 40FP converted to diesel with MECOA diesel head.
I have never converted engines before and was surprised that everything went so smooth with first attempt.

The data:
Fuel: Devis diesel fuel
Prop: APC

10x5 - 12000
10x9 - 10000
11x7 - 9300
12x7 - 8900

Also ran the engine with APC 13x8, but did not measure.


http://www.rcuniverse.com/forum/atta...mentid=2145420

Hi yyk,

I've got the same head on a 40 FSR.

I agree it's an easy conversion, and runs really well.

The general consensus is that the FP engines make excellent Diesel conversions, so you'll have a great conversion there.

Do you have a model in mind for it?

You've certainly covered the range of props.

Dave H

Hi Dave,

I recently bought Phoenix Sonic ARF. It is a .25-.30 low wing airframe. I think it will accommodate the engine properly.

Btw do you start your 40 FSR engine manually or with an electric starter? I found that my 40 FP easily starts with an electric starter but quite stubborn to start by-hand. Usually I start my 2-stroke glow engines without electric starter, so I am puzzled a little.

I'm a new diesel guy myself, and have not quite got the perfect recipe for compression and priming just yet. Most of my conversion engines tend to like a 1/2-3/4 turn more compression from the run setting and a good fat prime to hand start. The "diesel flick" takes some practice to master - the "lazy flick" of a glow engine doesn't work very well on a diesel. It's gotta be a swift flick. I've found ringed engines tend to need more compression added to start than an Ringless (ABC/ABN/AAC) engine because the cylinder pressure bleeds off a little more when flipping it over.

What I do to hand start my diesels is this; prime fuel up to the carb, add about 6-8 drops of fuel to the carburetor, add 1/2 turn more compression and flick the prop 4-5 times. If no fire, add 2-3 drops of fuel and flick again. If no fire, add 1/4 turn compression and flick 4-5 times. Once I get to about 12 drops, I stop adding fuel and add compression a little at a time flicking between adjustments until it fires. Once it fires, I just keep flipping. A flooded diesel won't start. Most of the time, I've gotten ignition before a third compression adjustment.

Some me folks prefer electric starters and just prime and spin it up until it fires and just run it at the run setting until it warms up and tweak needles and compression until it runs smooth. Either way works fine for the most part, you just need to be cautious of flooding the engine and causing a hydraulic lock which will inevidably bend a rod in some cases.

A friend also ran a 40FP RJL or Davis converted - probably Davis. We lost him over a year ago...

He also used a starter for the engine, which had been left at last running settings. I don't think he primed at all, just relied on the natural intake flow at starter RPM. First start took several seconds, later starts were quicker if there was any heat remaining in the engine.

The engine ran well, reliably and with great power. I think he used heavier-load props, which diesels handle with ease... 11-6 or larger..

He did shear a shaft at the crankweb on one: probably it got too wet and hydraulic locked on him with the starter cranking.

MORAL? Don't use a starter on a flooded diesel... Now, where have I heard that before....?

Davis conversions rarely need to be touched once set up, a 50 degree ambient temperature change might require it, other than that, not needed.

Hi yyk,

I'm not familiar with that model, but if the engine fits in it should be fine. The FP engines are not a heavy engine so balance shouldn't be too much of a problem. Diesels are quite frugal so the existing fuel tank should be sufficient. You will have plenty of power too.

I hand start all my engines, Diesels included. With the correct priming and compression setting they all start first flick. Sometimes the starting compression setting is close to the running compression setting, sometimes you may need to reset it for hand starting (it varies depending on what size prop you have, a large prop will need a low compression setting to run which may be too low to start, while a very small prop will run with a high compression which might be too high for comfortable starting).

Priming is important for hand starting, too little and it may fire but won't start, too much and you risk hydraulic lock as the others have all said. A flooded Diesel won't fire at all. They will start on just a whiff of Ether but need some fuel in the crankcase or at the carb to keep running until they start drawing fuel.

The vintage Diesels generally aren't designed for electric starting and can be easily damaged by it (plain bearing crank will move back and either the crank pin will rub on the back plate or the drive washer will rub on the case causing wear), however modern engines converted to Diesel can be electric started easily as long as you are careful not to hydraulic them. Electric starting will often allow you to start at the running compression setting although you might have to richen the needle a bit till the engine warms up.

In the end it's what works best for you and your set up. If you go electric make sure you flick the engine a few times to confirm it's clear before you use the starter.

Let us know how you get on,

Dave H

I don't run Diesels over 10,000 rpm, to do so seems to defeat the economy. If that .40 were my engine I'd run a 12x6. My LA .46 turns a Graupner 12x7 at 9,450, the .40 should turn a 12x6 in the 9,700 rom range. Here is my LA .46 doing that very thing.

I agree with Dave. Even though I'm pretty new at the diesel "thing", I try to shoot for around 10k. My beat up compact case Fox .40 with a gouged piston turns an 11x7 MAS at about 9,600rpm or so, seen here: http://youtu.be/NvqJdzuadYk It turns a 12x6 at 7,600rpm, but keep in mind this is a .25 sized case .40. It was never supposed to be dieseled due to a weaker rod. I have an ABC compact .40 Fox that might get some diesel abuse when I get around to it. The head is a Davis unit for a K&B .40 which is why the head fins are askew. I would think a normal larger case .40 to do a fair bit better as Dave suggests.

Hmm... That explains a lot! You just answered my question I was going to ask about diesel "low fuel consumption" :)

A dedicated Diesel will burn noticeably less fuel than a glow of the same horsepower.

Unfortunately our converted engines are optimised for glow use. The carb, transfer passages, and timing aren't ideal. This combined with the fact that we are actually producing more horsepower than the engine would on glow, means that we don't see quite as good fuel economy as we otherwise would.

I agree with Tim and Dave, the best prop for your model and engine is likely to be bigger than the engine would use as a glow (most likely 10X6), and best performance is likely to be at a lower RPM, so 11X6 or 7, or 12X6 might be about right. Like all model and engine combinations, it depends on the model and your flying requirements. Props are cheap(ish) so grab a few and try them out.

Are you worried about the tank in your model? As I said a tank sized for a .25 to .30 glow should be fine for a .40 Diesel (especially if the extra power lets you throttle back a bit), so I'd be tempted to try it first. You will need to check that the tank plumbing (bung) is compatible with Diesel fuel of course.

Don't listen to Tim when he says he's a Diesel newby, he know his stuff, as do Dave FDF and Lou.

Dave H

Thanks Dave H. I am still new, but I got it pretty well figured out. Not quite a "pro" yet, but I'm getting there. On the mention of fuel economy - my conversions are mostly bigger ones - .45s and .51s... My final needle settings ended up being the same or slightly richer than the glow setting (on 5% nitro fuel) and would burn through 2oz of fuel in about a minute and fifteen seconds at WOT. Maybe minute and a half. Some engines run at their fastest with the carb about 80% open, a couple of mine will turn an extra 800-1,200rpm if run wide open. I was getting acquainted and learning the techniques, so I more or less tested the limits and the fuel economy. Running WOT all the time will not save on fuel. It burns almost as much as it did on glow. Running slower will save fuel for sure.

Off topic, but good entertainment IMO... A diesel sounds funny in slow motion, especially at about 1,400-1,500rpm. It sounds almost as if it fires every other revolution or every second revolution.. Towards the end of this video, you can almost see the prop stop and pick back up. Funny to see. http://youtu.be/W73TxG0ph44

I think .25 size fuel tank will be enough for me, I usually do not fly longer then 8-10 minutes. The fuel consumption concerned me just because it was not as low as expected, which means something is wrong...

I definitely overlooked the simple fact that diesels are intended for lower RPMs.
I have just checked the specifications from Enya website for Enya SS25DBB (Diesel) and Enya SS25BB (Glow):

SS25DBB TN (Diesel) For middle size scale or sport plane
Power 0.8 HP, Revo. range 2,500~9,000 rpm


SS25BB TN (Glow) For small size sport or trainer plane
Power 0.70 HP, Revo. range 2,500~16,000 rpm


One more question...

What should be the color of the exhaust residue at peak RPM? If it is almost black is it acceptable? I mean the exhaust is still wet and oily, but contains black fraction (soot ?).
Can it be because of too high compression?

Some engines do run at peak with a dark oil color, but generally black oil residue means it's hot/overcompressed. I've had this happen on several occasions where the exhaust residue was very dark when set to peak settings. As long as it's not sounding labored/knocking hard, it shouldn't be a problem. I cured the symptom with a little bigger prop load or running a little rich of peak and just enough compression so it will recover if you throttle back up from idle/midrange.

Black oil residue can also be an indication your ether content of the fuel might be a little low. The ether can "go off" if the can isn't sealed perfectly. I mix my fuel in old acetone cans and I wrap the threads on the can with Teflon tape to keep it well sealed. If you use commercially made fuel, it might not be a bad idea to get a can of John Deere starting fluid to "spruce up" your fuel if it's been sitting awhile and doesn't run as nice as it should.

Just to give you an idea of the torque a Diesel can make, here is a shot of my Enya .25d turning a Graupner 12x5. According to YYK's post my rpm is ideal.

SS25DBB TN (Diesel) For middle size scale or sport plane
Power 0.8 HP, Revo. range 2,500~9,000 rpm

I have updated the initial post with more sample data.
Here is a spreadsheet to calculate some useful values: hp, max speed, prop load, static thrust, lift...
The spreadsheet uses reverse-engineered formulas from old thrust_hp windows program.
I usually use the spreadsheet to organize my test data. Also it allows to check and validate any "third party" data.

[ATTACH]2145973[/IMG]

NOW SOLD - I realize this isn't the for sale section, but I have a new in pack Mecoa diesel conversion for an OS FP40. Also fits others per Mecoa's page: FSR, Magnum, Thunder Tiger. $20 including shipping to lower 48.

I'll never use it. Thanks, Jim

Missed it by 5 minutes! :mad:

My RJL head / FP 40 diesel runs every bit as good as my PAW. I have tried several of the Davis Diesel heads with good results, but the RJL / FP 40 is my favorite conversion! I have a few more larger DD heads that I yet to get around to trying.

One of these days I'll have to do a side-by-side trial. I have 2 of the FP40s with Davis heads, 2 with RJL heads, 2 of the PAW 40s, (and a 35), oh and also an MVVS 40. It would be interesting to see the results! I have several FP40s that are still glow that I can use for comparison too.

If piston seal is good, they run well with an RJL or DDD head on them.

My two seconds worth with a 10 x 6 Taipan glass fibre prop

https://www.youtube.com/watch?v=eFa407riGj8

Jim Thomerson? (I am not sure of the spelling though.)

Very friendly guy.