Recycled Flyer

Hi guys, I am intending to dieselise a MVVS 40GFS/R ABC that is of yet un-run and new in its box.<o></o>

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The intended use is for a control line stunt model and the engine has the standard fixed venturi in place and has no supplied muffler as per MVVS’s normal practice.<o></o>

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The compression ratio as a glow engine is quite high at 12:1 and the construction extremely sound with a massive con-rod, twin ball races, a rotatable cylinder so rear; front or any side exhaust configuration is possible. It also weighs in at 380 grams minus the muffler so it would seem a very suitable subject.<o></o>

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I think that Davis Diesel has had conversion heads for these in the past, that’s one way to go, or I could get a head made up here in Oz by quite a few capable machinists.<o></o>

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So I have two questions here, does indeed this engine respond well to compression ignition and what venturi size would it need to come down to? (I am assuming about 6mm across the throat will be fine here.)<o></o>

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Thanks in advance.<o></o>

Jim Thomerson

Try running it on diesel fuel as a glow engine. Keep the plug lit for about 20 seconds after it starts and it should keep running just fine. I've done this on the bench with a K&B 4011. Exact same RPM on an APC 11 x 5, glow or diesel.

Recycled Flyer

Pardon?

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Do you mean using only diesel fuel with a glow plug still installed and lit only for starting?<o></o>

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I mean, would it really run at only 12:1 compression?<o></o>

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And the plug life, what happens to that?<o></o>

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Interesting though!<o></o>

AMB

This will help. complete review of MVVS 40 and 49 conversion Davis diesel head, Pull up RCM and E review by pinock , it was in Feb 2000 RCM and E , a quick search with Goggle will pull it up. I did get the 40 from Just Engines when they sold them. I also got a 6mm bore carb from them sent with it
If memory serves me right about 10K+ on a 12x6 wood zinger, the MMVS carb went on my PAW 40 which made that a new ball game>If Davis still has heads for the MVVS way to go martin

As an after thought I also got the MVVS61 combo glow+factory diesel head, I was not impresssed with the MVVS head again DAvis comes thru and makes a head for the 61 I think Hobbsy has one too with the Davis head

Missed that control line stunt thus an R/C carb is not an issue

Recycled Flyer

Hi AMB, yes I have already downloaded Malc Pinnock’s reviewand it speaks in glowing terms about the conversion – I mean what higher praise can be sung than actually buying those test engines on the spot!

One thing to really consider here with control line stunt,and I know that this is an RC forum so please bear with me, is that maximum power figures and revolutions are of almost no use to us as we do not run any engine at its maximum during our pattern. Tests that report a gazillion revs with the horsepower of a formula 1 car don’t give me any meaningful information– its all about a consistent run on a fixed venturi no matter what the attitude or load on the engine.<o></o>

And its here that I see a wonderful and interesting engine inits glow form, but I can also perceive an even better engine for my use hidingin the guise of a diesel.

Keith Renecle over at the Stuka Stuntforum already has this engine as a compression ignition in a control line stunter and he is pleased with it so if anyone else has some information to add here I would appreciate it very much.<o></o>

Thanks.

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AMB

Recycled Flyer C/L pattern I have no knowledge of and of course Pinocks review was a bench run only but does show what the engines are capable of as conversions
They have to be "set up" for this and playing with a few props my guess at any rate they re a top notch conversion
Do you go for larger diameter and smaller pitch or smaller diameter larger pitch to achieve the needs for control line pattern??? martin

Do not worry about what forum you are on diesels and diesel conversions go in anything R/C, C/L , boats, cars heli's any data in the air, one the ground, or on the water is useful

Recycled Flyer

Hi again,

Malc Pinnock’s review indeed does have a summary containing air testing in a Weston Jazz 3D (?), but anyway what I was aiming at is that its far more pertinent to state maximum power and revs in an RC model where that can be used at full throttle but in a control line model its all about consistent power at a 3/4 throttle by using a smaller venturi, generally lower compression ratios, smaller transfer ports to speed up the gas flow, often baffle topped pistons to slow the charge down in the combustion chamber and keep it rich.<o></o>

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It’s a whole different world when you don’t have a variable throttle at your disposal!<o></o>

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C/L stunt prop choice is interesting, you are limited in diameter to ground clearance and gyroscopic procession otherwise props greater than 12” would be used on larger engines a whole lot more.<o></o>

Square tips are popular to get the biggest swept area even though they may not be the most efficient tip shape; washout on the tips is employed to prevent wind up in the wind (again constant speed is prized in C/L stunt), three blades are generally used on larger engines to limit the procession, but basically you would use the largest diameter prop that you van get away with.<o></o>

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The pitch will determine the amount of speed around the circle and judges like a slow lap time so that they can appraise the maneuvers all the better, so on lower revving engines like four strokes or diesels a 7 or 8 inch pitch is popular but on tuned pipe glows that really like to rev they can be as low as a 4 inch pitch.<o></o>

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Thanks.

dogshome

I have one. Don't let it run cold when running in or run it in as a glow first! It needs heat or you get a cold seize (don't ask).

There is not much adjustment on the DD head and an electric starter is a must for getting it going as a diesel.


Other than that, fit a huge prop (12*6 at least) and enjoy hit-one, miss-one, clunk-clunk-clunk steam engine performance

Jim Thomerson

I've flown a lot of CL stunt with diesels. What I read, and my experience, is that a 40 size diesel will turn an 12 x 6 prop at 9,000+ RPM Which gives you about what you need for power, lap time, etc. Diesels are idiosyncratic and there will be exceptions to general statements. I like to get the engine set to run right, then use a starter, as it will be under compressed for easy flip starting. By the time I get to the handle, get the thong on, etc. the engine should be warmed up and running smooth. The engine should run smooth in level flight. If it slows in maneuvers, it is over compressed, if it misses in maneuvers, it is a hair lean. Once you get a needle setting, leave it alone. If you fiddle with the needle, you will get inconsistent run times. Of the exhaust is darker than honey color, it is overcompressed (with commercial fuel). My experience is that the compression needs to be backed off a little as time goes by. Maybe because of carbon accumulating on the piston. Some diesels run OK a little overcompressed, some don't.

I got the idea of running diesel in a glow engine from a South African I met at the Vintage Stunt Contest in Tucson. He said that was common practice in South Africa. He flew a couple of test flights with diesel and decided to fly in competition with glow fuel. Incidentally, there are 5 bonus points for flying a diesel in Old Time Stunt.

dogshome

Sould have explained mine is R/C [sm=red_smile.gif] So it cools and misses a bit at low throttle settings.

Hobbsy

My Feedback: (102)

There is not much adjustment on the DD head and an electric starter is a must for getting it going as a diesel.


I have about 23 Davis heads and all have more adjustment range than is required, also if you need a starter your engine is not set up correctly.

dogshome

Do you have a DD conversion for the MVVS 40 in particular? It is difficult to overcompress, even with the caphead screwed all the way in. It will run hard at that setting on full power, but is not great for hand starting.

I only have one DD conversion. I do have umpteen other PAW etc diesels to compare with though

AMB

Dogsome I can hand start my MVVS 40 davis head using a chicken stick. It will sometimes kick back and wacks the stick, if it was a finger it would be pretty sore,
there is a safety factor here and that is why a starter is recommended. it also spins it pretty quick for a fast start , in
seconds.Ditto with my Irvine 53 conversions. Even my MVVS 15 factory diesel requires too many flips using my 1/2A starter instant light off martin

My ST 40 being a ringed engine is much easier to light off with a starter

Some overcompresion may be needed for starting but should be backed off at once after it starts to its proper setting

Recycled Flyer

Hi Jim,
My PAW 40 is using an 11X7 prop at the moment and I would imagine that it cruises at about the same 9000 rpm as yours does - this prop was recommended to me by a good flying buddy of Tony Effliender's, the maker of PAW's.
I have also spoken again to Keith Renecle from South Africa who has extensively used MVVS 49 in a diesel form and has advised me on how to make a head for one - so if anyone needs to look at his email then get back to me.

Now the use of an electric starter I would not entertain as I have the 'diesel flick' down pat now and hand starting is half the fun anyway! But if the compression is too low for starting then that is a real concern - perhaps there is a compression loss elsewhere that is the root cause here? Too little ether maybe?

Anyway I find all the tinkering fun to do I will get this engine going yet!

Cheers, Chris.

Jim Thomerson

For most diesels, the ideal starting compression is more than the ideal running compression (vice versa for others). I don't like changing settings, so I like to start at the running setting. One can hand start at the lower compression setting, but it is not real reliable, so I use a starter. The problem is not with the engine but with my way of doing things.

Recycled Flyer

I agree that the starting of a model diesel needs more compression than the normal warm running of it - the added compression of the fuel mixture adds extra heat to the combustion chamber.

But what makes me shy off using a starter motor that revs well beyond what the human hand can replicate is the possible flooded state of an engine and the bending of a con rod whilst doing so.

You simply can't 'feel' what is going on through a hand held device and since the compression ratio is already 18:1 or beyond, adding a hydraulic lock to that ratio is very easy to achieve.

So its really something to keep in the back of your mind here, when I flick start by hand I always place my finger very close to the hub of the prop, that way the rotational speed is way less than out on the blade and the speed of the crankshaft maximized. I have yet to be bitten using the 'finger in close' technique.

Thanks.

AMB

recycled flyer I hand flip any of my engines before hitting then with the starter (chicken stick used) thus can easily see if a hydrolock, If there is I simply tip the plane and slowly rock the prop to drain the excess out of the cylinder for me its rare event, sometimes they start so no need for the starter ( the ignition is alway on on a diesel) martin

The only rod I every bent was on my PAW 033 and I was hand flipping it

Lou Crane

Generally a good point, Recycled, but Jim T mentioned one thing that works to prevent dreaded 'hydraulic lock' breakage...

He doesn't change settings for every start, then try to dial them in after the noise begins... The engine is left at the previously successful mixture and comp settings. If you are careful not to flood the engine while filling the tank, there is no excess of raw fuel inside it. It takes several turns of the external starter to light the engine off, but it it draws the fuel to the NVA while being spun. It would be worse if you tried to tried to hand-start it at the previous mixture and comp settings.

Hobbsy

My Feedback: (102)

DH, ironically my MVVS .49 wears an AJCoholic head and turns a Graupner 12x7 at 9,775, the .40 should easily turn a 12x6 at that or more. Mine is wearing a 7mm MVVS carb, I got this one from Dar Zeelon in a trade. It is a fine engine.
Davis conversions don't require a compression change to start unless there is huge change in the ambient temp in the order of 50 degrees or more. The AJCoholic head does not need any compresion changing either.

Recycled Flyer

I don’t have an electric starter and have never used one so perhaps I am out of my depth here discussing the pros and cons of them, its just that since I learned the ‘diesel flick’ the fear of starting anything under 10cc has just about evaporated.

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Owning and running a diesel to me is all about the extra functionality or fiddling available to you.<o></o>

I like to adjust compression, I like to change prop sizes and I like to hand start engines – it feels like you have achieved more when it all goes right.<o></o>

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I don’t like to touch the needle valve on a diesel though as I have had my share of lean engine destroying runs thanks very much!<o></o>

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But although I like to fiddle I will refrain from twiddling the comp screw just for the sake of it and will always try to get the beast up and running on the last known settings first – but sometimes this just ain’t possible and the comp gets increased just a tad for cold starting, then the engine warms and then it gets backed of again to where it was in the first place.<o></o>

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And I suppose that there is a certain amount of pride in not relying upon anything electric in starting up the engine.<o></o>

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Hobbsy, as to the AJCoholic head, would you happen to know if I could get one for the MVVS 40?<o></o>

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I have contacted the MVVS factory and spoken to Josef Svajda in the technical support division about a diesel conversion and he said that ‘at least the rear bearing and maybe the crankshaft are not strong enough for the diesel running.’<o></o>

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Now whether the use of the word ‘not’ in that quoted sentence is wrongly translated from Czech and he really means that the bearing and crank are fine for diesel operation I am not sure as I really thought that out of all the engines I have seen the MVVS range have massive cranks and bearings. And I have seen quite a few pics and reports of them being described as indestructible!<o></o>

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Cheers.<o></o>

Hobbsy

My Feedback: (102)

I don’t like to touch the needle valve on a diesel though as I have had my share of lean engine destroying runs thanks very much!

You cannot destroy a Diesel by running it lean, it simply quits when lean, in fact on tuning it the idea is to get it as lean as possible.
AMB talks to AJ now and then, I'll see if Mr. Davis has one.

Recycled Flyer

Hi mate,
I have ruined a piston/ liner assembly by running it too lean in the air - it seized solid mid flight and badly scored the piston. I checked the settings upon landing and found that the needle valve was in about a turn and a half more than what I would expect. The only thing I can conclude as to the cause of this was a very loose assembly and perhaps it rotated in on me, either that or I was just too dumb at the time to realize it on take off! The engine did not sound labored in flight, as in over compressed, and it simply just picked up more and more speed with plenty of power until the seizure.

But you say that you can't destroy a diesel this way? Ok, then I wonder what caused the seizure then? The engine was open to the wind with no cowl and no muffler - so cooling surely was not a problem, the fuel was a know brand mixture that I had used many times before, the mixture settings I am very sure I didn't touch and the engine has stacks of power in maneuvers so the compression seemed all good . And it only had about 2 hours flight time logged on it. But it was red hot to touch after landing so I assumed that it simply ran too lean and over heated.
The piston had huge scores down its sides but only in the exhaust area, this being the centre of heat you would think that there was too much heat coming from the combustion.

Anyway, I have already contacted Bob Davis about the MVVS 40 heads and he said that he "used to make them years ago." I assume (again) that this means he has none available but if any one else can source one then I am an eager customer!

Thanks again.

AMB

Recyled flyer...Check the retainer wire on the piston pin, if it rotated and partially popped out could have dragged created a lot of heat and friction and would explain the scores in the cylinder on the exhaust port side. I had the same thing happen on mine on the bench, the groove was not cut deep enough in the piston to fully seat
the clip, this occured on mine, the piston, liner, rod ,assembly was replaced under warranty martin
I do not think it had anyting to do with the needle setting, unlike glow a diesel will simply slow down and stop if it is overly lean

Jim Thomerson

I had a similar experience. In my case, the conrod was hitting the side of the crankcase and knocking off flecks of aluminum, Trashed the piston and liner.

Recycled Flyer

Hi again, I didn't think that a mark 13 Taipan 2.5 dieselhad wire retainers on the wrist pin but it certainly could have been something else in play here.
It's just that I wanted to solve this one immediately and the first solution that presented itself was finding the needle set very lean.

The compression I am sure was fine due to the amount of power in the air and clear oil on the wing - so perhaps it has a mechanical cause you say?

Any way a new piston/liner solved the problem nicely so again I am guessing that the problem may have been there instead?

Good forensics guys!