A new nitro engine coming soon (some say I am mad for doing this!)

[Ricky Neal]

It's a small world indeed - I've been using Peter's Irvine Specials for a very long time and still have a number of them. Strangely enough I only saw a tethered hydroplane once when the F2A World Champs were in Bulgaria where the two circles are next to each other.

I have a couple of Halman specials but as they are so hard to get nowadays I am reluctant to run them and in general, I have had better results with the Profi.

If you don't mind I would love to know the setup of your Profi, Prop, head clearance, plug type, etc - Getting F2A engines to run right is one of the more difficult things to do with our hobby and my runs are a bit hit and miss.

I have also been to Bulgaria, in fact, we run most of the world and the Euro's in Bulgaria because the facility is so good for tethered hydro's. I beat the british B1 tethered hydro record in Bulgaria with a Profi but as it was a practice run is was not recognised. I had such a difficult time getting it to go consistently for the rest of the event I never beat that speed so any suggestions/advice would be greatly appreciated

 

[Ricky Neal]

Hi Ricky
Will there be an option for reverse rotation for gearbox use in endurance boats in Europe.

Hi Tony,

At the moment I have not looked at having a variant for Multi's, etc but the great thing about using a Zimmerman disk induction is that changing the rotation is just a matter of changing the timing disk so I will look into this in the future.

 

[LohringMiller]

I haven't played with many experimental nitro engines, but have been a student of them for around 60 years. By first, and only, design is pictured below from my high school days. In my series on the nitro engine I emphasized the importance of friction especially as engines get smaller. The first big improvement was the ABC piston and liner. There's no question that various rear valve systems give more time area. However, they all come with more friction than the front rotary valve. I wonder at what displacement the cross over between friction and more time area is.

Nitro Engine Articles:
namba.com/content/library/propwash/2018/october/14/
namba.com/content/library/propwash/2019/april/24/
namba.com/content/library/propwash/2019/october/4
namba.com/content/library/propwash/2020/april/4/
namba.com/content/library/propwash/2020/October/4/

Lohring Miller

 

[Ricky Neal]

I haven't played with many experimental nitro engines, but have been a student of them for around 60 years. By first, and only, design is pictured below from my high school days. In my series on the nitro engine I emphasized the importance of friction especially as engines get smaller. The first big improvement was the ABC piston and liner. There's no question that various rear valve systems give more time area. However, they all come with more friction than the front rotary valve. I wonder at what displacement the cross over between friction and more time area is.

Nitro Engine Articles:
namba.com/content/library/propwash/2018/october/14/
namba.com/content/library/propwash/2019/april/24/
namba.com/content/library/propwash/2019/october/4
namba.com/content/library/propwash/2020/april/4/
namba.com/content/library/propwash/2020/October/4/

Lohring Miller

Thanks for the links, I will work my way through them.

I agree the most efficient from a frictional loss point of view must be conventional crankshaft induction. In fact, anecdotally I have seen this play out with the tethered hydro's that we run.

I am talking exclusively about .21 engines here but what I mean is that .21 engines that are normally very successful in RC use fail to perform when used in tethered models.

modern examples being the Novarossi .21 DD and any CMB drum valve engine, they simply have never performed very well when used in a tethered model. The current fastest tethered engines are Novarossi's that have been turned around and had Zimmerman disk valve induction systems fitted.

The current British tethered hydro .21 record holder is a very good friend of mine and together we have tried every engine on the market. The Novarossi DD, in my opinion, is one of the greatest engines available in the class but when used without nitro we have never been able to get them to perform, they just seem to lack low down torque to enable the model to get up and plane. Also, no one in the tethered cars seems to use them either. instead, they go through the pain of turning around the older 16.26mm bore Novarossi engines and fit a Zimmerman disk valve induction

Of course, the DD is not designed for this kind of use but what we started to understand that was any engines with higher rotational friction had real issues performing.

Another engine we use is a Soloev .21, this is based on the older Novarossi 16.26mm piston and liners as well but they are turned around and use a longer connecting rod 32mm vs the normal 30mm

The Soloev is also available with drum valve induction or with Zimmerman induction. From trying all of these engines the Soloev with the disk valve induction was the best out of the box performer, in fact, Peter dirs broke the British .21 tethered record in 2017 that had been held for something like 20 years with the Zimmerman induction Soloev

It seems as though running engines with straight fuel (20% Castor, 80% methanol, 0% nitro) really highlights the difference between engines that have low and high frictional losses.

I spent some time looking at the bell valve design that Jim Allen used on his engines and I think it's a great alternative but to scale up to production is difficult as it's not been done before.

It's a terrible shame that Jim Allen, sadly, is no longer with us, I really would have enjoyed discussing these details with him and I am sure insight would have been very helpful.

 

[Brandon Atwell]

Hey Ricky!
Is there anyone actively producing Zimmerman setups on the Novarossi’s for the tethered circuits or are they mainly custom one offs per person?

I’m strongly Interested in one of these .21’s once they are available. I hope they take off, the .45 market could benefit down the line if these .21’s warrant further development

 

[Ricky Neal]

Hey Ricky!
Is there anyone actively producing Zimmerman setups on the Novarossi’s for the tethered circuits or are they mainly custom one offs per person?

I’m strongly Interested in one of these .21’s once they are available. I hope they take off, the .45 market could benefit down the line if these .21’s warrant further development

Hi Brandon,

Unfortunately, none are commercially available. The people, running tethered models are making them as one-offs for their own personal use. It's not a straight forward conversion with a lot of bespoke engineering.

It involves removing the front of a Novarossi case but it has to be the correct casting or there is no way to mount the new induction system.

You then need to make your own crankshaft and Zimmerman induction system. Incidentally, I have been making a few, see pictures below.

This conversion is also done to the Novarossi .28 engines as there is a 5cc class for tethered cars and I am converting a .28 for use in a tethered hydro class that is up to 7.5cc. The .28's really perform well when fitted with a Zimmerman induction and I hope it will outperform most of the 7.5cc engines available.

If I can make a success of the .21 engines then I will look at other engine classes. .45's will be on the agenda but probably behind a .60/.67/80 engine. Again we use a .60 (10cc) engine in tethered racing. Currently, there is one engine for this class, the Picco .60 speed engine. It is a great engine but how long will Picco be producing this is up for debate now that Mr. Picco himself passed away. I am not sure how much appetite there is to keep producing it.

If I can make a .60 engine that can use .67 piston and liner or even possibly a .80 then it may be commercially viable to produce. I will likely mean 3 different cases and piston liner sets but the rest would likely be the same.

It would be nice if all the different sections of the hobby would settle on standardised engine capacities for classes

Some of these pictures are from work that Oliver monk completed for his tether car engines

 

[Ken Retallick]

I have built and tested a Bell valve induction in the early days of my 90 development. Not something that is easy to make or reliable enough for circuit racing were my findings.

 

[Tony Ball]

Hi has anyone tried reed valve on 3.5 or are there too many negatives to even consider.
Tony

 

[LohringMiller]

I have never been able to get reed valves to perform as well in a sim as disk valves. The reed was a low cost way to improve the low speed performance of piston port engines. Today with a lot fancier versions, especially crank case reed valve induction, the reeds can do well even at high rpm. It takes a lot of testing and experience to match the fixed, asymmetrical valve timing from rotary valves. Lets see how BZM engines do against older piston port engines, especially in SAW trials. The highest performance small two strokes (Aprilia 125) used disk valves. It was an expensive design with its gear driven, side disk.

Lohring Miller

 

[Steve White]

Hi has anyone tried reed valve on 3.5 or are there too many negatives to even consider.
Tony

Speaking from the past - reeds favor low end, piston port midrange, disc/drum high end. I don't see that ever changing, but who knows.

 

[Ricky Neal]

I have built and tested a Bell valve induction in the early days of my 90 development. Not something that is easy to make or reliable enough for circuit racing were my findings.

As much as I want to try to bring new and exciting developments to model engines I need to realise the challenges that present, that's why I have tried to use technology that is proven already so I know we have a product that will perform and be reliable, Once we have that done I will be looking at trying new developments

A bell valve is definitely on the "to try" list once we have established our engine in the market.

 

[Ricky Neal]

Hi has anyone tried reed valve on 3.5 or are there too many negatives to even consider.
Tony

Hi Tony

Its generally considered that a reed valve induction is one of the more inferior designs for performance, cheap, and easy to manufacture though. Maybe one day i will build one to test just for kicks more than anything else

 

[Ricky Neal]

I have never been able to get reed valves to perform as well in a sim as disk valves. The reed was a low cost way to improve the low speed performance of piston port engines. Today with a lot fancier versions, especially crank case reed valve induction, the reeds can do well even at high rpm. It takes a lot of testing and experience to match the fixed, asymmetrical valve timing from rotary valves. Lets see how BZM engines do against older piston port engines, especially in SAW trials. The highest performance small two strokes (Aprilia 125) used disk valves. It was an expensive design with its gear driven, side disk.

Lohring Miller

Like this one?

















Basically engine porn in my opinion

 

[Brian Spitzer]

Ricky,
Congratulations on this venture! I read where you've discussed bearings, machined inner races on the crank, etc. I may have missed the post, but would using a sleeve between the front and rear bearing to trap the rear bearing and not allow it to move on the crank be a possibility? The late Jim Allen incorporated this on his engines, and I believe Ken Retallick uses this on his KRE=90 as well.

 

[Ricky Neal]

Ricky,
Congratulations on this venture! I read where you've discussed bearings, machined inner races on the crank, etc. I may have missed the post, but would using a sleeve between the front and rear bearing to trap the rear bearing and not allow it to move on the crank be a possibility? The late Jim Allen incorporated this on his engines, and I believe Ken Retallick uses this on his KRE=90 as well.

Thanks Brian,

When were discussining the intergrated bearing crankshaft we were talking about some of the innovation that Profi have employed in some of their engine designs. In this case that technology doesnt really add any benefit and makes maintenenace a lot more diffcult so we will not be useing it.

I have spent a lot of time looking at what Jim Allen shared with the community, The man was clearly very gifted and a great innovator. I did look at his design on this but I am not sure what the benefit would be. I think it was related to using steel front ends and ensuring a consistent thermal expansion profile so the bearing tolernce was sam once heated up?

With our engine it will not be neccasery, with the modern machine tools we will be able to ensure consistent tollerence for crank end float and if we want to get specific with it we will indivdually shim each engine - Testing will confirm this soon hopefully.

 

[Brian Spitzer]

Thank you Ricky, look forward to seeing your progress and success. Will you publish the bore, stroke, and timing numbers once you've settled on your design?

 

[Ricky Neal]

Thank you Ricky, look forward to seeing your progress and success. Will you publish the bore, stroke, and timing numbers once you've settled on your design?

Hi Brian, Yeah - We have settled on 2 different bore to stroke ratios, testing will determine what we end up using. There is not a whole lot of difference between the 2 to be honest but one of the options will offer more options for the end-user. I can't say much more than that until the testing happens but as soon as I can I will everyone know.

One thing I can confirm is that we have ended up on a 28mm bore in the back of the crankcase, Novarossi's for example use a 26mm bore. This 2mm of extra space doesn't sound a lot but this has enabled us to use a larger timing disk compared to anything else that has ever been used on an engine of this size, even the ones that people have made themselves.

This will enable us to have a larger intake port area than any other comparable engine. The bigger we can make the intake port area, the better really - Of course it's not quite that simple as there are other considerations but this has all been taken into consideration.

We have also integrated an intermediary plate on the timing disk to reduce rotational friction, friction seems to be an important factor with engines of this size so we have looked at how we can reduce this as much as possible.

Here is are a couple of teaser pics (Of course this may not be the final design as it will likely change through development- in fact, the CAD drawings have changed a little since these screen shots were taken)

 

[Terry Keeley]

Thanks Brian,

When were discussining the intergrated bearing crankshaft we were talking about some of the innovation that Profi have employed in some of their engine designs. In this case that technology doesnt really add any benefit and makes maintenenace a lot more diffcult so we will not be useing it.

I have spent a lot of time looking at what Jim Allen shared with the community, The man was clearly very gifted and a great innovator. I did look at his design on this but I am not sure what the benefit would be. I think it was related to using steel front ends and ensuring a consistent thermal expansion profile so the bearing tolernce was sam once heated up?

With our engine it will not be neccasery, with the modern machine tools we will be able to ensure consistent tollerence for crank end float and if we want to get specific with it we will indivdually shim each engine - Testing will confirm this soon hopefully.

I was having problems with rear bearings on my CMB's when I would wind them up above the mid 20K mark, the races would turn blue from overheating. I'm pretty sure the problem was the inner race spinning on the crank, the fit was way too loose in my opinion at a half thou or more.

I tried locktite but it didn't hold leading me to think the bearing actually has to be able to slide on the crank for expansion. The front bearing has both races fixed and the outer race on the rear is fixed so something has to be left to "float". I did find one crank that had a nice light press fit into the rear bearing and it made all the difference, it's maybe a tenth or two under the nominal bearing size of 15mm.

 

[Ricky Neal]

I was having problems with rear bearings on my CMB's when I would them up above the mid 20K mark, the races would turn blue from overheating. I'm pretty sure the problem was the inner race spinning on the crank, the fit was way too loose in my opinion at a half thou or more.

I tried locktite but it didn't hold leading me to think the bearing actually has to be able to slide on the crank for expansion. The front bearing has both races fixed and the outer race on the rear is fixed so something has to be left to "float". I did find one crank that had a nice light press fit into the rear bearing and it made all the difference, it's maybe a tenth or two under the nominal bearing size of 15mm.

I have had the same issues with CMB engines, they just do not seem to have the correct fit in my opinion.

With regard to thermal expansion at higher RPM/temperature, normally this would be taken into consideration with the bearing clearance, most high performance engines use C3 clearance but some selectively use C4 clearance

This combined with a given amount of float on the crank normally takes care of any thermal expansion issues so I simply can’t understand why CMB run such a sloppy bearing fit?

They are more intelligent and experienced than myself so there must be a reason for it.

Its been a while since i have played with a CMB so I am not sure what clearance bearings they use but it could be as simple as they choose to run a normal clearance main bearing and when they get hot they start to seize causing the inner race to rotate?

Its always seemed a little odd to me but as i said, they know a whole lot more than i do and their engines are very good so i suspect there is a good reason for it

 

[Rody Roem]

This combined with a given amount of float on the crank normally takes care of any thermal expansion issues so I simply can’t understand why CMB run such a sloppy bearing fit?

Hello Ricky, first of all good luck with this venture. We do not know each other but I have some very old connection with the Metkemijer brothers and we all share the same passion.
I have read this post with interest and would like to share with you some of my findings and let you guess the rest...
To prevent the bearings from rotating in the crankcase we need to make a press-fit for the bearings. As you probably know there is always a working tolerance for the bearing fit in the crankcase as there is a tolerance for the outside and inside diameter of the bearing itself.
So there will be a situation where the combination of both the fit is very tight or less tight.
This is one of the reasons why we use bearings with more internal play(C3), just to compensate and to have a free bearing once the bearing is in place. A bearing with not enough play will prevent the engine from performing and also fail prematurely.