Rotaxaru

[marshallarts]

Wow, this is a very impressive project.  I've been following it on and off but had not realised that a turbo was going to be part of it. Will you be changing to fuel injection too?  That would seem to me to complete the package.  I'll be very interested to see the performance figures when you are in the air.

[RFguy]

yes ultimately there will be fuel injection, electronics ignition etc.... its a while away.

 

I'm just making sure I have room for various things. The turbo should be pretty easy. though the wastegate will need to be something a bit different. There's a waste gate built into most low end chargers I see just designed to limit boost, like 15psi.....call it the valve that stops overboosting. But in this case I want to hold a specific MAP, So I'll need to drive the wastegate (another waste gate? separately ) dunno, far in the future. maybe an actuator on the built in automatic wastegate. wonder if enough gas can be diverted to get zero boost. . I dont know too much about this stuff (yet).  I only want a pressure ratio of around 1.25 to 1.3- right down the bottom LHS of most compressor maps.  but I dont want a tiny turbo small small S/A running red hot.  Many water+oil cooled bearing types. Hmm there are standard flanges. rightio.... Wow variable geometry turbos. golly. I'll certainly look for choosing a high turbine A/R . 

 etc etc This is really small roots-blower supercharger territory, but its painful getting the engine direct coupling for it.... ANyway, no more talk abotu turbos right now ! 🙂 unless you have advice, turbo sizing suggestions. etc

Edited October 29, 2022 by RFguy

[onetrack]

You don't ever want to fit a Roots-type blower, the rotor scream will drive you insane!

[facthunter]

They are a positive displacement supercharger relying on rotor fit and have drive inertia problems , The early GM diesels had them and must idle fast or damage the drive and  they absorb engine power. Turbo's are simpler but the small ones revs are very high. There's a fair bit of  extra heat around under the bonnet with a turbo. Blowing through a carby isn't the best idea. Nev

Edited October 29, 2022 by facthunter

[RFguy]

Hi Nev. fortunately the turbo will be away from EVERYTHING.  seems that even the smallest garret is almost too big. But, the pressure ratio/ exhaust mass flow is inside the curve... too low though and it will take time to spool up. mind you that aint much of an issue, this is to get one's horsepower back  to sea level at high DA.  Ha. I can have an N2 turbine RPM indicator. There's quite a few turbos designed for 2-3L engines suitable. One must remmeber not to compare direct to vehicle use because the engine is running 100% WOT and th evehicle is not, so have to conservately rate the turbo. actually a Garret GBC14-200 or GT2052 at 40% rotor speed  would fit spec well (I think) 6kg. Qu for the MFR is that will the internal wastegate dump enough to bring boost back to zero ? and need to do back pressure calcs for it

 

Edited October 29, 2022 by RFguy

[facthunter]

A suitable auto one should be enough  The Bomber P&W 1830 motors flew at over 30,000 feet with turbos You are only restoring sea level to about 10,000 feet which is not much boost.  Nev

[RFguy]

yeah only looking at a pressure ratio up to about 1.5. Which is laughable territory for enthusiasts.  I've asked garrett if the wastegate can bypass enough flow to reduce the boost to almost zero at 5-8 lbs/min.  (since we have to observe the maximum engine ratings at sea level) -  other solution would be just to bleed  or bypass the inlet compressed air... If the turbo isnt doing any work (except for flow losses)  it wont chew much power but could overspeed I guess.  anyway, plenty of options there., could dump air directly out of the exhaust collector so its just going out another pipe.

[phlegm]

Not the most helpful contribution to this thread, but I can't believe you've called this a Rotaxaru when the option of Jabirax was right there!

[Kenlsa]

RFguy, 

how would a sonex turbo go? They work at the rpm you need and not too much boost to normalise for the MAP you need.

Ken

[onetrack]

11 hours ago, phlegm said:

Not the most helpful contribution to this thread, but I can't believe you've called this a Rotaxaru when the option of Jabirax was right there!

It wouldn't be Australian if it didn't have "Ru" in the name somewhere. 

[RFguy]

Hi Ken, I dunno where a 'sonex turbo' would go. I would use a Garret GBC 14-200. 

but, worthwhile consider is this :

https://www.recreationalflying.com/topic/38647-the-ideal-modified-jab-engine/

 

 

 

[Student Pilot]

On 29/10/2022 at 7:40 PM, facthunter said:

A suitable auto one should be enough  The Bomber P&W 1830 motors flew at over 30,000 feet with turbos You are only restoring sea level to about 10,000 feet which is not much boost.  Nev

You mean like in a Liberator? They also had crank driven superchargers, I think they called the turbo a power recovery turbine. The likes of the Neptune had 3 I think turbos geared directly to the crankshaft also had a gear driven supercharger. 

[onetrack]

The WW2 variants of supercharging and turbocharging were just amazing. They used superchargers with turbochargers, they added intercoolers and aftercoolers, they utilised fluid drive couplings as well as 2-speed mechanical couplings to drive superchargers, they used double superchargers, and they used aneroid-controlled intake valves to prevent overboosting. 

 

And all through, the engineers stated that every engine design was a compromise, designed to operate within the selected range of operational limits.

 

GM produced a little booklet in 1944 (when piston engine aircraft design was peaking) called "Happy Landings". It was reproduced by GMH, but it was written by GM people in the U.S. I have a copy of it, it's extremely interesting. There's not much they didn't know about piston engines in 1944, and not much they didn't experiment with, and actually put into operation.

 

A crusty old Capt by the name of Charles "Chic" Eather has kindly scanned this little booklet, and put it on his website to read. Despite the limitations of wartime censorship, it's still a revealing read.

 

http://www.chingchic.com/happy-landings---general-motors-holden---airplane-power.html

[Garfly]

On 06/11/2022 at 11:05 AM, onetrack said:

A crusty old Capt by the name of Charles "Chic" Eather has kindly scanned this little booklet, and put it on his website to read. Despite the limitations of wartime censorship, it's still a revealing read.

 

http://www.chingchic.com/happy-landings---general-motors-holden---airplane-power.html

Apart from the techno/historical insights, what strikes me about this booklet is the elegance of the language they used back then.

[BrendAn]

On 29/10/2022 at 5:59 PM, facthunter said:

They are a positive displacement supercharger relying on rotor fit and have drive inertia problems , The early GM diesels had them and must idle fast or damage the drive and  they absorb engine power. Turbo's are simpler but the small ones revs are very high. There's a fair bit of  extra heat around under the bonnet with a turbo. Blowing through a carby isn't the best idea. Nev

I have never heard of a supercharged GM. They never made one that I know of.

[tillmanr]

Weren’t GM making aircraft engines during WW11?

[Garfly]

9 minutes ago, tillmanr said:

Weren’t GM making aircraft engines during WW11?

See Onetrack's booklet link a few posts up.

 

 

 

Edited November 7, 2022 by Garfly

[facthunter]

SP the "normal" P&W 1830's had  mechanical driven superchargers The Liberator motors were the exhaust driven  turbochargers.. Some P&W had 2 speed superchargers where you engaged a higher gear as you climbed. R-2000 and R-2800. The "Power recovery" system was a different concept entirely where the 3 units drove the crankshaft for higher Specific fuel consumption figures .(efficiency).Nev

Edited November 7, 2022 by facthunter

[onetrack]

Both Cadillac and GM built a myriad of aircraft components during WW2. Cadillac specialised in the manufacture of superchargers and turbochargers for aircraft, because they were the leading world facility at that time for their ability to machine components to 1/10,000th inch, and to polish hi-tech components to superfine finish levels, which was needed for the extremely high speeds that the turbines and shafts reached.

 

The GM "71 series" 2 stroke diesel, largely the brainchild of Charles Kettering, a chief engineer at GM, was released in 1937 and reached full production in early 1938. The engine was a unique design, in that it used a 2-stroke cycle, with "unit" injectors mounted in the centre of the heads, actuated by pushrods off the camshaft, and "Uniflow scavenging" which was carried out by the use of a "Roots blower", which pumped air into the engine via ports in the lower part of the cylinders.

 

Uniflow scavenging is where the intake air flow and exhaust air flow all go in the one direction. Once the piston reaches the lower part of its power stroke in the cylinder of the GM diesel, the ports are uncovered, pressurised air from the Roots blower is admitted via the ports - and the fresh incoming air helps push the spent exhaust gases out as the piston rises. 

Once the piston travels past the ports in the cylinder, the fresh incoming air has displaced the largest proportion of the spent exhaust gases - the exhaust valve closes, and the compression stroke starts.

At TDC, the injector squirts diesel in under high pressure, and the power stroke starts.

 

A Roots blower is also known as a supercharger in many other circles. Despite the GM diesel being fitted with a Roots blower, the engine is not regarded as being supercharged by the SAE, and is still classed as "naturally aspirated".

 

https://en.wikipedia.org/wiki/Detroit_Diesel_Series_71#:~:text=7 Sources-,History,engine introduced as a replacement

 

https://www.dieselduck.info/historical/01 diesel engine/detroit diesel/

 

GM changed the name of their Diesel Division from GM Diesel to Detroit Diesel in 1965, and much of the younger generations only know the GM 2 stroke diesel as the "Detroit Diesel".

But all GM diesel 2 stroke engines produced between 1937 and 1965 were known as, and marked as, "GM Diesel".

[facthunter]

It's very hard to supercharge a 2 stroke and the GM diesel was scavenged by positive displacement  by the gear driven blower that did not like to be idled slow.  It's an in line motor built it 3,,4 and 6 cylinder versions. GM marketed aero products under the Allison Brand and Continental is REO. Ransom E Olds of Oldsmobile GM fame. Lycoming is by a car Mogul and Packard built under   their Own Name some under licence like the RR Merlin.  FORD built the entire Liberator. . Holden built Gypsy Major engines Here.  Velocette Motor cycles built Dowty-Rotol Propellers and undercarriage Parts in WW2. Nev

[BrendAn]

46 minutes ago, onetrack said:

Both Cadillac and GM built a myriad of aircraft components during WW2. Cadillac specialised in the manufacture of superchargers and turbochargers for aircraft, because they were the leading world facility at that time for their ability to machine components to 1/10,000th inch, and to polish hi-tech components to superfine finish levels, which was needed for the extremely high speeds that the turbines and shafts reached.

 

The GM "71 series" 2 stroke diesel, largely the brainchild of Charles Kettering, a chief engineer at GM, was released in 1937 and reached full production in early 1938. The engine was a unique design, in that it used a 2-stroke cycle, with "unit" injectors mounted in the centre of the heads, actuated by pushrods off the camshaft, and "Uniflow scavenging" which was carried out by the use of a "Roots blower", which pumped air into the engine via ports in the lower part of the cylinders.

 

Uniflow scavenging is where the intake air flow and exhaust air flow all go in the one direction. Once the piston reaches the lower part of its power stroke in the cylinder of the GM diesel, the ports are uncovered, pressurised air from the Roots blower is admitted via the ports - and the fresh incoming air helps push the spent exhaust gases out as the piston rises. 

Once the piston travels past the ports in the cylinder, the fresh incoming air has displaced the largest proportion of the spent exhaust gases - the exhaust valve closes, and the compression stroke starts.

At TDC, the injector squirts diesel in under high pressure, and the power stroke starts.

 

A Roots blower is also known as a supercharger in many other circles. Despite the GM diesel being fitted with a Roots blower, the engine is not regarded as being supercharged by the SAE, and is still classed as "naturally aspirated".

 

https://en.wikipedia.org/wiki/Detroit_Diesel_Series_71#:~:text=7 Sources-,History,engine introduced as a replacement

 

https://www.dieselduck.info/historical/01 diesel engine/detroit diesel/

 

GM changed the name of their Diesel Division from GM Diesel to Detroit Diesel in 1965, and much of the younger generations only know the GM 2 stroke diesel as the "Detroit Diesel".

But all GM diesel 2 stroke engines produced between 1937 and 1965 were known as, and marked as, "GM Diesel".

Exactly.  Scavenger blowers are what they were on DDS.  They 

Took power not increased it. I did a course years ago on the Detroit 16v149 and I remember the instructor saying that engine lost 40 HP driving the blower.  Hot rodders bolting them onto V8 petrol engines turned them into superchargers.  The silver series later model GM's had a blower bypass which reduced the blower power loss.

Edited November 7, 2022 by BrendAn

[RFguy]

hey you lot stop polluting this project forum !

[BrendAn]

1 minute ago, RFguy said:

hey you lot stop polluting this project forum !

Sorry 🙏

Edited November 7, 2022 by BrendAn

[Blueadventures]

2 minutes ago, RFguy said:

hey you lot stop polluting this project forum !

Ask mod to tidy up some posts as it distracts from your projects progression which will be great help to anyone considering a similar retro fit.  Mods can delete unrelevant text and the posters can start another thread.

[facthunter]

RFg you brought up supercharging.. Nev