Engine build up

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B

Bug_racer

Airman 1st Class
110
1
Oct 6, 2006
Sydney
This is an odd thread . please dont flame me

As most of you know the Reno air races in the unlimited class uses mainly ww2 aircraft with ww2 engines .
Most of these engines were developing under 2000hp . Im curious what you guys would do to make these engines more powerful / efficient and reliable . Would you ditch the supercharger for Turbo . Would you run water meth injection or full methanol , would you ditch the mechanical fuel injection / carburettors for programmable fuel injection . The point of this thread is to see where these engines can be improved and where is it best to leave them alone (hypothetically speaking)
 
All the suggestions you mentioned have been tried by the crews there. At this point I don't think the unlimiteds are going to get much more out of their engines. Its the aerodynamic tweaks that was now going to make the difference IMO.
 
FLYBOYJ said:
All the suggestions you mentioned have been tried by the crews there. At this point I don't think the unlimiteds are going to get much more out of their engines. Its the aerodynamic tweaks that was now going to make the difference IMO.
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This is where I think your wrong . I dont know of the engine specs of the planes in use but given the hp estimates I dont think they have changed a huge deal over the standard ones


If I had the chance to build a reno racer engine this is what Id follow :

find an engine with a larger bore and smaller stroke
I would use and inline over a radial
I would ditch the carburettors and run full stand alone EFI . Id add knock sensors to work with the MW50 system. 2 Injectors percylinder switching would be rpm/load dependant . A rising rate fuel pressure regulator and full return system . If Direct injection was possible Id set it up for that
Fuel - Id tend to use C16 . I know the planes run Nitro but thats way over the top . Tuning with Nitro is difficult , the engine really is on edge with that stuff
MW-50 System , 2 injectors sprays , 1 for cooling intake temps the other for anti-detonation (placing it in different places in inlet tracts has different effects)
NOS as a power added to be used in conjunction with 2nd set of injectors
Id convert the old style camshaft to a newer roller type with hydro lifters with boost friendly specs
knife edged crank , lighter rods and forged pistons . Rings would be special chromoly ones for extra boost . Machining tolerances would be a lot closer for pistons and rings . I believe the older engines would have had a lot of blow by past the rings .
For induction I'd throw the superchargers away . The issue would those is that to make power you need to loose it , so there is a certain drivetrain loss through the charger . I beleive a Quad turbo set up would be the go . Diesel Truck turbos due to the non-reving nature of the larger v-12's . Housings/wheels can be changed to suit the engine .

I think thats about it ? I'd hope with the right set-up I could run the engine about 1000rpm more and make 6000hp . Your thoughts on my set-up ?
 
Bug_racer said:
This is where I think your wrong . I dont know of the engine specs of the planes in use but given the hp estimates I dont think they have changed a huge deal over the standard ones
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I'd suggest you do some homework and look into the specs of the engines run at Reno and some of the things done to them by their owners. Strega had almost doubled the HP of its Merlin. Rare Bear is running over 4000 hp out of its 3350 and do run ADI, Water Inj. NOx.

I'm a crew chief on an airplane that raced at Reno the past 2 years and been there in the pits the past 3 years actively involved in the races. Rare Bare was in a hangar adjacent to where my plane was parked this year so I think I know a little about what they are doing to their engines. Most of the Unlimited gold racers ARE NOT operating engines under 2000 hp.

From your suggestions it sounds like you do a lot of work on automotive engines. All that is good but consider you have to take what you mention and subject it to 6Gs at altitude. It's not as simple as it sounds. Also consider the airframe will have limitations on the amont of torque coming from the engine and prop combo. Lastly, you could have all the hP in the world and if its not tuned in with the right propeller you've just wasted a lot of time and money.

Look at the sport class and see what some of those guys have done. They're pushing their planes over 400 mph on 350HP and it goes up every year.
 
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I am no expert but have done a little reading. It is amazing to me that those aircraft engines hold up as well as they do for air racing.

Considering that boosting RPM is just a little more diffucult that it might appear at first. The stresses on the crankshaft (and bearings) go up with the square of the speed so changing a Merlin from 3000rpm to 4000 rpm means about a 77% increase in bearing loads and loads on the crankcase even if everything else (pressure in the cylinders?) stays the same.

there is also an old rule of thumb when considering piston speed. To get a better idea of the stresses involved in an engine you multiply the mean piston speed by the square root of the stroke/bore ratio. Engines with an over square bore to stroke ratio have more stress because of the lager, heavier pistons.

Aircraft engines were built to be as light as possiable for the power they produced. Many car engines (especially racing engines) have to develop the most power per cu in that they can with weight being secondary.
An old example of this was in the 1930s. There was an english racing engine, the Austin 7 four of 744cc. It was tuned to produce 116hp at 7,600rpm using 2.5 Atm of intake pressure running on alcohol. Not bad performance for 1936. However, as an airplane engine it would have been a total failure. For long distance races it had to be de-tuned to 90-100hp and it weighed 260lbs without the coolant and radiator. At the same time for aircraft use you could get either a Blackburn Cirrus 'Minor' engine or a De Havilland 'Gipsy-Minor' of 90 hp for take off and 80-82 hp for cruise for 210-227lbs (depending on accessories, like prop hub and spinner). The aircraft engines would give you this power for hundreds of hours and do it on 70 octane fuel. They were 3.6-3.7 liter engines with max rpms of 2600rpm.
I would guess they could be "souped up" but their light weight construction is going to impse some rather severe limits as to what can be done. You can always walk back to the pits after you blow up a car engine. Walking back to the pits after blowing up an aircraft engine isn't always possiable.
 


Finding any specs is like searching the net for a fw190-d9 to restore . Just aint gonna happen . All I can do is determine what an engine has from pictures floating around .
Building an engine to run on Nitro is gonna give you big gains for little effort . Thats why they use that fuel in top fuelers .

I understand the 6g's at altitude, that is why I havent mentioned the fuel tank and fuel supply much . The setup thats in the planes now works and works well so I wouldnt change the initial fuel supply . It will have to have pressure increased before the fuel rail to crack open the injectors .
The airframe is a tricky one . Youd need to find an airframe already built for speed (I wouldnt start with a Harvard airframe for example) . FW190D-9 replica or if I had the $ Id build a DO-335 . Propellors I think it would be a little trial and error .

You got any good links to what guys are running ? Even finding any rules is hard . Seems that the only rule in unlimited is min weight 4500 pounds
 
The age of the engines and the extra load on them , well , they are proven performers !

I mentioned doing work to crankshaft/rods/pistons . The bearing material used 60 years ago would be far different than whats available today . Even simple things like raising oil pressure and increasing tolerances will put less load on bearings . You could add oil squirters under the pistons to cool the piston tops down after combustion .

I understand your whole point with engine size / rpm and power . But todays technology is far superior to what was available . Casting technologies , engine oils , fuels are all better today than when the engines were made . You can precisely add the right amount of fuel into the engine to each cylinder individually . You can change ignition timing to each cylinder individually so if the design of the engine in the airframe means cylinder 11 and 12 run hotter they can be retarded a few degrees . Even rebuilding the crankshaft/rods with new units you can get them X-rayed for grain structure of the metals . All things which werent available back then .


Just out of interest does anyone know if titanium was available to any country in WW2 ?


 
Bug_racer said:
Just out of interest does anyone know if titanium was available to any country in WW2 ?
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No
Kroll got out of Luxembourg just before the start of WWII with his research as he didn't want it to fall into the hands of the Nazis. He got to the UK but no-one was interested in a new metal with potential, they needed stuff that worked now.
Initially, he didn't have much more success on his arrival in the US until the Dept of Mining Ores showed some interest. I don't think he got his process off the ground until about 1947 or 48. Titanium production wasn't in full swing until the mid-50s.
 
Bug_racer said:
Finding any specs is like searching the net for a fw190-d9 to restore . Just aint gonna happen .
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You need to go to the individual website for each racer (Dago Red, Strega, Rare Bear, etc.)

Its more than the fuel supply, you have to consider the g loading on every component and again matching it to the engine/ prop and airframe.

Propeller performance is actually calculated and then tried - do you know several of the unlimited teams hire engineers to calculate and integrate systems and performance? Also consider that something like a D-9 or 335 is impractical. At the start of the race the aircraft has to be able to accelerate and if it don't have the pole position, its already at a disadvantage.
Bug_racer said:
You got any good links to what guys are running ? Even finding any rules is hard . Seems that the only rule in unlimited is min weight 4500 pounds
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http://www.airrace.org/RulesOfCompetition2009-v6.pdf

Reno Air Racing Association - Unlimited Class aircraft

Again, look up the individual aircraft's websites and they should have info on their engines.
http://www.airrace.org/RulesOfCompetition2009-v6.pdf
 
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Im curious , what extra things do teams actually do for the extra g-forces ?
I would have thought a modern day stand alone set up was far more efficient than the carburretor set up ?
The engine itself would have a crank girdle as well (something I forgot to mention) so the crank would be a lot more rigid and less suseptible to bearing damage due to the extra load from higher RPM .
In regards to the d-9 or 335 not being practical what makes you say that ? They were designed as a higher speed fighter . The design of the airframe would be better suited than say an E series 109 . As for the start , Quad turbos on full boost but dumping the excess pressure away to hold speed would accelerate far quicker than a supercharger set-up . Have you ever wondered why so few trucks use superchargers and so many are fitted with Turbo's ? And even if it didnt spool quick you could always dump a lot of N2O into the turbo and that would decrease spool time .
 
Also using titanium rods will help lower the reciprocating mass considerably and allow a slight bump in rpm with no other changes . Once you see the strength and light weight of titanium you try and replace steel wherever possible .
 
Bug_racer said:
Im curious , what extra things do teams actually do for the extra g-forces ?
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Actually not much - that aspect in inherent in the initial design of the engine when bearing types, seals and materials were chosen and matched to the engine block with the initial designers considering loads 3 dimensionally. Of course assesories and supporting components are saftey wired and clamped all over the place.

Bug_racer said:
I would have thought a modern day stand alone set up was far more efficient than the carburretor set up ?
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It seems not for the size of the engines being run


Bug_racer said:
The engine itself would have a crank girdle as well (something I forgot to mention) so the crank would be a lot more rigid and less suseptible to bearing damage due to the extra load from higher RPM .
Click to expand...
Actually aircraft cranks (at least on opposed engines I worked on) are designed to have some flexibility. This is due to loads being applied to the crankshaft and front spline when power is added or reduced during climbs or dives. Of couse this does not really apply to radials.

Bug_racer said:
In regards to the d-9 or 335 not being practical what makes you say that ? They were designed as a higher speed fighter .
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Again, weight and the ability to accelerate off a given starting point. Watch the way a race starts, you need to accelerate and dive quickly and then sustain the Gs in the first turns. I don't see a 335 with its high wing loading of 50 lbs per sq ft or even the 190s (over 45 lbs per sq ft) being able to do that. At that point aerodynamics, power and the ability of the pilot to run the course without pulling too many Gs will determine how well the aircraft will do. Once you're in the first turn and you start pulling Gs, you're loosing energy and the more energy you're going to loose if your running a plane with a high wing loading. The P-51s running at Reno are running well under 40 lbs per sq ft.

All good for a truck but that has to work on an airplane within a defined space at a density altitude of about 5000'. Again, you have some good ideas, look into the sport class, they are a lot more adventurous.


SDS EM-4: Aircraft
 
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Building a totally modern engine would allow a good portion of your ideas. Modifing an existing engine to a very large extent would be almost as expensive (if not more so).
However there are problems that the designers were aware of even back then (WW II).
one is cylinder size. THE flame front in the cylinder is only going to move at a certain speed from the source/s of ignition. This tends to limit the size of the cylinder in relation to the RPM.
Large diameter cylinders are also harder to cool. for instance going from the 5.4in bore of the Merlin to the 6in bore of the Griffon ment an increase of 23.4% in volume for every in of stroke but only an 11.1% increase in cylinder wall area.

As far as trying to cool some of these aircraft I believe ( and I could be wrong here) that some of the planes actually carry water tanks to allow them to spray a water mist onto their radiators to assist in cooling. THe heat transfer in the water evaporation upping the cooling ability of the radiator. Apparentl the extra cooling allows enough more power to be used to offset the weight of the tank and water.

Did you know that P&W had over 3000hrs of Bench testing on the R-2800 before they ever but one in a test mule aircraft?
Or that it is claimed that the only things in common between an "A" series R-2800 (1850hp take-off) and a "C" series R-2800 (2100hp take-off) were the bore, stroke and starter dog?

Modern systems (fuel injection and ignition) might go a ways in solving some of the problems that some of those old engines had but it would require quite bit of testing to sort them out and prove their reliability.

Most race teams (cars, boats, whatever) will tend to stick with what they know works unless A, they start losing big time. B. something promises them a big advantage. C they have a lot of extra money and time to play with something new.

As to certain planes doing well in the races it is also interesting to go back and look at some of the post war racers. There was one P-39 with about 9 ft clipped from the wings in one race. The pilot later confessed that whatever he gained on the straights he lost in the turns.

A successful air racer has to accelerate and take off quickly, go fast in a straight line, be able to turn without bleeding off more speed than his competitors, and be able to do it for the duration of the race.
 
Dang my stupid connection bumped me and lost my post. Oh well the gist of it was as FlyboyJ alludes, you're talking about spending $45K on what amounts to improving output on a 3500hp motor by something like 150hp but for nicer manners and less trouble, where you can do some aerodynamic sorting for more like $3K and that's as good as bolting on 300hp.

Don't underestimate the effectiveness of old tech like say slide valve carbs over ECU injection because when setup right they perform just as good. The laptop tuning facility is a nice luxury and beats six months sorting needle profiles but if you've got intuitive crew you find old tech is competitive with new tech on the track at about a quarter the price. I did in auto racing. I'll admit I always wanted to switch over to an ECU/injection setup but it wasn't worth any extra power, just a lot less mucking around.

You might be onto something with fresh tactics like turbos over mechanical blowers but safest bet is again like FlyboyJ says and find out the reasons why current crews are using what they're using first. No point spending a ton of money to learn what they already know if you can just ask.
 

There was a time until the late 1990s that on a drag car a carburettor would outflow in HP a modern efi system . Every year stand alone units were upgraded and not so long ago the carburettor was made redundant in the hp contest . EFI will give more power reliably for less fuel . The throttle response is also faster and there are less moving mechanical parts to fail . How many forms of motorsport still use Carburettors / mechanical injection as a primary fuel delivery system ?
 


I use to play with carburettors years ago . I got over it very quickly . Driving around with a box of jets and emulsion tubes , air density meter and vacuum plunger . Its all good when your young but when you get older you want to make things easier . As I mentioned earlier efi has overtaken carburettors .The new stand alone units have self tune which automatically tunes itself to the engine . it doesnt search for peak power but it does provide a safe tune with minimal work . With EFI you can log data , you can make changes to the engine at particular points around the track . At the end of the day your trusting a computer that can make a decision far quicker than you can . By the time you even see the first warning light the ECU can lower the boost / retard the timing and add watermeth too cool the combustion chamber down .

Id love to build an engine and have it tuned . Id never get it on any dyno cause I havent seen one that is rated for over 2500 hp . But who would build me an airframe , or better yet , who would be the mad pilot to test out the missile !
 
There are test cells that could support recips that put out well over 3000 hp. As far as finding a pilot, there would plenty of takers as what you're proposing isn't really that radical and it isn't going to push any racer that more faster than what you're seeing right now.
 
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