Nordberg Radial Engine

[Lazy JW]

Thought this design might be of interest.

 

[Anonymous]

Cool! So cool I don't get it yet, have to come back and think about it (wish I had a working model to look at). Part of what I don't get is the statement that the gear train transmits no power.

 

[Anonymous]

Well, I guess I see the part about the gear train; now I'm trying to visualize the advantage over a regular radial. I'm trying to see why the piston attached to the master rod gets any more side-loading than any of the other pistons . . .

If that B-17 is still around, they oughta clip the wings and run it at Reno.

 

[woodbutcher]

If you have noticed the date in the bottom right corner of the picture,it is November 1950.IF that particular B17 IS still around,it wont be in the picured configuration.It was used as flying test by by P&W.By using the registration number seen on the wing,you MIGHT be able to find out the history of that particular aircraft.IIRC, that B17 was,unfrortunately,junked.
Leo

 

[ludwig]

It or its twin could be in the aircraft boneyard in Arizona. Who knows?

 

[Geezer 300]

Why does it have to be an uneven number of cylinders in a radial ?

 

[Anonymous]

It or its twin could be in the aircraft boneyard in Arizona. Who knows?

I'd love to check that out for you, but unfortunately they don't let ordinary folk tour that place anymore.

 

[ludwig]

Oh, I don't want one. But I'd love to help somebody look for parts out there.

 

[Lazy JW]

Why does it have to be an uneven number of cylinders in a radial ?

I've wondered that myself

 

[ludwig]

So it's not directly opposite another cylinder on the power stroke? Keeps the crank turning (I suppose).

 

[Anlushac11]

IIRC a B-17 carried 4 Wright Cyclone radial engines rated at 1200hp each. That gves a total of 4800hp.

That turbo-prop makes almost 1000hp more, and at 2,225lbs weighs consideably less than the 4 Wright Cyclones (1000lbs each, 4,000lbs total).

Thats pretty darn big but there were bigger.

Late model Douglas C-133 Cargomasters had 4 x 6500hp P&W T34-P-7WA turboprops. The C-133's were used to haul missle and space program components and were not retired til the C-5 Galaxy replaced them but by then they were all tired and worn out.

 

[Anonymous]

There has to be an odd number of cylinders because of how the cam works. It actually spins backwards from the rotation of the crankshaft, and has to have an even number of lobes. For instance,, a 9 cylinder radial engine will have only 4 intake lobes and 4 exhaust lobes, and they will spin in the opposite direction of the crankshaft at 1/8 the rpm.

It's kind of hard to visualize, but it has to be that way. If I can find a pic that illustrates this better, I'll post it.

 

[Anonymous]

Well, I guess I see the part about the gear train; now I'm trying to visualize the advantage over a regular radial. I'm trying to see why the piston attached to the master rod gets any more side-loading than any of the other pistons . . .

If that B-17 is still around, they oughta clip the wings and run it at Reno.

The purpose of the master connecting rod is to keep the knuckle from rotating about the crank pin and causing all the slave rods to bind. The master connecting rod, however can only somewhat limit rotation of the knuckle though since it itself is pivoting about the crank pin, but the end by the piston is only translating.

Anyway, each time a slave piston fires, it creates a torque that tries not only to rotate the crankshaft, but is also trying to rotate the knuckle at the base of the master connecting rod. That torque is reacted out to the piston attached to the master connecting rod.

The idea behind the Nordberg is also to create a knuckle that translates but does not rotate at all. In this way the engine can be balanced by a mass balance on the cranskshaft. This is not the case with a master connecting rod because the knuckle is translating but also rotating slightly,, and a stationary mass attached to the crankshaft cannot balance out the mass because it's position on the crankshaft would constantly have to move.

The Nordberg creates this symmetry by using the gearing mechanism that essentially uses a stationary gear attached to the engine block as a reference, and then the idler gear attached to the crank, which in turn attaches to the connecting rod knuckle permits the knuckle to translate about the crankshaft, but restricts it from rotating at all.

However, unlike a master connecting rod knuckle,, the torque that prevents the knuckle from rotating is reacted out through those gears to the engine block rather than through the master connecting rod piston.

So the Nordberg permits the engine to be naturally balanced, eliminating NVH issues, and eliminates the additional wear on the master connecting rod piston.

 

[Anonymous]

Anyway, each time a slave piston fires, it creates a torque that tries not only to rotate the crankshaft, but is also trying to rotate the knuckle at the base of the master connecting rod. That torque is reacted out to the piston attached to the master connecting rod.

All right, I can see that. But it looks like the push from the slave rod would tend to counteract the normal side-loading of the master piston. First consider the master piston and rod and crank as a one-cylinder engine, rotating clockwise as we look at the drawing. The mixture goes bang, the piston starts down, the rod big-end goes sideways (to the right, in our drawing, and the piston skirt is loaded hard toward the left side of the cylinder wall. Now fire any one of the slave cylinders. The sideways push of the big-end of a slave rod is, again, to the right, or putting it better, clockwise. BUT, it is trying to rotate the master rod itself clockwise around the crankshaft journal. It seems to me that this action will tend to UNload the master piston away from the left wall of its cylinder. Maybe it does this to excess, maybe a master piston effectively has two thrust sides.

As you can see, I never had anything to do with radials, unfortunately. (Actually, this is a somewhat bitter subject for me. In about 1990 I had a chance to buy a Cessna 190 with a Continental 240hp radial for $18,500. I fooled around and that big ol' bird was sold elsewhere. To the dismay of all of us, in the next year the prices of light aircraft shot up, doubling and tripling, putting a big machine like that out of my reasonable price range. That C-190 with its pretty round engine would go for $80K or more today. My only consolation is that if I'd bought the plane, it would be too expensive to buy fuel for nowdays.

 

[Lazy JW]

Hey Smitty,
Build a two-stroke, five-cylinder Nordberg type radial and market it to experimental airplane builders 8) 8) 8) It should have a nice power-to-weight ratio and would look mighty cool in a biplane
Joe

 

[Anonymous]

How about a 3-cylinder, so we could afford to buy fuel for it?

 

[Anonymous]

As you can see, I never had anything to do with radials, unfortunately. (Actually, this is a somewhat bitter subject for me. In about 1990 I had a chance to buy a Cessna 190 with a Continental 240hp radial for $18,500. I fooled around and that big ol' bird was sold elsewhere. To the dismay of all of us, in the next year the prices of light aircraft shot up, doubling and tripling, putting a big machine like that out of my reasonable price range. That C-190 with its pretty round engine would go for $80K or more today. My only consolation is that if I'd bought the plane, it would be too expensive to buy fuel for nowdays.

I've always been fascinated with the radials,, especially the Pratt and Whitney R2800 and R4360's. But your right,, the price of one of ANY of the old radials is obscene in working condition.

2 years ago on eBay, there was an R4360 for sale. It was a static display unit, but had all the cert tags and overhaul records. It was rebuilt about 30 years ago and used solely as a static display. It sold for something rediculously low like $4500 or something. I kick myself every day for not jumping on that. That engine is probably worth over $100000.

I mean really,,, who doesn't need a 3500 hp 28 cylinder engine!

 

[Fred]

From my understanding you need an odd number of cylinders because the engine is a four stroke with only one crank throw. Every other cylinder fires as the crank rotates so you get a constant amount of crankshaft rotation between power impulses, thus you need an odd number of cylinders.

 

[Anonymous]

I wonder if those Polish radials (Camel?) like my brother used to fly for crop dusting are any cheaper...

 

[Anonymous]

Hey Smitty,
Build a two-stroke, five-cylinder Nordberg type radial and market it to experimental airplane builders 8) 8) 8) It should have a nice power-to-weight ratio and would look mighty cool in a biplane
Joe

There's a market for radial engines as it were. An Austrailian company called Rotec produces a 7 and 9 cylinder version of a radial. It is of traditional design, and is therefore unbalanced. They appear at the Oshkosh airshow every year, and you can see pictures of their engine and various aircraft they've been used on at their website:

http://www.rotecradialengines.com/

They've even got some pictures from the 2006 Oshkosh airshow with one of their 7 cylinder engines on a motorcycle,,, pretty bada$$.

http://www.rotecradialengines.com/Osh/O ... Model2.htm