Engine Design Gone Wild! Lycoming R-7755

[Frankenerd]

The maintenance costs would have been enormous. Plus the wide profile meant there was going to be quite some drag created.

Mounted inside the wing of a giant plane, it might not show at all. After all, the B-36 wing was over 7' thick at the root. In addition, most transports derive very little of the total drag from the engines and nacelles given the size of everything else.

 

[Frankenerd]

I agree with you on this. Yeah look how long it took the car makers to get as far as those old airplane engines of years past.

I find it interesting that we compare engines on everything but cost. The twin-cam, quad-valve, turbocharged engine in his car has ~250-300 HP and costs about three times as much as my all Aluminum 427 Chevy, weighs almost as much and makes about half the power with half the service life. (If you're lucky!) Yes, I'd say that was progress! AND my LS7 does not have a flat plane crank! Think how much more power it could have, or why bother with such exotic hardware when a Ram-Jet 572 crate motor is so much more fun and not as expensive as a FPC and the stuff required to make it last at 8,000RPMs.
PS. The small bore turbo motor also burns more gas than either of my BBCs at that 300 HP level of RPMs! (1,400-1,600 RPM for the two engines respectfully!)

 

[Frankenerd]

Yeah its too bad these and or similar engines aren't powering the aircraft of nowdays, instead of jets.
If this was a diesel with a .25 BSFC in a TC configuration, the fuel savings would be fantastic compaired to turbines.

I'm with you! The trouble with turbines is the temperature they have to use to be even halfway fuel efficient. On the other hand, an air-cooled radial diesel with a 17-20/1 compression ratio has an EGT of <500 C. Compounding this engine would not require the same exotic alloys required to turbocharge a conventional Spark ignition engine with it's >900 C EGT!
So instead of exotic super alloys to withstand the 3000 C turbine inlet required to get a half good SFC, we use hollow, mild steel turbine blades to extract 30-40% of the exhaust gas energy from a Schnuerle ported two stroke and get over 10,000 HP from a well known engineering and production design example to drive a counter rotating prop-fan on a M .86 passenger plane with a SFC of <0.32 Lb/HP/H! Doesn't that sound like fun?

 

[Frankenerd]

Yes, but this engine STARTED at 5,000, and had the potential to exceed 7,000 hp. look at the Wright R-3360, it started at 2,200 hp and ended up producing over 4,000 hp in the lockheed constellation. for a reference, even at 5,000 hp this engine still has a better power to weight ratio than the bristol hercules did, the BH came in at .7 hp/lbs or 1.4 lbs/hp.

I thought the R3360 TC installation in the Conny only made 3,750 HP and it was a maintenance nightmare? Didn't they also install the more powerful R4360 in the Constellation to get the ~4000 HP you mention? Just curious as I flew on one from Da Nang to Asmara in 1969.

 

[Frankenerd]

Never did like the Sabre.

Just curious, but why? Sleeve valve engines seem to be the best four stroke option for the future, if you want to be "Green" in your applications WO going to a two-stroke Diesel.
I would like your input on the entire efficiency question.

 

[gumbyk]

I'm with you! The trouble with turbines is the temperature they have to use to be even halfway fuel efficient. On the other hand, an air-cooled radial diesel with a 17-20/1 compression ratio has an EGT of <500 C. Compounding this engine would not require the same exotic alloys required to turbocharge a conventional Spark ignition engine with it's >900 C EGT!
So instead of exotic super alloys to withstand the 3000 C turbine inlet required to get a half good SFC, we use hollow, mild steel turbine blades to extract 30-40% of the exhaust gas energy from a Schnuerle ported two stroke and get over 10,000 HP from a well known engineering and production design example to drive a counter rotating prop-fan on a M .86 passenger plane with a SFC of <0.32 Lb/HP/H! Doesn't that sound like fun?

Sounds like a nightmare to build and maintain to me... How long would it be able to stay on-wing?

The technology's there to manufacture these exotic alloys, so why not use it?

Take the PW150A - over 5,000SHP (7,000 max), from an engine that weighs around 1,500lbs dry. No cooling systems or drag to worry about, fewer moving parts. And you get a bonus 750lbs of jet thrust from the exhaust.

 

[johnbr]

RECIPROCATING ENGINE The chief advantage of the reciprocating engine at the present time is in low specific fuel consumption, especially at partial load. This makes it particularly applicable to long-range flight at present cruising speeds. Typical reciprocating engines now in use have specific fuel consumptions which are in the neighborhood of 0.7 lb/bhp-hr at full-rated rpm, decreasing to about 0.45 lb/bhp-hr at cruising conditions.
The principle characteristics of several current and proposed reciprocating engines of higher horsepower of interest for comparison with gas turbines, are given in Table I.
The largest reciprocating engine now under development is the 5000-hp Lycoming R-7755. One of the chief aims of this engine is fuel economy for long-range bomb
1
pr application. The estimated minimum specific fuel consumption is approximately 0. 37 lb/bhp-hr, the improvement being associated largely with increased compression ratio. However, it is noted that there is no improvement in either specific weight or power per unit frontal area of the R- 7 75 5 over the R-4 360. Theratio of dry weight to take-off power is 1. 21 lb/hp for the R-7 7 55 as compared with 1. 14 lb/hp for the R4360 and the ratio of take-off power to frontal area is 178 for the R-7755 as compared with 198 for the R-4360.
Further increase of reciprocating-engine power involves further increase in cylinder volume, which is already at a critical stage as regards number and arrangement of cylinders, complexity of the drive, excessive frontal area, and difficulty of cooling. There are development projects at present aimed at increasing the output of the R-3350 to 3200 hp and the R-4360 to 4300 hp.
Some increase in fuel economy can reasonably be expected by utilizing higher pressure ratios, improved fuels, improved metallurgy, etc., but engine manufacturers consider that it would be difficult to attain a specific fuel consumption essentially lower than 0.35 lb/bhp-hr.pdf net

 

[johnbr]

net Lycoming xr 7755 engine

 

[Piper106]

net Lycoming xr 7755 engineView attachment 545284View attachment 545285

Not sure what it is (I think it is the Jumo 222) but it is not the big Lycoming. The Lycoming is 9 cylinders per row.

 

[MiTasol]

Not sure what it is (I think it is the Jumo 222) but it is not the big Lycoming. The Lycoming is 9 cylinders per row.

And the cross section is the same as the Wiki cross section for the Jumo 222 but inverted so my guess is Piper is correct
I say guess because Wiki is not known for accuracy

 

[Deleted member 68059]

Not sure what it is (I think it is the Jumo 222) but it is not the big Lycoming. The Lycoming is 9 cylinders per row.

Well spotted! That is indeed the Jumo-222, corroborative images below (my own photos)