Fw190A-8 vs. Ki-84 vs. LaG-7

[GregP]

It is quite possible that the mods were made simply to keep the engine functional since genuie Japanese spare parts might have been unavailable. I have no idea why they wouldn't run it on the fuel it used in combat ... unless it wasn't available or unless the equivalent US fuel didn't run very well in the Japanese engine for some reason. That is certainly possibl.

We had simlar issues with European fuels in the Allison early on with the P-38's before they figured out the intake manifold issue and rejetted for the increased aromatics in European fuel. It would be nice if detailed reports were available with the mods, the reasons for the mods, and explanations of the continued tests despite US engine modifications running US fuels. Without them we are running on speculation.

 

[tomo pauk]

I would note that the P&W R-1830 operating on 91/98 octane fuel could use 48in manifold pressure at sea level for take-off. 42in is about 6lbs boost and 48in is about 9lbs boost. The pressures being used by the Homare don't seem to be out of line with a reasonable estimate of allowable operating pressure for the fuel available.

I would also note that even with 100/130 fuel available it takes a mighty brave (or foolish) test pilot to over boost an engine in flight that has not previously been tested on the ground in the over boosted condition. And that is the ONLY way 100/130 fuel is going to give more power, by using higher boost and higher pressure inside the cylinders.

Seem like we agree on this.

It is quite possible that the mods were made simply to keep the engine functional since genuie Japanese spare parts might have been unavailable.

+1

I have no idea why they wouldn't run it on the fuel it used in combat ... unless it wasn't available or unless the equivalent US fuel didn't run very well in the Japanese engine for some reason. That is certainly possibl.

Reasonable thoughts. Allied techincal intelligence should have no problems to acquire several hundred of galons of Japanese 91 oct fuel by mid/late 1944, but US fuel of the same/similar octane rating should work just fine.

We had simlar issues with European fuels in the Allison early on with the P-38's before they figured out the intake manifold issue and rejetted for the increased aromatics in European fuel.

I'm not try to stir up another P-38 discussion here

It would be nice if detailed reports were available with the mods, the reasons for the mods, and explanations of the continued tests despite US engine modifications running US fuels. Without them we are running on speculation.

The rather detailed test report on the US test of the Homare is available on this forum, check out the post # 18 here (scroll down).

 

[FLYBOYJ]

The rather detailed test report on the US test of the Homare is available on this forum, check out the post # 18 here (scroll down).

I skimmed through it, thanks for posting - I see nothing at first glance about "mixture control." The engine had a carburetor so unless the unit was re-jetted, the only other thing you're going to do is make the vernier in the mixture cable finer. I'm going on my morning run, when I get back I'll read through this more. Although RG was correct about some modification being done to the engine during its testing, I think some "armchair speculation" attributed to some of his comments.

 

[GregP]

Regarding post # 7, great data! Thanks Corsning! A good bit of digging to get these number caomparisons.

Looks like in speed the La-7 is best under 10,000 feet. The Fw 190D-9 is best from 10,000 feet up to 21,000 feet where the Ki-84 takes over until about 27,000 feet, and the Fw 190D-9 again gains a slight edge going up … but not much. The Fw 190A-8 is never really in the hunt, speed wise and is from 30 to 50 mph slower depending on altitude, with the worst disparity being at 7,000 feet or so, right in the heart of the La-7's best performance, and again up at 30,000 - 32,000 feet where the other three are actually fairly close to one another.

In rate of climb, the data are quite interesting. The La-7 is best up to just over 5,000 feet where the Fw 190D-9 gains an edge up to about 15,500 feet. The Ki-84 is then best on up to service ceiling. The Fw 190A-8 climbs quite a bit worse than the other three up to 19,500 feet where it is close to the La-7 but still 40% or so below the Ki-84 with the Fw 190D-9 being right between the two. Above 30,000 feet the ki-84 and Fw 190D-9 have a 400 – 600 fpm advantage going upward.

Looks like the low-altitude choice is the La-7 with the medium-altitude choice being the Fw 190D-9, and the Ki-84 takes over at higher altitudes, especially in rate of climb.

The Fw 190A-8 seems to never really be in the hunt in speed and rate of climb. It has good armament and I'd expect the Fw 190A-8 to be better in roll with decent maneuverability, but roll, turn and armament are not included in the numbers.

It would be nice to see these type of data for the major types but, as I'm sure Corsning knows, digging it out is tedious, and the many sources no doubt do not have the same accuracy or believability depending on source.

Below are the charts (Microsoft Excel) with altitude in meters. I didn't bother to convert the speed and rate of climb to metric ... the shapes of the graphs are the same, the altitude units just change.

View attachment 230852

 

[CORSNING]

Nice comparison graphs and assessment of there comparisons Greg. You are right about the time involved to convert graphs to figures. I have spent the last year converting every military and manufacturers graph on WW2 fighter aircraft that I can get my hands on. And you are absolutely right about them being just that, cold hard figures. From all the books and military reports I have read I would say the Fw190A-8/9 have the advantage in roll rate up to about 325 mph. After that I would say the La-7 and Fw-190D-9 take over. A/C design come into play on turning ability but I'm going to go with the low wing loading puting the Ki-84 in first place up to about 330 mph. After that the La-7 probably goes into first place. There is an excellent roll rate graph at Mike Williams sight showing the Fw compared to other fighters. Acceleration is a tough one. Though the La-7 and Ki-84 are definite leaders in the power/weight category, engine power/span, A/C design and propeller used all come into play. I don't really have a good idea which is quickest.

Thanks for all the input Guys, Jeff

 

[GregP]

The late Ray Hannah said the La-9 he used to fly occasionally could out-accelerate the Grumman F8F Bearcat, and that was saying something since the Bearcat had been, up to that point, the best accelerating propeller-driven aircraft he had ever flown.

I have a lot of data, Corsning, but have not done the compiling like you did. Let me know if you want to swap data files some time. Would have been faster if you had not used multiple periods to delimit the data, but it went pretty quickly anyway. The longest part of the Excel work was converting the charts so the altitude was on the Y-axis instead of the X-axis. It's easy, but a bit time-consuming when so much else is so simple and quick to do.

 

[CORSNING]

GregP,
Sounds great buddy. I have very limited time on the computer due to family and work. My computer skills are not the best, but I'll do what I can. I sent you a PM. The multiple periods is the only way I have been able to keep the data from shifting to gether. Sorry If it slowed you down. It must have taken a bit of time to work up those graphs, nice.

Thanks, Jeff

Just one more thing. From what I have read the F8F was quite 1/4 mile vehicle, but the F7F was quicker.

 

[GregP]

Yah, the F8F was the smallest airframe they could wrap around an R-2800 and the F7F was the smallest airframe they could wrap around two R-2800's. Steve Hinton's guys are currently rebuilding one now for a private owner and they are doing a GREAT job. In 3 years or so it should look like a new, baby F7F Tgiercat.

Hopefully Ray Anderson will still be around to overhaul a couple of R-2800's in the correct manner ... maybe they'll chrome some engine pieces like they did for one particular R-2800 in a Bearcat that shall remain unidentified, but is pretty damned neat looking. Must be nice to be able to afford not only to own one, but also to actuall laugh off the fuel flow you KNOW it generates. Guess owning oil wells helps. Would ge great to see a glass cockpit but it will probabnly be all original except for a GPS and modern radios ... maybe radar, though if I owned it, I would only fly it in severe clear. I'd also install a gyro-stabilized bunch of GoPro cameras unobtrusively ... but that's another story.

Oh and .. you didn't slow me down. It was moving the damned axes around. Have to do it one data series at a time. There ought to be a checkbox to swap axes for the entire chart ... but isn't.

 

[tomo pauk]

Note that La-7 No. 452132-76 from the NII-VVS acceptance trial is dated april 1945 and not representative for very many pre-VE-day manufactured La-7 to appear on the front. I suggest to use data from august 1944 La7 serial No.452101-39 to get representative figures.

Hello, delcyros,
I've grabbed the flight test data for the La7 serial No.452101-39, and they are indeed lower than for the later example:

 

[drgondog]

To get reliable Calculated data on each of the aircraft you have to have reliable data on a.) engine horsepower as function of boost and rpm by altitude, b.) reliable zero lift Drag at at least SL for ALL a/c, then reliable dash speeds as a function of Hp by altitude with reliable weight data, c.) CL and CLmax for the wing, d.) Wing Area e.) consistent methodology to yield Oswald number.

That will get you symetrical straight line speed, climb, acceleration.

However in the asymetrical universe:

When you delve into turn, you need mfr spec on Limit Load factor and be warned that all a/c increased gross weight so the Original Load factors (i.e 8g Limit and 12g Ultimate) are liable to be significantly higher than the 'new' GW and therfore the Corner Speeds will be in error. This is only important if you want to test the a/c V-N diagram for boundary condition of failure/stall.

Also in a turn, the Profile Drag increase of most conventional fighters increases somewhat linearly with AoA - which is a Major "add Drag to CDo and CDi" Factor bleeding energy - which is completely Ignored by the game crowd. Additionally the propeller efficiency has to be looked at for underlying assumptions (i.e.".85) because that factor is dubious when the a/c is at or below Corner Speed.

If you don't at least look at the magnitudes and relevance for some of the latter calculations IMO you are fondling genitals with no joy.

 

[GregP]

I doubt if any of the game programs use the Oswald efficiency number or anything like a real V-N diagram. If they did, then the popularity of flight sims might seriously decline. In Microsoft Flight Simulator, the P-51 flew like crap in combat. The real one didn't.

I have flown a real USAF T-38 Talon simulator and the pilots there said it was spot on. I don't know from personal experience, having never flown or flown in a T-38. If true, you have to stay well ahead of it in landing configuration or you can develop some extreme sink rates that even full power may not arrest in time to prevent contact with the ground. It doesn't exactly have a lot of wing area.

 

[FLYBOYJ]

I doubt if any of the game programs use the Oswald efficiency number or anything like a real V-N diagram. If they did, then the popularity of flight sims might seriously decline. In Microsoft Flight Simulator, the P-51 flew like crap in combat. The real one didn't.

I have flown a real USAF T-38 Talon simulator and the pilots there said it was spot on. I don't know from personal experience, having never flown or flown in a T-38. If true, you have to stay well ahead of it in landing configuration or you can develop some extreme sink rates that even full power may not arrest in time to prevent contact with the ground. It doesn't exactly have a lot of wing area.

I was told by my father in law that a classmate of his was killed the last week of flight training by getting behind a T-38 and allowing it to sink. This is a common on high wing loading jets and I am told that even a Lear Jet could sink like a rock it you get behind it.

 

[GregP]

I once saw a Lear 23 at Scottsdale, about 1984 or so, with asymmetric tip tank fuel loads. He was leaning well over to the port side.

On takeoff, as he accelerated the port tank got lower and lower, with full opposite lock, uuntil it was only about 1 foot off the runway. Then, all of a sudden, he got enough speed and leveled abruptly before lifting off and climbing out wih some right alieron cranked in. Closest thing to a takeoff jet crash I had seen up until then.

When I flew the T-38 simulator at Williams Field (after they closed it as an Air base, but before the USAF actually left), we were at a fly-in. Everyone else took off and flew around as if they were in a general aviation Cessna. I lifted off, retracted the gear, accelerated for about 6 seconds, lifted the nose and did a roll.

I impacted the runway just as I got back upright. The sim operator laughed and said, "nice try!" Later, I got to try again and did a much more normal flight with some steep turns but no real aerobatics. Got it back down with some coaching about keeping the power up. It was fun!

 

[drgondog]

I was told by my father in law that a classmate of his was killed the last week of flight training by getting behind a T-38 and allowing it to sink. This is a common on high wing loading jets and I am told that even a Lear Jet could sink like a rock it you get behind it.

If you are in the downwash arena it has the effect of a major reduction of AoA.. as you know

 

[GregP]

Is there any time when at positive g-load that a wing is not creating downwash, assuming it is, in fact, flying?

 

[drgondog]

Is there any time when at positive g-load that a wing is not creating downwash, assuming it is, in fact, flying?

No. Downwash is result of lifting line circulation discontinuity at wing tip.

 

[GregP]

Thought so. So, what does it have to do with the T-38 developing a high sink rate when behind the power curve?

Stay on the fornt side of the curve and you don't have an issue ... get behind and you need altitude, time, or a great excess of thrust to get back on the front side and recover. Sometimes it isn't available. So pay attention.

That's the explanation I got from the USAF, and they gave me a curve to look at when I left. Long time ago, but still a fond memory.

Was fun.

 

[drgondog]

On the low side of the power curve you don't have enough excess thrust available to develop enough airspeed to achieve enough lift to sustain equilibrium.. so it takes time to spool up enough to develop the thrust required to accelerate to equilibrium airspeed.

 

[GregP]

Yah, I've heard stories about delta-wing fighters like the F-102 and F-106. Some say these could develop an extremely high sink rate and the drag was almost too great to overcome unless you had the altitude to simply push the nose over and accelerate while decreasing the AOA. They bled speed like a bandit in a sharp turn. Same can be said for the Mirage family, at least the delta wing members.

Makes me wonder about the hard-turn characteristics of such planes as the Girppen and Eurofighter Typhoon. I KNOW the Typhoon is maneuverable and wonder if the canards or the excess power ... or both are responsible for its ability to overcome this delta wing drag phenomenon. Either they're living with it or, more likely, the aerodynamic and avionics-related improvements since the early deltas have combined to render it a none issue. I know the early deltas could not fly with both leading edge slats and trailing edge elevons both tilted downward simultaneously, and the newer deltas can. It's probably due to fly-by-wire control systems that can keep the nose pointed forward even when the BG is actually toof ar aft.

 

[FLYBOYJ]

Also consider engine spool-up time, especially on earlier jets!