Electro Power for small aircraft and drones

As good as it gets.

Hi Ivan,

At the moment, with the 350 hp at 500 ft and by only tweaking Drag values a little more, without trying to be "just messing with some values and screwing with the tables in the Air file", I have reached a good balance between reality and CFS1 handling and performance:

90% throttle gives me 440.2 mph top cruise speed at 17500 ft with 350 hp, 34.8 Hg and 44.0 prop, and 100% throttle gives me 20.1 mph more: 460.3 mph, with 398 hp, 38.1 Hg and 45.6 prop. Thus, (A) it is easy for the simmer to toggle between top cruise speed and full throttle by just pressing Key "9", and (B) we can see that the simulator already increases power with altitude.

Then, top speed at 500 ft is now 383.5 mph, which looks just fine to me, and at 5500 ft, the simulator´s math give 411.7 mph with 368 Hp.
Note that the latter is a straight-line horizontal speed we are talking about, not an average in a pylon race with a really souped-up engine.
Sharp´s machine could do 435 mph in a straight line at this altitude, so I believe 411 mph for a not-so-souped-up machine sounds reasonable.

I can of course set 450 Hp at 500 ft instead of 350hp, as 350hp is only a rated power (probably at S.L.) for the 6-cyl twin-turbo TIO-540 engine, but who knows... The N777XT having an engine tuned for altitude would not really supply more than 350 Hp at S.L., but would rather do so further up, which in my .air file, it already does. Maybe such an increase in S.L. Hp would be mixing chalk and cheese, because the Nemesis N42XT´s 450 hp come from a naturally aspirated, fuel injected, 758 cu.in. 8-cyl engine with 8.7 compression ratio. That it came in second, may have something to do with the lack of turbo supercharging, so power loss with altitude must probably be taken into account, or possibly also the pilot - I wouldn´t know.

We are not talking about "the Nemesis NXT in typical form, which probably was not quite capable of 400 MPH at ANY altitude much less at 5000 Feet. It took a bit more than the typical engine to do that." - although yes indeed, early on they did do some race-qualifying at Reno with a standard TIO-540-NXT engine, just to see what that could do, but of course, the N777XT appears to have more than typical TIO-540-NXT engine.

Regarding wing tanks, they were inherited from aircraft whose .air file I started off with, and I had left it for later as it is not a major issue in early FD development. I eliminated them long ago, and now there´s a fuselage tank, which according to you would probably mean that I am no longer insane.

What remains to be corrected, apart from the aft wing fairing bleed, is pilot´s point of view, and possibly a SCASM-corrected virtual cockpit view.

Regarding your funny story about your daughter, it is always very pleasing when one´s offspring are so smart and do so well at school and professionally. Genetics and a good home seem to be key factors. I have that too with mine, but I believe you are absolutely insane to believe that just because of this, I should be able to handle the math for the calculations involved and to use a spreadsheet - it is inverted direction for genetics. The math in question is too abstract for me, and I can´t see it, so I act more practically.

So, have a nice week!
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
If you were reading my prior post, I don't think you actually understood it.
I see you type a lot of statements but many of them are just plain nonsense.
You have seen the TCDS on the Lycoming TIO-540 series engines. Probably AROUND HALF OR MORE OF THOSE LISTED will achieve 350 HP at low altitude.
So.... What you are really saying is that nearly EVERYONE who buys a kit and sticks a garden-variety TIO-540 with no special tuning should be able to break 400 MPH at 5,000 Feet. The general evals state the opposite that without some work or a special engine, the Nemesis NXT will not break 400 MPH at any altitude. I came across this from a couple sources without even looking for it. How can you miss it?

Your comments about the second place pylon race finisher are interesting. I suggest you actually watch a pylon race heat or two and see what the racing is really like. Your claims there do not make sense.

Your claim about the 45 Gallon wing tanks not affecting flight dynamics is just plain wrong. On a lightweight flea like the NXT, it drastically changes the handling to have such large weights that far outboard. Your solution seems to have been to increase the Moments of Inertia to hide this which is really creating yet another problem to deal with later.

Have you figured out why you have not found a TCDS on the Lycoming TIO-540-NXT engine yet?

The kind of math I suggest you try out is incredibly simple. You need to understand what the theory is behind why the speed difference is roughly approximated by the cube root of the power difference. That is a pretty basic concept.
You comment about reality, but reality isn't about just changing the drag coefficient when the results don't quite work out the way you want, especially when the other numbers are not correct.

What you appear to be learning is how to mess with Air files to change performance numbers.
What I believe you are NOT learning is when and why to make those changes and in the long run, that is much more important.

- Ivan.
 
Hi Ivan,
This is starting to become tedious. You certainly enjoy not only provoking an argument, and really digging in to continue it, especially with your tone.

You said "You have seen the TCDS on the Lycoming TIO-540 series engines. Probably AROUND HALF OR MORE OF THOSE LISTED will achieve 350 HP at low altitude." So? And?

You said: "So.... What you are really saying is that nearly EVERYONE who buys a kit and sticks a garden-variety TIO-540 with no special tuning should be able to break 400 MPH at 5,000 Feet." Where did I say that? I said exactly the contrary. I said the N777XT was tuned for higher altitude, and I never said a standard "garden variety with no special tuning", as you so despectively call it, could reach over 400 mph.

We are not talking about any standard TIO-540 here, and the engine in my .air file is not a standard "garden variety with no special tuning" because it can and DOES achieve over 400 mph.

Do you say what you say only because I have 350 Hp for S.L. in the -air file?
I would say that it IS quite specially tuned with non-standard supercharger, because power goes up considerably with altitude as the supercharger does its work.
Or, are you implying that a non-standard supercharger which brings a small plane weighing 2400 lb with a very low-drag coefficient plane such as the Nemesis NXT to High Speed Cruise of 440 mph at 17500 ft necessarily will not leave the engine with 350 Hp at 500ft, but rather more?
You don´t appear to like the 350 Hp I have in for S.L., so why not just say what it should be then?
Nowhere is there any information to be found to this respect.
Also, remember that we are not talking about Sharp´s multiple record-breaker N333XT either, which you say could well be making 400 or 450 Hp at S.L.

At the moment I have (in AirEd) Zero Lift Drag at 20, Skin Friction at 305, and induced Drag at 4785.
Are these Drag adjustments really so terribly bad as to warrant your despective comments like:
>"If you were reading my prior post, I don't think you actually understood it."
>"I see you type a lot of statements but many of them are just plain nonsense.", and
>"What you appear to be learning is how to mess with Air files to change performance numbers."
Indeed... You could change your tone somewhat.

You said: "The general evals state the opposite that without some work or a special engine, the Nemesis NXT will not break 400 MPH at any altitude. I came across this from a couple sources without even looking for it. How can you miss it?"
No, I didn´t miss it. I have already said from the beginning, the N777XT has some tuning work done so that it can reach the quoted speeds. Not as much as the N333XT, but rather more than standard. Probably the special titanium allow con-rods play a role here.

Regarding my mistakenly left-in 45 USG wing tanks, you have not been reading my messages properly, because I said I have long since changed them to a 90 USG fuselage tank. The only thing is, I haven´t sent you any more .air files, because you obviously don´t want them and aren´t interested in them.

Perhaps it would be time to give the subject a rest...

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
I don't think you are really putting things together all that well.
Example in point:
When an engine making 350 HP at Sea Level is able to achieve 400+ MPH at 5000 Feet, it doesn't really matter what it is doing further up. What you are saying with that assertion is that just about ANY TIO-540 making 350 HP at Sea Level should be able to make 400+ MPH at 5000 Feet. It doesn't matter how much excess supercharger capacity it is carrying for use higher up if a speed run at 5000 Feet is already higher than 400 MPH. What is hard to understand about that?

As for saying what things should be, I refuse to do your research for you. I already have given you the means to do your own calculations. You know what the 2nd place pylon racer had for engine output and its speed. Work back from that as I suggested a couple posts ago.

Regarding Wing Tanks, the last Air file you sent me to work with which was only about a week ago still had the wing tanks. It wasn't all that long ago.

You quote a bunch of Air file parameters from AirEd, but how did you arrive at those numbers? What are they based on? Did you just tune to those values to arrive at the performance you were looking for as I believe you probably did?

Regarding special tuning:
I would look harder at supercharger performance and not worry about Titanium con-rods. These are not high revving engines.
A typical NASCAR V-8 from a couple decades ago was running forged STEEL or Billet Steel connecting rods. It increased the weight of the rotating mass so the acceleration was not as quick as it could be but these guys were running at about 9,000 RPM sustained and not at 2700 RPM. They needed the durability of really tough steel.

- Ivan.
 
Hi Ivan,

The last .air file I sent you was already 10 days ago, and I put in the fuselage tank a day or two later, but of course, you didn´t get to see it. No problem.

Anyway, regarding 5500 ft performance for "my" N777XT, my reasoning was as follows:
Sharp´s super-souped-up-for-lower-altitudes N333XT averaged 407 mph and 416 mph in pylon races, and did 435 mph straight-line top speed - a 28 and 19 mph speed difference.

You mention:" What you are saying with that assertion is that just about ANY TIO-540 making 350 HP at Sea Level should be able to make 400+ MPH at 5000 Feet." No, I am definitely not saying that. In effect, it appears that a Nemesis NXT with a standard issue TIO-540 engine could not reach 400 mph, so "my" N777XT most probably has a more expensive and better supercharger than the standard issue one, as well as perhaps other mysterious enhancements we don´t know about.

With "my" tuned-for-higher-altitudes-and-not-so-souped-up N777XT, after setting 350 Hp and 383 mph top speed for 500 ft, and 440 mph at 90% throttle for 17500 ft, the sim came up with 460 mph top speed there, which seemed feasible.
The sim also came up with 411.7 mph at 5500 ft as a flat-out full-throttle 5-minute straight-line top speed. I might have liked it to be perhaps around 402 mph, as we had discussed before, but this is what CFS1 does to performance curves.
Anyway, even with 411,7 mph at 5500 ft, in a supposed pylon race, "my" N777XT could NEVER average above 400 mph - in fact, it would probably average around 383 mph and 392 mph here.

Now, what will happen if I put in more Hp at S.L.? Won´t it just get all worse? Even more power at 5500 ft, and too much power at higher up... It would definitely mess up the whole flight envelope. A more powerful supercharger would also mess it up. All we know is that top cruising speed is 440 mph at 17500 ft - ...presumably this is critical altitude, but we can´t even be sure of that.

We can talk ourselves silly, and do futile calculations until smoke comes out of our ears, but at the end, it´s all speculation.
At least the latest .air file I´ve done strikes a balance between S.L. and 17500 ft and uses the performance that the sim calculates for 5500 ft, and all this without touching your Airacobra propeller curves. I haven´t even breathed on them!

The 450 hp (at S.L.) 8-cyl naturally aspirated "Relentless" N42XT racer who came in 2nd in a pylon race, I´m sure was not delivering 450 Hp at 5500 ft - more likely about 374 hp, due to power loss due to altitude. What speeds could it have averaged with 374 Hp? 403 mph and 414 mph perhaps? (See?... we are speculating again). But: It definitely did over 400 mph, as its specs say.

"My" N777XT delivers 368 Hp at 5500 ft, i.e. 6 Hp less, so the average in a pylon race speed using this as an example would also be below 400 mph. I wouldn´t know how to use the 450 Hp N42XT to help in any calculations. In fact, looking at the comparative figures, it could even confirm that my approximation for the N777XT could actually be quite good.

You say "You quote a bunch of Air file parameters from AirEd, but how did you arrive at those numbers? What are they based on? Did you just tune to those values to arrive at the performance you were looking for as I believe you probably did?"
The answer is yes, of course I did, what else is there to do? I could also bend the corresponding Prop efficiency curve and shift the Prop power required curve to lower the 411 mph at 5500 ft to 402 or so, but I haven´t done that (yet!!).:devilish:

Anyway...
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
You are correct in your earlier post. This is getting quite tedious.
When people comment that the typical NXT won't break 400 MPH at ANY altitude, they don't mean in pylon racing. They mean bragging rights all out speed.

What makes "Your" 350 HP N777 different than Fred's kit plane with a more typical Type Certified TIO-540 engine? At Sea Level his engine also makes 350 HP. Fred's engine may run out of supercharger by 8,000 Feet but he doesn't care. He is making as good power at 5000 feet and consequently as good speed as the N777XT. That means that with a garden-variety TIO-540, Fred just broke 400 MPH like folks claim isn't possible.....

You are picking up on pylon racing as a fudge factor and that really isn't the point. Look qt what qualifying speeds are as compared to race speeds as compared to straight line speeds. We only test for straight line bragging rights speeds.

For power loss with altitude, suggest you look up Ram Effect and what it might have done for "Relentless".

Suggest you look up what critical altitude really means as far as superchargers versus aircraft performance.
When you have done that, you will probably answer your own questions. I have answered them before but you are not putting it together in a useful manner and I am tired of repeating myself.

Have a nice week.
- Ivan.
 
Hi Ivan,

You seem to credit me with more insight into this whole business than I have. The nuances behind it all escape my understanding I´m afraid, and it goes over my head. Apparently my logic isn´t applicable here, and it isn´t worthwhile losing anymore time on this, neither for you, neither for me.

Anyway... Fred´s garden-variety machine won´t high-cruise at 440 mph at 17500 ft, and Sharp´s probably won´t either.
There is too much speculation and not enough data. Do you reckon the small air inlet under the nose is big enough to produce a significant Ram Effect, and that it might do something for the Relentless? Maybe...(speculating again...) If so, that would apply to the N777XT too... (more speculation).

This set of aircraft with their individual differences seems to be shrouded in mystery, and one can only speculate about how to fill in the gaps between the scarce morsels of information the parties involved are willing to supply. So much smug secrecy, for what? There´s the Hubris. It´s just meant to add to the impression on people how these little wizz planes beat a large number of those bigger brothers, the 1000+ Hp racers...

Anyway, don´t lose your cool if I don´t quite understand. It´s not worth it. I can´t get my head around any more than what I´ve managed, so forget it. What I won´t do is waste my time looking for any more information to see if I can calculate whether the N777XT developed 400 or whatever Hp at S.L. based on speculation. The mind just boggles. Evidently I can´t put together the information you have supplied because it is so cryptic, and you often tend to answer questions with more questions anyway, so it all becomes quite a quagmire.
But not to worry! It´s supposed to be fun, until it isn´t.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
You give up way too easy. There is a lot less speculation if you know what information you are looking for.
If you have no background for understanding what you are reading, things get tough.

Do I think a little intake facing directly into the airstream with a dynamic pressure developed by around 400 MPH of forward velocity?
YES! Read the Allison memorandum on their V-1710-39 and -73. Allison believed that even at the maximum speed at Sea Level of the P-40, they might generate another 3 inches or so of manifold pressure through ram effect.
This would be necessary to give what the pilots were claiming which was around 70 inches Hg.
Do I think the N777XT would also have benefited from ram effect at 5000 Feet? No!
It was way below its critical altitude and was certainly dumping excess supercharger capacity out the waste gate.
If you don't, you break the engine.

The big unlimited racers these little aeroplanes are beating for qualifying speeds are more likely making 2,500 to 4,000 HP.

You seem to read what I am telling you and losing the essential ideas. I wasn't suggesting doing anything with N777XT at low altitude. There is no reliable data that you have even been able to quote. I was suggesting figuring out what the Cd0 should be from the likely power and speeds from Jon Sharp's record breaking runs. Not the Pylon Races, the record breaking sprints.
Note that this is about the third time I have made the same suggestion.

- Ivan.
 
Hi Ivan,

Talking about Cd0:
OK, granted, the Cd0 in my .air file being at 0.0097 is too low, because for example AAM quotes 0.01806 for the Mooney Bravo, for the Cessna 172 SP it quotes 0.02978, and for Cessna 182 S and Cherokee, it quotes 0.02929, so for Nemesis NXT I expect must be a bit lower than that.
AirWrench sticks in Cd0 at 0.00830, which is no help at all, obviously because of the S.L. and 17500 ft speed inputs.

In one of their official Nemesis NXT page headers, which I can´t find any longer, I remember CLmax being quoted at 1.55, and they also quoted CD0, and if I remember correctly, that was 0.013, which would probably make sense.

Incidentally, an article on the Nemesis NXT airfoil rekons that real engine power with that wing for the 350 Hp TIO-540-NXT is more like double that power. So this would coincide with your comment about putting in more than 350 Hp. How about 700 hp? :ninja:

Another two articles state state:
>"Lycoming has perfectly matched a twin turbocharged, 350 hp engine to the NXT airframe to maximize performance, speed and steadfastness."
Well... That´s what I did.
And also:
>"Much like a sports car, when you’re not racing it, it’s about enjoying it. Furthermore, it is the first airplane that travels at 400 mph and can be assembled by a buyer in his own garage." Oh? What´s this??? I did that too, only mine´s faster! But of course, thanks to a too-low Cd0.

So you mention calculating Cd0 from the record breaking sprints... Are those the 2015 speed blasts they mention?
"... two weight categories, C1b (1,102 - 2205 lbs) and C1c (2205 - 3,858 lbs) that Sharp challenged during Thunder Over Moriarty Speed Blast in Oct . 2015."

3 km C1b at 393 mph,
15 km C1b at 405.9 mph,
3 km C1c at 415 mph,
15 km C1c at 407 mph, and
100 km C1c at 397.2 mph.

...and what about the 435 mph they claim to have done on the last straight stretch in one of the races?

Now, calculating Cd0 from the Drag equation from this is quite another complicated can of worms. We shall see... Probably 0.013 will be fine, and I can save myself the trouble.

Cheers,
Aleatorylamp
 
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...third time lucky: Cd0 is the key.

Hi Ivan,
After your third time suggesting some work on the Cd0, I finally understood what was going on. It is not rare for things to take time to be absorbed...

Drag formulas (all 3 of them) are so daunting, that was avoiding that can of worms, even if you say they are simple math), but luckily remembered on one of the Sharp Nemesis NXT page headers a couple of weeks ago, which I never saw again, that quoted Nemesis NXT CLmax and Cd0 on two little beige banners below the Nemesis NXT Logo heading.

I didn´t expect it would work so clearly well, given the complications usually involved in adjusting things like this, and I can see your point about the "garden variety" 350 Hp TIO-540-NXT engines.

Anyway, with AAM I put in the Cd0=0.013 (26 in AirEd), and started flight tests at 17500 ft with 90% power, first messing with the engine torque and friction graphs, with which I began getting tangibly good results.

Then, and I started screwing with Skin Friction Drag, which I polished down from -305 to -250, like for the LearJet 45, gaining 1 Hp only with this, and lowering Induced Drag from to 3150, a bit less than the Learjet 45, scraping a little more Hp out.

Maybe this value should be higher, and another lower? CFS1 seems to favour rather large induced Drag values, so I don´t know. But of course, you are not about to tell me, so either I´ll leave it like this, or try it out for myself.

Well, after that I worked myself down to 500 ft, writing down what the Beckwith Gauge was displaying.

Here are the results of your suggested Cd0 adjustment:
500 ft: 382.3 mph, 402 Hp, 39.5 Hg, 40.2 prop.
5500 ft: 402.0 mph, 422 hp, 39.5 Hg, 41.7 prop.
17500 ft: Full throttle: 452.2 mph, 453 hp, 38.1 Hg, 46.5 prop, 90% throttle: 440.3 mph, 402 hp, 34.8 Hg, 45.0 prop
18500 ft: Full throttle: 450.5 mph, 434 hp, 36.6 Hg, 46.3 prop, 90% throttle: 437.3 mph, 385 hp, 33.4 Hg, 44.8 prop.

Like you said, more horses are needed to achieve more realistic N777XT´s speed specs.

Thank you very much.😎
Cheers,
Aleatorylamp.
 
Hello Aleatorylamp,
Just finished dinner a few minutes ago. It is amazing that all of us were actually having dinner at the same time (more or less) on a work night. This does not happen very often.

I see you are finally beginning to understand what I have been trying to tell you for a while.
I will now tell you something that when you think about it may have you smacking yourself in the forehead and saying, "How OBVIOUS!".
At this point you have a pretty good idea how much Horsepower and Manifold Pressure you need to achieve "Fast Cruise Speed" at 17,500 Feet. Write it down.!
Here is an interesting thing: If you take your aircraft's critical altitude LOWER, the lower air density and reduction in power will be the exact equivalent of a throttle reduction.....
Throttle is still Wide Open, but the manifold pressure is lower.... The same as a power reduction for cruise.
That is the thing about critical altitude. That is why I suggested you look up what critical altitude really means.
If I am running WEP, critical altitude may be fairly low because the supercharger can't maintain that level of boost very high.
If I am running just Military Power, it gets higher.
If I am running cruise power, it gets even higher.
Nothing changed in the supercharger, it is just what manifold pressure I am trying to maintain.

As for induced drag and skin friction, I believe you are going in the wrong direction.
Induced drag at maximum speed is relatively low in any case and would tend to affect the speed at high altitudes more because AoA has to be higher to maintain the same lift.
The Induced Drag (Oswald Efficiency Factor) is not necessarily all that low even for a Laminar Flow airfoil.
Now also keep in mind the difference between a Learjet and an aeroplane with a tractor propeller.
The Learjet has nothing to disturb the airflow over most of its airframe. Even bugs do not fly that high.
The NXT on the other hand has this big ole fan churning up the airstream before it hits the rest of the airframe.
Now what were you saying about skin friction again????

- Ivan.
 
Hello Ivan,
It´s pleasing when the family can get together for a meal. In our case it usually happens at weekends!

Yes, I´m sorry that it took so long for me to understand, but as you said, my lack of background on the subject makes things tough.
So... I already thought that what would follow was to improve induced drag and skin friction drag!

I had done some trials with my previous higher Boost gain settings, and then settled for the 2.56 you had suggested, and it did occur to me to have the last 10% throttle at WEP, which will not allow the simmer to abuse of full power so much. That would leave the high speed cruise as military power within the normal throttle lever travel. I might do that...

I thought thinking Critical Altitude was nothing else than the altitude at which a supercharger stops having effect and engine power and manifold pressure start falling. I also understand that setting it to different altitudes has a different effect on manifold power. At the moment, because top cruise speed for the N777XT is quoted at 17500 ft, I had assumed that this was critical altitude, so I had put Boost Gain at 2.63, but it came at a price of having less power and speed lower down, so basically, with your suggested Boost Gain of 2.56, critical altitude is at 16500 ft or 17000 ft, as a compromise for keeping a bit more power lower down.

Regarding skin friction, the Mustang and Thunderbolt have 364 here, and the Learjet 45 has 250, so possibly for the Nemesis NXT the 305 I had before was better - or maybe 315.

Then having induced drag at 3150 being too low, as you said, and the Mustang having 4330 and the Learjet 3656, perhaps something like 3850 would be better.

OK, I´ll try out some changes, and see what happens.🤔
Thanks for your feedback!
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
We just finished a rather late lunch together today because everyone was off work or school at the same time.

The 2.56 Supercharger boost setting was correct in a certain context which does NOT apply here. It is not a magic number. Don't take it out of place. It was a number that reduced the critical altitude in such a manner that the maximum speed was not significantly reduced WITH THE PARAMETERS IN USE FOR THAT PARTICULAR CONFIGURATION.
What we are discussing here is to reduce critical altitude with AN INTENTION of reducing maximum speed by reducing manifold pressure to that of a "Fast Cruise" setting. Totally different objective here.

As for skin friction, I have never messed with that. I don't think it is applicable for the types of aircraft I work on.
As for the Induced Drag, I believe you should not be doing this. The stock P51D is NOT a good example of how to do things.
Its Oswald Efficiency number is way too low probably because the person writing the Air file really wanted a great aircraft regardless of realism. That is also why the Zero Fuel weight is a couple thousand pounds too light.
Keep in mind there are a lot of things that are very very wrong with the stock flight models.

- Ivan.
 
Hello Ivan,
Just a short note to let you know I am studying your last two messages.
I was a bit ill today, recovering from a migraine, so I haven´t experimented with other than higher skin friction (which works to get minor speed adjustments) and induced drag values. The result now is simply that I need about 2 or 3 more horsepower to get the 440 at 17500 ft.

However, for the moment I didn´t know what to do with critical altitude i.e. Boost Gain.
With your clarification now, that lowering critical altitude because it is not 440 mph under maximum power we are looking for at 17500 ft any longer, is very interesting, and I understand that the difference between 38.1 Hg for full power and 34.8 Hg for 90% power = 3.3 Hg would be of significance.
Also, OK, I´ll see how I get a higher Oswald Efficiency number rolling!

I´ll think about it a bit more tomorrow and do some further experimenting.
Thanks, and more tomorrow!
Cheers,
Aleatorylamp.
 
Hello Ivan,
I changed induced drag to 4850. Just to look at the Oswald Factor I used AirWrench, which reports 990.
I´m afraid I can´t really seek what we are trying to do by lowering Critical Altitude. Performance now seems to be higher lower down.
I´ve lowered Boost Gain to 2.2, and had to increase Hp again, to keep the 403 Hp at 17500 ft with 90% throttle, so that I´d get 440 mph.
Also, I reduced Skin Friction to 240, in order to get there. Skin Friction does have a noticeable effect - otherwise, what other parameter is there left to work on?
Now of course, what I knew was going to happen, happened: There is an unwanted power surge at 15000 ft (I didn´t try any lower) giving 412 mph and 434 hp at 90% power and 455 mph with 481 hp.
I wonder...
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
I still don't think you understand the concept of critical altitude. Please go back and re-read post #151.

I am going to make up some numbers here for an example. Understand the concept!!!!

I have an aircraft making 430 HP at 17,500 Feet.
I have been told that this aircraft should achieve a fast cruise of 440 MPH at 17,500 Feet on 90% power.
I find that the power at 90% throttle is 403 HP.
So far, so good, right?

Next thing I do is to make it un-necessary to consciously throttle back at 17,500 Feet.
To do this, I reduce the supercharger boost to take the Critical Altitude DOWN.
First, I try for a setting that gets me C.A. 16500 Feet.
I find that the Engine Power at FULL THROTTLE at 17500 Feet is now 412 HP.
Still too high.
Next, I try an even lower supercharger setting...... At this point, I don't really care what the Critical Altitude ends up being.
I am actually just doing a Engine Power test at FULL THROTTLE at 17500 Feet. If it is too LOW, I raise the supercharger setting.
If it is too high, I reduce the supercharger setting.

At some point, I will hit the target Engine Power.
The engine is now running cruise power manifold pressure setting at WIDE OPEN THROTTLE.

If you are curious at this point, you go back and figure out what the new Critical Altitude really is and what the aircraft's actual maximum speed is, but that isn't the target you were aiming for.

Think about this!!!
- Ivan.
 
Hi Ivan,

All a bit complicated, and I can´t get my head around it, especially when you explain why you would like this done, apart from the fact that it also gives an unwanted power surge at 16000 ft or so.

It´s OK as an exercise, and you are also saying that at 17500 ft the simmer won´t be able to get 5-minute full throttle, because automatically the throttle lever at full throttle will only provide 90% throttle.

Anyway, I´ll try snd do the exercise. When you say supercharger boost, I suppose you mean Boost Gain... and when you say supercharger setting, I suppose you mean Max. manifold pressure, is that correct?

I´d actually prefer to put full throttle into F10, and leave normal throttle lever travel giving a maximum of 90% power. The difference for 10% to full power will be obtained with WEP, and that would be got with the erxtra 3.3 Hg I mentioned in Post #154. The Max. MP setting would be 34.8 (with Boost gain at 2.56), and the simmer will destroy the supercharger if 100% power use is abused.

However, as I say, I´ll try and do the exercise, even if I don´t understand it very well.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
You do whatever you like. Don't do this just because I suggested doing it.
I believe it makes sense, but this is your project.
As for an unwanted power surge at around 16000 Feet, WHY do you call this an "unwanted" power surge?
This would be the actual critical altitude or "Full Throttle Altitude". There is no inconsistency.
Again, this is my view of the world. Do things as you see fit.

- Ivan.
 
Hi Ivan,
I see your point. Obviously, lowering critical altitude means that engine power, which starts falling above that altitude, would fall sooner, so that there would come a point at which full throttle delivers only 90% power.

Update: I understand that Max. Manifold pressure should remain at 39.5 Hg, correct?

I just did your suggested exercise, first setting Boost Gain at 2.25, and balancing out horsepower to the desired 90% performance of 403 Hp and 440 mph at 17500 ft. Now at S.L., Power is now a bit high, with 468 Hp... so I´ll probably repeat the exercise with 2.4 Boost gain later this morning.

Of course Boost Gain at 2.25 turned out to be a bit low, because I actually got the power surge already starting at 14000 ft, meaning that Critical altitude was about here. "Top Speed-Cruise" is 443.6 mph, which means that at 17500 ft it isn´t really "Top Speed-Cruise", because Speed-Cruise is faster lower down. I also found (of course) that full throttle speed changes along with 90% throttle speed.

Update: Raising Boost Gain to 2.42, maintaining 403 Hp at 17400 ft with 90% Throttle, I got an unwanted speed peak of 443 mph with power peak at 15500 ft, and for full throttle it was an unwanted power peak at 15000 ft and speed peak at 15500 ft.
Increasing Boost Gain to get Critical altitude to 16000 or 16500 ft increases performance about there, also below the quoted 17500 ft.

Even arguing that 3 or 3.6 mph is not too excessive, the fact that speed starts peaking lower down raises the question as to why 17500 ft altitude would be quoted for N777XT "Top speed-cruise", if this speed were to be available already below that altitude.
That´s why I called the power surge "unwanted" at 16000 ft (or at 14000 or 15500 ft for that matter).
The only thing I´m trying to do is to avoid getting speeds higher than quoted Top Speed-Cruise to be obtained below 17500 ft.

Anyway...
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
I just read your message in detail with all the updates and realize that you still don't understand what I was suggesting.
First of all, whatever you had the manifold pressure at for SL doesn't change for this exercise.
The original number of 39.5 was pulled out of a hat basically because you asked me for a guess for an aircraft engine that I had done no research for. If you were still trying for 350 HP at SL, I believe it is a pretty good guess. Now that you have changed your target HP at Sea Level, what the manifold pressure really should be is YOUR guess. Use the TCDS examples as a guide and try to understand what manifold pressure really means.

The general idea when doing this kind of engine tuning is to get to a reasonable baseline and try to work from there. The problem is that you seem to be changing so many different things all at the same time that it isn't clear what a good baseline version of this engine really is. Think if you were Jon Sharp and knew what the average TIO-540 Type Certified engine could do. Why would you use a more expensive custom Thunderbolt version? Why would you equip the aeroplane with Water Injection? Why does it need water injection?

The reason I do not believe you understand what I was trying to tell you is that if what I was suggesting was properly done, the Sea Level manifold pressure, Horsepower and speed DO NOT CHANGE. I am really not sure what you are doing at this point. You are doing something which changes Sea Level and low altitude (5,000 Feet) Horsepower and that is definitely out of scope for this exercise.
I am about to do a very similar exercise with my A6M2 in the next day or two but had a few things going on recently.

It is quite difficult without working on this flight model myself to see all the different things that may arise and tell you exactly what to do in each case, but it seems like that is what you are expecting from me. On top of that, you are also messing with induced drag and skin friction which may have some consequences you do not expect.

- Ivan.
 
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