Electro Power for small aircraft and drones

Hi Ivan,
I have explained most of this already, but I shall repeat.

Reno is where the records were set for the Sharp Nemesis NXT with its 350 Hp TIO-540-NXT dual turbocharged engine. Performance specifications correspond to tests done at Reno, so evidently it would be inaccurate to conduct flight tests for these figures as S.L.
RoC is 3000 fpm.
For the moment, critical altitude is set at 12000 ft, as I have found no reference to it, but this can be set higher if needed. There is no reference as to ceiling either, because this aircraft performs at altitudes above ground visible to the public. Probably no more than 7000 ft, so ceiling would be irrelevant.

The sum of empty weight 1500 lb, 140 lb pilot, plus 90 Gallons (540 lb) of fuel, gives a gross weight of 2180 lb, although MTOW for the airframe is quoted as 2600 lb. It appears that they didn´t do their record breaking at full MTOW.

Rolls Royce have been quite secretive about their 535 Hp Spirit of Innovation weights. The only reference I found is is that their airframe is the Sharp Nemesis NXT, and that they used a 50% reduced battery pack weighing 845 lb, and that the weight is 500 heavier than the NXT. So, my RR Spirit has a MTOW of 2640 lb.
RoC is 4000 fpm.
There is no reference as to ceiling, but it is probably irrelevant, as it won´t be flown anywhere near that.
At any rate, it would be the aerodynamic ceiling for the wings and propeller, not the electric motor.
The RR Spirit was tested in England at S.L.
Why the RR Spirit is a bit slower than the Nemesis NXT, I don´t know, although I´d put it down to the 500 lb extra weight. Note that the RR Spirit was tested at slightly above MTOW, at S.L. and the Nemesis NXT at 2180 lb gross weight at Reno.

Regarding the jet .air file for the electric engine, as I have already mentioned many times, the main reason is that there is no other .air file that can emulate batteries with a 1 USG fuel tank by regulating fuel consumption. This way, the weight loss with battery drain is only a negligible 6.6 lb.
The other advantage is that a jet .air file has less power loss due to altitude than a piston engine, even if the latter is highly supercharged.
I believe we have gone through this several times.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
I can see we are running into our usual communications problems.
For the "Reno" speed testing, I wasn't asking why you didn't test at Sea Level.
I was asking why you are testing at 5700 Feet per post #18 when 4600 Feet is more consistent with the data.

Regarding the flying weight of IC NXT for speed runs, I believe your weight estimate is quite low.
The only place that I have seen US aircrew weight down at 140 pounds is for the P-39D and I believe that was because Larry Bell was playing games when testing the early Airacobra. My Son is skinny as a stick at 120 pounds, but in flying suit and wearing a parachute I don't think he would come in under 160 pounds. The typical weight allowance is 200 pounds per aircrew.
Not only that, but for speed runs, the aircraft was equipped with Anti Detonant Injection (Think Water-Methanol), though the exact volume is not specified.
The other thing worth noting is that extra weight does not affect maximum level speed by much. A few hundred pounds typically costs 3-4 MPH or so. It kills rate of climb though.

I wasn't asking about altitude performance about the actual NXT.
I was wondering what you were getting with your AIR file.
I believe the engine output and performance curves might be quite revealing.

The reason I believe the electric NXT is so much slower is because of a difference in propeller advance ratios, but you certainly won't see that when comparing a jet and a propeller AIR file.
If you are using the P-51D propeller tables, you still may not see it because the fellow who wrote them must have really liked the P-51 and tried to give it every advantage he could. The graphs typically terminate well before they begin to drop significantly which means that the simulator thinks efficiency does not drop off as we know it does.

- Ivan.
 
Hi Ivan,
I was using Reno Stead airfied, where the ground is at 5053 ft in CFS1. The flight was between 5300 ft over the plains and 5700 ft over the more shallow parts of the nearby mountain sides.
Regarding the prop efficiency and engine torque graphs, I had to give a substantial increase to those in the range used by the airplane to get the desired speed, so they are by no means the P51D´s anymore, and then also drop zero lift drag significantly.
Anyway, all this is rather splitting hairs and getting a bit tedious for me, and I don´t think it´s worth much more effort, so I´d be quite happy leaving things as they are.
Thanks a lot for your comments, and cheers for now!
Aleatorylamp.
 
Hello Aleatorylamp,
Working on AIR files and doing anything but basic tuning does tend to be quite tedious with lots of test cycles.
It gets even worse when your project happens to be a bit unusual in one aspect or another. It generally forces you to learn a lot more about how real aeroplanes work and how it is reflected in AIR files.

- Ivan.
 
Hi Ivan,
Yes indeed, especially if we add to the fact that for planes that are a bit unusual, available specifications are often incomplete and/or contradictory.

Update:
For the sake of accuracy and given your comment a while back about a problem of data consistency, I have revised the weight calculations for both planes, as the weights I was using wouldn´t tally with what I´d read about a 500 lb weight difference between the two planes, so I´ve discarded the latter piece of information.

Empty weights for the two planes are 1500 lb for the electric one and 1600 lb for the petrol-driven one.
This is because the Lycoming TIO-540-NX weighs 438 lb, and the 3xYASA-750R electric motor stack weighs 244.2 lb, (inverter, cabling weights etc. aren´t mentioned, but account for the rest of the weight difference).

Both planes have a MTOW of 2600 lb, because they use the same airframe.

Sharp Nemesis NXT 2-seater Reno Racer
Empty: 1600 lb
Fuel: 540 lb
Pilot: 200 lb (only 1 pilot was used for the successive record breaking flights from over a number of years).
-----------------
Gross: 2340 lb
-----------------
Dry weight in the .air file: 1800 lb.

Rolls Royce Spirit of Innovation single seater
Empty: 1500 lb
Batt: 845 lb (a reduced weight battery pack as the full one weighed 1350 lb, exceeding MTOW).
Pilot: 200 lb
-----------------
Gross: 2545 lb
-----------------
(Dry weight in the jet .air file: 2349 lb, as "fuel" in the 1 USG Tank is only 6.6 lb).

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
I still believe your estimate for the record breaking NXT is a little on the low side.
The reason is because it was equipped with Anti Detonant for the speed runs. The weight of the tank, plumbing, and the actual water / methanol would have some substantial weight.
When I was calculating the weight of the FW 190D, I used only half the weight of the KNOWN volume of the MW50 that was carried, but it still made the Zero Fuel / Zero Ammunition weight of the Dora a bit higher than Anton. That part surprised me a bit.

I also believe it is unfair to quote an empty weight of 1500 pounds for the electric NSX. That weight is very much like the "empty weight" of some fighters that is often listed but is basically useless information for our purposes. Those weights do not include essential non-disposable military loads such as guns.

Perhaps you are doing something different in your math with the electric bird, but as I see it, Gross weight is 2545 pounds which would mean a "dry weight" of 2539 pounds once the one US Gallon of Avgas is deducted. 6.6 pounds is the typical weight of a US Gallon of Lubricating Oil. Aviation Gasoline is more like 6 pounds per US Gallon.

For many obscure aircraft, data may be hard to find, but in this case you are lucky. This is a kit aeroplane with suggested engine (Lycoming TIO-540) and I believe a recommended Hartzell Scimitar propeller. For some of these parts, the FAA is not a bad source for information.
Finding reference information is pretty much a never-ending game. In the last three days or so, I believe I have downloaded over 500 MB of reports and flight tests and specifications for the Airacobra, P-40, and A6M and I am not even actively working on any of them at the moment.

- Ivan.
 
Hi Ivan,
Thanks for your comments!
Regarding the Nemesis NXT, being a 2-seater, and the record breaking flights being done without a passenger, adding another 60 lb for the sundries you mention, I could arrived at 2400 lb for the gross weight. The net weight of 1860 lb, would include pilot and any other necessary sundries like oil and ADI. It is still quite hard to make up the 4 mph lost, but I´ll manage.

Revised Sharp Nemesis NXT weights:
Empty weight: 1600 lb
Sundries: 60 lb (oil, ADI)
Pilot: 200 lb (no passenger for record breaking flights)
Fuel: 540 lb
----------------------
Gross weight: 2400 lb (MTOW = 2600 lb)
-----------------------
Dry weight in .air file: 1860 lb

Regarding the 1500 lb empty weight for the RR Spirit single-seater, I got this from the official Rolls Royce Spirit of Innovation page, where the article also states that they had whittled away as much weight as possible so that they could use a reduced-weight battery pack of 845 lb, specifically to stay within the 2600 lb MTOW weight spec for the Nemesis NXT.

There is not much more weight to add, unless the 1500 lb did not include the DC-AC inverter, which would seem illogical. But, before I had excess of 39 lb in my MTOW calculation, and the plane worked fine, and now I am about 55 lb under, so there would be no problem with adding these 55 lb (coolant and oil, perhaps), so we would have the RR Spirit operating at 2600 lb MTOW.

Revised Rolls Royce Spirit of Innovation single seater weights:
Empty weight: 1500 lb
Battery pack: 845 lb (reduced weight battery pack, as the full one weighed 1350 lb, exceeding MTOW).
Sundries: 55 lb (oil, coolant)
Pilot: 200 lb
-------------------------
Gross: 2600 lb (= MTOW)
-------------------------
Dry weight in .air file: 2594 lb

So, I suppose this would sound more logical and more plausible now!:)

Anyway, I hope you have a nice Sunday!

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
I am not so sure you need to include oil in the weight allocation for your NXT.
The reason why is because the standard NXT would also use engine oil. ADI is different. It is something that is NOT regular equipment on the standard NXT, so the plumbing and tanks are additional weight as is the weight of the actual Anti Detonant fluid.

This is a great opportunity to do that "Pilot Sh!t" as the term they used in Top Gun.
Presumably by now, you have a pretty good idea what your speed gradient is for your supercharged NXT.
You know what the rules for the speed runs are. You also know how much fuel you typically have remaining after a couple passes at maximum power over the course. Allow a few gallons for take-off and getting back to the field.... There is nothing to say that you MUST make each flight with a maximum fuel load if you believe that reduced weight will give better performance.
There is a maximum altitude for the speed runs. I suspect you will get best speed toward the upper limit of that altitude range where the air is slightly thinner.
I presume that you are making your speed runs with ADI in use. (Using War Emergency Power.)
I don't know what your protocol is for maximum soeed testing but if it is like mine, it is on Auto pilot.
This is not a great amount of fun, but I do it because it is very repeatable.
Keep in mind that a human pilot usually can't achieve quite the same speeds, so I figure that whatever I get on auto pilot, I deduct about 5 MPH for the shorter sprint for a human pilot and the lack of precision altitude holding. In other words, your regular protocol for speed tests may give you significantly higher numbers than you achieve on the record breaking speed run protocol.
Hope this is useful.

- Ivan.
 
Hi Ivan,
OK, then the extra 60 lb I included would be for only ADI+Methanol-Water. Thanks for the tip.
Also, thanks for clarifying the ADI/Methanol-water issue. It has given this whole exercise a fascinating turn!
I realize now that the record-speed problems I´ve been running into are because I was trying to reach 416 mph with the regular non-WEP engine performance, but after reading your message just now (and some previous ones pointing towards ADI and WEP), I realize I´ll have to implement it after all.
The Nemesis NXT had Methanol Alcohol and anti-detonant, (WEP type 2 in the CFS1 .air file), and obviously didn´t use it all the time, so it activates with F10. It seems that extra MP is required, so I´ll see how much.

It appears that without ADI/Methanol-water, record speeds were also achieved: The latest mention is for is 405 mph. Later, with ADI/Methanol-water, they got to 416 mph, so I´ll try and see what comes out.

At the moment, I have Max Manifold pressure at 38.75, with 2.07 Boost giving 350 Hp, so I´ll go with that to reach 405 mph without WEP, and then add Manifold Pressure with WEP-2 to reach 416 mph. Would this sound OK?

Like you, I find Autopilot very useful for these tests - it makes life much easier!

Update: non-WEP and WEP test results at 5300 ft:
Implementing WEP makes for a great improvement!
-Non-WEP2: With 38.75 MP, gives 350 Hp and 404.1 mph
-WEP2: With MP increase 2.35, gives 383 Hp and 416 mph
This is starting to look very interesting, I´d say. What do you think?

Thanks very much again!
Cheers for now,
Aleatorylamp
 
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Hello Aleatorylamp,
Have you thought about how little weight 60 pounds actually is?
I figure that represents about 4 Gallons or 5 at most of actual ADI fluid (presumably 50% capacity), a holding tank, pipes, and an injector pump. Running out of ADI when running high boost is REALLY REALLY as in engine destroying kind of bad.

I still believe you are giving way too much credit to the standard Nemesis NXT.
I figure at low altitude, I would expect something like 385 - 390 MPH. The record plane is probably better prepared aerodynamically with better paint and polish, so figure on maybe 400 MPH on the standard engine. I don't know what altitude you will achieve this with the standard aircraft, but I don't expect it will be very near Sea Level.
THEN figure that these guys know they will be either racing or trying for records, so most likely be running a higher than normal boost for higher horsepower AND tjey know they will be running at very low altitude.
How high the boost, I don't know.
Here are a couple good indicators:
The Sakae 12 engine on the A6M2 ran at 2550 RPM and 39.76 inches Hg - No ADI required
The Sakae 21 engine on the A6M5 ran at 2750 RPM and 41.73 inches Hg - No ADI required
I suspect the boost for the racing TIO-540 was a bit higher than this if it needed ADI.
Not knowing any better, I would use these as guides for what can normally be accomplished by a mildly supercharged air cooled engine.

I also strongly suggest doing a power vs altitude graph to see what your engine is really putting out and where the actual maximum speed is really being achieved. On most projects, I do a check at 2500 Foot intervals. On yours, I suggest 1000 Foot intervals. This is a quick test, it should not take you more than about 30 minutes and most of that time will be spent writing down numbers in your notebook.

As for actual speed goals, I would shoot for 420 MPH minimum for the record breaker at low altitude. Keep in mind that this is human piloted and that some of the records were closed course runs.

Just for grins, I would also do a quick calculation on how fast the propeller tips are moving.
This plane is using a 6.5 foot propeller, but it is turning at 2700 RPM.
When you have one of the big warbirds, it has a propeller of twice the diameter but the propeller is geared down typically to about 1/2 the engine speed.
Trans Sonic prop tips are BAD. They just burn up a lot of power making noise.

- Ivan.
 
Hi Ivan,
Thanks very much indeed for your comments and suggestions.
There is one thing I didn´t mention: As Jon Sharp´s Nemesis NXT record breaker has paint scheme with nose and lettering in pink, which is not available in CFS1, I chose is the Dan Wright Sharp Nemesis N777XT Sports Class Racer. After much digging, I found a concrete speed reference documented with it: 440 mph at 17500 ft, and amongst the extra equipment installed, I found no ADI.

The first thing I did was raise critical altitude to 15000 ft, and tested the plane with the supercharger and WEP data I had. (Boost Gain 2.07, Max. MAP 38.75 and a WEP increase of 2.35 MAP).
At 17500 ft it was 30.8 MAP, giving only 281 hp and 411 mph,

So, I decided to put in Boost Gain 2.353 and a WEP increase of 2.5 MAP, leaving Max. MAP at 38.75 as before.
At 17500 ft it was now 35 MAP with or without WEP, giving 345 Hp and 440.2 mph, which tallies very well with the N777XT performance data available.

Then I tested performance at 5300 ft and S.L:

At 5300 ft it was 41.2 MAP with WEP, 385 hp and 416.7 mph. Without WEP it was 38.7 MAP, 350 Hp and 403.7 mph.
This would tally with the acclaimed +400 mph no ADI record, and with WEP, the 416 mph record.
Going for 420 Mph I ´m afraid could distort things...

At S.L. (500 ft), it was 41.2 MAP with WEP, 366 hp and 395 mph. Without WEP, it was 38.7 MAP, 332 hp and 382.5 mph.
S.L. performance would now tally with your suggestion of having it a bit below 400 mph.

BTW, the sim conks out the WEP after 5 minutes, because of engine damage, which would also happen in real life, I suppose.

I´d say it´s looking quite good.
Thanks in advance for your comments.
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,
I believe you have just opened a monster sized Can of Worms though you may not realize it yet.
Some are related to your testing process and what you are not testing. Some are more philosophical which ae much harder to argue.

As for testing process, I described a fairly thorough and repeatable process with the thread "Flying Swallow" about the Ki-61 Hien.

Flying Swallow

These are my first tries through the Paint Hangar with this aeroplane. My son Michael says he likes the smaller pattern better. I am not quite satisfied with either one. I think the pattern should be somewhere in between. Opinions? - Ivan.
sim-outhouse.org

Consider what you just stated in your last post:
Dan Wright with his Sports Class racer had the SAME low level speed and record breaking capability as Jon Sharp did with his tuned Record breaking aircraft and could achieve the same speeds WITHOUT ADI equipment. That would mean that Jon Sharp was a fairly poor engineer if he could not figure out that he didn't need Water Injection to get the power he needed for record attempts.
I very much doubt Jon Sharp was a poor engineer in any respect!

Just out of curiosity, where did you get the indication that Dan Wright had the capability for additional boost in his aircraft's engine?
I suspect that he probably did not and that 440 MPH was achieved with a standard engine or perhaps he did an adjusment to his waste-gate for better altitude performance.
For what it's worth, I don't believe the altitude number that is specified in the AIR file for "Critical Altitude" actually has any effect at all.
I believe it is all in the boost numbers.
I also believe you will achieve higher speeds if you make your speed runs at a slightly lower altitude. because 17,500 Feet is clearly PAST your engine's critical altitude. Note that it can NOT maintain sea level boost at that altitude.
This is why I suggested that you do a Manifold Pressure and Horsepower check every 1000 Feet.
Note that on the first page of the Flying Swallow thread, I did exactly that except I was doing it every 2,500 Feet because I was taking it up to about 40,000 Feet. I don't think you need to go that high. This is a VERY quick test.

There is still plenty more to comment on, but this will do for now. I need to get some Lunch.
Hope this helps clarify a few things.
- Ivan.
 
Hi Ivan,
I have the impression that the Critical Altitude entry does work. Set at 12000 ft, power starts dropping off soon after 12000 ft, and raising Critical Altitude to 15000 ft, power starts dropping off soon after 15000 ft.

When I decided to make a piston-driven Sharp Nemesis NXT after the electric RR Spirit, I thought all the piston-engined models had the same engine and performance, and I went for the yellow N777XT because the colour scheme was easier and pink is not in the FS colour pallet. Also, the FS98 jet .air file made it quite easy to get a reasonable approximation.

However, now that I´m trying to do a more exact CFS1 .air file, it turns out that there were also different TIO540 engine models that could be installed. Apart from the 350 twin turbo engines, with or without ADI, there were others, ranging from 250 to 450 Hp.

Jon Sharp´s pink and white record breaking Nemesis N333XT was equipped with ADI, but not always. Some of his records were achieved without ADI (390 and 405 mph), and later some were achieved with ADI (411 and 416 mph). I thought that these speeds could be applied directly to Dan Wright´s Nemesis N777XT as well, but now it seems that this is not the case.

Yesterday I found some specifications relative to Dan Wright´s Nemesis N777XT which I didn´t have before, namely the 440 mph at 17500 ft, and the lack of any mention relative to ADI. To make matters worse, one source had the N777XT with a Lycoming TIO-540-SER, which is a 250 Hp model, and another source stated "Engine Manufacturer: Lycoming TIO540-NXT", and on top of it all, no source states the actual Hp.

Also, one cannot rule out an engine change after a landing accident caused by hot runway wind shears that ruined one landing gear and the propeller (which probably damaged the engine). I can hardly believe this machine doing 440 mph at 17500 ft with a 250 Hp engine, so they must have substituted the 250 Hp -SER for the 350 Hp -NXT, but without ADI.

It is indeed a barrel of worms...

So, I will try and adjust the .air file with non-WEP supercharger/turbo values, but adjust boost gain and max. MAP to get the 440 mph at 17500 ft, keeping 350 Hp at S.L.

Let´s see what happens.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
I was just about to post again a couple hours after Lunch and after taking care of a few chores.

I strongly suggest you test power versus altitude and write down the results with different values of the Critical Altitude record and see if they actually make a difference. I believe we tried that a few years back and it made no difference. It is cool when different fields match though.
There are a few other fields in the CFS AIR file that really don't seem to do anything. One of them is related to Spoilers if I recall.

It occurred to me that you are REALLY trying to construct two DIFFERENT flight models.
The one that is closer to stock and may actually be a stock aircraft is the Dan Wright version.
It should not have any WEP of any kind and its critical altitude is 17,500 Feet at which it achieves 440 MPH.
That means it should hit the same Manifold Pressure at 17,500 Feet (or close to it) as it does at Sea Level and it should not exceed 440 MPH below 17,500 Feet. Unfortunately with the way that CFS AIR files actually work, it WILL probably go a bit faster a couple thousand feet lower.
At that point, you do your best to adjust to best fit the curve so it isn't too far off at any particular altitude in between.

Refer to the Engine Tuning Tutorial for specifics on how to do this.
My guess is that when you finish this, you will have an aircraft that is noticeably slower at Sea Level than what you have now.
This is not a problem. There is a reason Jon Sharp went to all that effort with ADI and probably increased boost in order to achieve his record breaking flights.
As for flights, keep in mind which are closed circuit flights. Figure those are not a real indication of the actual speed of the aircraft because they involve turns to make the closed circuit.
Once you have finished with the Dan Wright flight model, pretend that you are Jon Sharp, Engineer / Pilot approaching a stock aircraft and thinking about what can be changed to achieve the necessary speed to challenge the record.

- Ivan.
 
Hi Ivan,
Thanks again for your answer(s) - and your pacience, of course!
You are right, the Critical Altitude parameter is ineffective - the effect is managed by Boost Gain, so sorry!

Two different models? Well.... not really. I am just trying to get Dan Wright´s non-WEP stock machine to reproduce some of the performance I got with and without WEP/ADI from my previous experiment with the record breaking machine, namely the documented 440 mph at 17500 ft, as well as the +400 mph record Jon Sharp achieved without ADI before equipping his machine with ADI.

Slowly I am getting somewhere. Settings are now: 38.8 max. MAP, and Boost Gain. 2.353, zero WEP.
I must say, performance very much resembles your comments in your last message.

Now results are as follows:
17500 ft: 440.2 mph, 35 MAP, 345 Hp.
5300 ft: 403.3 mph, 38.8 MAP, 351 Hp.
500 ft: 383.4 mph, 38.8 MAP, but only 333 Hp.

I wonder if the 333 Hp at 500 ft is an issue. However, raising it to 350 Hp will cause an increase in Hp at 5300 ft...

Anyway, I think it looks better now, I´d say.

Update: On second thoughts, perhaps it would be more correct to have S.L. Hp readings increased by 17 Hp, by increasing power in the torque curve, so that it reads 350 hp at S.L. according to engine spec, and increase zero lift drag to get the correct the speed again. This way at 5300 ft Hp we would get 368 Hp, and at 17500 ft, 372 hp, but having the correct speeds.

Update 2:
This might be the correct way to go about it, although the 5300 ft mark is slightly lower, but still above 400 mph. The S.L. mark is also slightly lower. It was more difficult than I thought, because apart from torque curve and zero lift drag, also boost gain needed adjusting to 2.38.

17500 ft: 440.4 mph, 35.4 MAP, 370 Hp. (very slightly higher than before).
5300 ft: 401.3 mph, 38.8 MAP, 369 Hp. (slightly lower than before).
500 ft: 380.5 mph, 38.8 MAP, 351 Hp. (slightly lower than before).

What would you think - which of the two would be the most adequate?
Maybe it´s much of a muchness...

Cheers,
Aleatorylamp.
 
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Hello Aleatorlamp,
Glad things are coming together for you.
You remember that earlier I mentioned that there was a bit of a Philosophy Discussion in this as well?
The "Philosophy Discussion" is that what do you choose when you must decide on priorities of
Speed, Climb Rate, and Engine Power?

The way that CFS handles things, often it isn't possible to get all three correct. Some will be more correct and some will be less correct when compared to known values. Maybe there is a way to get everything, but *I* don't know it.
The problem arises because CFS tends to generate pretty much the same kind of power vs altitude curve.
The power at Sea Level will be a certain amount, it will rise to a peak between Sea Level and Critical Altitude and then fall off again.
The data points that we have from specifications normally describe a nearly straight line between SL and Critical Altitude.
So how does one fit the curve that is the actual graph to the straight line in the specifications?
Do you fit the Top and Bottom points and accept that the midpoint will be WAY too high?
Do you fit the curve so that it doesn't match ANY point but isn't far off at ANY point in the curve?

My choice is usually to match the performance as best I can so there is very little that can be exploited and accept that Engine Power will be a little off in various places. As stated before, this is really a philosophy choice. Your choice may not be the same as mine and there is nothing wrong with that.

The reason I keep insisting on recording power versus altitude is that you first need to know what the power curve looks like before you can decide where it is most incorrect and needs to be adjusted. These are simple knee pad recordings of power and manifold pressure versus altitude, not speed runs. The time needed to do each point is probably not more than about 10 seconds waiting for the new altitude reading to stabilize while writing down results of last altitude.

A Test Pilot's Work is Never Done!
- Ivan.
 
Hi Ivan,
Thanks for your nessage. I wasn´t ignoring your suggestion for an altitude vs. power and MAP test, it´s just that hadn´t yet done it because I was still deciding about the kind of super/turbocharging to use, and which power to have at S.L. At the end, rather than choosing the first option I mentioned in Post #35, with 333 Hp at 500 ft, I went for the second one with 351 Hp at 500 ft, and here´s the chart:
(Max. MAP: 38.8 in. hg., Boost Gain: 2.38)

...ft.....in.hg...Power.... speed
500....38.8....351......385 mph
1500...38.8....354
2500...38.8....358
3500...38.8....362
4500...38.8....366
5300...38.8....369 < at Reno Stead, no ADI (specified 405.7 mph for N333XT, and model does 401.3 mph - not bad, as N777XT was no champ. )
5500...38.8....370
6500...38.8....373
7500...38.8....378
8500...38.8....882
9500...38.8....386
10500..38.8....390
11500..38.8....394
12500..38.8....399.......434.2 mph
13500..38.8....403......437.5 mph
14500..38.8....408......440.8 mph > power peak
15500..38.4....406......446.8 mph > manifold pressure starts falling off but power peak rises
16500..36.8....388......443.3 mph > power peak starts falling
17500..35.4....370......440.4 mph > Performance documented for 440 mph for N777XT
18500..34.0....351 > goes back down to S.L. power
19500..32.6....333
20500..31.3....316

I tested a bit further above 17500 ft, just to check that I was getting expected behaviour. The power drop after critical altitude of about 15000 ft is more pronounced, as manifold pressure falls off.

What remains to be seen is what the top speeds are like around the power peak...
Update: I get the unwanted, but now expected power peak giving higher speeds than desired as of 14500 ft. but there´s not much to be done about it.

I´ll probably also do a power vs. altitude test for the first option in Post #35, and see what where the power peak occurs, and happens to speeds there.

Regarding the reference points along the graph that there are to fit performance, in this case there are only two, as no S.L. performance is quoted, only N333XT´s non-ADI performance at Reno with 405 mph, and N777XT´s documented 440 mph at 17500 ft.

Must rush...
Cheers for now,
Aleatorylamp
 
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Hi again, Ivan,
I thought I´d do a similar performance chart for the first option in Post #35,that started wit 333 hp at S.L. and has the nominal engine power of 350 hp at Reno Stead altitude. All in all, results are similar but more discrete, with a less pronounced power peak.

Boost Gain: 2.353 Max. MAP 38.8, lower torque curve.
--------------------------------------------------------
..ft..in...hg...Power
500....38.8....333 Hp...383.4 mph
1500...38.8....336
2500...38.8....340
3500...38.8....344
4500...38.8....348
5300...38.8....351...404.2 mph > Reno Stead. non-ADI N333XT record = 405.7 mph
6500...38.8....356
7500...38.8....359
8500...38.8....864
9500...38.8....368
10500..38.8....372
11500..38.8....376
12500..38.8....380...436.7 mph
13500..38.8....385...441.0 mph
14500..38.8....389...445.9 mph > Power peak
15500..37.9....380...436.7 mph > Manifold pressure starts falling
16500..36.5....363...445.0 mph
17500..35.0....345...440.4 mph > Documented top speed for N777XT
18500..33.6....328...436.6 mph
19500..32.2....309...432.3 mph
20500..30.9....293...427.6 mph

Both power options have their advantages, although one could say, it really won´t matter which one is chosen!

Anyway, it was an interesting exercise!:D
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,
Now you know why I was telling you to do this Horsepower versus altitude test as soon as possible to get a feel for what your engine was doing. From the two listings, there isn't much that I can tell you that you haven't already figured out from reading the listings.
With this kind of graphing, you can at least quantify the effect of the changes you make.
The first listing has a Critical Altitude of around 15,000 Feet.
The second listing has a Critical Altitude of around 14,500 Feet.
The higher the Critical Altitude is, the worse the discrepancy will be at middle altitudes.
Keep in mind that for most of the data points, you are already within 1%.
The rest is really a matter of choice or "Philosophy". You have to determine what you want to prioritize.

- Ivan.
 
Hi Ivan,
Yes, I see... thanks for your analysis!
So lower Boost Gain determines lower critical altitude
These listings work with quite low Zero Lift Drag entries - perhaps justifiable by the sleek surface finish of the Nemesis NXT. For the first listing, in AirEd, it is 19 and in the second it is 21.
At first, with the WEP versions, Boost Gain was 2.0, but I never tested beyond 5500 ft. Then I found that this gave insufficient power at 17500 ft to get the 440 mph needed, so I put in 2.353 and 2.8.
Before keeping one or the other of the two listings, perhaps a third one with Boost Gain at 2.2 is in order, to get Critical Altitude lower still so as to further smoothen the curve with more discrete power peaks, and still give enough power at 17500 ft... I think I´ll try that.
Update: I just did a small trial with the smaller Boost Gain entry, and saw that it also needed higher max. manifold pressure, so I raised it from 38.8 to 41.2 in. hg., but speed was still far from enough at 17500 ft. It would require Zero Lift Drag to be even lower than 19 por 20 in AirEd, which would in turn imply too much speed at S.L., even if critical altitude was remarkably lower, around 11000 ft. Maybe further changing and testing will not be of any good.

Thanks again for your support!
More tomorrow!
Cheers,
Aleatorylamp
 
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