Knights of the Sky Foundation

[ZachariasX]

10 hours ago, Holtzauge said:

Now if Chill gets over rated rpm already static I think this indicates either that the Germans who put a 2.62 X 2.3 m propeller on the Dr.1's at the time did not know what they were doing since they put on a propeller lacking the solidity to absorb the power that the engine produced or, which seems more likely, that Chill's engine is producing more power and torque than the average WW1 Oberursel did.

Another point could be is the intended operating altitude of the aircraft. At 4000 m the engine only does 90 hp. Hence a propeller that is „too small“ turn out to be fitting much better. Question is, if you have just one setting for your aircraft, where do you want it to be most efficient.

[Todt_Von_Oben]

18 hours ago, ZachariasX said:

 drag increases to the cube vs airspeed.

 

Wrong.  Squared.  Takes four times the thrust to go twice as fast.

[ZachariasX]

27 minutes ago, Todt_Von_Oben said:

Wrong.  Squared.  Takes four times the thrust to go twice as fast.

You are right, I worded that wrong. I am talking about engine power requirement vs speed increase. We don't know the drag of the aircraft precisely. But we know the power.

[Holtzauge]

@ZachariasX: As far as I know the Dr.1 only had the Oberursel II which is to a large extent a copy of a Le Rhone 9J with IIRC some differences in bore and stroke but should supposedly have had the same power output.

 

Now the problem with the “110 hp” Le Rhone is this: It is often referred to as the “110 hp Le Rhone” referring to its nominal output but IRL it was often run a higher rpm giving higher power. Here are some power numbers for the “110 Le Rhone” in a British Air Board data sheet from 1917: Mounted in a Camel: 137 hp at 1250 rpm. Mounted in a 1.5 Strutter 126 hp at 1250 rpm…….

 

OTOH the Fokker Dr.1 Baubeschribung states the engine as a “110 PS Le Rhone” at 130 PS (128 hp) at 1200 rpm and in the fine print lists a 2.62x2.3 m propeller so I don’t know what to think anymore…….

Edited May 31, 2021 by Holtzauge

[ZachariasX]

3 minutes ago, Holtzauge said:

OTOH the Fokker Dr.1 Baubeschribung states the engine as a “110 PS Le Rhone” at 130 PS (128 hp) at 1200 rpm and in the fine print lists a 2.62x2.3 m propeller so I don’t know what to think anymore…….

I guess they invented engines faster than proper documentation. If Fokker thought of the Ur-II as the engine basically being what Chill has in hands, then it only makes sense that mounting too small of a prop is helpful at higher altitudes. Can you simulate actual power output (rpm) at .75 atmospheric density? Would the engine deliver more / be more efficient with the smaller propeller, and if so to what degree?

 

Your simulations show that the Camel in principle has the edge over the Dr.I at altitude. Yet the Camel is the aircraft that was not appreciated at altitude. I am not aware that the Dr.I has drawn similar criticism. Can this be due to the choice of the propeller?

[Todt_Von_Oben]

3 hours ago, ZachariasX said:

 I am talking about engine power requirement vs speed increase. We don't know the drag of the aircraft precisely. But we know the power.

 

 

Right.  Thrust versus Drag = Airspeed.

 

Generally, if we're flying straight and level at full throttle with the mixture set for maximum performance at that density altitude; and we're getting 100 mph out of 100 horsepower with a fixed pitched prop; we'll need to quadruple the thrust to double the airspeed.

 

Most Instructors I've known would ballpark it by saying "You need 400 hp to push that airframe to 200 mph."  And as long as relative powerplant and propeller efficiency remain the same, that's about right.

 

But we can figure it the other way, too: to determine how much speed we'll get out of an engine modification, for example.

 

Say we install a bigger engine: increasing power from 100 hp to 150 hp (again: with a prop as relatively efficient as the one we had before) we're only going to see 125 mph at full throttle in straight and level flight.  Increasing power by 50% only got us twenty-five additional miles per hour; drag ate the rest.  

 

Either way: since Chill's engine and prop specs are known and the math determining the relationship between thrust and drag is standard; we don't need to calculate the airframe drag specs.  Performance has been demonstrated in flight tests; and performance (speed at that drag configuration) is what we need for the math.  

 

So, with the specs you have on Chill's Dr.1 powerplant and prop; you should be able to very accurately determine (1) how much more power is required to increase speed by a certain amount; or (2) how much more speed a specific power increase will provide.

 

In the case of modifications that yield relatively small increases in power / thrust; drag penalties will absorb most-all practical benefits.  

 

What would more powerful engine mods mean to a Dr.1?  I don't know but I get the impression she would only be a little faster in the sprint; but noticeably quicker: climbing and maneuverering a whole lot better.

 

Edited May 31, 2021 by Todt_Von_Oben

[Chill31]

A brief history of the "110" Le Rhone.

 

It started as the Le Rhone 9J, usable horsepower at 1200 rpm was about 113 after windage from the rotating cylinders was removed.

 

Then there was the "110" Le Rhone 9Jb which was the same engine but with lighter (and more reliable) aluminum pistons replacing steel, which increased the horsepower by a little more than 10.  This is the 120 hp Rhone that the Germans copied, and in my opinion, improved upon as it is over 30 lbs lighter and has a few minor improvements for serviceability.

 

The 120 Le Rhone was used on the FI prototypes in addition to finding itself on a few production aircraft. 

 

Regarding power increases and airspeed increases...

 

Drag is a function of the square of airspeed. To get power required, we multiply drag by velocity.  This means we end up with power req = V2 x V which of course is V3 (cubed).

 

If you have 100 hp yielding 100 mph and switch to 150 hp, you could expect a 12% increase in speed, or 112 mph.

 

1 hour ago, ZachariasX said:

 

Your simulations show that the Camel in principle has the edge over the Dr.I at altitude. Yet the Camel is the aircraft that was not appreciated at altitude. I am not aware that the Dr.I has drawn similar criticism. Can this be due to the choice of the propeller?

Air density decreases uniformly as altitude increases. As the engine has less air to make power, the propeller has proportionately less air to resist it.  The result is that the engine will generally hold the same rpm as altitude increases, with the exception of the aircraft slowing down due to increased induced drag and propeller efficiency losses (both of which cause the propeller to turn slower).

Edited May 31, 2021 by Chill31

[Holtzauge]

3 hours ago, ZachariasX said:

Your simulations show that the Camel in principle has the edge over the Dr.I at altitude. Yet the Camel is the aircraft that was not appreciated at altitude. I am not aware that the Dr.I has drawn similar criticism. Can this be due to the choice of the propeller?

 

The edge is limited to turns at a high Cl where induced drag had a very large impact. In climb the Dr.1 has the advantage in the simulations just as IRL.

[Todt_Von_Oben]

8 hours ago, Holtzauge said:

 

The edge is limited to turns at a high Cl where induced drag had a very large impact. In climb the Dr.1 has the advantage in the simulations just as IRL.

 

 

What does your reference to CI mean?

 

BTW: you claim to be an engineer; are you an aeronautical engineer or is your degree in some other technical field?

 

 

[Holtzauge]

8 hours ago, Todt_Von_Oben said:

 

 

What does your reference to CI mean?

 

BTW: you claim to be an engineer; are you an aeronautical engineer or is your degree in some other technical field?

 

 

 

Yes, I happen to be an aeronautical engineer and if you insist on the details you can find them at the end of this paper on Fokker Dr.1 versus Sopwith Camel turn performance which also explains “Cl” in the context of the Camel.

 

Finally a friendly pro tip: Judge what is written in the forum based on content not credentials. There are a lot of knowledgeable people in the forum who are not professional pilots or aeronautical engineers.

[Todt_Von_Oben]

Holtzauge,

 

When someone asks a simple question, you should give them a simple answer.  And being dismissive and condescending to someone you don't even know is a sign of ignorance; or possibly worse.  You might want to reconsider your approach.

 

FYI: I do judge content.  For example: the thread you recently participated in where ANGLE OF ATTACK (probably the most fundamental aspect of flying an airfoil) was explained as the difference between an aircraft's heading and course.   (I actually laughed out loud when I read that one.)

 

I'm just an old pilot and yet I've seen many red herrings like that in these threads over the past couple months that nobody else noticed; not even you.  

 

I documented it all to share here but I'll do you like you did me: "look it up."

 

I'm out.

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Chill31]

@Holtzauge @Todt_Von_Oben 

 

Gentlemen, I am thrilled to see aviation, more specifically WWI aviation,  stirring your passions! If I may be so bold though...we are all friends here.  It is easy to get lost in the internet and see things 2D, black and white, but really we are people on the other end of these keyboards.   Misunderstandings and misinterpretations are abundant when we can't feed off visual and aural cues.  Let's go easy here!

 

I've put my foot in my mouth more times than I can count on the internet...and after 37 years in aviation (I'm 37 years old, think about that.) I am still learning something new every day. 

 

I hope you fine Gentlemen, as well as anyone else, will continue to participate in our passionate group of aviation enthusiasts and historians on this thread. Go forward softly! If you are right today, you may be wrong tomorrow and vice-versa.  

 

We are all on the verge of a real treat as I get the Dr.I ready for some real testing! Let's have fun with this!

[Holtzauge]

5 hours ago, Chill31 said:

@Holtzauge @Todt_Von_Oben 

 

Gentlemen, I am thrilled to see aviation, more specifically WWI aviation,  stirring your passions! If I may be so bold though...we are all friends here.  It is easy to get lost in the internet and see things 2D, black and white, but really we are people on the other end of these keyboards.   Misunderstandings and misinterpretations are abundant when we can't feed off visual and aural cues.  Let's go easy here!

 

I've put my foot in my mouth more times than I can count on the internet...and after 37 years in aviation (I'm 37 years old, think about that.) I am still learning something new every day. 

 

I hope you fine Gentlemen, as well as anyone else, will continue to participate in our passionate group of aviation enthusiasts and historians on this thread. Go forward softly! If you are right today, you may be wrong tomorrow and vice-versa.  

 

We are all on the verge of a real treat as I get the Dr.I ready for some real testing! Let's have fun with this!

 

Absolutely, and looking forward to seeing those test results @Chill31. Stay safe and don't wreck your engine!

[ST_Catchov]

C'mon you two. 

 

21 hours ago, Chill31 said:

.and after 37 years in aviation (I'm 37 years old, think about that.)

 

Ahhh ....     Hmmm .... 

[J2_Trupobaw]

 

[Chill31]

With new pushrods installed and running full power at 1300 rpm in level flight, my first test run gave me something between 105 and 111 mph.  This test was interrupted by toilet paper cutting ? which was an exciting endeavor to be chasing a roll of toilet paper toward the ground.  The plane will really hit the Gs in a descending turn, sustaining 4-5 Gs easily.

 

Tomorrow, I will not be so easily distracted, and should have some very accurate speed results.

[ZachariasX]

@Chill31, can you measure speeds at lower rpm as well, say 1000 and 1100 (or whatever seems practical or reasonable to you). It would be nice to have that to get a more detailed idea of the propellers efficiency across the rpm range.

[Chill31]

10 hours ago, ZachariasX said:

@Chill31, can you measure speeds at lower rpm as well, say 1000 and 1100 (or whatever seems practical or reasonable to you). It would be nice to have that to get a more detailed idea of the propellers efficiency across the rpm range.

I will do it at 1000, 1100, 1200, 1300

[Chill31]

Ok, so I have done max speed tests using 4 leg GPS groundspeed averaged out to account for wind...I did this on two separate days to make sure my results were consistent...

 

My RPM is indicating 1275 +/- a little and my average GPS ground speed is 104 mph.  Altitude 1800 ft, temperature 26 C, Altimeter setting 30.12.

 

This is not as fast as I expected!  and I now I am very curious about the Camel's top speed...115 seems quite fast, considering they have the same horsepower.  I am easily chasing down other aircraft that are flying in the 75 mph range, and it climbs quite well.  

 

Hopefully, the weather will cooperate this week, and we will conduct some dogfights between the Dr.I and a Warner powered Great Lakes biplane.

[Chill31]

-----------------

I just did some math...I don't think the Camel went 115 mph until it got the BR1. Prior to that, I think it was maybe good for 108 mph with the 130 Clerget and 112 with the 140 hp long stroke Clerget.  In FC/ROF, I think we have a BR1 Camel modeled.

In Josef Jacob's diary, he states about the triplane.... "It is slower than the Albatros DV, and therefore, of little use to sneak up on the enemy at altitudes. Low down, the triplane is extremely maneuverable and equal to any of the English fighters."

 

From this I take it that the Albatross DV should be 110 mph or more as 5 mph is only slightly discernable in the air.

[US41_Winslow]

I’d be interested to see how the British got the top speed of an airplane, because from what I’ve seen, 115 would make sense for the 130 Clerget Camel.  I’ve seen two books that both list Clerget Camels as having a top speed of around 115, Le Rhône Camels being slightly slower, and Bentley Camels going at at 120 or so.  I’m not sure if both books used the same tests, but both give several examples of each type.  Regarding the Albatros, I think that the Camel was faster in level flight but it had an edge in a slight dive.  V. M. Yeates seemed to think both the Triplane and Albatros were better at altitude.

[SeaW0lf]

4 hours ago, Chill31 said:

Ok, so I have done max speed tests using 4 leg GPS groundspeed averaged out to account for wind...I did this on two separate days to make sure my results were consistent...

 

My RPM is indicating 1275 +/- a little and my average GPS ground speed is 104 mph.  Altitude 1800 ft, temperature 26 C, Altimeter setting 30.12.

 

This is not as fast as I expected!  and I now I am very curious about the Camel's top speed...115 seems quite fast, considering they have the same horsepower.  I am easily chasing down other aircraft that are flying in the 75 mph range, and it climbs quite well.  

 

Hopefully, the weather will cooperate this week, and we will conduct some dogfights between the Dr.I and a Warner powered Great Lakes biplane.

 

Hi, Chill, thanks for all the tests. If you could, I do have some questions.

 

1 - Do you think the GPS could be a factor? So every plane now has to be tested with the same GPS, something they did not have in 1920?

2 - The D8 tested in the US in 1921 (Oberursel) reached 1390rpm in its max speed test if I recall correctly. Do you know why the discrepancy, since you are on max throttle?

3 - 26ºC (summer) is a bit too high for the 15ºC ISA standard. The D8 was tested in May in Ohio. Is there a way to convert for ISA?

 

Because on temperature and RPM alone you could gain some numbers. Perhaps you might have a friend with a Spad to ask about his numbers as well.

Edited July 11, 2021 by SeaW0lf

[ST_Catchov]

6 hours ago, Chill31 said:

 

This is not as fast as I expected!  and I now I am very curious about the Camel's top speed...115 seems quite fast, considering they have the same horsepower.

 

Would it not simply be the thinner wings of the Camel, and only two of them vs the three thicker wings of the Dr1? Trading speed for lift.

[Chill31]

2 hours ago, Miners said:

I’d be interested to see how the British got the top speed of an airplane, because from what I’ve seen, 115 would make sense for the 130 Clerget Camel.  I’ve seen two books that both list Clerget Camels as having a top speed of around 115, Le Rhône Camels being slightly slower, and Bentley Camels going at at 120 or so.  I’m not sure if both books used the same tests, but both give several examples of each type.  Regarding the Albatros, I think that the Camel was faster in level flight but it had an edge in a slight dive.  V. M. Yeates seemed to think both the Triplane and Albatros were better at altitude.

Why does 115 make sense for a 130 Clerget Camel?

2 hours ago, SeaW0lf said:

 

Hi, Chill, thanks for all the tests. If you could, I do have some questions.

 

1 - Do you think the GPS could be a factor? So every plane now has to be tested with the same GPS, something they did not have in 1920?

GPS speed averaged out for wind is the absolute in determining true air speed. There is nothing I can do to be more precise than this. 

 

I used 2 independent GPS units to verify this speed.

 

I don't know enough about what they did in the 1910s through 1920s for determining speed to say whether this is better or not, but I can say with great confidence that the Dr1 is not a 110 mph airplane.

2 hours ago, SeaW0lf said:

2 - The D8 tested in the US in 1921 (Oberursel) reached 1390rpm in its max speed test if I recall correctly. Do you know why the discrepancy, since you are on max throttle?

The D8 has only 1 wing! Achim Engles said they uses uses same propeller for the D8 as they did on the Dr.I.  A faster plane with the same prop will turn more RPM. I have it on good authority (TVAL) that the D8 is capable of 120 mph and completely stomps the Camel in dogfighting...

2 hours ago, SeaW0lf said:

3 - 26ºC (summer) is a bit too high for the 15ºC ISA standard. The D8 was tested in May in Ohio. Is there a way to convert for ISA?

True air speed is impacted by seasonal changes in weather, but it isn't going to be a huge change. We are +/- 2 mph on the actual speed of the Dr.I. 

2 hours ago, SeaW0lf said:

 

Because on temperature and RPM alone you could gain some numbers. Perhaps you might have a friend with a Spad to ask about his numbers as well.

I do have a friend with a SPAD 7, but it will be a couple of years before he flies it.

51 minutes ago, ST_Catchov said:

 

Would it not simply be the thinner wings of the Camel, and only two of them vs the three thicker wings of the Dr1? Trading speed for lift.

If the Dr.I is at 104, a Camel with 2 wings plus a bunch of wires at 108  makes sense. Especially when you consider that 115 mph is mathematically attainable with 150 hp if 128 gives you 108 mph.

Edited July 11, 2021 by Chill31

[US41_Winslow]

2 hours ago, Chill31 said:

Why does 115 make sense for a 130 Clerget Camel?

Compared to the speed given for Bentley and Le Rhône Camels, 115 does make sense.  However, the way the British measured airspeed may be off for these tests, so all the measurements may be wrong but the Belgians also got a similar airspeed for the Camel and other 130 Clerget scouts.  I’d be interested to see what the speed the British got for the Dr.1 and if it is higher than the speed that you got.  I do not have much of an understanding of how much different props affect top speed, but could this speed difference be due to the Camel being fitted with a prop pitched for a higher speed rather than the Dr.1, which was fitted with a climb prop?

[ZachariasX]

3 hours ago, Chill31 said:

If the Dr.I is at 104, a Camel with 2 wings plus a bunch of wires at 108  makes sense. Especially when you consider that 115 mph is mathematically attainable with 150 hp if 128 gives you 108 mph.

Thanks a lot for your test, this is very interesting!! I got about the same as power requrement for the Camel based on your Dr.I. But this assumes similar propeller efficiencies and I got my doubts as well about any Clerget Camel going 115 mph.

 

Could it be possible that the steeper Camel propeller delivers more net thrust at top speed? But how much could that be, especially given the considerable power requirements to get an added 10 mph?

 

In either case, I think your data will be important to calibrate @Holtzauge‘s simulations further.

[ST_Catchov]

12 hours ago, Chill31 said:

My RPM is indicating 1275 +/- a little and my average GPS ground speed is 104 mph.

 

This is using the 120hp Le Rhone right? The specs for the Oberursel 110hp FC Dr1 indicate a max speed of 105mph at sea level. So do you think FC's version, all things considered, is about right?

[BMA_Hellbender]

13 hours ago, Chill31 said:

-----------------

I just did some math...I don't think the Camel went 115 mph until it got the BR1. Prior to that, I think it was maybe good for 108 mph with the 130 Clerget and 112 with the 140 hp long stroke Clerget.  In FC/ROF, I think we have a BR1 Camel modeled.

In Josef Jacob's diary, he states about the triplane.... "It is slower than the Albatros DV, and therefore, of little use to sneak up on the enemy at altitudes. Low down, the triplane is extremely maneuverable and equal to any of the English fighters."

 

From this I take it that the Albatross DV should be 110 mph or more as 5 mph is only slightly discernable in the air.

 

The 130hp Clerget 9B produces 130hp at 1200 RPM and can temporarily (up to a few hours) reach 150hp at 1400 RPM in overdrive (sur régime) before seizing.

 

British license-built 140hp Clerget 9Bf (British-French) manufactured by Bentley can hold overdrive indefinitely.

 

http://www.hydroretro.net/etudegh/moteursdelegende_clerget130ch.pdf

 

 

 

 

By comparison: the Bentley BR.1 produces 150hp at just 1250 RPM. I couldn't find a source that states its max RPM.

 

https://collection.maas.museum/object/213286

 

 

In FC the Camel reaches ±1450 RPM which equals 190km/h ASL.

 

 

 

 

At 1400 RPM it reaches 182km/h.

 

 

 

180-185km/h is the speed noted by the Belgians for both the 130hp Clerget Camel and the 120hp Le Rhone Nieuport 23 and Hanriot HD.1.

 

Hence it's quite possible that what we have is a Camel with a Clerget 9Bf that can somehow go above 1400 RPM.

 

On a sidenote: what's the deal with WWI airplanes/engines and adding an F/f to make it better? I demand a Hanriot HD.1f.

 

Edited July 11, 2021 by =IRFC=Hellbender

[ZachariasX]

19 minutes ago, =IRFC=Hellbender said:

I demand a Hanriot HD.1f

Don't cry if you get an HD.1aü.

[Holtzauge]

Interesting trial data @Chill31: I was also expecting a higher speed figure than 104 mph. OTOH the trial was not done at 15 C and you only get 1275 rpm and you should get a few more mph when converting from the 26 C trial temp but that would hardly serve to go all the way to 110 mph I think. I’m also a bit surprised you don’t get a higher rpm than that: The 1275 figure sounds low given that you did not get a much lower rpm static and in a climb trial you did earlier with the "old" rods IIRC?

 

One thing that springs to mind though is that the Idflieg did measure the speeds of a number of German scouts in WW1 and they gave the figure of only 149 Km/h (93 mph) at around 3200 m. This figure and another data point (94.5 mph at 2700 m) has been extrapolated in Rudiger Kosin’s book Die Entw. der Deutch. Jagdf. to 140 Km/h compared to the Fokker firms claimed (and often in books quoted) 165 Km/h (103 mph) at 4000 m.

 

From British Air Board data I have six measured Camel speeds with a Clerget engine and a Lang LP2850 propeller (basically same pitch as Dr.1 at 2.27 m) with speeds at 10,000 ft ranging from 102.5 at 1205 rpm to 114 mph at 1315 rpm. So according to these trials the Camel is fast. Each has a reference to a trial report number so that is reassuring and the only question that remains then is how reliable are the measurements? In my simulations I expect about 3 mph higher speed for the Camel at 1800 m compared to 10,000 ft so this would mean 105.5 to 117 mph at 1800 m if this is added to the Air Board data for Camel at 10,000 ft.

 

What about climb? Maybe you could try that as well? If we get some data from that and you get a high climb speed then things would point towards high drag. OTOH IIRC you did not get the climb rate you were expecting either in an earlier trial (before changing rods?) and in that case one can start wondering about the power output: I mean if both climb and speed are lower than expected then what other reason could there be unless of course the propeller is not as efficient as expected but that also seems strange given its templated from the real thing.

Edited July 11, 2021 by Holtzauge

[Chill31]

@Holtzauge It is interesting indeed!  I am becoming ever more skeptical of their performance numbers from WWI...I did a climb test with the BOM attached, and it climbed from 2000 feet to 3000 feet in 1 minute at 66 mph.  Is it possible I am not getting full power?  Perhaps.  The 120 Rhone should be getting approximately 127 horsepower.  If I take a 20% reduction in horsepower to 106, which would take it from 1200 fpm climb to 1000 fpm climb, I would expect to go from 110 mph to 104... very interesting.  I will look into it more.  I do think I have an induction leak, so I will see if I can find it and perhaps that will account for some of the difference.

 

@=IRFC=Hellbendersee my attached photo for the Clerget rpm limits from the operating manual.

Edited July 11, 2021 by Chill31

[BMA_Hellbender]

9 hours ago, Chill31 said:

@Holtzauge It is interesting indeed!  I am becoming ever more skeptical of their performance numbers from WWI...I did a climb test with the BOM attached, and it climbed from 2000 feet to 3000 feet in 1 minute at 66 mph.  Is it possible I am not getting full power?  Perhaps.  The 120 Rhone should be getting approximately 127 horsepower.  If I take a 20% reduction in horsepower to 106, which would take it from 1200 fpm climb to 1000 fpm climb, I would expect to go from 110 mph to 104... very interesting.  I will look into it more.  I do think I have an induction leak, so I will see if I can find it and perhaps that will account for some of the difference.

 

@=IRFC=Hellbendersee my attached photo for the Clerget rpm limits from the operating manual.

 

Very interesting!

 

I just bought a French Clerget-Blin 9B operating manual and will check if it has the same values.

 

[DD_Arthur]

I've asked this before but never had any sort of clear answer;

 

How exactly were airspeeds and rates of climb measured in the 1914-18 period?

 

How were engine power outputs measured in the same period?

[ZachariasX]

4 minutes ago, DD_Arthur said:

How exactly were airspeeds and rates of climb measured in the 1914-18 period?

For airspeed, most reports describe a system of theodolites maikng the aircraft fly between two known points at various altitudes. Of course, the higher the aircraft is, the less exact the measurement is.

 

For climb, they brought along a barograph that plots altitude vs time.

[Holtzauge]

15 hours ago, Chill31 said:

@Holtzauge It is interesting indeed!  I am becoming ever more skeptical of their performance numbers from WWI...I did a climb test with the BOM attached, and it climbed from 2000 feet to 3000 feet in 1 minute at 66 mph.  Is it possible I am not getting full power?  Perhaps.  The 120 Rhone should be getting approximately 127 horsepower.  If I take a 20% reduction in horsepower to 106, which would take it from 1200 fpm climb to 1000 fpm climb, I would expect to go from 110 mph to 104... very interesting.  I will look into it more.  I do think I have an induction leak, so I will see if I can find it and perhaps that will account for some of the difference.

 

Yes, I was expecting much higher numbers both for climb and speed since as I recall it the first 120 hp Le Rhone number you mentioned was 1220 rpm static. Now if you get that standing still, I would expect both the climb and especially the top speed rpm's to be substantially higher. However, as I understand it you only got 1275 at top speed now so not that much of a difference.

 

Have you tried re-doing the static test to see if you get 1220 now as well? If not then I guess that could indicate that something has happened with the engine since then.

 

About performance numbers with a pristine engine delivering 122 hp, I was based on simulations expecting 110 mph SL and an average of around 1200 fpm between 2 and 3000 ft so substantially higher than what you are now seeing. 

 

Reverse engineering to match the 104 mph figure you measured, I get this if I assume 105 hp in the simulations and with this power I get an average of 890 fpm between 2-3000 ft so quite close to the numbers you calculated for 106 hp.

 

Another thing I can't understand is why you got 1220 static and the manual you posted above says 1150 tops. Sure, that could be (the lower revs static) with a higher pitch propeller but then again the Lang LP2850 propeller was supposedly used by the British on both the Le Rhone and Clerget powered Camels and had a diameter of 2.59 m and a pitch of 2.27 m so an even SMALLER propeller than you now have mounted.

 

Still confused, and now not even on a higher level.........

Edited July 12, 2021 by Holtzauge

[Chill31]

@Holtzauge yesterday, I found my number 7 cylinder has a small induction leak.  I will be checking the rest today. A tedious process.  So I was for sure not getting full power from this engine...I hope there are a couple more with leaks! ? then I might get a lot more power.

 

I will also re check my rpm with the digital light sensing tachometer.

 

The manual above is for the Clerget, not the Rhone, so that may be part of the reason. 

[Holtzauge]

30 minutes ago, Chill31 said:

@Holtzauge yesterday, I found my number 7 cylinder has a small induction leak.  I will be checking the rest today. A tedious process.  So I was for sure not getting full power from this engine...I hope there are a couple more with leaks! ? then I might get a lot more power.

 

I will also re check my rpm with the digital light sensing tachometer.

 

The manual above is for the Clerget, not the Rhone, so that may be part of the reason. 

 

Great news! I don't mean the leak of course but that there is an explanation for what we are seeing and that there is hope for better performance. Fingers crossed that this will give more like 1200 fpm between 2-3000 ft average and that we can look forward to 110 mph at 1800 ft!

 

PS: My bad on the manual: I missed that it was for the Clerget and not the Le Rhone.

[SeaW0lf]

On 7/11/2021 at 5:38 AM, ST_Catchov said:

This is using the 120hp Le Rhone right? 

 

The engine is the Le Rhone 9J, which is commonly called 110hp. The 120hp classification comes from Chill after analyzing the engine. People have to keep this in mind when comparing engines.

 

Quote

So do you think FC's version, all things considered, is about right?

 

The FC version flyes around 160km/h at Summer Kuban, 300m (quick mission). Around the same temp and altitude from Chill if I'm not mistaken.

 

So FC version sounds closer to a Le Rhone 80hp.

 

Edited July 13, 2021 by SeaW0lf

[ST_Catchov]

5 hours ago, SeaW0lf said:

 

The engine is the Le Rhone 9J, which is commonly called 110hp. The 120hp classification comes from Chill after analyzing the engine. People have to keep this in mind when comparing engines.

 

 

The FC version flyes around 160km/h at Summer Kuban, 300m (quick mission). Around the same temp and altitude from Chill if I'm not mistaken.

 

So FC version sounds closer to a Le Rhone 80hp.

 

 

Fair enough, I'm going by the FC stats which list the max speed of the Dr1 at sea level at 169kmh (105mph) with a 110hp Oberursel. So it seems the stats don't match the in-game performance. Come to think of it the Dr1 is not alone in that respect, and I think we've been here before. But it gives us something to talk about while we wait for them to fix the Se5a ....

[Chill31]

The Rhone 9J is rated at 110 hp. The Rhone 9Jb is rated at 120 hp. Both are commonly called "110" Le Rhone, but the Germans definitely made a distinction and reference the 120 hp version as the 120 Le Rhone.  The 120 version is what they copied, and in many respects improved upon, for the Oberursel URII.