Not sure if there is a fix for this issue, but here is the model and then the problem.
Handley Page HP 42 (FSX version) (Original file is HP42vX.zip) . This aircraft was originally fitted with 9 cylinder Bristol Jupiter engines with a low compression ratio and a fixed pitch prop.
I have been reworking some aspects to correct some data via the cfg. file. This has caused no issues and actually improved the general handling to more realistic levels.
The major issue I have is this: The Engine RPM on the gauge over reads by 100%, so instead of idle 500RPM, it shows 1500, 1000 RPM the gauge reads 2000 and maximum RPM which should be 2200 RPM is 3200. I have set the correct HP, cyl displacement in the config file but it changes nothing. I have looked at the gauge xml and can see nothing there that would cause this error. I have played with the scalars for piston engine friction (up and down below 1.0) to no avail and no good change.
I am sure this is not a gauge issue because the gauge merely takes its dynamic data from the main data files. That the aircraft, is as far as raw data, is concerned is developing way too much power, the aircraft take off and flight acceleration is excessive and the speed of the aircraft is also way to high, it accelerates though 80 knots like a fighter and quickly is climbing at 2000 fpm at about 130 knots which of course is completely ridiculous for a low powered heavy biplane like the HP42, which lifted off at 60 climbed at about 70 and cruised at about 90 knots max with a max rate of climb about 500-700 fpm. It was as Anthony Fokker originally described it an aircraft with built in headwinds. I have cross checked all the data in the cfg and can see no significant issues and it all tallies with the original aircraft and engine data I have been able to find.
Are these parameters for power etc actually set via the .air file or via the .mdl file? I am a bit stumped at the moment as to how to fix this. It ruins what is otherwise not a bad sim model.
The values for setting engine power & propeller efficiency are in the .air file, tables 508, 509,511 & 512. The other setting for the prop pitch is in the aircraft.cfg file.
To massage the tables 511 & 512 it is best if you download Herve Sors AFSD program for your appropriate FS. You can then run this looking at the engine parameters & fly the model simultaneously. With a fixed pitch prop do not try to get the expected max rpm & hp when static.
Make sure that you have set the config engine, fuel & prop scalars =1 before starting.
Its a lot of trial & error, so I hope you have kept a copy of the original cfg & air files.
Good luck
Keith
Thank you for that, I was unaware of that program have downloaded it and we will see what it has to say.
Getting original data on this aircraft and its engines has been a real challenge and some bits allude me, like the propeller correct length and pitch. There are a couple in museums but so far no response from them on this. I am sure the prop data is wrong as well.
Dev One. Thanks again, I found a nice little airfile editor program (FS98 vintage) that works just fine with FSX tables and sure enough the power and rpm values were way out of whack.
After a lot googling I managed to fine some old 1920's and 1930's engine test data on the Bristol Jupiter engine and even a report on the HP 42 by NACA in the US which was invaluable.
These have all been adjusted and tested and the HP 42 is now performing like I estimated it would. It still accelerates a little too quickly for a big biplane but I have no idea how FSX deals with biplanes. Alas as only 9 were ever built no pilot notes but the designer of this particular model incorporated a feature which I am really surprised with which is the automatic slat/slots on the top wing which deploy at 60 mph for landing and take-off which I thought was very clever (not sure how it was done). I am now just getting used to flying the beast and working out power attitude settings to handle it correctly based on the rare film footage of it taking off and landing, etc. It is quite weird in FSX doodling along in FSX at 60 mph (50 knots). Really gives you an appreciation for early aviation.
And I have learnt a lot about how the FSX engine interacts with the mdl, the cfg and air files.
Real world prop pitch is defined as the helix length, so is normally in feet at (IIRC) 75% dia, whereas FS quotes it as an angle in degrees, so RW data not much good.
If she is accelerating too quickly, then one needs to adjust the 508 & 509 curves below the static rpm achieved, there aren't many points to fiddle with. The other more complex route is the prop efficiency/RPM curve which is where the AFSD program helps as one can hit pause & at any one particular value of rpm it will show the value of 'J' which one can then modify in the table.
Anyway glad you have nearly got the performance to your liking, well done.
As for the automatic slats/slots, they were designed by Frederick Handley-Page, & were fitted to lots of 30's aircraft, the Tiger Moth for example has them.
BendyFlyer, since you seem to enjoy fixing up and improving aircraft, why not invest a few dollars in the Airwrench utility.
As long as you have good data about the aircraft engine and performance, you can easily generate proper flight models for these aircraft that hits the performance numbers in all flight phases.
Afterwards you can tweak the flight model for the handling you think is most appropriate for the make.
Now there is also packaged with that utility an GUI interface that allows tweaking by air file table with just point and click on graphic interfaces.
Aircraft Engine Data and Modification
Reply With Quote
Bookmarks