4.33 F-15 ?
-
Hi Folks,
First of all - thanks so much for the humongous effort to get 4.33 out the door - much appreciated - gents…
While I’m far from an expert - I was playing around with the F-15 - as soon as I point the nose upward it starts decelerating pretty rapidly even with the AB on - my understanding is this fighter greater thrust to weight ratio than a 1:1 meaning it should actually be able to accelerate in a vertical climb - am I out to lunch or doing something wrong ?
Thanks…
Regards,
Scott -
That number is derived off the thrust the engine produces at sea level on a standard day. As you climb the engines produce less thrust. So it really depends on where you start climbing and to what degree. Climb out at like 60 degrees and you’ll still get awesome climb performance.
And also, that’s for a clean jet. Not sure if you’re loaded. So try it at sea level, clean, with like half a bag of gas.
-
Hi Folks,
First of all - thanks so much for the humongous effort to get 4.33 out the door - much appreciated - gents…
While I’m far from an expert - I was playing around with the F-15 - as soon as I point the nose upward it starts decelerating pretty rapidly even with the AB on - my understanding is this fighter greater thrust to weight ratio than a 1:1 meaning it should actually be able to accelerate in a vertical climb - am I out to lunch or doing something wrong ?
Thanks…
Regards,
ScottBecause of FM. Simply do not raise your AoA above 22 deg. The amount of extra lift comparing to 22 deg according to FM as I can remember is about 7-8% higher while your drag is almost double.
If you are referring simply clibing with a certain pitch rate. The modeled thrust and drag of F-15 is more than good. I set the empty weight of Streak Eagle and I flew all the recored of SE with well sett fuel qty. The difference between RL and simulated climb records between smaller than 3% even the most extreme case what I did the 30 km climb where you fly from most dense atmoshpehere from low speed at M2.2 at 36k feet before the final climb.
Considering how old and is not AFM the F-15 has good thrust modeling comparing to MiG-21/23 (any variant.)
I still have at least one ACMI (30km clibm) and as I can remember the 10km climb record in video.I can give you the comparsion between game thrust data and RL data of F100-PW-100 thrust curves what I have.
-
F-15s and F-14s turn into “barn doors” when the AoA gets to high-no engine thrust is going to beat the huge amount of drag created when the pitch gets too high.
-
…if the BMS FM for F-15s is still using P&W F-100 curves…the model is well behind the…er…curve.
And I’ve personally witnessed a clean Pratt-powered F-15 accelerate straight up out of a nose vertical stall at an airshow back in the lat 80s…most impressive thing I’ve ever seen at an airshow. Talk about excess thrust…
May the bridges I burn light the way
-
…if the BMS FM for F-15s is still using P&W F-100 curves…the model is well behind the…er…curve.
And I’ve personally witnessed a clean Pratt-powered F-15 accelerate straight up out of a nose vertical stall at an airshow back in the lat 80s…most impressive thing I’ve ever seen at an airshow. Talk about excess thrust…
This depends of fuel level, temperature and speed because of thrust char of F100 + intake.
-
We can make it much simpler for the OP.
If a jet has a thrust/weight ratio of 1.2 (really quite high), F16 has ca 30000pnd of thrust.
it has thrust to weight ratio of 1.2 at a total weight of 25000 (thats 5500 pnd of internal fuel without any weapons)it also means going straight up it has about 5000 pnd left to overcome drag. Thats less then 1/3rd of its dry thrust.
Not really precise and ignoring pretty much all the factors but this ballpark calculation would be a best case scenario
-
This depends of fuel level, temperature and speed because of thrust char of F100 + intake.
Yes…I used to design jet engine components for a living…but the fact remains that I’ve witnessed a Pratt powered F-15 do an accelerating vertical climb in RL, and the jet is capable of such depending on gross weight. Your installed performance data are likely for an NACA standard test inlet or entirely theoretical (or some student project - I have to question the source, looking at this), which isn’t a bad start but still needs to take aircraft GW into account as far as aircraft performance goes.
This is another case where “flight testing” another sim could yield some insight - I’ve had RL F-15 Test Pilots tell me in the past that the FM in the old Janes sim is really good, and that the trouble with the F/A-18 one is that they just took the F-15 FM and wrapped it in a Super Hornet.
What would be really nice is if 3rd party aircraft and FMs could be added to BMS somehow…allowing dedicated teams to contribute detailed models of their choosing. There would just need to be some sort of design/programming interface defined for them as add-ons.
May the bridges I burn light the way
-
F-15 in BMS4 could accelerate in vertical. I really do not understand your problem….
The thrust curves what I linked is not theoretical…This is another case where “flight testing” another sim could yield some insight - I’ve had RL F-15 Test Pilots tell me in the past that the FM in the old Janes sim is really good,
In what Jane’s sim…? Because in Jane’s USAF F-15 was ridiculously underpowered…
What would be really nice is if 3rd party aircraft and FMs could be added to BMS somehow…
Anybody can edit FM because it is a text file just understand the meaning of modeling values and calculate back or get data. Only problem this is not so easy….
-
F-15s and F-14s turn into “barn doors” when the AoA gets to high-no engine thrust is going to beat the huge amount of drag created when the pitch gets too high.
This statement makes no sense. If the jet is vertical and “accelerating” straight up then the AoA is 0. Gravity (the thing AoA is usually combatting) is in a direct line with the thrust. Any AoA and this vertical climb is turning into a slow loop.
-
This statement makes no sense. If the jet is vertical and “accelerating” straight up then the AoA is 0. Gravity (the thing AoA is usually combatting) is in a direct line with the thrust. Any AoA and this vertical climb is turning into a slow loop.
That was just a general comment on AoA vs acceleration capability.
And BTW AoA is not 0 except if you do 90 dg pitch climb but not even that case is 0 technically.
-
F-15 in BMS4 could accelerate in vertical. I really do not understand your problem….
The thrust curves what I linked is not theoretical…
…Hi Molni, the thrust curves you posted are estimated, which in laymans terms means theoretical…
-
Hi Molni, the thrust curves you posted are estimated, which in laymans terms means theoretical…
It is not easy to measure the thrust because you have to measure the weight and accel of of AC, and know the Cd and calculate back the thurst. Another way is measure the pressure (both), cross section. Honestly I do not know how is done but you can find usable and not theoretical thurst data for many engines as they are built in to AC. This mean what I linked is not garbage. Estimated means some percent of error and not “fantasyt thrust”. The lower thrust then dry trust data 100% indicates this. This is the effect of intake loss and speed.
As I can remember I checked the thurst in FM when I got this document and within some percent of error I found this thrust in dat file. So at least in low AoA ranges both the drag and thrust values of F-15 are quite good regardless of other parts of FM. During the Streak Eagle reconrd climbing the highest sustained G was about 2.5G and for a very short time is 4-5G.
If you see a man or woman in front of you you can esetimane his/her height but this does not mean theoretical…
-
It is not easy to measure the thrust because you have to measure the weight and accel of of AC, and know the Cd and calculate back the thurst. Another way is measure the pressure (both), cross section. Honestly I do not know how is done but you can find usable and not theoretical thurst data for many engines as they are built in to AC. This mean what I linked is not garbage. Estimated means some percent of error and not “fantasyt thrust”. The lower thrust then dry trust data 100% indicates this. This is the effect of intake loss and speed.
As I can remember I checked the thurst in FM when I got this document and within some percent of error I found this thrust in dat file. So at least in low AoA ranges both the drag and thrust values of F-15 are quite good regardless of other parts of FM. During the Streak Eagle reconrd climbing the highest sustained G was about 2.5G and for a very short time is 4-5G.
If you see a man or woman in front of you you can esetimane his/her height but this does not mean theoretical…
Wow! Sorry man, no offence meant! Bit too touchy…
-
Yes…I used to design jet engine components for a living…but the fact remains that I’ve witnessed a Pratt powered F-15 do an accelerating vertical climb in RL, and the jet is capable of such depending on gross weight. Your installed performance data are likely for an NACA standard test inlet or entirely theoretical (or some student project - I have to question the source, looking at this), which isn’t a bad start but still needs to take aircraft GW into account as far as aircraft performance goes.
This is another case where “flight testing” another sim could yield some insight - I’ve had RL F-15 Test Pilots tell me in the past that the FM in the old Janes sim is really good, and that the trouble with the F/A-18 one is that they just took the F-15 FM and wrapped it in a Super Hornet.
What would be really nice is if 3rd party aircraft and FMs could be added to BMS somehow…allowing dedicated teams to contribute detailed models of their choosing. There would just need to be some sort of design/programming interface defined for them as add-ons.
ROFL
f15 janes FM is the worst F15 FM ever created in a flight sim.
that is funny because this is because of it you have HFFM and AFM in BMS.
long story short :
in 1997 i performed a few test i janes F15…it was far off on such basic things as top speeds or ceiling capabilities…
i wrote janes and i posted on their forum. they answered me that i was not informed enough nor competent enough to critisize their modeling.
so disapointed by Janes and by the F15 FM is started playing falcon 4.0
in2002, so disappointed about f16 FM i started working on F16. with raptor one…same year i discovered Cat1 limiter was inactive… start of a long love story
-
-
Hi Folks,
Ok - thanks for the info - LOL - actually I didn’t expect so much discussion on my simple question… I’m a real world prop pilot and reading through it all now… I know a real world F-15 driver on another board - I just posed a similar question to him - anxious to see his reply as well - I’ll share it here when he responds…
Thanks again…
Regards,
Scott -
F-15 in BMS4 could accelerate in vertical. I really do not understand your problem….
The thrust curves what I linked is not theoretical…In what Jane’s sim…? Because in Jane’s USAF F-15 was ridiculously underpowered…
Anybody can edit FM because it is a text file just understand the meaning of modeling values and calculate back or get data. Only problem this is not so easy…
Janes F-15 but is was F-15E
-
And I’ve personally witnessed a clean Pratt-powered F-15 accelerate straight up out of a nose vertical stall at an airshow back in the lat 80s…most impressive thing I’ve ever seen at an airshow. Talk about excess thrust…
Unless you were in the jet watching the dials …how do you know it was accelerating in terms of gaining speed? …just because it was gaining altitude doesn’t mean it was accelerating.
-
Hi Folks,
First of all - thanks so much for the humongous effort to get 4.33 out the door - much appreciated - gents…
While I’m far from an expert - I was playing around with the F-15 - as soon as I point the nose upward it starts decelerating pretty rapidly even with the AB on - my understanding is this fighter greater thrust to weight ratio than a 1:1 meaning it should actually be able to accelerate in a vertical climb - am I out to lunch or doing something wrong ?
Thanks…
Regards,
ScottThe T/W weight ratio is a bit overdone…IMO. A stripped down F-15 can scoot, but change that over to a combat ready aircraft, and it’s a bit different. You start loading in all the boxes for threat detection, ICMS equipment, higher fuel loads, etc and you have greatly changed the performance. Plus you take engines that are older, regulated lower on allowable RPM and FTIT, and you have changed the aircraft quite a bit over what you see in those TTC records. In the case of the E, you have 2 different motors, with greatly varied performance between what a -220 can do and what a -229 can. If you watch them in person, it’s ridiculously easy to see the differences between the two. Takeoff distance and acceleration alone are night and day apart.
Once you get into the other aspects, you still get a bit further off just because the AFCS system is nothing like the F-16. You have a greater pitch authority, higher alpha limits, etc. It’s just a limitation, so it is what it is. You can generate all the flight performance data that’s in the -1 and -1-1 charts, but still not really get anywhere close to what they have done with the -16 flight models in BMS. I’m not sure that there is enough available data to do so.
