P3D v4 Drag in relation to weight

#1
Good morning, everyone,

I would like to be able to increase the drag (decrease the speed) according to the weight on board...! I do have an idea to more or less extend "fictitious" speed brakes, i. e. not visible, depending on the weight...
But would anyone else have a more elegant idea?
 
#3
Because, on a fighter aircraft, depending on the weight on board due to flunts, rockets or bombs, the speed of the aircraft is lower than when the aircraft has no load.... According to the original pilot's manual!
 

Heretic

Resource contributor
#4
If you don't want to use virtual speed brakes, the only other option would be using XMLTools for manipulating the acceleration and velocity variables or using the SimIn SDK for shifting the drag table in the AIR file.
 
#5
Thank you for that quick and accurate answer, Heretic!

It will give me the opportunity to continue my learning of the possibilities of XMLToll, and to get to know SimIn SDK...
 

Roy Holmes

Resource contributor
#6
You should not have to do anything if your loads actually increase the weight. The airplane would the have to fly at a higher AOA for the same speed which increases induced drag an requires a higher power supply.
However most of the good fighter models use variable drag index where a spoiler is extended to increase drag but that movement is not animated.
Roy
 
#7
However most of the good fighter models use variable drag index where a spoiler is extended to increase drag but that movement is not animated.
HI Roy,
This is exactly what I wanted to do, and it was my first idea, because, according to my test pilots, who are all former military pilots, the decrease in speed, especially in climb flight, seems almost nil...
And you think this speed brake method is better than the other two...?
 

Roy Holmes

Resource contributor
#8
It’s a combination of drag and weight.
Drag requires a structured drag index system, similar to that used by real fighters. As you add stores the drag index increases so you increase the amount of spoiler extension based on its drag coefficient per radian to give appropriate drag. Releasing stores reduced drag so that also retracts the spoiler by an appropriate amount.
Weight is increased as you add stores and decreased as you drop them. The weight increase by itself reduces performance without further coding and dropping stores restores performance.
This gives you results that should track with the performance manual.
The drag method requires some clever coding, once you can change actual weight, the rest follows.
Roy
 
#9
I understood, and I more or less see how to solve the problem with a fictitious spoiler. I'll do my tests, and come back, if necessary!

Thank you all for your advice!
 
#11
One of the TacPack users, Corrado, created a package to "TacPack Mod to Any Plane" . It's freeware, and available here: http://www.isoliti4gatti.it/warbirds/Tacpack.htm

You don't even need to buy TP to download and examine it, but you will need TP to make it functional. It's located at the bottom of the P3D section/top of the FSX section.
The point being, Corrado wrote some really excellent xml gauges. Two of them are involved with adding weight and drag (using the plane's spoiler, invisibly!). You might get some ideas on how to use XML coding to add weight and drag to a plane as you add or remove ordnance, fuel tanks, and so on. I'm not saying to use Corrado's code word-for word, at least without his permission, but you might get some ideas on how to accomplish what you desire.

Hope this is some small help...
Pat☺
 
#12
The only drawback with the spoilers is that they only work correctly with a symmetric loadout.
This is generally the case for fighter aircraft....

One of the TacPack users, Corrado, created a package to "TacPack Mod to Any Plane" . It's freeware, and available here: http://www.isoliti4gatti.it/warbirds/Tacpack.htm
Very interesting! Maybe I'll take inspiration from it... But it doesn't seem extremely complicated to me to set an invisible spoiler according to weight.... I'm already working on it!

Thank you all for your very useful feedback!
 

taguilo

Resource contributor
#13
Hi,

Very interesting! Maybe I'll take inspiration from it... But it doesn't seem extremely complicated to me to set an invisible spoiler according to weight.... I'm already working on it!
The invisible spoiler solution works really good. You can apply many different formulas for different drag conditions in different situations (on ground, in normal flight, icing, etc).
And when you want assymetric effects in flight, using XMLTools (or any other Simconnect gauge) acting on ailerons/elevators you can trigger wings drop, nose drop, rise, etc to achieve whatever effect you want/need. It might be a little tricky to code/test first time, but becomes rather simple once you get the idea on how it works.

Tom
 
#14
And when you want assymetric effects in flight, using XMLTools (or any other Simconnect gauge) acting on ailerons/elevators you can trigger wings drop, nose drop, rise, etc to achieve whatever effect you want/need. It might be a little tricky to code/test first time, but becomes rather simple once you get the idea on how it works.
Hi Tom,
It's funny, I was just reviewing the possibilities of your very useful XMLTool. Thanks again for this gauge!
Un fuerte abrazo y hasta pronto!
 

Roy Holmes

Resource contributor
#16
A/A missiles are light in weight and low in drag. Firing one has very little effect on airplane performance and almost zero asymetrical effect.
It things like bombs that slow you down, limit turn and climb performance and increases fuel consumption.. Usually you drop them in twos to minimise asymetrical effects, but even if one hangs the airplane is only minimally affected. On a weapons test flight I dropped four 1000lb bombs, one at a time from a F-4 and it was completely controllable through all four patterns. The bombs were on wing stations.
Roy
 
#17
There is an easier way to do this and do it correctly. If you use a spoiler you will affect all the wrong aero characteristics. Add fuel tanks with no useable fuel. For example, to model a 1000lb payload, position the tank using the X,Y,Z coordinates in the air file and set total and unusable quantities to 1000.

Then using a fuel gauge or simconnect, set it to read the presence of the item and set the tank full if present or zero if not. This will load the wing center of lift, the trim and control surfaces, and all the other things the are needed to create accurate simulated flight dynamics from the model....assuming the air file is accurate in the first place.

All that being said, I have never tested the payload system to see if it models weight correctly, but I will say this...

IF the sim is adding the correct weight to the aircraft when weapons are added, and in the correct position, AND you're performance is different from the real airplane, then YOUR flight dynamics are wrong. The sim is a math engine using real world math. It only has a few specific bugs that the original ACES team got wrong. All the fundamentals are 100% correct and when the air file is correct the airplane will output identical data to the real airplane within 1 or 2%. Using trickery like invisible spoilers should never be needed unless the function is outside the scope of the sim....otherwise you are getting further from accuracy than you think.
 
#18
Ideally you need to be able simulate whether a weapon has been loaded into an internal bomb bay, or hung in the air flow, e.g. F-111.
Same weights, totally different extra drag (especially when supersonic).
 
#19
All that being said, I have never tested the payload system to see if it models weight correctly, but I will say this...
I also wonder if the weight is really taken into account correctly, especially if the loads are all external (bombs or flunts for example...). But when I see the reports of my test pilots, and I read this.... :

However most of the good fighter models use variable drag index where a spoiler is extended to increase drag but that movement is not animated.
... it seems that, indeed, something needs to be done for the model has, in particular, a lower climb rate! Because as far as my model is concerned, although I am not yet a huge specialist in the .air file, I have the impression that it corresponds quite precisely to the technical data of the original aircraft!

But all your feedback shows that, even if the mathematical elements of FSX are extremely precise and correspond to reality, the lack of official information (FSX or P3D) on the use of the .air file allows interpretations... according to everyone's experiences!

In any case, a big thank you to all of you for helping to complete my knowledge!
 
#20
"the lack of official information (FSX or P3D) on the use of the .air file allows interpretations "


These interpretations ARE the problem. I'm almost certain your jet suffers from excessive thrust. There is an exact amount of thrust that must be produced for a given climb rate because level flight drag (thrust required) does not change in the climb. In order for your sim airplane to out climb the real airplane, but maintain the same level flight speed as the real airplane (at the same thrust setting), your airplane has a mismatch in the drag balance and the thrust table has been fudged to compensate.
 
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