|
Author
|
Topic: A WWI FM question
|
silas
Pilot
|
posted 02-04- 11:48 PM
   
With all the interest in WWI planes I just had a question about the FM of the Sopwith Camel and the gyroscopic forces that were generated by the interaction of the engine, aircraft speed and control input.
The plane had very different turn rates when turning left or right. Some pilots made all turns to the right because the plane could turn 270 degrees in a right hand turn as opposed to only 90 degrees in a left hand turn in the same amount of time. The Camel was much faster right turning.
Can this be handled by OP. Just wondering? ------------------
silas
Fortune favours the brave.
Demon's Runway
[This message has been edited by silas (edited 02-05-2000).] IP: Logged |
Sv
Pilot
|
posted 02-05- 01:13 PM
From what I have seen so far, engine tourque can be very well modeled, but there are no gyroscopic effects  We may indeed be able to do some very creative FM stuff to "simulate" this though. Maybe a hidden airfoil that is attached to the throtle, the higher the throtal the more it forces the plane to the right. Using the fuselege foil I use for enhanced rudder efrfectiveness I can simulate the tourque kinda, well maybe. Would the gyroscopic effect cause a constant yawing force, or only when the engine RPM is accelerating? I am not too good with understanding gyroscopic effects. Could the force somehow be tide to the throttle setting in any meaningful way? Just thinking...
------------------
-Sv =FC=
WWI in SDOE!
IP: Logged |
Maury Markowitz
Pilot
|
posted 02-05- 01:25 PM
I've always been curious about the turn issues too. Is the idea to "work" the plane against the precession of the engine to "force" it around?If so, shouldn't any of the planes with the rotaries have pretty much the same sort of bonus? Or was their something about the camel's design that made it more effective? Maury IP: Logged |
silas
Pilot
|
posted 02-05- 01:51 PM
From what I have read all rotary-engine planes had different left/right turning, but the Camel was to the extreme. In left turns the nose always pitched up, in right always down. Without lots of rudder to correct it would spin. The elevator was powerful and sensitive but the rudder was too small and not very effective. According to one test pilot, W/C Paul Hartman RCAF, the Camel has no "dynamic longitudinal stability" in steep turns. It needed constant control input.Accelerating caused the nose to climb and swing to the left, there was no trim adjustment on the plane. The plane needed constant forward pressure to fly level. When entering a dive the plane yawed left, correcting this with the rudder caused the nose to pitch down sharply.. By today's standards the plane was totally unacceptable yet it was piloted by young men with less than 100 hours flying time to lethal effect. When this plane is completed, it's going to be "fun" to fly. ------------------
silas
Fortune favours the brave.
Demon's Runway
[This message has been edited by silas (edited 02-05-2000).]
[This message has been edited by silas (edited 02-05-2000).] IP: Logged |
Tailslide
Pilot
|
posted 02-05- 02:13 PM
In WW2 this affected planes as well. The direction the engine rotated affected tactics, particularly which side was best to attack from since the planes turned better in one direction than the other. I have to disagree with SV about the gyroscopic effects. Take a plane straight up full throttle until you are almost stopped for a very sweet example of a torque roll. TS
IP: Logged |
Sv
Pilot
|
posted 02-05- 02:31 PM
TS, that's not a gyroscopic precision effect, is it? That is just engine tourque and prop-wash, right? I would say in that cae it is prop-wash. In order to have a rolling tourque from the engine you need a change in the engines angular momentum - acelleration of decelleration the engine RPM.Prop wash is quite noticeable in SDOE... But gyroscopic precision is a result of a force on a gyroscope - the force is directed in perpindicular to the initial force direction, like silas's last post. This is not modeled in SDOE, right? -Sv IP: Logged |
silas
Pilot
|
posted 02-05- 02:57 PM
Sv, I also think the weight of the engine, guns, and the pilot all being concentrated in he first 7 feet of a 18 foot fuselage had an effect on the handling. You had the propeller attached to the engine crankcase and the engine attached to the crankshaft and the crankshaft attached the to the plane, than the propeller and engine revolving at more than 1250 rpm. It all reminds me of a colossal kids spinning top. ------------------
silas
Fortune favours the brave.
Demon's Runway
[This message has been edited by silas (edited 02-05-2000).] IP: Logged |
Tailslide
Pilot
|
posted 02-05- 05:00 PM
It's not prop wash SV. Prop wash is not modelled, its just hard coded in the airfoils on the plane and you see autorotation even on planes that have no prop wash specified. TS IP: Logged |
Sv
Pilot
|
posted 02-05- 07:26 PM
Then what is (airWash ('prop .9)) doing on the horizontal stablizer? What does this do?-Sv IP: Logged |
Mirthain
Pilot
|
posted 02-05- 11:39 PM
Interesting if propwash is not modeled since I can see a marked difference in plane handling with the engines at idle, or with some thrust... and I am talking a P-38 in a shallow dive at over 200 MPH.
Torque and a "Gyroscopic" effect are going to be confusing to a pilot that doesn't understand the difference... bear in mind that for the most part pilots in WWI weren't like pilots today... mostly just gutsy guys that had more cajones then sense.. ;} They weren't the warrior scholars in the cockpit like they are today....
The P-51 will snap your head off going into a right hand turn and if you weren't ready for it it would hurt you.... That is something that is well known about the 51. She didn't turn into the left as well, but coming into the right bank she just snapped over.... The gyroscopic effect is going to be evident at the start of a flat turn or pull up or push down... whenever you start trying to move the gyro out of the plane it is in, once moving though, it will move right along, till you go to stop it. Then force is required to stop it.. but the gyro effect can be thrown off by just slowing the prop.
From what the report of what the pilot is talking about, it is engine torque.... not a gyro effect.
------------------
Mirthain=FC=
 IP: Logged |
Michael
Pilot
|
posted 02-06- 01:24 AM
I do not believe the simulation models gyroscopic effects (as distinct from torque). I've modelled a rotary engine by giving the prop the weight of the engine and it makes no discernable difference. I suppose I could have an additional invisible rudder and elevator that are cross linked to the real elevator and rudder. But how could I link the amplitude or effectiveness of the hidden control surfaces to engine rpm? Could you switch in different airfoil files (for the hidden foils) based on the position of the RPM guage? Any ideas?I have lots of detailed information on the Camel's flight characteristics (including the notes of W/C Hartman refered to above), so I know the exact effects desired. I had actually given up on trying to model the gyroscope thing until reading SV's post about the hidden airfoil idea. I think something could be made that way that would work. [This message has been edited by Michael (edited 02-06-2000).] IP: Logged |
Sv
Pilot
|
posted 02-06- 07:40 AM
Michael,I have no easy answers, but I will tell you that you can rotate a hidden airfoil via the throtle setting, not rpm - but it is close - even the sound of the engine is tied to the throtle, not the RPM. Just make a parent LODless object that is of type 'CDial. Now point it to the qryThrotle setting. Now make your airfoil a LODless child of the dial parent. I would copy the horizontal stabalizer - you need to get the airPnt the right way. Now add the rotate DOF to the CDail part. You don't need to hind them if they have no LODS. (just delete the LODS of both those parts) Now when you change throtle the airfoil will rotate and alter the force vector of it's lift/drag. I used this to create a fuselege airfoil that made the rudder more effective. It works perfect for positive and negitive AOA - and the horiz stab uses a semitrical aitrfoil so you get even response in both directions. Now just fool with airArea and the DOF min/max until you get the desired forces. I think this can be done unless the direct relationship of the forces, throtle and airspeed are not close enough to the desired results...  Keep us posted! Let me know if you need help, this sounds cool! -Sv IP: Logged |
Michael
Pilot
|
posted 02-06- 02:47 PM
Why can't it be tied to rpms? the rpm gauge queries the engine speed, not the throttle setting (although the effect would be similar). But anyhow I don't want to link the movement back and forth with the rpms. Rather, when the stick is pulled back, that should cause the nose to move to the right and to the left when the nose is pushed down with the stick. I would link the hidden rudder to the fore and aft movement of the stick. But what I also want to do is have the strength of the hidden rudder force (in either direction) vary with the engine rpms (or throttle if necessary). And that's the part I'm not sure is possible.IP: Logged |
Sv
Pilot
|
posted 02-06- 05:17 PM
This brings up a question - I think that SDOE only models vari-pitch props - notice that the rpms don't go up with the throtle movement, it just bumbs and falls back. Idle is less - anyway it looks like a vari-pitch prop RPM. Is this indeed the case?I think what we realy need to tie it to is yaw and pitch angular change. There is a query for turn rate in degrees per second. If you used that to drive an elevator-like airfoil it would give you part of the gyro effect - push the rudder and the tail raises or lowers. I don't think there is a querry for pitch change though Another problem with this whole airfoil approach is that it is speed dependent, the gyro effects should not be. But I guess it is a close match - you cant turn the plane as fast at slower speeds so the gyro effect will never be initiated. What we really want to see here is this right? Rudder input causes pitching forces on the plane (in addition to the yaw), and elevator inout causes yaw forces (in addition to pitch) This being the case I think we could, as you suggest Michael, tie a rudder-like and elevator-like airfoil to the stick input. What would be the ill sideffects here? Drag is one - gyro forces would not add drag... many more? -Sv IP: Logged |
Michael
Pilot
|
posted 02-06- 08:03 PM
SV, you can have a fixed pitch prop. In OP studio just display the props properties and change both min and max pitch to the same value, say 25 degrees for example. On the gyro topic, I would set the hidden foils to zero drag. They would also have a relatively small area and the effect of engine rpm could be simulated in part by cranking the propwash effect up to the maximum. [This message has been edited by Michael (edited 02-06-2000).] IP: Logged |
HAROLD
Cadet
|
posted 02-06- 10:00 PM
T.O.M. Sopwith designed the Camel to use the gyrosopic force. His previous plane,the Pup was said to be joy to fly. The Pup's rotary engine was mounted far ahead of the center of gravity,where the camel's was almost right on it. At take-off's the camel pilot had to be quite careful for there was no room for correction.IP: Logged |
Tailslide
Pilot
|
posted 02-07- 11:22 AM
>Then what is (airWash ('prop .9)) doing on
>the horizontal stablizer? What does this do? Like I said, it's not modelled you have to hard code it into the plane. If a plane doesn't have a line like this it has no prop wash at all even if you have a dozen propellers pointed at an angle to your rudder. Even if it does have this line since you haven't specified an angle it just makes the controls more effective at low speeds but the air is not at an angle to the airfoil. Planes that do not have this line included still autorotate. Is that any clearer? TS [This message has been edited by Tailslide (edited 02-07-2000).] IP: Logged |
Sv
Pilot
|
posted 02-07- 11:29 AM
I see, I just didn't cosider the airWash a hard-coded thing, I see what you mean now - it is not automaticaly modeled based on aircraft set-up.Thanks TS Wow Michael, cool about that fixed prop thing! I just assumed you couldn't since the Fokker DR1a came with the vari-prop. I just looked, it is like this: (propMinPitch 0)
(propMaxPitch 65) This is great news for WWI planes! Now I can fool with this... no more vari-pitch! -Sv -Sv [This message has been edited by Sv (edited 02-07-2000).] IP: Logged |
Whirlwind
Pilot
|
posted 02-07- 02:46 PM
Whatever happened to someone adding a hidden object with a cylendrical obInertia property (something like that, haven't got the dock's handy) set as the prop, and have the prop attached to that to simulate a rotating engine? Someone tried that once...IP: Logged |
Tailslide
Pilot
|
posted 02-07- 03:08 PM
I find that the WW2 single engine planes turn better to the left.. is it just me? IP: Logged |
Michael
Pilot
|
posted 02-07- 03:59 PM
Whirlwind:I tried that and aside from an engine that was very slow to rev up, there was no discernable effect. IP: Logged |
Tailslide
Pilot
|
posted 02-07- 05:46 PM
This sounds like a good candidate for a patch if the semi open source thing goes through.. TS IP: Logged |
Whirlwind
Pilot
|
posted 02-08- 06:34 AM
Michael,Does that mean we can assume other forms of momentum aren't modelled? Logically, that should have worked. IP: Logged |
Sv
Pilot
|
posted 02-08- 08:35 AM
Slow to rev up = momentum modeled.It just seems that gyroscopic precision is not modeled - that is a whole other beast... -Sv IP: Logged |
Whirlwind
Pilot
|
posted 02-08- 09:06 AM
There goes the gyroscopic sight I was going to put in the Viper. I was planning on putting a second gun site on the nose with a quick view assigned to simulate a gun cam.IP: Logged |
FSIC Messageboard
UBBFriend: Email This Page to Someone! 
