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Guest Ron Freimuth

Touradg Morassaei's PA28 in FS2K4

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I currently own a 1973 Challenger (Cherokee 180). I'm looking for a MSFS 2K4 model similar to this. The closest I have found is Touradg Morassaei's PA28 Real Dynamic model with a panel from Roger Austli and Ole Egholm. The rpm's are basically good, but it flies too slow. It's off by about 15 or so knots, maybe 20. My plane cruises at around 115 - 120 knots, and this one cruises at less than 100. Also, I am expecting a little more downward pitch when extending the flaps. Does this have to do with the FDE conversion issue I've been reading about? Is there something I can do to maintain the basic flight dynamics and engine rpm levels, but increase the speed (increase power at same rpm's? decrease drag?) and effectiveness or whatever of the flaps? The total effectiveness of the flaps may be ok, but I am definately expecting a little more pitching on extension.The flap issue isn't so important to me, but the speed is definately off.Thanks,Thomas

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Oh, and also, as I've seen somebody else note about the internal pa28, there is an awful lot of down elevator active when the plane is cruising. This could account for a significant amount of drag. What should I do to remove that? Move the CG? I assume then I need to move contact points.I generally like the way the plane handles, it's just too slow by about 10% - 15%, which is pretty significant.

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Ok, if I put in a ton of elevator trim, the elevator returns to a level position and the aircraft picks up some speed. It is now at 120 knots at 2700 rpm. I'm looking for around 115 down to 110 knots at 2450 rpm I believe. It's at 105 now.Is there any way to crank in some elevator trim up front?I notice some parameters for the Horizontal stabilizer. The 180 has a stabilator, is this accounted for somehow? Why do I need to put in so much elevator trim to keep the plane from pitching up? what can be done to correct this?Oh, I also changed the Cdo Drag Coefficient - Zero Lift from 60 to 57.I haven't changed the !FS2K2 Drag Derivatives or !FS2K2 Pitch Derivatives.Thanks

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>I currently own a 1973 Challenger (Cherokee 180). I'm>looking for a MSFS 2K4 model similar to this. The closest I>have found is Touradg Morassaei's PA28 Real Dynamic model with>a panel from Roger Austli and Ole Egholm. The rpm's are>basically good, but it flies too slow. It's off by about 15>or so knots, maybe 20. My plane cruises at around 115 - 120>knots, and this one cruises at less than 100. I did a PA 28 for a commercial product which now has instructions (or some simple app) to transfer to FS9. However, that means I can't send you my FD files. ;)> Also, I am>expecting a little more downward pitch when extending the>flaps. Does this have to do with the FDE conversion issue>I've been reading about? No.>Is there something I can do to>maintain the basic flight dynamics and engine rpm levels, but>increase the speed (increase power at same rpm's? decrease>drag?) and effectiveness or whatever of the flaps? The total>effectiveness of the flaps may be ok, but I am definately>expecting a little more pitching on extension.>Thomas I spent a lot of time on the drags, engine, and prop and set them against tables in the Archer PoH. About all you can easily do is get AFSD from Herve' Sor's site and check the HP. But, you should only see '180 HP' at rated RPM at SL. This means you have to fly low and let the AC get up in speed before HP will reach 180. 10% off doesn't change top speed by much -- about 3%. "Number of Cylinders" and "Displacement per Cylinder", both in aircraft.cfg are the main adjustments for HP. NOT the 'HP' line. Regardless, it's likely 'Cdo', parasitic drag, is too high. Induced Drag should be appropirate if the wing is set appropriately in aircraft.cfg. The "Oswald Factor" should be about 0.70. "parasite_drag_scalar", in aircraft.cfg, could be reduced to increase speed. I'd suggest dropping it to 70% to start. Be sure you base speed on TAS, not IAS. However, higher TAS will also increase RPM. There is a 'prop pitch' line in aircraft.cfg under [prop...]. This could be increased (I assume it is set for Fixed Pitch) to reduce RPM. Flaps Pitching Moment can be changed in the aircraft.cfg [flaps.0] block. Also, the Flaps Lift and Drag scalars. If you aircraft.cfg doesn't have the scalars (they can be left out and '1.00' is used) check other aircraft.cfg files to see what they look like, then add to your file. I put 200 hours on a PA-28 Cherokee decades ago and could have purchased it when our Club disbanded for $4500. :) Ron

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>Ok, if I put in a ton of elevator trim, the elevator returns>to a level position and the aircraft picks up some speed. It>is now at 120 knots at 2700 rpm. I'm looking for around 115>down to 110 knots at 2450 rpm I believe. It's at 105 now.>>Is there any way to crank in some elevator trim up front? Possibly the CoG is off. Otherwise, one has to change REC 1101 "Cmo at AoA=0" in the AIR file (There is a similar parameter in the new AIR file records). Changing "horizontal_tail_incidence" in aircraft.cfg may have a similar effect to the AIR file parameter. Though, some AIR file have the pitching moment for the H Stab set to zero -- in that case it only affects "Lift - H Stab". Normally the tail lift is downward, and adds to the wing loading. That's why it affects speeds. Same for the elevator.>I haven't changed the !FS2K2 Drag Derivatives or !FS2K2 Pitch>Derivatives.>Thanks If the new 'Derivatives' records are in the AIR file it means FSEdit was used. By itself, FSEdit messes up the flight dynamics. Including the requirement for a lot of trim. They can be hand edited, but generally their existance means the originator used FSEdit and doesn't even know what it did. Only the most recent AFSD(s) work with such AIR files. And, I'm not sure it has been released publicly so far. My beta copy doesn't see FSUICP 3.06 when running in FS9. Ron

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Hi Ron,Thanks for the reply.In record 1101 there is a term "Cmo Pitch Moment Coeff at AoA=0 (trim os)"= -21Do you mean that I can decrease this value further to zero out the elevator trim? IOW, does this term add in a preset amount of elevator trim? How does its current value seem, is that high or low or about right? Given its value, should I instead go through the whole file to bring it into balance? As I said, it controls well compared to the other ones I've tried (i.e. LN-ROG), it's just too slow, way too slow as far as I'm concerned.Yeah, I really don't think the problem is the engine power. I think the problem is the airframe setup as regards to drag and CG etc. etc.. What is "The Oswald factor"?I think the flaps are fine now, as I got rid of the excess down elevator, the effect of adding flaps became more realistic to me. I'll definately compare drag scalars, however, though that seems to be cheating to me.Regarding Htail incidence, as I know you know, a Cherokee doesn't have a fixed horizontal tail, so I'm reluctant to change the horizontal tail incidence, in fact I imagine there should be some way that MS takes into account the stabilator and I'd like to understand that better. I would imagine changing the htail incidence to fix the problem here would add more drag and slow the plane down. If I'm going to fudge a fix, I imagine a trim tab has pretty minimal frontal area so provides the minimum drag.Regarding the "Derivatives" records and the fact that this means it was edited using FSEdit. You said and I have heard before that FSEdit screws up files. How? Is it fixable? Can I remove the Derivatives lines? Should I? I am using Aired with the latest .ini file. Regarding your comment about AFSD's, what is an AFSD in this context? I do have FSUICP 3.06 loaded. I don't have any other tools that I am aware of. Point is, I didn't understand what you meant when you said only the most recent AFSD's work...Thanks againThomas

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Cool :-)I don't know how interested you are in my numbers, but here they are:Airplane is set up as Payload is 1-200 lb, 2-130 lb, 3-45 lb, 4-45 lb, 5-95 lbEmpty 1380 lb, GW 2203 lb (Max 2460 lb)It says that thrust @ max throttle, 800 ft altitude is 381 ?(no units) RPM is 2779 (limit is supposed to be 2700, my own airplane is around 2500 I think (It's been awhile since I flew, hope to start flying again in the next couple of weeks)) Thrust Power is 139.6 HP?, Indic Power 246.4, Friction 76.2, Shaft Power 170.2, Prop efficieny .82, J .687, Ct .047, Cp .040.TAS is 119.6 Knots, Wing AoA .33, Pitch .31, CL .291, CD .0487, L/D 5.97, CL Wing .254, CL Elevator -.001, CL HS .038, Lift Slope Fact 1.000, CDp .0449, CDi .0038, CDo .0379.Elevator .18, Elevator Trim -7.22MP 28.09, Boost Gain .967, EGT 1102.6 F, CHT 322.0 F (Are these temps a little high? That EGT is half the melting point of Al)CG %MAC 5.12, CG Offset 12.3 X -.4 Y -1.3 Z.If I pull back to 2360 RPM, 700 ft altitudeThrust 287, Thrust Power 85.7, Indic Power 167.1, friction 61.5, Shaft Power 105.6, Prop Efficiency .811, J .660, Ct .050, Cp .040TAS 97 Knots, Wing AOA 2.10, Pitch 2.53, CL .435, CD .0542, L/D 8.03, CL Wing .403, CL Elevator -.002, CDp .0449, CDi .0093, CDo .0379, Elevator .49, Elevator trim -4.58MP 22.52, Boost Gain .773, EGT 998.3 F, CHT 316.2 FCG %MAC 5.07At about 2400 RPM 1K-2K ft I'm expecting around 110 to 115 knots. This is my target.Thanks :-)Thomas

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Any suggestions of good similar planes that have good numbers for which I could compare?ThanksThomas

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>Cool :-)>>I don't know how interested you are in my numbers, but here>they are:>>Airplane is set up as >Payload is 1-200 lb, 2-130 lb, 3-45 lb, 4-45 lb, 5-95 lb>Empty 1380 lb, GW 2203 lb (Max 2460 lb) So, you have a bunch of young kids aboard. >It says that thrust @ max throttle, 800 ft altitude is 381>?(no units) RPM is 2779 (limit is supposed to be 2700, my own>airplane is around 2500 I think (It's been awhile since I>flew, hope to start flying again in the next couple of weeks))> Thrust Power is 139.6 HP?, Indic Power 246.4, Friction 76.2,>Shaft Power 170.2, Prop efficieny .82, J .687, Ct .047, Cp>.040. Those numbers look good. Shaft HP is 170 HP out of 180 rating. Typical at 800 ft. Prop Efficiency 82% is about right. 85% is about the highest one might see. Many of the other numbers are calculated and engineering related. Perhaps you will get more interested in what they mean and get to understanding real AC performance better. Most of what I understand I learned over years of working on MSFS flight models. For now, the main thing is to understand the main performance numbers and ignore the complex details. Also, be careful of what units AFSD is displaying. It can also give power in ft-lb/sec and some Metric units. Your data is in HP, etc. I think the default. Further, one window gives TAS in ft/sec. The units are displayed, but one might be confused at first.>TAS is 119.6 Knots, Wing AoA .33, Pitch .31, CL .291, CD>.0487, L/D 5.97, CL Wing .254, CL Elevator -.001, CL HS .038,>Lift Slope Fact 1.000, CDp .0449, CDi .0038, CDo .0379. L/D is Lift/Drag. Which also means the AC would glide at a 5.97:1.0 slope at that high speed. That value is rather low. I see 'CDp' is 0.0449. That is high; 0.035 is about right. Dropping it would incrase L/D by about the same percent. CDp is parasitic drag, and since CDo shows 0.0379 there must be 0.011 extra Landing Gear Drag (CDg). I assume the LG is fixed. One could either set its drag to zero and made CDo = 0.035 or leave the LG drag and drop CDo so the sum is 0.035. >Elevator .18, Elevator Trim -7.22 Yes, your trim is rather negative. Though it will generally go somewhat negative at maximum speed; but I like to see 0.0 at cruise speeds. >MP 28.09, Boost Gain .967, EGT 1102.6 F, CHT 322.0 F (Are>these temps a little high? That EGT is half the melting point>of Al) Actually, EGT should be more like 1450 F. The exhaust manifold is steel. 500 F is typically considered the CHT limit, that is Al. In fact, it is much better to keep CHT under 400 F. >CG %MAC 5.12, CG Offset 12.3 X -.4 Y -1.3 Z. The CG is only 5% aft of the wing's leading edge. 25% is nominal. However, if you move the 'wing_leading_edge' forward a foot or so (in aircraft.cfg) your trim will have to be even more negative. As it is, the forward CG would normally requre UP trim. If you load the seats more evenly the CG would also move aft. I suspect the AC is set up (in aircraft.cfg)'incorrectly'. AFSD doesn't display CG correctly in such cases. Nor, is the CG symbol in the FS9 Aircraft Loading menu correct. That is, an AC can be fly balanced, but CG (which is an FS variable) doesn't show appropriately. My comments at the end may help with this problem. My lost reply mentioned changing 'Cmo'. While the value you mentioned was typical, it can be as much as +/- 180 or so to get near zero trim at cruise. If the new records are present, 'Cmo' is given in real units in 'Pitch Derivatives'. REC 1101 is mostly in integrers scaled by 2048. However, changing 'horiz_tail_incidence' in aircraft.cfg should have a similar (but not identical effect). You could try changing it by 1 deg at a time to see the effect. Neg or Pos depends on some signs in the AIR file, so use the sign that works. ;) I see you show "CL HS .038". Normally the tail lift is negative, pushing it down. I expect horiz_tail_incidence is set to some value. Try reversing the sign. That will require even more Down Trim. So will moving the CG back. Adjusting Cmo will bring it to balance, but if you need more than +/- 200 something else is wrong. However, that will increase the load on the wing, which increases Induced Drag. More at low IAS. Decreasing CdoCdp should more than make up for that.>If I pull back to 2360 RPM, 700 ft altitude>Thrust 287, Thrust Power 85.7, Indic Power 167.1, friction>61.5, Shaft Power 105.6, Prop Efficiency .811, J .660, Ct>.050, Cp .040 Note Shaft HP has dropped more than Friction HP. Engines are generally most efficient at full power. However, the FS code keeps engine efficiency constant, something I'd like to work around some day. Engine efficiency is given as Specific Fuel Consumption. 0.46 lb/hour per HP is typical when leaned some. Note gasoline is 6 lb/gallon, so GPH is 1/6 PPH. And, PPH would be SHP * 0.46.>TAS 97 Knots, Wing AOA 2.10, Pitch 2.53, CL .435, CD .0542,>L/D 8.03, CL Wing .403, CL Elevator -.002, CDp .0449, CDi>.0093, CDo .0379, >Elevator .49, Elevator trim -4.58 L/D has increased, correct. Though it should be more like 10 at that speed. Again, Cdp (similear to Cdo, but accounts for LG, flaps, spoiler, is too high.>CG %MAC 5.07>>At about 2400 RPM 1K-2K ft I'm expecting around 110 to 115>knots. This is my target.>Thomas Right, 2400 RPM is typical cruise RPM. However, RPM will increase with the FP prop when you reduce parasitic drag since TAS will increase. To get a good fit to the PoH tables I have to get the prop diameter, pitch, and SHP consistent with the current TAS and weight. I often adjust the prop tables, but one should be able to get appropriate cruies performance with default tables. If you are lucky, just increasing prop Blade Angle in aircraft.cfg will get your RPM back down after reducing drag and trim. I think 20 deg is a typical value, but don't worry about the exact value. In noted the FP prop tables in many FS9 AC don't change for 15 to 25 deg pitch setting. I guess they were set so that range of blade angles has no effect. More or less appropirate since it's a FP prop anyway. To sum things up: CdoCDp is too high. The CG is too far forward. But, horiz_tail_incidence or 'Cmo' in the AIR file will have to be changed to get trim near zero in cruise. ** I have a commented 'aircraft.cfg' at Herve's site that explains how I set the wing leading edge. Also, the reference_datum, etc. ** Moving it forward about 1 ft should move CG closer to 25% MAC. Since MAC is a bit over 5 ft for the PA-28. But, first see what CG goes to with more balanced seat loading. Herve' might make a simplifed AFSD some day so one doesn't get confused with all the detail. But, main effort is in adding still more details. Ron

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"If the new 'Derivatives' records are in the AIR file it means FSEdit was used. By itself, FSEdit messes up the flight dynamics. Including the requirement for a lot of trim. They can be hand edited, but generally their existance means the originator used FSEdit and doesn't even know what it did."Hey Ron, i certainly admire your knowledge and work, but please do not be so sure here...The exsistance of the derrivatives section does not necessarily mean what you are assuming here and your conclusions are somewhat uncalled for.One other reason for the "Derrivatives" in the air file could be that the flight model was developed using Jerry Beckwith's "Flight model workbook" (a great tool btw).Moreover, it doesn't necessarily mean the person who developed the air file "doesn't even know what it did". Besides, i personally prefer to work with derrivatives sections rather than with the values in the Primary Aerodynamics sections in the airfile, for the simple reason that the values in the derrivatives are more natural and don't have to be converted/multiplied by factors for the FS to read correctly. Although must agree with you on the point that FSEDIT, FUBAR's the air files. Cheers.Eugene ShneyderAerodesigns

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>"If the new 'Derivatives' records are in the AIR file it>means FSEdit was used. By itself, FSEdit messes up the flight>dynamics. Including the requirement for a lot of trim. They>can be hand edited, but generally their existance means the>originator used FSEdit and doesn't even know what it did.">>Hey Ron, i certainly admire your knowledge and work, but>please do not be so sure here...>>The exsistance of the derrivatives section does not>necessarily mean what you are assuming here and your>conclusions are somewhat uncalled for.>Eugene Shneyder Correct, most times the new records in an AIR file mean they were added by FSEdit. I know Jerry's 1% SS sets them, in fact I've done a few AIR files with those records myself.Ron

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