blue_six

Thanks for this Sokol1_br, but blimey, don't you have something else you should be doing on Christmas morning? And for that matter, why am I here too? Blue six out.

Hi fenderplayer, I see what you mean. In the sim, pushing the idle cut-off lever forward before priming seems to deplete the fuel pressure you've built up with the boost or wobble pump - the low fuel pressure warning light comes back on 1-2 seconds after to lever goes forward. I think this explains the subsequent no start. Whether or not this modeling is representative of the RW remains open to discussion. Not a biggie to most of us, but the purists likely would disagree.

In its description of the fuel system, the RAF Pilot's Notes for the aircraft indicate that the "blister" auxiliary fuel tanks feed the engine direct, rather than being plumbed through the two main tanks. The two main tanks, just ahead of the cockpit, can be pressurized at altitude if needed. This is controlled by the fuel tank pressure cock. The source of the pressure is the oil separator on the aircraft's vacuum system.

Hi Roblex, the confusion here is traceable back to some loose terminology in the DCS Flight Manual. When the FM says to have the "fuel boost valve" turned OFF, what they are actually referring to is the fuel tank pressure cock, found below the instrument panel on the right hand side. They are not talking about the fuel boost pump. As Sokol1_br notes, the fuel boost pump can be switched ON briefly instead of using the wobble pump during the start-up sequence, but must be switched OFF again before start-up. Once the engine is running and adequate fuel pressure is confirmed, the boost pump should be switched ON again, and left on for the remainder of the flight. Again, the FM is weak in this regard.

For Redglyph, I found the fuel pump, boost pump and wobble pump situation pretty confusing at first, but think I've got my head around it now. Having gone through the RAF Pilot's Notes (PN) and the DCS Flight Manual (FM), here's my take on it: The fuel pump shown as item 5 on Figure 41 in the FM is the engine driven fuel pump discussed at paragraph 2 of the PN. The rectangular shape shown at the bottom of the lower main fuel tank at Figure 41 in the FM, drawn in dashed lines but not labeled, is meant to represent the electric boost pump. As discussed in the thread Sokol1_br mentioned, the electric boost pump eventually replaced the wobble pump as a device to raise fuel pressure at the carburettor for start-up and to ensure steady running while switching between external and internal tanks. Three configurations are possible: wobble pump only, wobble plus boost pump, and boost pump only. The version we have is the interim one, with both wobble and boost pump. The boost pump is definitely there: in a cold start, you can hear it when you switch it on (keyboard zero will toggle it). Using the boost pump instead of the wobble pump during start-up, you will see the low fuel pressure warning light extinguish within a second or two of the boost pump operating. Although the FM currently focuses on using the wobble pump during start-up, a good start can be achieved in the sim using the boost pump instead. It appears it's not essential to run the boost pump for the full 30 seconds recommended in the PN, at least in the current cold start instant action mission. I've had good starts even when I switched the boost pump off as soon as the low fuel pressure light went out. I believe the FM and Quick Start Guide need revision to bring them into better compliance with the PN in this area. Figure 41 needs attention – the boost pump (item 19?) should be added to the legend and the upper and lower main tanks (items 17 and 18 should be labeled on the diagram. The start-up process should include description of using the boost pump in lieu of the wobble pump, as presented in the PN. Note that the boost pump is to be switched back ON during engine warm-up, once you confirm that the low fuel pressure warning light remains OFF, and the boost pump remains ON for the remainder of the flight. This item should be added to the warm-up, before take off and landing check lists in the FM/Quick Start Guide. NOTE: item (iv) in the FM "before take-off" check list reads “fuel boost valve in the OFF position.” This is referring to the tank pressurization valve, not the boost pump – see para 8 page 140 in the FM. To alleviate confusion, it would be better to replace “fuel boost valve” with “fuel tank pressure cock” as seen in the PN. Hope this helps, rather than confusing things further.

I thought the same – surely it would have one or the other, but not both. Turns out I was wrong. Goblin researched this a while back, drawing upon the Monforton Spitfire e-book mentioned here: https://forums.eagle.ru/showthread.php?t=176679&highlight=ebook&page=9. It turns out all three configurations are possible. Here's what he found, quoted from Spitfire pilot’s notes, 3rd edition, dated September 1946, Air Pub 1565J, P & L—P.N. “On early a/c with Bendix-Stromberg carburettor installation where no electric booster fuel pump was fitted, a hand operated wobble pump is provided to ensure good fuel flow is established when switching between the main fuel tank and the auxiliary slipper (drop) tank and back again. Later on when electric fuel pumps were installed, the wobble pump was retained as a backup and to save the batteries during engine start up. Late production a/c relied on the electric fuel pumps alone and did not have this pump installed."

Here's another source for A.P. 2095, Parts I through IV. You may have to sign up to the forum to gain access. Many type-specific warbird manuals can also be found on this site, in the World War II - Aviation / Technical / Other Mechanical Systems Tech area. https://ww2aircraft.net/forum/threads/ap2095-pilots-notes-general.26671/

Hi BravoFoxTrt, if you're recently updated to 1.5.5, have a look at this discussion: https://forums.eagle.ru/showthread.php?t=176837 blue six

Большое спасибо за быстрый ответ и внимание к этому вопросу, Foxhound_vva. Пожалуйста, передайте мои наилучшие пожелания и поздравления всем членам команды Belsimtek F-86. Они проделали великолепную работу. Исправление этого незначительного вопроса сделает выдающийся продукт еще лучше. ------ Thank you very much for your prompt reply and attention to this matter, Foxhound_vva. Please pass my best regards and congratulations to all members of the Belsimtek F-86 team. They have done a magnificent job. Correction of this minor issue will make an outstanding product even better.

A quick update for everyone contributing to or following this item. Four days ago, with assistance from Google Translate, I posted this message on the Russian language F-86 forum: “For Belsimtek, please read the final post on the English forum here: https://forums.eagle.ru/showthread.php?t=163309 I believe the flight model requires improvement. The response in the pitch axis to flap movement is incorrect. It acts in the wrong direction. Thank you.” I received a very gracious and positive reply from Foxhound_vva (Third Party Developer) today, which you can review here: https://forums.eagle.ru/showthread.php?t=176196 Given this development, I'd suggest our spirited discussion on this topic has gone as far as it needs to for the moment, and we can all move on to things we'd sooner be doing. blue six

Thank you for your recent attention to this thread, Yo-Yo. After a seven month wait for any acknowledgement from ED or BST, it's good to have you here to address this concern. I must say you have a rare talent for diverting the discussion in unexpected directions, and for making the simple appear very complicated. It seems at least one of our recent participants may have fallen by the wayside as a result of this, along with others before him that simply lost faith during the prolonged wait. That is unfortunate; they are paying customers who appreciate the high quality of the F-86, and raised a concern not in an attempt to score points on the devs, but in the interests of improving the fidelity of the model. They do not deserve to be ignored, or worse, belittled. If I understand your most recent post correctly, you are suggesting there is no point in attempting the experiment I proposed, because the joystick I am using (a very good stick, by the way, equal to or better than that used by most of your customers) by its very nature depends upon displacement rather than force, and is therefore a rather poor simulation of the real world item. In the interest of keeping our discussion rolling, let's say I accept your reasoning. We'll set the PC joystick, with all its shortcomings and complications, aside. For my sake let's keep things very simple, and just talk about airplanes and flight models. I think we both agree that in the real world, NACA found that if their F-86 was fully trimmed, in straight and level flight at 140 knots, and flaps were lowered 55 degrees, a seven pounds pull on the stick was needed to maintain altitude. What does this tell us about how the real world aircraft had reacted to flap extension? It can't have merrily continued along undisturbed, or there would have been no need to pull on the stick. It can't have tried to climb, because having to pull on the stick to arrest a climb would be totally unacceptable from the perspective of aircraft handling qualities (as you well know, from your large experience). We can only conclude that real world F-86's immediate response to flap extension was to descend, and that a seven pound pull on the stick was needed to overcome this tendency and maintain altitude. I invite you again to try the experiment I proposed earlier, in the sim. With one change. Once you're in straight and level, fully trimmed, low level flight at 140 knots, release the stick (it only complicates things), lower the flaps, clasp your hands together behind your head, lean back in your chair and watch. If your trusty Sabre noses over, descends and perhaps even flies into the ground, our flight model has adequately simulated what the NACA report implies and what the RAF Pilot's Notes describe. If it doesn't, IMHO we have found a small problem that should be fixed. Again, let us know what you find. On my installation, after a brief, transient up and down nose movement while the flaps are in motion, the nose rises of its own accord and the model climbs steadily away.

Let's not confuse the issue with discussion of stick movement versus force, or pitch angle versus velocity vector. Let's just talk stick force, and more importantly pull versus push. We all agree on this point. NACA flight test showed that seven pounds of pulling force were needed to maintain the same altitude, when flaps were dropped. Let's try a simple experiment. Go into the sim, select the F-86 Instant Action "takeoff" mission. Get airborne but immediately throttle back to approx. 80% and remain at low level, say 200 feet AGL. Raise the flaps fully but leave the gear down. Establish straight and level, fully trimmed flight at approx. 140 knots. When you are satisfied that both airspeed and altitude are constant and you are properly trimmed, lower the flaps and attempt to hold a constant altitude using stick movement alone. Do you find you need a sustained pull on the stick to remain at your entry altitude? Or are you pushing? Let us know how you make out.

Cheers Ramsay, you've clearly got too much free time on your hands, to have gone through all that info so quickly. This table speaks directly to our concern that the response in pitch to flap extension is incorrectly modeled in the sim. and is consistent with the supporting info I've already provided. The second line says it all - when flaps were lowered to 55 degrees down from a previously trimmed condition (140 knots, 80% power, gear down, BLC off), a pull of 7 pounds was needed to maintain constant altitude.

No I don't, Yo-Yo. All I have is RAF Sabre Pilot's Notes which advise that the aircraft has a mild tendency to pitch nose down when the flaps are extended, and confirmation from a real world pilot who has flown the aircraft recently that this description is accurate. In my opinion, bearing in mind that we're dealing with a transient effect that is only encountered a few times a flight, this evidence should be sufficient. If anyone has similar or better information which suggests the F-86's nose pitches sharply up as flaps extend, this would be a good time to share it. For bbrz, thanks for the links, your Googling skills clearly surpass mine. I'll take a good look through this info when time permits. I expect support for our concern, in the form Yo-Yo seeks, is found in there somewhere.

Well put, bbrz. You and I are on the same page here. The incremental pitching moment due to flap extension can act in either direction; on some aircraft it is nose up, on others nose down. On the real world F-86 it seems clear it is nose down. For Yo-Yo, I think part of our disagreement here may be due to language. In particular, the term “trim change” perhaps is confusing. To bbrz and me (and to the author of the RAF Sabre 4 Pilot's Notes) “trim change” means a change in the balance of the aircraft around its pitch axis. When we describe this change as “nose down” we could also say “nose heavy.” We are not referring to the act of changing the elevator trim to reduce the stick forces. That comes later. In the real world F-86, as the flaps extend the nose wants to drop – additional aft stick is needed to maintain the desired pitch attitude, and eventually nose up elevator trim is applied to compensate and re-balance the aircraft. We don't see this in the sim. In fact we see the opposite. This is what needs to be fixed.

Для Belsimtek, пожалуйста, прочитайте заключительный пост на английском форуме здесь: https://forums.eagle.ru/showthread.php?t=163309 Я считаю, что модель полета требует улучшения. Ответ на оси основного тона махать движение является неправильным. Он действует в неправильном направлении. Спасибо.

Incorrect Pitch Response to Flaps Note: this issue was previously reported by several users at https://forums.eagle.ru/showthread.php?t=163309. I am repeating the bug report and providing additional supporting data in the hopes of seeing the problem resolved. It detracts from an otherwise outstanding flight model. The issue is simple – in the sim, when the flaps are lowered in preparation for landing, the nose of the model tries to rise. A moderate amount of forward stick pressure is needed to compensate. Conversely, when flaps are retracted after takeoff in the sim, the nose wants to drop and a moderate pull on the stick is needed to maintain the desired attitude. In the real world F-86, the trim changes due to flaps are less pronounced and in fact act in the opposite directions to what is currently modelled in the sim. Clear evidence of this is found in A.P. 4503D-P.N. (Pilot's Notes for the Sabre Mk 4) found here http://www.rafjever.org/sabrepictures.htm Note in particular the description of pitch trim changes found on page 47. For those not familiar with RAF Pilot's Notes, please bear in mind that the term “pitch trim changes” refers to the reaction of the aircraft when the systems in question (flaps, gear, speed brakes) are activated – not the changes in elevator trim setting needed to compensate. The real world Sabre's response to flap extension is described as “Slight nose-down” - conversely, for flap retraction the response is “Slight nose-up.” To confirm the validity of these notes, and their applicability to later Sabre models, I contacted an ex-Air Force friend and former display pilot who has flown “Hawk One” here in Canada (see http://www.hawkone.ca/). He reviewed this portion of the Pilot's Notes, reassured me that the comments are “spot on” and described the nose movement with flap selection as “slight but noticeable.” Having searched long and hard, I don't believe we'll find any better data than this, nor do we need it in this specific case. Certainly, the differences between “weak”, “slight” and “strong” pitch trim changes can be debated endlessly. They are subjective to begin with and the outcome of attempts at simulating any of them likely will vary somewhat based on the controller in use and related settings. That said, IMHO the pitch response to flaps we see now in the sim is clearly more than “slight” and more importantly is in the wrong direction – nose up when it should be nose down, and vice versa. This at least should be fixed.

Understood, Buzzles. That said, this isn't a quibble over a couple of knots of airspeed or a few feet per minute in climb rate – it's a bit more fundamental. The qualitative data cited in my earlier post suggests the incremental pitching moment due to flaps, in the sim, seems to be acting in the wrong direction. In this circumstance, I don't think it's unreasonable to expect at least a brief response from BST. As matters now sit, we're not even sure our concerns have registered.

Similar problem here, offline, current 1.5, standard map, lost engine and gun sounds in cockpit view. Both OK in external view. Landed, opened canopy, still no engine or gun sounds in cockpit view. Haven't seen this problem with any other module.

Thanks bkthunder, done, here: http://forums.eagle.ru/showthread.php?t=163309 Hope this is the thread you had in mind.

This and more recent discussion of tailplane trim sensitivity in the sim got me interested enough to look for sources describing the response in pitch when the RW Sabre's flaps, gear and speedbrakes are extended or retracted. I expected to find some PIREPs on the 'Net which would clarify things, but haven't located anything suitable. The best and clearest source I've come up with to this point is RAF Pilot's Notes for the Canadair Sabre Mk 4 (F.4 in RAF terms), dated June 1953. This doc was found on a website dedicated to RAF/GAF Station Jever, here: http://www.rafjever.org/sabrepictures.htm The Sabre Mk 4, roughly equivalent to the F-86E-10, had a less powerful version of the J47 engine than the F-86F-35 in DCS and initially at least, a slatted wing. See pp. 21-22 of the DCS F-86F Flight Manual for a description of the differences between the slatted wing and the “6-3” wing on our F-86F-35. For the most part, the Pilot's Notes on the Jever site deal with the slatted wing Sabre; Appendix I provides supplemental info for the Mk 4 updated with the slightly larger “6-3” wing. Here's what the “slatted wing” portion of the Sabre Mk 4 Pilot's Notes says regarding tailplane trim and the response in pitch to flap, gear and speedbrake movement: a. trim sensitivity – p. 46 para 58 (iv) notes all three trims are “powerful and quick in operation” and suggests tailplane trim in particular be applied in blips to avoid over-controlling; b. pitching moment due to flaps, landing gear and speedbrakes – p.47 para 58 (vi) describes the reaction when undercarriage extends as “weak nose up initially and finally weak nose down.” Response in pitch as gear retracts “slightly stronger nose up.” “Slight nose down” reaction as flaps extend; “slight nose up” as flaps retract. Strong nose up reaction as speedbrakes extend at high speed, decreasing to mild at low speed. Strong nose down response when speedbrakes retract at high speed, decreasing to mild at low speed; c. takeoff tailplane trim setting – p. 42 para 56 (viii) notes that the tendency to pitch nose up when flaps are raised will be reduced if the forward limit of the trim indicator light is used for the takeoff setting. Appendix I dealing for the Mk 4 with a “6-3” wing provides no new info regarding the response in pitch to flap, gear or speedbrake movement. An argument likely could be made that this indicates the reactions are at least approximately the same as seen with the earlier wing. With regard to the takeoff tailplane trim setting, Appendix I para II (ii) (a) goes even further than the recommendation in the “slatted wing” portion of the Notes, suggesting nose up trim be applied until the indicator light just comes on, at which point you stop, reverse and trim the stick one and a half to two inches forward. If we're inclined to accept these excerpts from the Mk 4 Pilot's Notes as being generally applicable to the F-86F-35, tailplane trim sensitivity and power, and the response in pitch when speedbrakes are opened or closed seem reasonably well modeled in the sim. The trim changes in the sim when flaps and gear are lowered are problematic, however. Extending full flaps at 180 KIAS currently produces a mild nose up response for the first second or so, followed by a couple of seconds of stronger nose down, finally changing direction again and settling into a sustained moderate nose up reaction as full flap extension is approached. Clearly not the “slight nose down” described in the Notes. Dropping the gear at 180 KIAS generates a moderate to strong nose down response, which steps up to full strength abruptly less than a second after selecting gear down, at a point in the cycle where the nose gear is only partly extended and the mains have just begun to drop. Again, not a good fit with the description in the Pilot's Notes (“weak nose up initially and finally weak nose down”), or with expectations. My feeling at the moment is that the pitch trim changes due to flaps and gear are not realistic, and twice per flight detract from an otherwise very satisfying and immersive flight model. That said, I'm new here and may have missed an earlier post which cites more definitive sources and proves me wrong. If so, perhaps someone could point me in the right direction. Alternatively, if Belsimtek based this portion of their work on a better source than the one I've offered above, it would be good to hear from them, to put these concerns to rest.

In view of this discussion of tailplane trim sensitivity in the sim, plus comments earlier regarding the changes in pitch trim due to flap and gear movement, I've done a bit of digging looking for RW descriptions relevant to these concerns. The best source I've come up with to this point is RAF Pilot's Notes for the Canadair Sabre Mk 4 (F.4 in RAF terms), dated June 1953 and squirreled away on a website dedicated to RAF/GAF Station Jever, here: http://www.rafjever.org/sabrepictures.htm Admittedly, this is not a perfect match for the F-86F-35 modeled in our sim. The Sabre Mk 4, roughly equivalent to the F-86E-10, had a less powerful version of the J47 engine and initially at least, a slatted wing. See pp. 21-22 of the DCS F-86F Flight Manual for a description of the differences between the slatted and “6-3” wing on our F-86F-35. For the most part, the Pilot's Notes on the Jever site deal with the slatted wing Sabre; Appendix I provides supplemental info for the Mk 4 updated with the slightly larger “6-3” wing. For what it's worth, then, here are the key areas of the Mk 4 Pilot's Notes relative to tailplane trim and the response in pitch to flap and gear movement: a. trim sensitivity – p. 46 para 58 (iv) notes all three trims are “powerful and quick in operation” and suggests tailplane trim be applied in blips to avoid over-controlling; b. pitching moment due to flaps and gear – p.47 para 58 (vi) describes the reaction when undercarriage extends as “weak nose up initially and finally weak nose down.” Change in trim as gear retracts “slightly stronger nose up.” “Slight nose down” as flaps extend; “slight nose up” as flaps retract; c. takeoff tailplane trim setting – p. 42 para 56 (viii) notes that the tendency to pitch nose up when flaps are raised will be reduced if the forward limit of the trim indicator light is used for the takeoff setting. For the Mk 4 with a “6-3” wing, Appendix I para II (ii) (a) goes further and suggests applying nose up trim until the indicator light just comes on, then reversing and trimming the stick one and a half to two inches forward. Bottom line – if we're prepared to accept these comments and suggestions from the Pilot's Notes for an earlier Sabre variant as being generally applicable to the F-86F-35, tailplane trim sensitivity and strength seem to be well modeled in the sim. The response of the model to changes in flap and gear position may bear further consideration, as to strength and rate of onset. Presumably Belsimtek had something better to work with than what I've offered here – it would be good to hear from them in this regard.

May have something to do with outside air temp. I had the same problem initially, then opened the mission file and changed January to July, and she started up fine. blue six