Aircraft Overstressing
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@Delta558 The POH doesn't say that the Piper Arrow is not approved for any negative load, only that inverted flight is not approved. In the absence of specific data on negative G (other than inverted flight) for the Piper Arrow, it would appear to be reasonable to me to use what Bernie has referred to.
Looking at what Bernie referrred to, the 0.4 x positive load limit he referred to is a maneuvering load limit.
However the reference he linked to also includes gust load factors (separately from maneuvering load factors). Gust load factors would appear to be relevant as well, particularly as I was getting bumped around by the wind at the time in my case. Calculating that appears to be complex but maybe somebody more knowledgeable than me knows what to do with that?
If gust load factor isn't included in the flight modelling, maybe it would be reasonable to make some allowance for that in the negative G maneuvering load limit?
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Response from JF to my ticket says: "I would recommend turning off Aircraft Stress Damage and Engine Stress Damage in the Assistance menu of MSFS when using all third party add ons."
I'm surprised at this response. I purchased the Piper Arrow for realism so I balk at turning realism off. I'm going with the following changes in the flight_model.cfg file (as per the Bonanza):
negative_g_limit_flaps_up =-2
negative_g_limit_flaps_down=-1I'm no expert by any means but given that there are bound to be some negative G loads on the aircraft in normal flight, those figures make a lot more sense to me than 0 for both of them.
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Recalling old study material, but the figures BernieV quoted are correct for both CS23 and FAR 23 in the Normal category (to which the Arrow will have been built), stating +3.8g and -1.52g with a 1.5x safety factor. That means the aircraft has to be designed not to fail structurally below 5.7g or -2.28g. Permanent deformation may occur between these figures.
With respect to the dev team, setting 0 for the negative limit doesn't make any sense.
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@ShadowSix My opinion is that the G limits in the config file should reflect the structural limits, not the approved limits. After all, the message you get not only says that you have overstressed the aircraft (overstressed, not "gone over the approved limit"), but it is also an instant end to the flight.
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If you can find me the structural limits, documented officially rather than just some website that says 'about this', I will happily make the change. Believe me, I have looked since this topic was started and I keep ending up directed back to the POH.
It is not something which has attracted a lot of complaints, we didn't encounter it during testing but as suggested above, if you want to make the fix yourself feel free to change it to whatever you feel suitable.
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@Delta558 said in Aircraft Overstressing:
... I keep ending up directed back to the POH.
But with respect, the POH doesn't give any indication what the maximum negative load factor is. It only says that no inverted maneuvers are approved, which doesn't give any basis for setting a limit, so I don't understand the logic of using that to justify setting the limit at 0 when it is clear that the aircraft must be capable of some negative G in normal flight. "No inverted maneuvering" does not mean that the negative load factor limit should be zero.
In the absence of anything more specific on this particular aircraft it therefore seems perfectly reasonable to me to use information that is available, such as what BernieV and ShadowSix have referred to.
For me the purpose of starting this post and raising a ticket was to address the issue of unrealistic termination of flights due to supposedly exceeding the aircraft limitations for normal flight when that isn't actually the case. So I don't even think it's critical that the limit be calculated exactly, as long as a reasonable figure(s) is/are used to achieve the desired result. On that basis, the -1.52 calculated by BernieV would appear to be reasonable to me. -2 (flaps up) and -1 (flaps down) as per the Bonanza flight_model.cfg file would also appear to be reasonable to me.
If either of those options (or something similar) achieve the desired result, does it really have to be any more complicated than that?
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@Delta558 said in Aircraft Overstressing:
If you can find me the structural limits, documented officially rather than just some website that says 'about this', I will happily make the change. Believe me, I have looked since this topic was started and I keep ending up directed back to the POH.
It is not something which has attracted a lot of complaints, we didn't encounter it during testing but as suggested above, if you want to make the fix yourself feel free to change it to whatever you feel suitable.
I've not experienced this issue myself, I tend to fly with 0 wind, or 0 gusts because I really don't like the way MSFS moves the aircraft.
However, these figures aren't just quotes from any old web site, they're really quite specific requirements laid down by the FAA/EASA and other such legislative bodies. I don't have an FAA quote, but this is from EASA CS23 which governs Class B aircraft (like the Arrow)...
"CS 23.337 Limit manoeuvring load
factors
(a) The positive limit manoeuvring load
factor n may not be less than –
(1) 2.1+ (24000/W+10000) for normal and
commuter category aeroplanes (where
W = design maximum take-off weight lb),
except that n need not be more than 3·8"If you're not getting many complaints then of course you have to consider whether or not it's worth your time to make the changes, but the figures are there and the POH really only scratches the surface for a potential owner and pilot.
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I was responding to Delta558 who was asking about documented references to limits, and trying to illustrate that design specification limits exist outside of the PoH.
As has already been mentioned in previous replies, the negative limit specified by governing bodies for aircraft in this category is -1.52g with a 1.5x safety factor ensuring no structural failure below that.
Perhaps I should have included this excerpt (although I think it's already been quoted more or less) also from CS 23.337:
"(b) The negative limit manoeuvring load
factor may not be less than –
(1) 0·4 times the positive load factor
for the normal, utility and commuter
categories" -
@ShadowSix , Thanks for this info... Based on this I would agree that the negative G limit should be set to 3.8 * 0.4 = -1.52 to meet the certification authority requirements. When combined with the existing "load_safety_factor =1.2" this should be sufficient to resolve the problem of overstressing in rough air.
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@RetiredMan93231 That works for me :) Thanks to all for the input on this thread.
For further information, this is the load_safety_factor line from the Bonanza flight_model.cfg file:
load_safety_factor = 1.5 ; Flap negative load limit when down. Same dimension as gravity vector FEET/SECONDS^2
If this is correct it appears from this that the load_safety_factor line only applies when the flaps are down, which further justifies changing the negative G limits in the Piper Arrow file rather than change the load_safety_factor.
