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Basic Aeronautical Knowledge questions

Old 16th Apr 2022, 02:16
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Basic Aeronautical Knowledge questions

I flew a V35 Bonanza for about 10 years. VH-CFK. Wonderful aircraft.

The VNO was 167 Kts IAS. I never flew her above that IAS, because I never knew, for sure, when I might encounter unexpected turbulence.

Attached is a photograph of an actual flight in VH-CFK, during which the Ground Speed shown on the GNS430 is 239 Kts. BAK questions:

How is it possible that my V35 had a Ground Speed of 239 Kts while the IAS was only 167 Kts (a difference, if my maths serves me correctly, of 72 kts)?

I should add that the VNE of that aircraft was 196 Kts IAS so, if my maths serves me correctly, the indicated Ground Speed in the photograph is 43 kts in excess of VNE. Why didn’t my wings or ruddervators break off?

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Old 16th Apr 2022, 02:38
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72 Knot Tail wind perhaps?
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Old 16th Apr 2022, 02:46
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Were you on oxygen with a tail wind?
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Old 16th Apr 2022, 02:48
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Perhaps, TS. It's a pretty big and unusual number though.

No Squawk. Not on oxygen.

Another BAK question the answer to which might be a clue to another potential factor: An aircraft is cruising at e.g. 9,500' and there is (hypothetically) ZERO wind. The pilot then trims for descent at an IAS equal to VNO. What happens to the aircraft's GS? Does the GS increase, decrease or stay the same?
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Old 16th Apr 2022, 03:23
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At 9,500 you're TAS'ing in the region of 197Kts for 167KIAS, so your tailwind component is only around 42Kts, not 72. Still good, but not particularly unusual.

For your second question, I would imagine your GS would gradually reduce, as a function of increasing parasite drag & consequent lower TAS in the lower altitudes for a constant IAS.
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Old 16th Apr 2022, 03:31
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Agree with your first answer, KR. But are you sure about the second? Every time I point an aircraft's nose 'down hill' and trim to stay pointed that way, the GS increases, substantially, compared with the cruise GS. But maybe I should have included "initially" in the second question...
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Old 16th Apr 2022, 03:33
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Higher True Air Speed (TAS) at altitude and a strong tailwind is the answer to your first question. Re the descent, the Ground Speed (GS) could increase or decrease depending on the wind direction and strength as you descend through the levels. TAS will decrease on the way down unless you power up going down thatís normally unlikely in most aeroplanes.

I currently fly old 100 series Dash 8s and they are lucky to indicate anything over 160 kts in the cruise, however the TAS at altitude is normally about 240 kts, then throw in the wind effect and the GS could be anything more or less.

Good questions Clint and I hope your doing well these days.
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Old 16th Apr 2022, 03:46
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Livin' the dream, Duck! Good point re wind direction and strength at different levels.

As the preface to the final BAK question in this series, some more facts:

Based on my GS on the reciprocal 'outbound' leg (another photograph of the GNS screen I have) the actual tailwind on descent to YCTM, from about 9,500' to about 7,500' was about 45 Kts. Based on my first hand experience with the (very slippery) aircraft, pointing downhill and trimming for VNO would usually add about 25 Kts to the GS. It was a completely relaxed descent during which the IAS never went above VNO (much less anywhere near VNE).

Final BAK question in this series:

What would you say about the basic aeronautical knowledge of someone who (purely hypothetically) decided to prosecute me for not operating VH-CFK in accordance with the flight manual – exceeding the VNE of 196 Kts IAS – because the forecast winds indicated I had a tailwind of only 30 Kts and Centre’s radar showed I had a Ground Speed of 239 Kts? I admit both: The forecast winds for the location, altitude and track were for about only 30 Kts of tailwind and my GNS430 indicated a GS of 239 Kts inbound on descent to YCTM.

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Old 16th Apr 2022, 05:33
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You blokes have got nothing to do obviously
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Old 16th Apr 2022, 05:46
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You obviously haven't been prosecuted for exceeding the VNE of an aircraft you've flown, Cedrik, on the basis of 'evidence' comprising the forecast winds and the aircraft's ground speed. This will all make sense, eventually...
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Old 16th Apr 2022, 06:21
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I donít know why you donít just consider that it was very strong tail winds. Iíve seen a ground speed of over 200kts in a 182 once, simply because of very strong tailwinds.
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Old 16th Apr 2022, 06:26
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Iíve been prosecuted by the beer pole on the ASI on several occasions, not by CASA though! And not in Australia, nor in an Australian registered aircraft.

With regards to CASA prosecuting pilots for breaches of the regs, maybe they need to educate their inspectors in how to gather evidence relating to a supposed breach prior to getting their legal department and their investigators involved, some of whom are ex cops based on a recent senate estimates meeting with CASA that is available publicly, just do a YouTube search and you will find.
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Old 16th Apr 2022, 06:40
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Originally Posted by morno View Post
I donít know why you donít just consider that it was very strong tail winds. Iíve seen a ground speed of over 200kts in a 182 once, simply because of very strong tailwinds.
Precisely, morno. It's an unremarkable set of circumstances, explicable on the basis of 'Basic Aeronautical Knowledge' informed by a little bit of experience.

It seems to me that a hypothetical prosecution on the basis that groundspeed minus forecast wind = a number bigger than the aircraft's VNE 'proves' an aircraft was operated in excess of VNE would, at best, be based on very poor Basic Aeronautical Knowledge.

(Yes, Duck: Some of the things said by Senator Macdonald in recent hearings about what she has been told about the activities of an investigator would, if true, be very concerning.)
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Old 16th Apr 2022, 06:43
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Centre's radar showed you had a Ground Speed of 239kts at what altitude? Are we talking during level flight in cruise, at the start of your descent so 9,500ft or somewhere further down the descent?

If you're talking at the beginning then assuming you were maintaining VNO of 167kt IAS in the descent then you'd have about 200kts of TAS and therefore with a tailwind of 30kts you'd be at ~230kts GS which would reduce as you descend assuming tail wind stays the same and you maintain IAS of 167kts.

Things change if you're talking further down the descent though, say that reading from Centre was down around 3000feet you're more likely at 176kts TAS, if the 30kts tailwind has stayed the same all the way then you should be doing ~206kts GS, if you were still doing 239kts GS then you'd have had to be doing over 200kts IAS.

BUT this would be a relatively unusual situation having a tailwind of 30kts staying the same all the way down instead of more likely decreasing. In the more likely situation of the tailwind decreasing then it paints a grim picture of what your IAS was.

What you're saying though doesn't make sense overall, you're talking about trimming for VNO in the descent but then that the Aircraft is going to increase in GS simply by pointing the nose down, you also don't mention anything about what you're doing with the throttle so this all doesn't make much sense.
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Old 16th Apr 2022, 06:59
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I know this isn't going to make sense to you, Ix: In my (normally aspirated) Bonanza, I set full throttle at the start of the take off roll and didn't touch the throttle again until joining the circuit at the destination. A bit of fiddling with the RPM after take off then reaching cruise, to produce a nice sounding and feeling engine. Mixture was the important control. (Google "WOTLOP".)

As matter of interest, how many hours do you have in aircraft with the kinds of engines fitted to and the performance of say a Bonanza or a Cessna 210?
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Old 16th Apr 2022, 07:23
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WOTLOP is fine and all, but it seems like we're talking about descent here and furthermore that you're continuing with WOT even in the descent? That sounds like a perfect recipe for busting through your VNO and VNE on descent. My hours here are largely irrelevant to this discussion though but if you must know I have plenty of time on aircraft with IO-550s and plenty doing Skydiving where getting down fast was the main goal without tearing the wings off.
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Old 16th Apr 2022, 07:27
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I hope the regulators arenít taking the very amateur approach of correlating flight radar or any other publicly available data available, to use as an evidence base to a prosecution, particularly with regards to airspeeds and altitudes. If so, it clearly demonstrates that CASA is totally incompetent with regards to their aviation technical expertise within the organisation.
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Old 16th Apr 2022, 07:31
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Yes we are talking about descent, Ix.

And yes, I left the throttle wide open until in the circuit at the destination.

And no, I never busted VNO or VNE on descent. I have qualified, in-cockpit witnesses (and the data collected by the APS folk and many folk who follow their recommended procedures).

You're confusing descending quickly with getting to the destination quickly.

It's just BAK.

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Old 16th Apr 2022, 07:34
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Originally Posted by Duck Pilot View Post
I hope the regulators arenít taking the very amateur approach of correlating flight radar or any other publicly available data available, to use as an evidence base to a prosecution, particularly with regards to airspeeds and altitudes. If so, it clearly demonstrates that CASA is totally incompetent with regards to their aviation technical expertise within the organisation.
I'll be starting another BAK thread on altitudes and area forecast margins of error and instrument margins of error and...
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Old 16th Apr 2022, 07:36
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I would get a good lawyer and make sure there is a counter suit for wasting every bodies time that will cost whoever is peddling this crap so much they won't do it again. No way you could charge somebody for exceeding limits based on forecast weather and a radar/ADSB return, winds below 10k feet are rarely the same as forecast and can vary wildly especially down the inland side of the ranges where you might encounter the 'low level jets'. Unless of course your ADSB sent IAS for some reason, or other hard information that might give away your actual IAS.

I assume you reduced mixture/RPM to control power in the descent or made a very shallow descent to avoid VNE (assuming you maintained WOT), I mean it's not that hard to see the IAS gauge and make sure its below the red line.

BTW theories like the wind decreases as you descend or always veers etc assumes it's flowing over a flat surface, then things like temperature lapse rates and so on that vary so much from theoretical ideals we use in theory, I always laugh when I penetrate a big Cu mid height and its about the same temp as the surrounding clear air, just bumpy as hell, ie it's -5 outside and inside its still -5 and you pick up ice like mud being flung at you. But muh IFR theory told me it would be warmer inside the cloud by heaps...

Last edited by 43Inches; 16th Apr 2022 at 07:50.
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