Author Topic: P-38 dive flaps produce no drag  (Read 13748 times)

Offline Ack-Ack

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Re: P-38 dive flaps produce no drag
« Reply #135 on: March 22, 2014, 05:24:36 PM »
Is it no drag or is it so small, it can't be measured in the game?  You assume the drag is sufficient to be detectable.  Maybe it is not.

Doesn't seem to be all that small according to the chart posted by gripen 10 years ago.  Totally forgot that we had this discussion back then until I found the thread again.

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Offline nrshida

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Re: P-38 dive flaps produce no drag
« Reply #136 on: March 22, 2014, 07:11:00 PM »
Randy you don't need to have something in writing to know something is amiss.  Common sense says the dive flap would produce some drag, that drag is going to slow the airplane…really no ifs, ands or buts about that.  The big unknown is "how much".

This is what I have found particularly exasperating about this thread. We can infer how much. Anyone with an intuitive understanding of aerodynamics (including you colmbo, apparently) would reasonably agree that a 45 degree deflection of airflow followed by another 90 degree change in close proximity at the apex over such an extensive span is going to produce an awful lot more separated turbulent air than the streamlined bomb / drop tank pylons of the Mosquito, for example (other less significant causes of drag notwithstanding).

The drag might indeed be mitigated in the presence of localized supersonic flow or a pitch change of the wing in a very steep high speed dive (I can imagine very strange things happening there) but even if that was the case the drag would still anounce at lower and indeed cruise speeds where the flow is completely subsonic.

Since the Mosquito's extra drag is observable, the absence of any extra drag with the P-38L dive flaps deployed is clearly an omission, most likely by oversight (although there are at least two other possibilities).

Campaigning that the drag is negligible (with no evidence) or that no change should be made without exact data (also therefore no evidence) surely results in less realism by having absolutely no drag at all?


Or is my logic terribly flawed? Obviously I have to ask because I have a complex now about being wrong all of the time  :lol

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Offline GScholz

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Re: P-38 dive flaps produce no drag
« Reply #137 on: March 22, 2014, 07:14:00 PM »
Your logic is perfectly sound.  :aok
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Offline GScholz

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Re: P-38 dive flaps produce no drag
« Reply #138 on: March 22, 2014, 10:50:29 PM »
Doesn't seem to be all that small according to the chart posted by gripen 10 years ago.  Totally forgot that we had this discussion back then until I found the thread again.

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That chart still around?
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Offline FLS

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Re: P-38 dive flaps produce no drag
« Reply #139 on: March 23, 2014, 01:39:21 AM »
An interesting point on the dive flap instructions that Cactus posted is the assurance that if only one dive flap deploys you wont even notice it at low speeds. It will only roll you at high speeds and can be countered with aileron. That does not sound like there would be a pitch moment at low speeds when both deploy.


Offline Ack-Ack

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Re: P-38 dive flaps produce no drag
« Reply #140 on: March 23, 2014, 02:17:49 AM »
That chart still around?

The link I quoted from gripen's original post is no longer valid but the link does contain the NACA report name that had the graph/chart he quoted.

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Offline GScholz

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Re: P-38 dive flaps produce no drag
« Reply #141 on: March 23, 2014, 10:55:33 AM »
Perhaps I misunderstand, but I can't find a link in your previous post...
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Offline Ack-Ack

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Re: P-38 dive flaps produce no drag
« Reply #142 on: March 23, 2014, 02:34:50 PM »
Perhaps I misunderstand, but I can't find a link in your previous post...

Sorry, the hyperlink in gripen's post I quoted was kind of hard to spot.  This was the link, you'll get a server access denied error message.

http://naca.larc.nasa.gov/reports/1947/naca-rm-a7c24/index.cgi?page0023.gif

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Offline FLS

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Re: P-38 dive flaps produce no drag
« Reply #143 on: March 23, 2014, 02:38:43 PM »

Offline GScholz

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Re: P-38 dive flaps produce no drag
« Reply #144 on: March 24, 2014, 03:53:49 AM »
So what am I looking at? Page 23? I can't identify anything drag related there, but then I'm no expert all this...
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Offline FLS

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Re: P-38 dive flaps produce no drag
« Reply #145 on: March 24, 2014, 04:33:30 AM »
« Last Edit: March 24, 2014, 04:57:21 AM by FLS »

Offline GScholz

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Re: P-38 dive flaps produce no drag
« Reply #146 on: March 24, 2014, 05:49:45 AM »
According to that the drag coefficient is significantly increased.

I've reported this bug. Now it is up to HTC if they want to do something about it.
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Offline Randy1

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Re: P-38 dive flaps produce no drag
« Reply #147 on: March 24, 2014, 06:35:28 AM »
According to that the drag coefficient is significantly increased.

I've reported this bug. Now it is up to HTC if they want to do something about it.

Which page or pages did you find that information?

Offline GScholz

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Re: P-38 dive flaps produce no drag
« Reply #148 on: March 24, 2014, 07:54:05 AM »
Second link figure 15 at page 24 shows the increase in drag coefficient at various speeds and flap angles. Consider that the P-38's zero-lift drag coefficient is 0.0268, those flaps add a lot of drag. Even the lowest figures at 35 degrees flap angle approximately doubles the P-38's drag at Mach .5 (~370 mph at SL).
« Last Edit: March 24, 2014, 08:02:55 AM by GScholz »
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