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LessDragProd(at)aol.com
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 Posted: Thu Mar 29, 2007 9:18 am Post subject: TAS and Vne & Flutter at Altitude |
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I was told that the MU-2 has an airspeed indicator that shows the critical airspeed for that flight altitude. The critical airspeed is shown as a moving (red?) line on the IAS indicator.
Another method I've heard of using is an indicated airspeed to a fairly low altitude like 10,000' and a limiting Mach number above that altitude.
Part 23 identifies a maximum operating airspeed (Vmo) and a maximum operating Mach number (Mmo) as airspeed limits. Where Vmo is an IAS? And Mmo as a fixed Mach number is a varying TAS? (Mach 1 being about 760 knots TAS at sea level to about 660 knots TAS at 35,000?)
The RMI Microencoder in my RV-3 can provide a Mach number readout. I haven't tried it, but if I remember correctly, I can input a set point for an audio alarm and/or flashing display to the Mach number.
BTW, I estimated a limiting Mach number of about 0.26 for 230 mph TAS at 10,000'. Anyone have a better number?
The Dynon D-10 & D-10A provides a TAS readout when their OAT is used. I understand that there is no provision at this time for an alarm on the TAS.
Anyone have information on their flight system and the ability to set an alarm on TAS or Mach number?
Regards,
Jim Ayers
See what's free at AOL.com.
[quote][b]
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billderou(at)yahoo.com
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| Posted: Thu Mar 29, 2007 10:17 am Post subject: TAS and Vne & Flutter at Altitude |
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I communicated with John Cox earlier in the week on this same subject. My air data computer is providing accurate numbers [OAT, IAS, Palt] and with the proper formulas could provide the pilot with information to fly right on Vne. My assumption here was that Vans margins far exceed the sum of my errors.
However, this brings up several issues that need to be addressed first:
1) Is it safe to fly at Vne? This needs to be answered by Vans and other aerospace engineers.
2) Is it safe to fly through turbulence at Vne? I know its the turbulence that kicks off the flutter but need to ask the question. Are there maximum stick forces that cannot be exceeded when recovering from this turbulence? Would the autopilot exceed these forces?
3) What is the true significance of the IAS red area?
4) Assuming its safe to fly at Vne, what are the resonable HP increases or turbo increases that make good engineering sense for the RV-10?
5) Up to now I have not been a proponent to logging PFD data to a flash file that could be used after an accident by the NTSB or lawyers. However, if we are going to help our pilots fly at Vne then it would make sense to log all information so we could learn should something go very wrong.
In general, I have mixed emotions about helping the pilots boost the horsepower and fly at Vne unless it can be accomplished safely.
Bill DeRouchey
WTDAviationTechnology
N939SB, flying slowly at 196mph TAS
bill(at)wtdaviationtechnology.com (bill(at)wtdaviationtechnology.com)
LessDragProd(at)aol.com wrote:
[quote] I was told that the MU-2 has an airspeed indicator that shows the critical airspeed for that flight altitude. The critical airspeed is shown as a moving (red?) line on the IAS indicator.
Another method I've heard of using is an indicated airspeed to a fairly low altitude like 10,000' and a limiting Mach number above that altitude.
Part 23 identifies a maximum operating airspeed (Vmo) and a maximum operating Mach number (Mmo) as airspeed limits. Where Vmo is an IAS? And Mmo as a fixed Mach number is a varying TAS? (Mach 1 being about 760 knots TAS at sea level to about 660 knots TAS at 35,000?)
The RMI Microencoder in my RV-3 can provide a Mach number readout. I haven't tried it, but if I remember correctly, I can input a set point for an audio alarm and/or flashing display to the Mach number.
BTW, I estimated a limiting Mach number of about 0.26 for 230 mph TAS at 10,000'. Anyone have a better number?
The Dynon D-10 & D-10A provides a TAS readout when their OAT is used. I understand that there is no provision at this time for an alarm on the TAS.
Anyone have information on their flight system and the ability to set an alarm on TAS or Mach number?
Regards,
Jim Ayers
See what's free at AOL.com.
[quote][b]
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Tim Olson
Joined: 25 Jan 2007
Posts: 2882
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| Posted: Thu Mar 29, 2007 10:48 am Post subject: TAS and Vne & Flutter at Altitude |
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I thought this was the whole purpose of the yellow arc...
And, thru any significant turbulence it's much wiser to ensure you're
also below Va, (maneuvering speed), which is also not a fixed number.
Va decreases as the gross wt. decreases....so a heavier plane has a
higher Va, and in any kind of significant turbulence you'd want to
be below Va. To complicate matters, some certified planes also
have a maximum turbulence penetration speed that is a separate
number.
To me, this whole worry about Vne is pretty irrelevant to my
flying the RV-10, as I have no need or interest in passing up
the listed 200kts be it using IAS or TAS. But, the issue of
turbulence....now there's one that quickly gets my attention.
I don't often descend under full cruise power and it's not
to stay away from Vne, but to stay closer to the lower numbers
on the yellow arc, as I descend into the rougher air. In short,
I'm much more turbulence squeamish than a top-speed-monger.
John knows exactly some of which experiences helped to reinforce
that with me. Just smacked my head on the canopy 2 weeks ago too.
Tim Olson - RV-10 N104CD - Flying
do not archive
| Quote: | 2) Is it safe to fly through turbulence at Vne? I know its the
turbulence that kicks off the flutter but need to ask the question. Are
there maximum stick forces that cannot be exceeded when recovering from
this turbulence? Would the autopilot exceed these forces?
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jjessen
Joined: 22 Apr 2006
Posts: 285
Location: OR
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| Posted: Thu Mar 29, 2007 11:33 am Post subject: TAS and Vne & Flutter at Altitude |
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Yes.
I think it's been a valuable dialog about IAS and TAS and flutter. It
raises awareness, and the topic is woefully lacking in any flight manual of
any certified that I've flown. With experimentals, especially with folks
trying to explore the envelope, its important to keep in mind. From a
practical standpoint, however, given a close to stock plane, it is probably
not all that important, unless you spend a great deal of flying time in the
teens and wanted to trade some of that altitude for speed. Should you want
to do that, turbulence is more likely an issue. You go into a turbulent
zone after all that smooth air, and you do it high into that yellow arc,
then you are being a true test pilot.
I for one would like to know what my TAS limits are at altitude. Why not?
And, if I had to get down in a hurry, I'd sure like to know what they are at
that moment, and clearly so. Not have to look them up somewhere. (So, they
will be calculated and part of my high tech emergency get down quick
laminated card that is stuck somewhere in the side pocket, unless I left it
back at the hanger after I cleaned the plane out because of that damn
turbulent ride across the Rockies that made me spill my enchilada with taco
sauce all over my good jeans).
John J
do not archive.
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wvu(at)ameritel.net
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| Posted: Thu Mar 29, 2007 8:57 pm Post subject: TAS and Vne & Flutter at Altitude |
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First off, don't forget many other factors can kick off flutter than just
turbulence.
Secondly, I'm not so much worried about flutter at Vne as I am careful about
exceeding the structural limits (G-limits) at this speed This is probably a
good opportunity to point out exactly where the design limits are, then give
some tolerance for altitude. According to the V-n diagram (attached):
Vne - 230mph (200kts)
Va - 145mph (126kts)
If turbulence results in negative-G:
Va- 100mph (87kts)
You can see that accidentally going outside of the envelope can happen
easily especially when negative-G forces are involved. When I am tired from
fighting with turbulence trying to keep my body vertical is when I slow way
down below the bottom of the yellow arc, at which point it's no longer fun
to fly.
On the other hand I wouldn't hesitate to explore the other end of the
envelope but do it incrementally, in smooth air. Once turbulence is not a
factor pay special attention to flutter near Vne. I've gone as far as
207mph.
Anh
N591VU-45hrs
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wvu(at)ameritel.net
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| Posted: Thu Mar 29, 2007 8:58 pm Post subject: TAS and Vne & Flutter at Altitude |
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Diagram attached this time. Anh
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