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10-26-2007, 06:33 AM
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Join Date: Mar 2005
Location: Northern California, USA
Posts: 537
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TAS = CAS + 1.5% per thousand ft
Quote:
Originally Posted by Russ McCutcheon
My question is, if I maintain the same indicated speed from 1k? to 10k? how much true airspeed did I increase for each 1000? I went up? Is there a rule of thumb??
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Up to about 10,000' or so, I use this rule of thumb: add 1.5% to CAS for every 1,000', and that's my TAS.
So I'm indicating 120 KCAS at 4,000', my TAS is 120 + (4 * 0.015 x 120) = 127.2 KTAS. (The correct number is 127.3)
If I'm indicating 120 KCAS at 10,000', my TAS is 120 + (10 * 0.015 x 120) = 138 KTAS. (The correct number is 139.6)
__________________
Martin Gomez
Redwood City, CA
"My RV-7 is a composite airplane: it's made of aluminum, blood, sweat, and money"
RV-7 Slider QB
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10-26-2007, 07:18 AM
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Join Date: May 2005
Posts: 64
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IAS vs. TAS
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10-26-2007, 03:25 PM
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Join Date: Jan 2007
Location: Bay Area California
Posts: 123
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Quote:
Originally Posted by Ted Johns
...Anyone in a hurry to get down from the teens needs to understand VNE is based on TAS...
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In the certified world where I?ve done the most of my flying, Vne is based on IAS and not on TAS. As my instructor used to say, the FAA doesn?t want pilots, in a potentially stressful situation, be required to do math in order to keep the wings or control surfaces on the airplane. This is one regulation I couldn?t agree with more and I wish it applied to the experimental world too.
During a descent when you have constantly changing temperatures and altitude and if you have steam gauges, just how the h_ll are you supposed to know the TAS at any given level?!? The need to use some ballpark estimate or rule of thumb formula to seems so amateurish to me.
__________________
Tom
Flying RV-4
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10-26-2007, 04:58 PM
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Join Date: Feb 2006
Location: Sherwood, Oregon
Posts: 236
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Quote:
Originally Posted by Low n Slow
In the certified world where I?ve done the most of my flying, Vne is based on IAS and not on TAS. As my instructor used to say, the FAA doesn?t want pilots, in a potentially stressful situation, be required to do math in order to keep the wings or control surfaces on the airplane. This is one regulation I couldn?t agree with more and I wish it applied to the experimental world too.
During a descent when you have constantly changing temperatures and altitude and if you have steam gauges, just how the h_ll are you supposed to know the TAS at any given level?!? The need to use some ballpark estimate or rule of thumb formula to seems so amateurish to me.
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In the glider example earlier in this thread, it was a Certified glider.
You may want to click on that link as well. In it, Van explains why the majority of spam-can (you might even say low n slow) pilots don't need to worry about TAS effects on VNE.
I myself have no experience with fast, high ceiling certified ships. Perhaps their POH goes into this issue. Perhaps their steam airspeed gauge is one of those fancy TAS reading types, those have been around a long, long time.
__________________
Dog is my co-pilot.
Ted Johns
RV9 emp & wings
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10-26-2007, 06:40 PM
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Join Date: May 2005
Location: Santa Barbara, CA
Posts: 1,324
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Vne indication
Quote:
Originally Posted by Ted Johns
I myself have no experience with fast, high ceiling certified ships. Perhaps their POH goes into this issue. Perhaps their steam airspeed gauge is one of those fancy TAS reading types, those have been around a long, long time.
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In the case of the big turboprop that I flew for a living, the airspeed indicator was IAS, but the red line (actually a striped "barber pole") moved as the altitude increased. At sea level it was 250 kts, at 25,000 it was 210 kts. Both those numbers are .50 Mach. Also, since it was a turboprop, the limitation was at Vmo not Vne, but that's another story.
John Clark
RV8 N18U "Sunshine"
KSBA
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10-26-2007, 07:15 PM
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Join Date: Feb 2006
Location: Sherwood, Oregon
Posts: 236
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Quote:
Originally Posted by John Clark
In the case of the big turboprop that I flew for a living, the airspeed indicator was IAS, but the red line (actually a striped "barber pole") moved as the altitude increased.
John Clark
RV8 N18U "Sunshine"
KSBA
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Thanks John. I suspected that there were fancier airspeed gauges than the one in the old Skyhawk I putt around in.
It's worth noting that a 180hp RV4 can exceed VNE in level flight, and has a solo weight ceiling of over 28000ft! At that altitude, I bet pointing the nose down until the IAS reads 183kts is going to get you in a heap 'o trouble.
__________________
Dog is my co-pilot.
Ted Johns
RV9 emp & wings
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10-26-2007, 10:33 PM
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Join Date: May 2005
Location: Santa Barbara, CA
Posts: 1,324
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FL280
Ted,
The numbers get a little frightening at that end of the scale. At 183 indicated the TAS would be around 280 kts. Yikes! Besides, it is way too cold up there.  I have had my RV8 up to 22,000, but it isn't much fun.
John Clark
RV8 N18U "Sunshine"
KSBA
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10-27-2007, 05:31 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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Adjustable AS
Quote:
Originally Posted by Low n Slow
.........., just how the h_ll are you supposed to know the TAS at any given level?!? The need to use some ballpark estimate or rule of thumb formula to seems so amateurish to me.
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Hi Tom,
I've seen many adjustable airspeed indicators where you line up the temp with the appropriate altitude to see your TAS. After a few flights where you calculate your TAS on the E-6B, you'll have a good feel for what your TAS is or make up a small card to stick near the A/S indicator. Personally, I always have my E-6B in the side pocket....use it often,
Regards,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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