Cold weather flying

[FastEddieB]

Chris,

 

Excellent summary.

 

Was that copied and pasted, and if so, from where?

 

For us lowly piston pilots, suffice it to say,

 

1) Vne is the red line on the ASI.

 

2) Don't worry about IAS vs CAS vs TAS (vs EAS!)

 

3) Just keep the darn needle below the red line!

[opticsguy]

The reason I tried to stay under 125kt was because it was bumpy (cumulous clouds all around) and IAS and TAS were pretty much the same. If it was smooth I would have let it run faster. There was also an icing AIRMET and I wanted to get under those clouds. The jets at 6000 ft were complaining about rime ice.

 

On Monday coming into KSUE a sleet drizzle was falling from the 6000 ft ceiling. It was above freezing, though. Our spring vacation is more like a winter one this year.

[Ian]

From the CTLS manual (European EASA version)

 

2. LIMITATIONS

 

2.1. Airspeed Limitations

 

Maneuvering Speed V_a 184 km/h 98 kts CAS

 

Maximum Rough Air Speed V_ra 222 km/h 120 kts CAS

 

Never Exceed Speed V_ne 269 km/h 145 kts CAS

 

* The never-exceed speed (VNE) demonstrated during flight testing is 301 km/h. However VNE is limited by the maximum deployment speed for the ballistic recover system or national regulatory requirements.

 

Two interesting things - the "real" V_ne is therefore 162 knots - but I don't think I want to verify that, and the V speeds are all given as Calibrated Air Speeds - which to all intents and purposes are Indicated Air Speeds within the range we fly.

[Dan Kent]

Pipistrel also has quite a discussion in the POH. It starts in section 9-4, pg 76. They had 2 planes "break" in flight due to flutter.

 

http://www.mcp.com.au/sinus/manuals/Virus%20SW%20LSA%20FAA-ASTM.pdf

[Roger Lee]

Like I said the CT Vne was set for the chute deployment even though the actual Vne is higher. This BRS chute is not in another plane nor the same size, different rigging, ect... so each aircraft may have different Vne limit considerations when published for public use.

This is a FD Mfg decision and any aircraft Mfg can lower the Vne from actual if they choose. FD did it for safety and reliability of chute deployment and I'm sure from collaboration with BRS.

 

Other aircraft Vne considerations may be based differently, but we are talking about the CT.

 

"* The never-exceed speed (VNE) demonstrated during flight testing is 301 km/h. However VNE is limited by the maximum "

[Ed Cesnalis]

Chris,

 

Excellent summary.

 

Was that copied and pasted, and if so, from where?

 

For us lowly piston pilots, suffice it to say,

 

1) Vne is the red line on the ASI.

 

2) Don't worry about IAS vs CAS vs TAS (vs EAS!)

 

3) Just keep the darn needle below the red line!

 

Eddie,

 

Read this quote from Pipistrel's POH

 

The maximum structural speed is linked to IAS. But light planes, manufactured of carbon reinforced

plastics, with long, slick wings are more prone to flutter at high speeds than to structural failure.

So flutter is the main factor of determining VNE for us and most other carbon-reinforced-plastic

aircraft producers. Flutter speed is linked to TAS, as it is directly caused by small differences in

speed of air circulating the airframe. Hence air density is not a factor. For all who still doubt this, here

are two quotes from distinguished sources on flutter being related to TAS:

“Suffice to say that flutter relates to true airspeed (TAS) rather than equivalent airspeed (EAS), so aircraft that are operated at or beyond their VNE at altitude - where

TAS increases for a given EAS – are more susceptible to flutter...”

New Zealand CAA’ Vector Magazine (full passage at page 5 of http://www.caa.govt.nz/fulltext/vector/vec01-4.pdf)

“The critical flutter speed depends on TAS, air density, and critical mach number. The air

density factor is almost canceled out by the TAS factor; and most of us won’t fly fast

enough for mach number to be a factor. So TAS is what a pilot must be aware of!”

Bob Cook, Flight Safety International

The airspeed indicator shows you the IAS, but this is sadly NOT the speed of air to which the

aircraft’s airframe is exposed.

IAS and TAS are almost the same at sea level but can greatly differ as the altitude increases. So

flying at high altitudes, where the air is thinner, results in misinterpreting airspeed which is being indicated. The indicated airspeed value may actually be pretty much lower than speed of air to which

the aircraft is exposed, the TAS.

So is VNE regarded as IAS or TAS? It is in fact regarded as TAS above 4000m/13100 ft!!! You

should be aware of that so that you will not exceed VNE like the two pilots ment

[Roger Lee]

Good info Ed's,

 

 

The maximum structural speed is linked to IAS. But light planes, manufactured of carbon reinforced

plastics, with long, slick wings are more prone to flutter at high speeds than to structural failure.

So is VNE regarded as IAS or TAS? It is in fact regarded as TAS above 4000m/13100 ft!!! You

should be aware of that so that you will not exceed VNE like the two pilots ment

[Brian]

Thank you, Opticsguy! You answered my question. In those circumstances I would have done the same.

[mocfly]

From the Grob Operating Manual. The glider guys are quite familiar with limitations

 

 

Now hold on, common sense said IAS should be the limiting factor not TAS. What was I missing? How could the aircraft be exceeding Vne if the needle was way down in the green arc, which the sailplane's POH and a placard demanded?

 

TAS is the true speed an aircraft moves through an air mass, and the lying air speed indicator doesn't show that, at altitude, because it's confused by the lower air density. To get the true story we have to pull out our prayer wheel and correct IAS for altitude and temperature--in other words correct IAS for air density--to get TAS. No new news there, every student pilot learns how and knows why.

 

[mocfly]

Forgot the placard picture

[Ed Cesnalis]

The engineers cite IAS for all airspeeds. Second guessing the structural and aeronautical limits of the plane using something other than IAS is ill advised and counter to the Aircraft Operating Instructions.

 

Our CTs are not immune, in fact as Pipistrel points out in their POH a light carbon fiber plane is more susceptible to flutter than structural failure. At some altitude our flutter speed will be in the green arc we just don't know where that occurs because Flight Design doesn't publish it. It doesn't matter if you use IAS with reducing speeds as altitude increases or TAS at altitude the fact is that the flutter speed decreases with altitude and one single Vne cannot account for that.

 

Converting to TAS is an adjustment used by some manufactures and it looks the others that provide a chart are simply converting TAS to IAS so where is the harm in limiting your TAS to 162kts or even 145kts? Limiting my TAS in this manner in no way counters the AOI.

[Ian]

The engineers cite IAS for all airspeeds. .....

 

If you are going to make definitive statements you might ensure they are correct!

 

Did you read my post #29?

 

For the CTLS the Pilot's Operating Handbook (the legally definitive document certainly in Europe) all the relevant speeds are quoted as CAS - Calibrated Air Speed - http://en.wikipedia.org/wiki/Calibrated_airspeed

[sandpiper]

Here's a little something for your bedtime reading on this subject courtesy of Van's Aircraft. Nothing to worry about in the CT but it may answer some of these questions.

 

http://www.vansaircraft.com/pdf/hp_limts.pdf

[chanik]

This is all pretty good info; one of my favorite threads. The only thing I would add is that while the practical Vne speed varies with TAS, FD is very much required by FAA part 23 (ref. earlier) to use a number in the AOI and airspeed indicator (IAS) that is safe throughout their published envelope (so up to 14,000' service ceiling). Or else they would have to explicitly placard and say so in the AOI. Now if they tested to 162kts then it is pretty clear they have lots of margin anyway. 120kts IAS is just 153kts TAS at FL140.