Could this kill you?

[Guest J430]

Think about this...........

 

Cruising along in my Millenium Falcon MkIV

 

White arc at 45-80kts

 

Green Arc 80-120kts

 

Yellow Arc 120-137kts

 

Red VNE 137Kts

 

At 9500' I commence a descent and I am indicating 130kts IAS in a typical standard atmosphere.

 

Is there a problem here?

 

J:wave:

 

 

[rick-p]

Yes because of your height and the less air your speed has actually exceed your VNE.

 

I haven't got the formula in front of me but isn't it what you call the flutter factor which in simple english converts to the pucker factor as your aircraft breaks up around you.

 

Rick-p

 

 

[poteroo]

There's a cogent explanation on the VANS site - www.vansaircraft.com where van Grunsven does the numbers to show why he opposes using high HP engines in RV-9 types because it's very easy to break them at higher altitudes.

 

And in answer to the question of what I have installed in my recent RV-9A...........yes, I ignored his advice and put in a 180+ HP engine, instead of the 160, but then I'm a devout coward in rough air and always pull back to < Va.

 

happy days,

 

 

[Ross]

I thought the very rough rule of thumb was to add about 2% airspeed for every 1000 ft AMSL.

 

So 9.5x2 % = 18%

 

130 I.A.S x 1.18 = Approx.153 knots T.A.S.at 9,500 AMSL

 

 

and it could be worse than this depending on QNH

 

 

 

 

 

[Guest pelorus32]

I always like this one: to the best of my recollection this is the only one of the important airspeeds where TAS matters. If you think about it most other airspeeds - eg stall speed - are IAS.

 

Flutter is not the only potential outcome of flight in excess of Vne but it is one potential issue. The current safety series in the RAAus mag had an article about high speed flight. I think it was the first one in the series. Worth a read.

 

Regards

 

Mike

 

 

[Guest J430]

I am impressed!

 

71 views so far and several good responses.

 

The reason I posted this in the first place is when I first learnt about this issue, I thought to myself why has this never been explained elsewhere in simple plain english.

 

I wondered how many folk really knew of the dangers. Clearly a few do, however I would bet a fair chunk of change that most are blissfully unaware.

 

Of course the numbers I posted above were deliberately high so that it would really put you over the limit (except if you are from star wars in your Millenium falcon!). Its probably not likely you would achieve such a high IAS in normal ops, but you could get over VNE quite easily, and not realise it. Of course flutter problems may not necessarily occur at VNE or even a few knots over it, it may be well in excess of it. Or it may in fact be under it for some homebuilt designs.

 

This is not something widely talked about.

 

So next time you hear or see someone doing a high speed descent ask them did they check their TAS?

 

J:wave:

 

 

[Ultralights]

IAS is 130 kts, then your speed through the air is only 130 kts....weatehr your at sea level, or 9500ft. a more accurate measure would be the CAS. 130 kts is within the yellow arc..... TAS is irrelevant to airframe performance.. as IAS is indicating the air hitting the airframe.

 

just think, a 747 at 38,000ft only has an IAS of about 260kts. yet its TAS is sometimes up to 500Kts.

 

 

[Guest Bubba]

Hi y'all. First post, but I gotta say - "It depends"!

 

For a certified aircraft, I would go look at the "Limitations" section in the POH.

 

The one I have open in front of me says quite clearly and unambiguously:

 

"SPEED Never Exceed (Vne) - 195 KCAS / 196 KIAS"

 

That is good enough for me.

 

Bubba

 

 

[facthunter]

True airspeed.

 

Counts in navigation, and airframe aeroelasticity (flutter). Aerodynamic loading. (Lift ,drag stall speed rely on air density, as does the airspeed indicator, so you can land at a 10,000ft altitude aerodrome using all the standard INDICATED speeds for flap/gear extend/approach speeds, but the countryside will be going past at a fair rate.

 

It's accepted that FLUTTER reacts to TRUE airspeed throughout the entire aircraft design industry, so if you want to believe otherwise, you are free to do so, but the information is out there, if you are interested in the FACTS. Nev..

 

 

[rick-p]

Right on Nev.

 

Ask glider pilots what they know about this issue and you may be surprised by some very real life incidents.

 

I remember hearing of a glider, I think a Blanik, if that's how you spell it, a few years ago almost coming to grief in circumstances I would now, knowing the physics of the matter, say that is what happend to it namely flutter induced by excessive TAS above the VNE when from a great height whilst practising stalls the student over recovered, with stick fully forward, rapid increase of speed past VNE thus dramatically reducing the flutter margin to a point where it arrived at a negative value.

 

The ensuing flutter in the control surfaces saw the plane almost impact the the ground before pulling it out by the grace of god or it breaking up.

 

WHAT HAPPEND TO CT whatever (sorry Ian) in Italy?

 

Don't forget that gliders have very long and flexible wings with a propensity to be quite slippery it doesn't take much them to exceed VNE in a dive or fast decent from height and this is where the problem can lie for the uninformed.

 

Rick-p

 

Don't let this be you

 

 

[Guest J430]

Even found this on the RAA website.

 

http://www.auf.asn.au/groundschool/flutter.html

 

J:wave:

 

 

[Guest High Plains Drifter]

DANG, I learn something new every day - have to admit I never would of thought I'd see this discussion in relation to ultralights

 

.

 

 

[youngmic]

There seems to be a lot of confusion here.

 

Readers responding with the confirmation that flutter is related to TAS are quite correct.

 

However it's not a simple as been given in this forum. Sailplane designers are acutely aware of this issue and you will see published in the POH a graph for calculating the corrected Vne as an IAS for altitudes, generally above 10,000'

 

Many will also have several Vne's placarded on the ASI face given for various altitudes, again generally over 10,000'

 

Sailplanes have a somewhat unique difficulty in that there large wing span versus chord, (high aspect ratio) makes them very prone to torsional and elastic issues.

 

Whilst the same principals do apply to all aircraft the short broader wing section is far more tolerant and the frequency response to flexure different. Such that for the sort of speeds mentioned and the relatively low altitude of 9500' it is probably not of a great concern. Unless it is a poorly designed wing (structurally) and proper consideration to mass balancing not followed.

 

In the example scenario given the aircraft is operating in the yellow arc of it's flight envelope, and this means it is in smooth air, or there's a test pilot at the controls.

 

What is of more concern perhaps, might be that you could extrapolate the scenario to a situation where it's about to leave the smooth air and pass through the inversion layer into the layer of convective activity and perhaps into a strong thermal shortly after that may exceed your Va gust envelope, which by looking at the relationship of the Vs to present IAS it will.

 

M

 

 

[rick-p]

:juggle:The air temperature is also a factor, why?

 

 

[Flyer]

:juggle:The air temperature is also a factor, why?

It relates to density altitude. The hotter the day the thinner the air the higher the apparent altitude....

 

Regards

 

Phil

 

 

[rick-p]

It relates to density altitude. The hotter the day the thinner the air the higher the apparent altitude....Regards

 

Phil

Correct Flyer so there must be a formula for calculating the flutter margin (the risk factor) not rule of thumb but a scientific matamatical formula.

 

Does anyone know it?

 

Rick-p

 

 

[rick-p]

AND J430 you thought that this may get too easy for them

 

 

[youngmic]

I think it is:

 

Experienced aircraft designer + compotent aircraft builder + Certified test pilot + 250,000 X $1 USD/annum. + 1 pen and note pad = Vd speed.

 

Or:

 

1 + owner/builder + 1 borrowed parachute + new undies = terminal poo speed.

 

M

 

 

[facthunter]

Calculation ?

 

rick-p, at the level of sophistication that we operate to there are rules of good practice basically and then the reality is verified by TEST FLYING and operational experience.

 

The vast resources of the lockheed aircraft company were not sufficient to prevent the disastrous in-flight failure of the Lockheed Electra (L-188) wings due to a design fault and exacerbated by a small change in driveshaft alignment due to engine mount distortion. this had happened on 3 ? occasions before an in-flight break-up was viewed from another plane. The timeframe is in seconds, and since harmonics were involved (They always are ) a CRITICAL speed rather than just an excessive one was the factor.

 

Later another problem with the wings manifested itself with the same aircraft type, but the cause was metallurgical . an exotic alloy was used which was found to suffer from inter-grannular stress corrosion after some time in service. Nev...

 

 

[Captain]

The vast resources of the lockheed aircraft company .......

Which is fastest or more dangerous?

 

 

 

facthunter's Vast or youngmic's Vtps?