Question: Instruments

[asra]

Wasp??? How would you know?? How could you check?Ted

[asra]

Alright Ted I'll have a go!!!!!If on climb out my airspeed indicator seemed to be showing a slower than normal reading I would check 4 things.1) My Vertical climb rate using my VSI and compare it with what is norm.2) My engine RPM and compare with what is norm.3) My Pitot Tube ensure its clear of any obstructions4) My ASI static air vent and ensure it is clear and un-obstructed.Can't think of eny others !!!!Did I pass [?][?][?][?][?]Regards Sam.

[asra]

Well actually, I'm still in love with Jo Grant !Robert DunnMackay. Qld.Growing old is good while it lasts.

[asra]

Actually you are right! what an ass!

[asra]

Oops we are all getting a little off topic....Here Ted, let me do it for you....On climb from your takeoff point, everything is normal except you suspect the Air Speed indicator is acting strangely, in fact it appears to reading a little slower than normal. What could be the problem?

[asra]

Sam, Good effort but not quite on the money."On climb from your takeoff point, everything is normal except you suspect the Air Speed indicator is acting strangely, in fact it appears to reading a little slower than normal. What could be the problem?"Remember I said "everything is normal except you suspect the Air Speed indicator is acting strangely ".... That means engine rpm, oil pressures etc are normal, its just the air speed indicator which is acting up. Since two of the mandatory instruments on your registered gyro are pressure related ( ASI and Altimeter) it is worth noting that only one relies on the pitot tube. The ASI reads the difference between the pitot air pressure and the static vent pressure, whilst the Altimeter only feeds off the static vent pressure. Its possible to reasonably confirm the pitot tube may be partially blocked, by simply checking the altimeter to see if it is functioning correctly. If the altimeter is also acting up then the blockage is in the static vent and not the pitot tube. Its worth also noting that a complete blockage of the pitot will ensure that your ASI will read zero.Therefore if the Pitot tube were to become partially or totally blocked, as you climb out the ASI will tend to over read as the static vent pressure declines. Conversely as you descend the ASI will tend to underead.In my question I said,"in fact it appears to reading a little slower than normal." So in fact the pitot tube is not blocked, nor is the static vent. What else could be the matter?Here is the more likely issue. The ASI is calibrated to read correctly at sea level ( in standard conditions of temperature and pressure). If the air density is less than that at sea level,(which is the case at altitude)the airspeed indicator will indicate an airspeed that is less than the true airspeed(TAS). Some ASI's have a small rotatable scale that allows an adjustment for the density error. If the correct altitude and temperature is manually set, the pilot can read the TAS as well as the IAS ( Indicated Air Speed).So,.... in actual fact in the question I posted, you are either taking off from a higher than normal altitue or the QNH is significantly lower than 1013hPA or a combination of both.Ted

[Tim]

quote: it appears to reading a little slower than normal.There are only two alternatives (1)"it appears to reading a little slower than normal" because it is slow, or (2)"it appears to reading a little slower than normal" because it is correct but only appears to be reading slow.(1) Fault in guage reading, caused by any amount of factors including fault in guage itself, fault in pitot or static lines and air density.(2) Things like gyro attitude (climbing) and something on aircraft causing extra drag - can indicate lower airspeed for the same engine RPM's and a tail wind can give the illusion of an ASI reading slow.Tim McClure

[asra]

Sam, Sorry but you are wrong here. Go down to the local Aero club and ask the Chief Flying Instructor and they will confirm what I have outlined to you.Your reply "An Aircraft Airspeed Indicator displays the speed by comparing ram air pressure from the pitot tube with static air pressure from the static port, so the greater the difference, the greater the speed.", is correct to this point, however it is the second part which is incorrect. "Both of these are effected equally so no calibration is required due to changes in altitude, or pressure." Ted

[asra]

Ok TedI did a search and found that you are right.Although I have never seen a ASI with an adjustable dial for QNH.Seems this applies more so to higher altitude flying aircraft. An Expination can be found on the link below.http://www.avsim.com/geoffschool/com...intro.htmSorry mate !!!! [B)]Regards Sam.

[NiqueNaque]

Ted,One assumption has bee made that may not apply to all aircraft, ie, that the static vent is common to the altimeter and the ASI.On my gyro the altimeter and the ASI do not have a common static vent. This has implications for my machine, but only that I cannot trouble shoot the ASI using the altimeter.Cheers,Nick.

[asra]

Since we are talking about instruments, can anyone tell me were and who sells the instrument pod in the photo below ?Also aprox Price.I beleive this is Murray.Image Insert: 79.57

[asra]

Sam, That's okay. I found it hard to believe at first too. The important thing here is that we may not always recognise that the ASI is showing us an error.In a perfect nil wind situation, any differance in QNH or Altitude may have an effect. Greater differential between true air speed and indicated airspeed. Say for this example you, with a number of others, were entered into the Nation event, the "Tim McClure Cross Country" (time challenge). There 3 legs in this phantom race. One at sea level, another at 3000 ft elevation, and the third leg on the second day with a vastly different QNH than that on the first day. The overall object of the cross coutry event is to nominate the time per leg to travel and the overall time taken. Points are awarded per leg and bonus points for the overall time. Could you work out your time/s? Once you understand the possibilities given the altitude and QNH factors, then you are starting to flight plan professionally.Ted

[asra]

Yes thats me in John Hills machine.I will find out who has the mould for that pod and get back to you. This gyro is now for sale as John has decided jet ski's are more fun.M Barker

[asra]

SamL,Ian Sganzerla's son has the mould for these intrument pods and makes them ... he was last year when I asked Ian about them ... they were pretty cheap also - from memory approx $150 but cant be sureSafe Flying ... ding Good judgment comes from experience and experience comes from bad judgment

[asra]

Thank Geoff, I will ring Ian as soon as I get a chance.Murray, could you also confirm were John Hill got his.Thanks Both Regards Sam.