Re: X-Air Ultralight Aircraft Indicated airspeed problem
|
Hi,
I don't visit here as often as I used to and just come across your post.? I ran foul of this about this time last year.? I think other owners have also had problems because the Tech Office sent out a leaflet in December 17 which explains what they think we're doing incorrectly.? You may now have resolved your problem but I post today in case someone else gets into difficulty.
The leaflet was entitled BMAA - Airspeed clarification, Issue 1.0 12 December 2017 and may be available from the Tech Info section of the BMAA website (I haven't checked).? It goes on to explain that unlike factory built aircraft which are all built and perform to the same standard, home builts vary greatly in their performance.? From the leaflet "In particular, kit aircraft owners are incorrectly check flying using the calibrated V NE in the HADS, rather than the indicated V NE for their aircraft in the approving MAAN."? I was using the details on page 7 of my POH at Issue 1, AL1, July 1999 for my Vne until I got Permit Refused and an explanation as to why.
Those of us with homebuilt aircraft need to use the figures on the approving MAAN for that particular airframe.? If you don't have a copy (like I hadn't), a request to BMAA will get one e-mailed to you.? This should be inserted at Annex A in your POH.? My Vne turned out to be 94 Kn IAS.
A couple more quotes from the leaflet: "When an aircraft is designed, the limiting speeds - stall speed, flap limiting speed, manoeuvring speed and never-
exceed speed - are defined in terms of calibrated airspeed (CAS). If, and it’s a big IF, the airspeed indicating system
on the aircraft was 100% accurate, the airspeed displayed to the pilot by the airspeed indicator - indicated airspeed
(IAS) - would be exactly the same as CAS. Unfortunately, many of the airspeed indicating systems on Permit aircraft
have significant errors: large enough that it makes no sense - and could be dangerous - for the pilot to fly using the
CAS limiting speeds. Therefore, the aircraft manufacturer measures (as part of the aircraft’s flight test programme)
the airspeed indicating system errors, and works out IAS values for each of the CAS limiting speeds. These are then
provided to the pilot to fly to."
and: "Amateur-built aircraft are all slightly different, and there are often significant differences in the airspeed indicating
system errors between different examples of nominally the same aircraft type. The test pilot therefore measures the
errors, and the Technical Office generates a set of IAS limiting speeds, for each individual aircraft. While this is great,
it does mean that the generic documentation - such as the Flight Manual (or Pilot’s Operating Handbook) and HADS -
has to list the CAS limiting speeds. The IAS limiting speeds specific to each aircraft are provided in that aircraft’s
approving MAAN (Microlight Airworthiness Approval Note) in the form of a placard to be displayed next to the ASI on
the instrument panel."
I hope that's all helpful information.
Best regards, John B
On Wednesday, 23 May 2018, 23:01:32 GMT+1, avia1or01@... [X-Air_Ultralight_Aircraft] wrote:
?
I have a problem with my 912 X-air F. The BMAA have kicked back my
permit renewal as they say I ran the VNE test at 85kt IAS and they say I
should have run it at 106 kt IAS and must repeat it.?
The reason is my
POH has a calibration chart which says 85kt IAS = 85 CAS. They say this
is wrong and for my aircraft the calibration card should red 85kt CAS =
106 kt IAS.?
After 4 years of flying it and comparing to GPS ground speed
I thought my IAS was very accurate. The ASI is the B?uniger glass
cockpict LCD display which was recently serviced and calibrated by
Br?uniger themselves.
?What doe other peoples Calibration charts read ,
especially if there is anyone else with the Br?uniger LCD flat screen
instruments.
|
