Hi all, just joined forum recently and thought that I'd start by asking a question in regards to my AGK exam this Thursday in regards to contradicting text between the Bob Tait and ATC books.

Firstly though I want to personally thank Bob Tait for the effort you have put into these text's. My first two exams were Air Law and Aerodynamics, and I passed them both 90% and 95% respectively, and I have your books to thank for that.

Now to my question, to keep it short, I have found in ATC that they claim that in a turobcharged system, the wstegate closes after starting for idle and taxi to compensate for the lack of exhaust gases at low power settings, then re opens for take off, then works as required for climb etc, and the reverse for landing, meaning when you shut down, the wastegate springs from closed while at idle, to open after the engine stops. In the Bob Tait text I found it stated the wastegate remains open for ground operations, and the lack of exhaust gases at low power settings while on the ground is not mentioned.

The second piece of contradicting text I found is on EGT and mixture operation. ATC states as mixture is leaned from full rich, the order is full rich, max power, peak EGT, best economy. While Bob Tait says full rich, max power, best economy, peak EGT.

Something also mentioned in the DAY VFR Syllabus which is not mentioned in the Tait text is Helix Angle, a minor thing but just thought I'd mention it while here; as I had noticed Superchargers in the DAY VFR Syllabus for Aerodynamics, but since it wasn't mentioned in Tait's text, I didn't bother studying it, and sure enough a question popped up on effect of altitude on endurance if supercharged.

Last of all speaking of the DAY VFR Syllabus, it mentions effect of height on turbo and superchargers, I am still a little vague on this area. I know Ground Boosting and Altitude Boosting and why they are used, but how does it effect performance as in fuel use, volumetric efficiency, and endurance as altitude is increased, with supercharged engines, and turbocharged (Both fixed and automatic wastegaes)

Appologise for the long post, but this covers up all my vague areas in the AGK syllabus, and thought I'd put it all in one post. After througholy going through the Bob Tait AGK book these are my only queries. Otherwise I found it very informative and well presented just like all the other books in the series

Waste gate. When it comes to the waste gate position during ground operation, there are many types of turbo/superchargers and not all use the same system. In the case of the manual waste gate, it is normal to have the waste gate open for ground operations and close it during climb to maintain a given manifold pressure as height increases. I have done research on the idea that the waste gate is closed for ground operation, but I can’t find any engine operation data that says that. I have also checked with a number of very experienced LAMEs who also tell me that the waste gate is definitely open for ground operation and taxi.

Mixture. The significant performance items achieved as mixture is progressively leaned from fully rich will always be best power followed by best economy. As to whether best economy comes at or before or after peak exhaust gas temperature, that depends on the recommendations of the engine manufacturer. As I have said on page 3.16 of the General Knowledge book, best economy may occur at peak or lean of peak. You should check your operating handbook for details for a particular engine. The diagram on page 3.16 does not represent the case for every engine as indicated by the note below it.

Here is a link to a Lycoming Service Note that says the best economy is actuall AT peak and not lean of peak for this particular engine. Mention is also made of economy being slightly rich of peak for some engine models.
www.lycoming.textron.com/support/publica...ons/pdfs/SI1094D.pdf

Flying for range or endurance. The requirements for range must be considered separately for the airframe and the engine. As far as the airframe is concerned, maximum range will occur when ever the best lift/drag ratio angle of attack is used [maximum efficiency]. For a given weight, this will require the aircraft to be flown at a particular IAS. If that was all that mattered, it wouldn’t matter what height you were at, as long as you flew at that IAS, you would satisfy the requirement for maximum range. However, maximum efficiency for the engine is quite a different story. Assuming the mixture is correctly leaned, the engine’s maximum efficiency will be achieved when the throttle is wide open. That is, maximum volumetric efficiency. Maximum range then, will be achieved when the aircraft is flown at a height where full throttle also produces the IAS for best lift/drag ratio. It doesn’t matter whether you are turbocharged or not, theoretical maximum range occurs at full throttle height for the maximum range IAS. See also Mechanics of Flight by A. C. Kermode page 175.

Maximum endurance on the other hand, is achieved a minimum power. Since more power is required to maintain any given IAS as altitude increases, maximum endurance occurs at the lowest safe level with the least power that will maintain level flight.

Helix angle. Funny that. I made the decision not to include helix angle in the General Knowledge book because I considered it was not necessary for a practical understanding at the pilot’s level. Maybe I should give it a mention in future prints of the book. Thanks for the feed back.

Thanks Bob greatly appreciate it. I value your information on the wastegate being open on the ground, this is not the first piece of information I have found that puzzled me in the ATC text.

As for the order of mixture settings, I do remember reading that you said it varies, it was just that all the practice questions specifically said Power, Endurance, then peak; while ATC specifically states that best economy is leaner than peak EGT. I even got my hands on a graph which states economy is ALWAYS on the lean side. But as usual I will stick with your instruction over others

As for endurance and range I understand from what you wrote it is basically exactly the same as an N/A engine then, thanks for clearing that up.

As for the helix angle and helical path I think I have the concept from the ATC text, I will let you know after Thursday if it was covered in my particular exam at all.

Just finished your practiced exams and feel another strong mark coming on, thanks, I only wish you provided ATPL text, it would be worth it's weight in gold.

I can remember the buzz of the first solo takeoff - and it is as exciting now as it ever was - it never leaves you.

Check out my YouTube and you'll see plenty more of what to expect as you do more flying.

www.youtube.com/user/brentonrule

Stay safe and enjoy...

They are some nice video's. The night landing in the sim looks brilliant

G'day - I see you live in SA. I was born there. Started gliding at Gawler when I was 15. got my PPL at 18 through Masterflight and Rossair at Parafield. Flew into Parafield last year and it has certainly changed, Used to be more 'club like' with plenty of access to facilities. Not any more. Very industrial now.

Anyway, the SIM. It is a company called Flight Experience www.flightexperience.com.au/ and I did it in Melbourne. (We Live in East Gippsland Victoria).

I am now retired and my wife and I love flying so I am just about finished my CPL (only the flight test to go). We fly out of Bairnsdale so if you are ever over this way give me a yell.

OK will do, cheers mate.