Wallace McNair’s Hirth Powered Mynah

Here’s a great close up of Louis McNair in the Hirth F23 powered Mynah.

Wallace says ‘It is running very well, as expected. The 72  x 36 inch prop driven with a 2.7  : 1 reduction is proving ideal.  At the time I ordered the F23 I tried to buy the Hirth belt reduction with that ratio but was told it was not produced. A pity because the big prop gets a very good grip!’

Thanks for the photo and feedback Wallace!

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Sparky Stuff

by Phil Kennedy, SprintAero.
As published in Sport Flying Magazine, Spring 2015
SAA SP1961

A LITTLE TOYOTA that hasn’t had it’s plugs checked in years, because the mechanics thought it had Iridiums that need changing only every 100,000 km, developed a misfire the other day. Upon investigation I found that this 160,000 km old engine has had its spark plugs changed only once in its life and the very
worn spark plugs have gaps that are enormous and have been for at least a year, by my reckoning.

Read the full article: Click here

Posted in Aero Articles

Some things change … and some things stay the same

by Phil Kennedy, SprintAero.
As published in Sport Flying Magazine, Spring 2015.
SAA SP1961

As many of readers may know, I am a reader of historical aviation stuff and have an evergrowing collection of the Jane’s All The World’s Aircraft annuals within my library. The latest to arrive is slightly more modern than most of my collection, being the 65th edition and covering the 1974–1975 timeframe.

A casual wander through the “Memory lane” section brought up some interesting finds but also some truly disheartening ones as well. 1975 is now 40 years ago, and within this recorded year there were aircraft and engines already in production that are still sold as current products in 2015 without an ounce of shame!

Read the full article: Click here

Posted in Aero Articles

The Engine Cooling Fan Club

by Phil Kennedy, SprintAero.
As published in Sport Flying Magazine, Winter 2015.
SAA SP1961

Some of the most successful manufacturers of air-cooled engines, in both numbers and horsepower outputs, have updated their engines with close fitting cooling shrouds and fans. So when the majority of the air-cooled engines fitted to homebuilt aircraft have neither proper shrouds nor fans, the question needs to be asked—WHY?

So before we get into the technical stuff, let’s qualify some of the statements made.

The most successful and prolific air-cooled engine manufacturer would have to be Volkswagen with the various
versions of the Beetle and Combi. The Type 1 through to the Type 4 all have carefully designed multi-piece shrouds and barrel type centrifugal fans.

The most successful air-cooled engine manufacturer for horsepower would have to be Pratt & Whitney with four R-4360s buried in the wing of the XB-35 flying wing. These engines had very close-fitting shrouds on each cylinder and fans placed at the front to force feed air into the ducting.

Read the full article: Click here

Posted in Aero Articles

Forced Induction

SPF Cover Summer 2015by Phil Kennedy, SprintAero.
As published in New Zealand Sport Flying Magazine Summer 2015 issue.
SAA SP1961

Unfortunately for those of us based in reality, the likes of “Knight Rider” and other silly TV programmes have given the public a very strange slant on what supercharging of any form really does for an engine.
The most common real-world reasons for wanting to use supercharging and turbo-supercharging are:

  • Wanting to maintain standard power to a higher altitude:  Known to us older guys as turbo normalisation, but I bet there’s a really cool TLA (three letter acronym) for that now. The plan is to keep the pressure at the intake valve the same as it would be if it was at sea level and didn’t have a turbo. The idea behind this is that we want to maintain the standard performance, without undue strain on the engine etc, up to a nominated altitude.
  • Wanting more power: Taking the “more must be better” approach, this is for more horsepower down low and hopefully maintaining it when we get to those upper altitudes. Shortened takeoff runs, shorter time to climb numbers and SPEED. Grunt is what you are after and pushing more air into the cylinder is how you intend to get it!
  • Wanting to silence the motor somewhat: If you choose to place a turbine in the exhaust pipe you will, by the very nature of the device, mash all the exhaust pulses together and then chop them up with the wheel. This is actually the only muffler in the world that improves the performance while it attempts to silence the barking exhaust.

Read the full article… Click here

Posted in Aero Articles, Custom Design

Why So Cranky?

by Phil Kennedy, SprintAero.
As published in Sport Flying Magazine, Autumn 2015.
SAA SP1961

STARTING OUR ENGINES and supplying enough power to allow us to do it again is the subject of much consternation among the light aircraft community.

We have three distinct groups within this community, each with its own issues with regard to this subject.

First is the good old “I can’t afford the weight of the system” group, closely followed by the stuck in the mud “we can’t change that ‘cause it was a hand-me-down from my grandpa’s grandpa …” group, and not forgetting the non-technical “I don’t understand the little electrons in the electron pipes” bunch to finish off.

To sort through these issues, let’s address the various technical challenges and changes in sequence.

Read the full article: Click here

Posted in Aero Articles

Induced Drag vs Form Drag

by Phil Kennedy, SprintAero.
As published in Sport Flying Magazine, Spring 2014.
SAA SP1961

A RELEVANT QUESTION to our sport might be: “Is drag of low importance because we fly slowly, or do we fly so
slowly because of the drag issues we ignore?”

In recent days we at SprintAero have been blessed with the support of an engineer who just loves to review
things from a first principles point of view. So when I make bland “statements of fact” you can see the lights go on behind his eyes as he determines how to prove or disprove my comments.

The issue that started this article was the discussion of overall drag
and the part that aspect ratio had to play in it.

My statement was the usual “you need high aspect ratios to be efficient” which immediately got the raised eyebrow treatment. He quickly picked
up his laptop and began creating a spreadsheet using the first principles, then after plugging in the basic dimensions of my Corby (all the while
muttering that bland statements that cover everything in one sweep almost never work) we started to get data.

Read the full article: Click here

Posted in Aero Articles


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