Remember you have a 2 blade too :)

[Ian P]

I actually really like the look of the aircraft with the big 2-blade prop, but when we're doing things as realistically as possible, the big word "EXPERIMENTAL" rules out a lot of non-private flying activities. I don't know what the rules are in the US, but most non-certified aircraft in the JAA area cannot legally fly IFR, for example, unless on a specific and planned designated test flight.

I guess it comes down to the fact that some places such as Europe and Japan are a lot more risk averse than other places... If it says "Experimental" we don't trust it enough to allow it to do much.

Cheers,

Ian P.

[AKar]

I don't know what the rules are in the US, but most non-certified aircraft in the JAA area cannot legally fly IFR, for example, unless on a specific and planned designated test flight.

Which brings to mind my fun fact of the day.

One consideration when selecting the propeller for an aircraft with powerplant having certain rpm range is the interference with ILS signal. Both localizer and glideslope signals are basically constructed the same way. If we take the localizer for example, in it the same carrier frequency (the one you select in your NAV radio) is sent in two directional beams, one to the left and the other one to the right side of the runway centerline. They are amplitude modulated, that is, their strength is varied, at 90 Hz and 150 Hz respectively. Comparing the local prevalence of these two signals (technically done by using something called difference in depth of modulation) the receiver forms an error signal displaying the deviation from centerline.

Glideslope works the same way, except it uses different carrier frequencies (at 328.6 to 335 MHz band; the glideslope frequencies are paired with localizer frequencies so that the glideslope receiver can tune the correct frequency automatically based on what you tune as localizer frequency), and the beams are laid vertically instead of laterally.

Now, you may note, that the passing frequency of the propeller blades in front of the glideslope antenna particularly, is of similar magnitude to the frequencies at which the strength of ILS signal beams vary due to their amplitude modulation. For example, in 182S and T a three-blade propeller at 2000 rpm swings a blade across the line of sight 100 times a second; at 2400 rpm it will do that 120 times a second. A two-blade propeller at 2400 rpm does that 80 times a second. Note how these frequencies, corresponding to the green arc RPMs, just avoid the frequencies at which the ILS signals vary in strength (though their common frequency contents surely overlap some, certainly in case of two-blade prop at just slightly less than 2000 rpm, likely requiring some flight tests to confirm that its not a problem).

If the passing blade altered the reception of the signals at the frequencies they are varied in strength in transmission, that will surely cause unreliable ILS indications.

I have read and heard about several airplanes which had an issue from propeller interfering with glideslope during development. It makes yet another example of how complicated the interactions of different airplane systems can be, and why these extensive certification programs are there in first place - even if some aspects of them might very well be questioned.

-Esa