Hi.
Use free samples like from here: https://www.zapsplat.com/music/steady-engine-rotors-of-a-helicopter-idling-on-the-ground-loop/
Add in Montage / Modx Effect processor (FX) like Phaser

There's probably an FM-X + LFO + insertion effect(s) solution.

The version that uses an ARP (because the guy didn't have his Prophet 5 available) starts with a sequenced slap bass kind of sound sliced up and an external phaser. There weren't gory details of what was done - but you can hear the original tone and the sequence pattern. At least that much can be replicated and then try using LFO amplitude to try to slice up the sound. Of course flange or phase is the easy part with insertion or system effects. Pitch drift can be applied using motion sequence or even LFO on pitch.

I checked Soundmondo and found Reface (CP and DX) helicopter sounds. The existence of DX ones suggests that you can probably do this in FM-X although I don't know how close they are to what you're looking for. I'm more pointing to these as some indication that FM-X can probably do helicopter and tweaking can likely get you there.

Also, assuming you (or someone else) does this with FM-X - then it can be shared completely on Soundmondo assuming no user LFO patterns, user curves/pulses, or user ARPs are used.

And then one could probably also use an AWM2 preset bass that sounds like that ARP version which could also be shared on Soundmondo assuming no user custom stuff as listed above.

If preset curves/LFO can be used or not is unknown. I'd probably create a user LFO pattern.

Here's my 2c....

Not a helicopter.

I think roughly this...

Sound -> Slicer -> Flanger

Sound is then slowly pitch shifted down.

If I didn't know any better I'd even suggest it was possibly played on guitar, and the pitch shift down was the guitars tremolo bar "pitch diving". Hard to tell.

First thing you need is a Slicer effect. That is basically a high depth tremolo effect (amplitude modulation) with almost a square wave modulation. ..... on off on off on off, set to the tempo you hear on the record.

You could use a Part LFO for this, Square or Pulse Wave, governing Amplitude. There may also be a dedicated Tremolo/Slicer effect in MODX Insert or Var effects.... you'd need to check.

Flanger - really slow rate, medium depth, turn up the regeneration/feedback until you start to hear the (comb) filter sweep. Try Flanger before or after Slicer..... try both, choose which sounds best. TIP: The Manual control can be used to set the resonant frequency.... a bit like pseudo tone control... use it to "tune in" the sound of the filter sweep.

Sound.... so what is the base sound? Hard to tell. You'll have to experiment. I recommend starting with a Clean Guitar sound on the MODX and Sustain it.... that'll give you the general idea to get you going.

Sustain the sound, let the slicer do the "picking", then slowly pitch shift down.

Also be aware of a Throbber effect, which, with the right settings can also produce a Choppy Filter Swept Tremolo effect in one shot...

although I think Slicer+Flanger will get you in the ball park.

Here's my 2p
Nick Rhodes says this was a sequencer played on a Prophet V
If you listen closely (i had to slow it down, a lot!), its not just one note but is actually this sequence D1 C2 D2 D1 C2 D2 C2 D2.
The sound can be emulated with a couple of saw waves and some white noise and very short envelopes
Its probably easiest to make a user Arp of this sequence.
Then whack on that Flanger.

I'll put a version on Soundmondo tomorrow

To Dave.... I aimed at the ball park, I think Graham hit the bullseye. Incidentally.... Pink Floyd used the Slicer/Filter effect in the middle section of the song "One Of These Days" if you care to have a listen to it.

To Graham.... hey dude, it looks like you know your stuff. I have a few "sound design" questions of my own. I've not got the Soundmondo thing working yet, but will. Would you be willing to help me out on a couple of headscratchers? (I am novice level btw).

Anthony. please ask away and i'll help if possible. One byproduct of the great European lockdown is that i have more time on my hands!

Thanks Guys!

It seems to be one of those ones wheres there's more than one way to skin the cat...(sorry cats)

I did get something going with an LFO on a saw wave - not matching the original exactly but I will try your suggestions over the weekend.

While I get the "better not to get too hung up on exact replication" idea, the attempt at replication is a good way to work out how to program sounds and recognize stuff that you hear.

I haven't got much in to the effects side of things so far - but I've just bought some studio monitors and I'm thinking I should be a bit careful as I'm plugging straight from the MODX to the speakers - I have been advised earlier by the Bad Mister that a small mixer in between can provide some protection...

thanks again

'Planet Earth Intro' now on soundmondo. I like the line "better not to get too hung up on exact replication"

LH: Sequencer
RH: Strings

SK: Fades sequencer in on Scene 2
MW: Filter Cut Off
Assign 1: White Noise Only

The correct notes for the sequencer are D1 C2 D2 D1 C2 D2 C2 D2 which can be played manually (or put in to a User Arp), although holding D1 C2 D2 instead comes pretty close

The flanger on the sequencer is controlled by Part 1 - Part LFO for depth and speed (i've got it currently synced to tempo. Not very 80's!)
Sculpt the sound by selecting Part 1 and the Tone controls

I put a version on Soundmondo as well, for comparison.

I didn't use a sequence as such - just an LFO and flanger.

Like a lot of MODX stuff at the moment - I tend to do learn something for a particular task but then don't come back to the method for a while and tend to forget the procedures..