I keep looking at my youngest son’s Star Wars light sabre with the collapsible plastic shaft and thinking “collapsible low D conical bore whistle”.
If you can manage to get it to make music AND still light up, that would be most excellent… 
Actually, the idea of a flute/weapon is not new. The Japanese Shakuhachi was designed to serve both purposes. In Samurai Japan, only Samurai were allowed to own weapons and itinerant monks were constantly being robbed of their meager money. The heavy root-end Shakuhachi flute made a formidable club to deter would be robbers.
Nah, forget it - it’s unlikely to the point of impossibility that it would be airtight at the overlaps of the telescopic sections - even if heavily caulked with grease or wax…
Anyway, I bet the thrumming noise wouldn’t be the right pitch for a drone…
I have one that makes noises as well and when you hit them together they make a clanging sound.
David O’Brien makes a telescoping high D whistle that works well. Jemthe flute has a point: as the number of joints increases, getting the tube to stay airtight might be a problem. If it’s the weapon aspect you are after, Dixon low Ds in aluminum are sturdy enough to make a good dent in someone’s noggin without hurting the tone much.
So is my home made one:
http://picasaweb.google.co.uk/gordonhudsonnu/Instruments#5293005763299008530
How important is airtightness in a woodwind instrument?
I suppose the risk is that if you have a leak in a whistle its like having another hole and it will upset the whole system.
In natural trumpets we sometimes make openings (called vents) to interfere with the nodes and change the pitch of certain naturally occurring notes. Rotary valve trumpets have at least one key (doubling as a water key), sometimes as many as three the same for certain notes.
I used to have a thing called a “clip on scope” it was a minature telescope that looked like a fat pen, it had a three or four section proper telescopic construction. That would have been a potential donor for an experiment but it has long since gone missing.
Airtightness of the tube is fairly crucial. Ask any Bohm flute player about leaks due to worn pads or damaged or mis-adjusred mechanism: a tiny leak will at the very least make low end notes very difficult or even impossible to sound. However, the precise effect may depend on the precise position of the leak and its size.
We do use venting to assist harmonics on flutes and whistles - e.g the oxx xxx fingering for 2nd 8ve D (1st harmonic) which is vented near the node to improve strength and clarity and maybe to tweak intonation - that function is one of the compromises involved in siting and sizing the C# (L1) tone-hole. Most of the 3rd 8ve fingerings on any of the flute family involve cross-fingerings that manipulate the harmonic scale by venting at or near nodes. This fact is the root of the availablilty of multiple possible fingerings in the third 8ve - e.g 3rd 8ve D may be played as oxx ooo = 2nd harmonic (12th) of fundamental G or as oxx xxx = 3rd harmonic (double 8ve) of fundamental D. The further up you go, the more choices you get, in general.
Going back to leaks, any multi-segmented telescopic tube whose segment joins are not engineered to very close to airtight (with appropriate lubrication) will make a very poor if not useless whistle/flute tube.