I see lots of flutes with slides, and lots of flutes without slides. In this day and age of electric tuners, and everyone agreeing on playing A=440 as a standard and makers who make flutes that play “in tune”… How come we have slides in flutes. Is it really a mistake to buy a flute without a tuning slide if you want to play with other musicians? Why would I need a slide if my flute is designed to play @ 440? help please…
Apologies to Paul Simon,
Deisman
Try playing a gig with a piper, you’ll see why a slide comes in handy… 
Well, I have two otherwise identical, keyless D flutes, same model, same maker, but one of the flutes has no tuning slide, while the other does. Long story short, the flute without a tuning slide is for my own enjoyment, while the other could allow me greater adjustment to other players, if need be.
I play them both, regularly, and they’re both fine flutes, but I prefer the one without the slide.
When the flute is cold, the notes will be flat, as the flute warms up the notes get sharper. Players have different embouchures, some play flat, (like our “SillyDill”) others play sharper, having the slide helps customize the flute to the player.
Or the other person you’re playing with isn’t in tune,
despite all the technical doodads, and it’s a lot easier
for you to tune to her than for her to tune to you.
Definitely happens.
I play a slideless Flute and have no problem playing with others what-so-ever, my Eb has a slide but I rarely play that with others. You don’t ‘need’ a tuning slide to play with others a Flute is still tuneable without one it just makes it a bit easier to tune when you have a slide. I think they are a good thing to have, but it is not essential that you have one. Plus you can change the pitch in other ways than moving the slide or tenon joint such as lipping up or down and turning the headjoint.
In addition to the above, different atmospheric conditions have different effects - both heat and humidity tend to push flutes’ effective pitch in relation to their scale length sharper. I’ve just come back to Wales from Spain. In Spain it was hot and dry and I had to tune my flutes significantly longer to get A=440 than I normally do at home. Changing micro-climatic conditions in a performance venue can have quite significant effects, especially when the same conditions have an opposite effect on any stringed instruments you may be playing with - they go flat in heat and damp!
ok - thanks folks for clarifying that to me. looks like having a slide is a good thing in the long run, unless of course you are playing with a piper, they’re always out of tune… ; 0 thats why they sound so great!
Deisman
I find my current slideless flute quite in tune and quite tunable. I used to think a slide was critical and required to play in tune with others–not so anymore.
Not mentioned, though, is how a slide can affect the tone of a flute. I find my slideless to be very mellow and wonder if a slide might give more of an edge to my tone which I’d like to have at times.
i’m going to second that everyone plays differently. i played an olwell the other day, which the owner had the slide pushed all the way in. i pulled it out almost an inch to play it in tune.
I’m not going to pretend to know the physics involved (apart from the usual air-density stuff), but different flutes/players seem to react differently to changing conditions. My Cochrane Pratten stays pushed all the way in, all the time. Big holes, easy to lip around. My little german 6-key goes noticably flat even when an outside door is opened, but tends to stay in tune with itself as I boogy the slide around. My B&S moves less than the german (yeah, I know, it’s the air density that’s moving), but I have to chase around the intonation a bit more. Patent head, here I come.
BTW, if you want a drastic demonstration of air-density vs. pitch, just belch while playing. Good for at least 100 cents!
At one point, I was playing in sessions with a slideless flute, but between a change in my embouchure and our box player having an out of tune box for a year…I found it to be too difficult to play in tune without the slide.
So…you might be fine, you might not…depends on you, the flute, and those you want to play with.
Eric
Thought I might tell about a wooden French flute I loaned to Eric once:
He said he liked the flute, but the slide wasn’t long enough for him to play it in tune.
Funny, I played the same flute in tune with the slide shut! 
Guess I’m just saying Eric is a sharp player! 
I figure Eric and I are near the extreme opposite ends of the spectrum.
But everyone is different! 
cool - thanks everyone for the good info - that helped. Reason it came up is I’m considering buying a new keyless, and the choices I am weighing is between a Forbes derlin and a Burns folk flute - both about the same $ but obviously 2 very different animals. I still don’t know which I prefer, so as I always do I’ll wait a bit until I feel comfortable with a decision.
milli gratzie,
Deisman