hi everybody, i’m a tinwhistle beginner. I’ve come across some whistlers that play a D tune on C whistle? how can you do that? i mean, when you cover all the holes in a C whistle the note is gonna be a C, not a D like in those D whistles. and beside the F in a C whistle isn’t F# like that in D whistles.
To paraphrase the classic wisdom: A gentleman is someone who can play in D on a C whistle … and doesn’t. 
Seriously, when people play tunes on a C (or any) whistle, they generally finger them exactly as on a D whistle. The C whistle acts as a transposing instrument, and the tune simply comes out one tone lower. That is probably what you’ve come across.
What you’re describing is playing in the fingering of E Major on a C whistle. As you suggest, it’s not pretty. The whistle is simply not designed to play E Major fingering, though it can be done with practice.
Oh, and welcome. 
Welcome!
It’s perfectly possible to play a tune in D on a C whistle, but it requires a motorbike. Until you’ve mastered riding without having to hold on to the handlebars, I’d stick to playing in D (and G) on a D whistle though.
Let’s see: fingering D major on C whistle:
D XXX XXO (as E on D whistle)
E XXX XOO (as F# on D whistle)
F# XXD OOO (as G# on D whistle, third hole half-holed)
G XXO OOO (as A on D whistle)
A XOO OOO (as B on D whistle)
B OOO OOO (as C# on D whistle)
C# XXX XXD (as D# on D whistle, sixth hole half-holed)
D# and G# (in D whistle fingering) are the awkward ones.
If the tune has not got any seventh or third it helps.
If you get clean G#s and D#s you got it nailed.
And you can use it to play in E major/F# minor etc. on a D whistle
Oops. 
Also, xxoxxo works as a quite good G# in the second register of many whistles.
Yes, there are a few E-ish tunes that crop up now and then. Calliope House (EMaj), Andy de Jarlis (EMaj) and Aherne’s Egg (EMix) come to mind. In session, it’s nice to be able to just launch into them without grabbing for a different whistle.
Oops indeed 
thanks for the alert! corrected my typo to E XXX XOO
If I recall correctly, it requires a C whistle, a motorbike and Andrea Corr…
Best wishes.
Steve
oh thank you for fast responding people, i didn’t expect your answers so soon. guess this forum is very active then.
now i finally got it.
oh and by the way i figure out a trick to play a E major on a C whistle: just put a tape half cover on the third hole from the bottom.
it worked quite well.
My Bracker C whistle has a pretty decent cross-fingered G#. XXOXXX in the 1st octave. XXOXDO in the 2nd octave. I don’t know any trad. tunes where you’d need the E maj. scale but a good jazz tune in E (concert D) is Sweet Georgia Brown. It starts on E maj. and resolves to G maj. (D maj. to F maj.). It’s a fun tune to play and improvise on.
well, E maj= E F# G# A B C# D#
so your one tape solution on a C whistle is not convincing
Oh my. The ultimate hat trick. Am I dreaming? Don’t wake me up if I am.
Sportster 
Might he be referring to D dorian, which is not a problem at all on a C whistle?
Jaydoc
who might be referring to D Dorian?
Good point, if the OP overlooked the difference. C whistle is indeed usually the right choice for D Dorian tunes, using E Dor fingering. It’s one of the reasons session whistlers often carry a C whistle in their kit.
Oh right, he was reinterpreting the “D tune” reference in the OP.
Thanks.
Yes a “D tune” in the key of C/Amin is indeed Dorian as is an “E tune” in the key of D/B min
but neither on the respective C or D whistles need taping to obtain the right note/s so I am having difficulty with the sequitur of the posts in this topic unless the thread itself is nourished by confusion/confusing content at key junctures.