Need loop to copy chunks from byte array

I have to process a large byte array that is passed to my function. I need to copy the content from this incoming byte array in smaller "chunks" to an outbound byte array.

For every "chunk" of data created in the outbound array, I need to call a web service.

Upon return, I need to resume looping through the incoming byte array, continuing to pass a whole or partial chunk of data until the complete incoming array is processed (i.e. sent to the web service in chunks).

I am very new to C# and I am struggling with a loop that works. I know how to call the web service to handle a "chunk" but I can't get the looping correct. Here is a sketch of the pathetic mess I currently have:

int chunkSize = 10000;
byte[] outboundBuffer = new byte[chunkSize];     
while (BytesRead > 0)
{
long i = 0;
foreach (byte x in incomingArray)
{
    BytesRead += 1;
    outboundBuffer[i] = incomingArray[i]
    i++;
}
uploadObject.Size = BytesRead;
uploadObject.MTOMPayload = outboundBuffer;

// call web service here and pass the uploadObject 

// get next "chunk" until incomingArray is fully processed 
 }

I know this is a mess and won't work; could someone sketch a proper loop to get this done? Thanks very much.