<aura:component ...>
    <aura:attribute name="message" type="String"/>
    <aura:attribute name="vfHost" type="String"/>
    <!-- Input field for message "data" -->
    <lightning:input type="text" label="Message:"
        value="{!v.message}"/>
    <lightning:button label="Send to Visualforce"
        onclick="{!c.sendToVF}"/>
    <!-- The Visualforce page to send data to -->
    <iframe aura:id="vfFrame"
     src="{!'https://' + v.vfHost + '/apex/myvfpage'}"/>
</aura:component>