solved it based on another answer previously posted. The key is basically you have to set scale to zero and then scale both quivers after plotting.
figure;
h1=quiver(xt,yt,quiverXt,-1*quiverYt,0,'filled','k');
hold on
h2=quiver(xc,yc,quiverXc,-1*quiverYc,0,'filled','r');
hold off
scale=5;
hU1 = get(h1,'UData');
hV1 = get(h1,'VData');
set(h1,'UData',scale*hU1,'VData',scale*hV1)
hU2 = get(h2,'UData');
hV2 = get(h2,'VData');
set(h2,'UData',scale*hU2,'VData',scale*hV2)