I TRIED A 14X4 PROP YESTERDAY ON MY BIPE INSTEAD OF THE 13X6...DIDNT HELP AND SWITCHED BACK TO THE APC 13X6. HAVE A SAITO 72 IN NOSE AND MOUNTED THE ELEV SERVO IN TAIL AND USED A PULL-PULL FOR RUDDER , AND HAVE MORE ROOM TO MOVE BATTERY INSIDE OF FUSE OF PLANE......I DID SEAL THE HINGE GAPS AND IT DID MAKE A DIFFERENCE FLYING, BETTER ROLLS FASTER AND QUICKER RESPONSE. I SAY URE HEADING TOWARDS MORE POWER, SAITO 91. THE YS 63 OR FX 91 WILL ALSO GET THE NEEDED EXTRA POWER. A 14 PROP FITS MINE WITH 3 INCH WHEELS AND NO WHEEL PANTS WITH ROOM TO SPARE. ANYONE OUT THERE WITH A SAITO 91 CARE TO MENTION HOW THE VERTICAL IS.....?