C172 ENCOUNTERS STRONG DOWNDRAFT AND UNABLE TO MAINTAIN 8000 FT. REQUESTS AND GRANTED BLOCK ALT 7000-8000 FT. CTLR ADVISED HAD NOTED DEV TO 6300 FT. REQUEST DIRECT HRS VOR TO ENABLE LOWER ALT.

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RETURN LEG OF A BUSINESS TRIP FROM CEU; SC; TO JWN; TN; AT NIGHT ON AN IFR FLT PLAN IN VFR CONDITIONS. HAD PROCEEDED THROUGH THE AREA EARLIER WITH FEW DIFFICULTIES. OBTAINED WX BRIEFING PRIOR TO INITIATION OF TRIP. REQUESTED ALT WAS 8000 FT; DUE TO TERRAIN OF 5499 FT ALONG RTE. ENCOUNTERED SEVERE HEADWIND ACCOMPANIED BY DOWNDRAFTS APPROX 10 MI N OF ODF VOR. GND SPD DECREASED TO A LOW OF 34 KTS (AIRSPD 110 KTS) AT ONE POINT. UNABLE TO HOLD ALT EVEN WITH A PITCH UP ATTITUDE OF APPROX 7-10 DEGS. CALLED CTR; REQUESTED AND CLRED FOR BLOCK ALT OF 7000-8000 FT. CONTINUED TO HAVE DIFFICULTY HOLDING ALT FALLING TO ATC RPTED 6300 FT. QUERIED BY CTR ON ALT. INFORMED THEM CAUGHT IN DOWNDRAFT CONDITION. ALSO NOTED TO THEM THAT HIGH ANGLE OF ATTACK REQUIRED TO MAINTAIN EXISTING ALT; ALONG WITH DOWNDRAFTS MAY BE CAUSING ERRORS IN PITOT STATIC SYS. THEY QUESTIONED IF ICING EXISTED -- NEGATIVE. AFTER STRUGGLING WITH CONDITION UNTIL E OF HIGHEST TERRAIN AREA; REQUESTED DIRECT HARRIS VOR (HRS) AND THEN V54 TO CHOO CHOO VOR (GQO). THIS RTE ALLOWING A 6000 FT MSA. CLRED AND PROCEEDED TO CHA FOR REFUELING. NO ADDITIONAL DIFFICULTIES CONTINUING TO JWN. SOME CONTRIBUTING FACTORS INCLUDED THE LIMITED PWR OF THE C172 (150 HP ENG MODEL); AND THAT THE CTL OF THE AIRPLANE WAS A HANDFUL AND MADE IT DIFFICULT TO CALL ATC AND REQUEST HELP FINDING A LOWER RTE SINCE THIS WOULD HAVE MEANT TRYING TO READ A CHART WHEN CTL OF THE AIRPLANE REQUIRED 100% ATTN. THIS; IN ADDITION TO THE ASSUMPTION THE PHENOMENA WOULD BE SHORT LIVED; DELAYED A CALL FOR ASSISTANCE UNTIL AFTER THE ALT WAS OUTSIDE PARAMETERS. THE APPREHENSION RESULTING FROM BEING BELOW 8000 FT IN THE MOUNTAINOUS TERRAIN FURTHER RAISED ANXIETY AND RESULTED IN A STRUGGLE TO MAINTAIN ALT AND LIMITED COMS WITH ATC UNLESS QUERIED. WHEN THE STRUGGLE FOR ALT CTL BECAME SO CONSUMING OF PLT'S ATTN; I SHOULD HAVE REQUESTED ATC ASSISTANCE IN CLRING A NEW RTE TO A LOWER ALT. I WAS HESITANT SINCE I ASSUMED ZTL WOULD BE BUSY AND UNABLE TO ASSIST.