MAIL ADDRESSBOX 156. MOULTONBORO. N. H.

03254

TELEPHONE603-284

IRA H. ABBOTTCONSULTANT

AEROSPACE RESEARCH & TECHNOLOGY

SANDWICH, NEW HAMPSHIRE

Nove ber 14, 1974

r. Ed ar Cortri ht, Director,Langley es reh St tion.

,H pton,Virginia 23655.

Dear Ed.:

article on echnolo y Req-for Planetary Aerothermodyn iea

eronautics. I wa e peciallycar on dioxide and th

I r ad with int re~t Olstad'uir nd Experimental Facilitiesin the ove ber issu of Astronauticsint rest d in Lan ley's us of uch aseflloronat'd carbons lor s1 ulation u os

hile I w at Langley ome 35 y ars go e ere v ry inter st din the use of the e s gase~"n wind tunnels for obvious re ons,but we were conc rned a out hether their use w uld result in tru

i ulation.

So e imple experiment conducted by us at that time indicatedthat e ch of these gases might not h ve con tant value for theratio of th pecific he ts t constant te perature, but th t thivalu varied with the sp ed ith hich the gas a heated. 0 suchffect as found for oxygen, nitro en or the noble 9 se, ut a. ilar ut ller ffect s found for ter v par. 1 0, if I

r eber correctly, si ilar but rather large effect a foundfor chlorin •

pecifically, "e found that the value of the impact pressureasured by sharp ended impact tubes at su onic speed v ried with

the size of the tu es. We used tubes foo normal sizes do to veryall on s at rather 10 speed. Th r te of heating at the sta ­

nation point at con tant velocity as, of cour e, depen ent onthe size of the tub. By varying th size of the tu s and the peein th exp ri ent , it was det rmined th t th effect wa not there \lIt of 0 e experi ntal error, ut that it w in fact controllby the time r q ired to bring the gas to rest.

OUr conclusion at the time as th t this .ffect re ulted fra finite ti required for equilibriu in ~he quipartition of

en rgy ong the v riou od s, probably s re ult of lag in onor ore of th vibrational odes. e ere encoura ed i. this bell f

y the fact tha 11 th e showin thi effect er tho whoseratios of pecific heats did not corre.pond 11 ith those calcul­

t d Y th cl ssical ethod regardless of th n b r of modesr son bly a sum Al 0, thos gase which did not show this effect

r thos for which thi ratio correspond d closeiy with thecalculat d value without vibr tion 1 mod s. At that tim the

application f quant mechanics to the problem did not help. Ihave not kept up, so 1 do not kno hat the situat~on i no.

A r ult, e concluded that it as not safe to u e such gasefor si ulation purpose •

I notice in figur F-12 of Olstad's article that the calcul tand measured hock position for c rbon dioxide agrees w 11 altho ghthe figure i rath r sm 11 to deter ine any m 11 con i tentdeviatio. I ould expect, however, that this ould not be a verycritical ure of the deviation of the flo from that e ct dusing the published values f the ratio of the specific heat •This r ult bec use the usu 1 values are obtained by u ing theme ured value of the velocity of sound in the 0aS as one parameter,

nd ccordingly were obtained at hating rates of the sam order ofrna nitude as t ose existing in the shock front.

Since Imatters oth r

st too uckno which of

retired I no longer h ve any real interest in t esethan curiosity, so please do not have any of your peopti e in r plying to t is. I would m rely like to

the following pertains:

1.kno

L gley has not really considered th e pos ib~litie •L n ley, I think this is hichly unli ely.

If I

2. Our results were wrong. This is lways possi I but appearunlik ty in a uch a the same re ults weee obtained by ore thanone person in ore than one apparatus and ere closely ob rved bymany skeptical p ople.

3. Our interpret tion of the results as wrong. This is verypossible as we had little to go on and were strongly 1nfl enced bythe de ir not to ake i t ke in i ulation.

4. This matter h been considered and it has been concl dedth t any effects ar not i portant to the simulation desired.This i the most likely.

-incerely,

/Ira H. Abbott