Tail Flutter in the CG-4A

UPdated

Tail flutter was in issue reported by the glider pilots in some of the later missions which had them very concerned, and rightly so. I never could find a full explanation but recently came across and old article in which FO Sigmond Granacki wrote abou

t the tail flutter which seemed to be an issue in 1943. This is an issue which is not talked about often but could be deadly. The 442nd also experienced this issue with their gliders. F/O Granacki was with the 63rd TCG in Grenada Mississippi participating in a War -Bond rally which included being towed down the main street and throwing out cartoon containing $25.00 war bonds (who knew?) when he noticed a tail flutter but thought it was due to the rough air. He marked the tail with an "X" in the long and described the issue. The next day the glider was taken out by Lt. David Ihrig for a demo flight - the glider crashed in an outside loop during that flight after he had communicated with the tow pilot he was having an issue with the tail and needed to make an emergency landing. Later, he was flying a co-pilot with Bob Winer and again experienced a tail flutter but landed safely but as a jeep pulled up to tow him to tie down he told him not move because his tail struts were dragging the ground.

After investigation it was determined "the early struts were thin ovals which positioned so as to be streamlined with the air flow. If, as happened on several occasions, they got out of line they created a fluttering effect. They were fastened on the horizontal stabilizer with a single bolt, which after a period of time was fatigued by the flutter actions, and broke loose. Thus the vertical stabilizer had no support and its negative lift lost, allowing the ship to nose in."

The fact that the air flow hit the different wires at so many different angles prevented the wires from being “aligned”

The solution was to use a “rigid forges fitting”, however, “they looked so much alike that some of the people assembling the gliders didn’t notice the difference between the 30 degree bottom ones and the 4 degree top ones, and put some in the wrong position causing an eccentric load on the bolts and fittings. To make matters worse some riggers would put the bolts for the bottom fittings with the head up and the weaker threaded end down at the fitting. The lower wires had different bolts from the top ones so the lower and upper fittings were under the bolt heads.”

F/O Granacki was successful in reducing the wire vibration with the aid of section of a broomstick.

“One day I decided to try to dampen the wires by tapping across the middle pieces of broom sticks that the ground crew found and stole for me. I went up in the glider as passenger to watch the wires and to my dismay the sticks were stationary but the wire halves were vibrating in harmony on both sides of the sticks. After coming down I asked the ground crew to help me move the upper sticks down about eight inches and bottom ones up six inches. The next trip up to watch and I found that the vibration was ended. The base shop sawed up a lot of one by one sticks for rest of our gliders.”

It was after this that the “streamlined steel tube struts at the bottom and round aircraft guy wires at the top.”

F/O Granacki joined the service in 1942 at 33 years old and was initially military police as my father was and both were assigned the rank of Warrant Officer. He was transferred to gliders and graduated in the class of 43-01, one of the first classes of glider pilots. He was also one of the older glider pilots at 33. During one mission he diverted a group of gliders to a safe landing area. He was assigned to the 44 TCS /316 TCG and 71 TCS /434 TCG. He flew in Normandy and may have flown in other missions.

The photos of the issues with the guy wires and the changes made are courtesy of Jean Soldi a fellow researcher with the NWWIIGPA and who has his own site which anyone interested in gliders should definitely check out

https://www.operation-dragoon.com/glider-cg4a-project/glider-renovation/?fbclid=IwAR3U9YPqB-jRMct1hV8e-SOQGF1tK15eWaqXMHbQbUsc2MnAVI317FbBj5g