I have not yet hit a tree or large under growth, But recently in Iraq we had a large landing air pannel, (the large orage things that Identify friendly vehicles, or LZ's) come up and hit or main rotors on landing. They hit hard enough to cause lage dents covering the entier cord wise lenght of the main rotor an 3 in across. Plus the numorouse bullet hole seen in blades, they make a funny sound but did not fail. The only mishap I know about caused by blade failure was a AH-1W over Brown field in 1991. Internal corrosion cause mid blade sep. and unbalanced rotor situation. No reported sounds or anything, it just came apart.

I never regarded "nicks and gouges" as a real problem as long as the crewchief had a good supply of blade tape. "Big" pieces and "beats" were the problem. Integrity of the spar a major concern. How much damage was accepatable was directly related to how hot the zone was, the pucker factor and how far it was to a relatively secure area.
Q

Blade Damage

While nothing is substitute for a good pre-flight, there were those times that you just couldn't avoid brushing those trees and bushes while hovering for an extraction, etc. I would listen during "hot" refueling for any tell-tale "whistleing" sounds that might indicate a round through a blade or a tear, etc. If we REALLY cut up some trees, we'd shut down for an inspection at the first opportunity for a good look-see. Every now and then we'd shake and shudder back home because we took too much off of one or more blades. Didn't need to be very much to make a noticable vibration or to make us all real nervous either, since we were flying CH-46A's and they had a propensity to fall out of the sky back then anyway! Even a blade tip light knocked off would make a slight difference. The hot tip was to miss the trees, and we did every chance we got! If they looked bad when we got back, we changed them and the next launch was never an issue. If the Crew Chief thought they were good enough they generally were. Never had a HAC come behind me and want blades, or anything else as far as that goes.
John Dulligan tells the story about the loss of a CH-46 and crew because someone taped over a bullet hole in the main spar! The blade finally weakened to the failure point and the when it failed, the bird came apart, quickly. All perished needlessly because the tape had hidden the damage from everyone. This was a "D" model, but no matter same story regardless. Couldn't let spar damage go, too critical for strength issues. Trailing edge.....not as bad but care was needed. A bullet hole in the spar would've grounded my bird wherever it was until we got a replacment blade. We could change them in minutes, no point in the risk.
Semper Fi
Joe

Your question has many different answers depending on the type of Helo. Every helo has it's own reles for such indicents. The 46 could take bit of blade abise wit the ols type blades, in later years the ISIS blades took less. Most aircres I knew and flew with would not take off if they developed an severe beat and/or vibs on the grouns or in attemptint to lift..
I had a former Corba driver who had trans to the 46's in reserves tell of shooting off the tips of his blades once on a gun rin and returned to homeplate afety.

BIM indicators

On Sikorsky , Uh34Ds, CH53D-E and SH3 and later Helicopters the hollow main spars were filled with Nitrogen gas and the indicated would show if it lost pressure indicating a crack etc. This of course was part of the preflight. One notable case where this was ignored resulted in an CH53 helicopter from the reserve unit at Alameda crashing on return flight from Reno Nevada (believe that was in late 1971). The crew chief saw a BIM indicater showing low pressure and judged it to be a leaking indicater instead of a crack as should have been the decision. The spar is the critical part when damage has ocurred. Gouges in the spar area are defined in the maintenance manual & are diffrent limits for the locations along the length of the blade. Repairs are specified for gouges that are not over the limit, which consists of blending out the nicks. (Caution no metal files or metalic paper may be used due to electrolitic action of diffrent metals reslting in corossion). In a combat situation for returning to base some judgement has to be determined by the Crew Chief & Pilots. Many times I have seen Helicopters flown with the Tip caps torn off & several pockets missing. That is usually not too serious except for vibration & noise. Damaged pockets act as airfoil effects if bent downward or upwards causing out of track conditions. Main blades are airfoils traveling at hundreds of miles per hour. Recent photo here showed the CH53 flying with only 3 main blades so it is possible to survive considerable damage for a one time flight. While with the VNAF H34s I found a main blade with a bullet hole completely through the main spar about 3/4 out the length of the blade. The VNAF had drilled eight holes top & bottom of the spar and installed metal patches with metal screws. I found by the maintenance records that this blade had flown 122 hours with that unauthorized repair. Sikorsky could not believe this and requested the main blade. VNAF frequently flew intrusion personnel behind the enemy lines and their tactic was to fly just over the trees landing rapidly & frequently in small trees & undergrowth until they unloaded the personnel. This in order to cover the final off loading area. These Helicopters often returned with great damage to the main blades. On solid blade strikes, such as larger trees etc, the end lead weights would fly like shrapnel for hunderds of yards. SF PM

('67) On a night formation training flight, UH-1E, during the last part of a break up and rendezvous, we instantly developed a huge 1 to 1 beat (vibration that comes from one rotor blade). I put the collective in a position that gave us the least beat but that was in a slow descent. We were over Vista but I figured we could make it back to the CamPen strip. Made the landing OK. A bit of corrosion in the hollow trailing edge "spar" caused it to fail sending a crack forward to the aft side of the leading edge spar then outward, towards the tip about 3 feet. This was about 2/3 of the way down the blade. The crack was completely through the blade so that piece could flex on its own. I think the fix was to drill a drain hole at the end of that "spar" so that moisture would be slung out.

Another blade story: On an emergency recon team, 5 man, extraction ('66) they popped a smoke in a thinly wooded area but the trees were too high to get close enough to the ground for them to get on. They were being chased, talking loud on the radio. I slowly chopped my way down to them, keeping the tailrotor clear, through 5 or 6 feet of small tree tops until they could grab the skids and getup. No real damage to the blades but I did not know they could do that kind of stuff. Not something you normally test or try out for practice.

Feb/March of 70 we were day Medevac out of Marble. Ran one mission where we used the Stokes litter to retreive a Marine out of the bush using the hoist. Dropped the Marine at the med facility, but lifted immediately because we had receiived an emergency while inbound to med.
Unfortunately, in our haste to get airborne, we left the stokes behind.
Got out to the evac site and found a member of a recon team had fallen off a cliff and they suspected a broken back.
The only way I could have lifted him with the hoist was with a horse collar and I suspected that, if he did have a broken back, the collar would be a "finishing touch" on his injury. Went into a hover and asked crew for their analysis of the trees we would have to decend through. The crew chief (Fisher) said he was only worried about one at our 4. Asked about diameter and he said about the size of his thumb. I replied that was no sweat and directed all aboard to watch for other obstructions as we decended.
Got onto the ground, but as we lifted the entire aircraft seemed to be bucking. We were in Antenna Valley and I decided to take her home to Marble, called ahead and asked for a replacememt a/c since we had developed severe beat and "loping" in flight. Upon landing, ambulance was on our flight line and Marine was taken away. Upon shutdown, we discovered about a foot missing from five of the six blades.
Looked at Fish and asked him about the tree only being the size of his thumb; he calmly replied that that was at the top.
Line chief came out and told me CO (Bennie Mann) wanted to see me in his office. While copilot was preflighting our new bird, I went in to face the music, remembering the CO showing up for the early brief to tell us there were no aft blades left in country and we were not to take any chances of damaging the ones on the a/c.
After a few moments of making me sweat and inquiring about my attention to his mornig brief, he finally asked for my side of the story. After hearing the story he allowed how he would have done the same thing and dismissed me back to my mission.
Always wondered how the sixth blade escaped without damage, but that phabulos phrog brought us home.
Q

Bennie Mann

What a great CO!

I recall flying with Lt Col Mann in Nov / Dec "70 with HMM 161. He put me in the right seat and let me "lead" the section.

We took a bullet hole in a blade that day.

Next thing I knew I found myself on the schedule as a HAC and shortly thereafter a section leader.

I am sure everyone knows that as a Major, Bennie Mann was featured in Life magazine along with some other Marines.

Always wondered how the sixth blade escaped without damage

Maybe it was out of track?

Nahh. 161 never had birds out of track!
Q

Rotor Blade Damage

Tom,
Rotor blades can withstand a lot of damage. Bullet holes can be temporarly patch with 500 MPH tape and flown. Missing sections will cause an out of balance and or out of track condition. The one place you never want damage is in the spar. A nick or scratch can develope into a crack. Cracks cause blade failure and seperation (slinging of damaged section). Depending on how far in the seperation is; and it does not have to be much, the aircraft will self destruct from the out of balance condition. Don't confuse the leading edge with the spar, you can't see the spar. Sikorsky has a good indicator of spar damage with their pressurized spars. You can never be too safe!
Semper Fi,
Tim McMahon HMM-262 65-67

Rotor Blade Fix

Been many , many , moons since I repaired a blade, but this is how we repaired bullet holes in 364. This goes for small arms only. First you round out the hole takeing as little metal away as possible, then you deburr the inside of the hole{ smooth the edges by rubbing with a harder piece of metal than the blade. } Check carfefully for cracks, dye penetrant if in doubt. Zinc chromate for corrosion. Cut the blade tape in a circle at least 3 times the size of the damage, stick it on , shoot a little O. D. on it & if you would fly on it, it was a good fix. When in doubt , throw it out. At least that is how I rember it. S/F ED

Blade Repairs

Ed,
Rotor blade repairs have come a long way since the old blade tape (500 MPH tape) days. It worked pretty good but a real repair should be done ASAP. I worked as an A&P, IA in civil aviation since I got out of the "Green Machine" in 68 and have had the pleasure of working on Sikorsky corporate aircraft (S76) and attending their trainning. At the Sikorsky composite course in Bridgeport, CT the instructor would use a ballpeen hammer to smash holes all over a blade and make you repair the damage. Once the blade is repaired properly and balanced it is good to go to retirement. A spar can't be repaired! The course is now taught at the Flight Safety facility at West Palm Beach, FL. I would recomend it to anybody for any kind of composite repair work. It's a fun course and very informative.
S/F
Tim

53 blade strike............

It was late '67 going into either the Rockpile or the Razor Back that we had a shelter half go through the blades.

I was flying port gunner as we came in and there was a loud POP! from outside.

The pilot hollered over the ICS: "What was that!" .... it had sounded like a shot!

The sound came from all the canvas being popped out of the shelter half inside of the rolled riveted edge.

When I saw the "frame" (it looked like a picture frame) flutter back down through the blades,
I answered back; "A shelter half just went through the blades, Sir." To the tune of a whup-whup
sound coming from the rotor blades.

We aborted the lift and went over to Dong Ha and shut down to examine the damage.

The spar was fine, all that was missing was three feet of pockets on one rotor blade.

The pilot downed the bird and a replacement blade was sent up later in the day for replacement.

The pilot was none too happy about loose material in an LZ and let some folks know.

I forget now how we got back to Marble that afternoon. It seems like we flew as passengers on
a returning 53 later that afternoon.

Rotor Blades

In the fall of 67 (at Quang Tri) we were a flight of four Huey gunships getting ready to take off for Khe Sanh. The bird right in front of us had just lifted off the deck, and suddenly the tail rotor flew apart and the Huey fell to the ground with helicopter parts flying everywhere. (Fortunately no one was hurt.)
The investigators decided that the transmission mast was fatigued and ordered all the choppers to Phu Bai for x-raying.

With the rotor head and blades were sitting on the deck while we were waiting for the transmission masts were being checked, I happen to notice on the top of one of the blades, that had been previously patched from a bullet hole, that it was cracked across the width of the blade. The blade was about ready to crack in half and fall off. The normal daily and preflight inspection did not lend itself to inspecting the top of the blades account there was no way to see; the view of bottom of the blade looked fine, but the weight of the hanging blade exposed a pretty good size crack. The normal procedure (at the time) for repairing bullet holes in the blades was to patch the hole with plastic putty.
Thereafter whenever the rotor blades were hit the blade had to be replaced.
Thank God the higher ups decided the cause of the accident was the transmission mast or sooner or later we were have fallen from the sky. By the way, it was a tail rotor problem, not the mast.
Pete Greene, Crew Chief VMO-6 1966-68

Rotor Blades

The key to rotor blades was the spar. If that was intact it almost didn't matter about the blade pockets. I don't know if an H-46 was flown with no blade pockets but I've seen them with most of the pockets missing.

I would down a bird with any damage to the spar. Bullet holes were bad news but especially hits in the vertical face of the spar. Where the the airplane was was key. Hits would not usually cause an immediate failure so if the zone was hot, flying it out was the best course of action. There are no survivors when a blade fails.

Rotor Blades

I have been reading this thread about rotor blades with interest. Most of the comments involved combat or tree damage. My first awareness of the fragility or unreliability of H46 blades started at HMMT302 in California during the April through July 1968 timeframe, while I was transitioning to CH46’s. This also gives me an opportunity to honor the memory of several Marines, but especially Robert Trigalet, a young 1st Lt.
I was on a training flight doing parachute drops at Oceanside with the HMMT302 CO (name?). We were refueling before shutdown when the CO got a message of a 302 helicopter crash in the Saddleback Mountains. We immediately flew out the crash site.
S3 (name?), Vietnam veteran crew chief, and Bob Trigalet were on a training mission in the late afternoon. The instructor pilot was performing one of the favorite demonstration approaches to a mountain zone. The approach started by auto-rotating down the sheer vertical face of a mountain from a 5-6,000 ft height. After 3-4,000 ft vertical drop down this mountain, the pilot would transition a 90-degree right turn and be perfectly positioned for a short final to a finger extending out from the face of this mountain. This zone was just large enough to fit the wheels of the CH46.
Unfortunately, while on short final they lost 37” of an aft yellow blade. The out of balance aft rotor tore the aft pylon off at roughly station 410. The tail crashed and burned. The forward portion pitched up and crashed in the zone while rotating to the port side. There was a 4,000 lb. internal load of jeep and concrete, which broke loose and killed the crew chief. Bob Trigalet’s seat bolts broke and Bob and the seat passed from the right hand seat through the left hand side of the cockpit crushing the S3 and exiting out the left emergency door. It was a miracle that Bob was the only survivor.
Weeks later we were informed that the rotor blade had a defect. In the process of machining the D spar, some of the metal was folded over on itself, creating a weakness, corrosion and ultimate failure. The solution was to magnaflux and xray blades on a periodic basis to detect this kind of weakness.
Bob Trigalet got to Vietnam several months after our group and flew with HMM262. He was involved in a midair incident at the LZ Vandegrift in May 1969. There was marginal weather over Vandegrift. Bob saw a hole in the cloud cover and took off through the hole. An army huey not communicating with the Marines (different radios) happened along and decided to descend at the same time in the same hole. Two helicopter crews and passengers were lost. The HMM262 web site has the list of crew and passengers who died in the crash. If anyone remembers the HMMT302 incident, please help me remember the names or correct the facts. Brave Marines.