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HomeAircraftHelicopterHelicopter Main Discussion › Why we dont tie down our helicopters
10-13-2005 01:27 PM  13 years agoPost 1
ChrisMoore

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Bay Village, OH

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10-13-2005 02:12 PM  13 years agoPost 2
ChrisMoore

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Bay Village, OH

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The force makes the heli look like a wet noodle.

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10-13-2005 02:14 PM  13 years agoPost 3
lrogers

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Mobile, Al

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That was un-freaking real. Now I know why you guys took Ray to task for showing a helo strapped to a step ladder in his book (also now know why he was wearing a helmet)!

Larry Rogers - R/C Helicopter Pilot

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10-13-2005 03:32 PM  13 years agoPost 4
ChrisMoore

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Bay Village, OH

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bigger helmet?
Maybe Ray just needs a bigger helmet?

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10-13-2005 03:41 PM  13 years agoPost 5
brooksnb

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Sussex , New Brunswick , Canada

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Did the fact that the heli was tied down create that problem ?? It didn't look like that to me in the video...did it to you ?

.

Never, under any circumstances, take a sleeping pill and a laxative on the same night.... Dennis

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10-13-2005 03:42 PM  13 years agoPost 6
ChrisMoore

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Bay Village, OH

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I think that you can hear the blades spooling down and then the heli gets the shakes. I dont quite understand exactly how being tied down caused it directly, but it does appear that there is an enormous amount of strain that the heli can exert if tied down.

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10-13-2005 03:52 PM  13 years agoPost 7
brooksnb

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Sussex , New Brunswick , Canada

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I dont quite understand exactly how being tied down caused it directly, but it does appear that there is an enormous amount of strain that the heli can exert if tied down
That's what I am refering to...in the pictures it does not seem to strain the tie downs...I am not saying it won't cause the problem but I don't see it being the cause in this particular case.

.

Never, under any circumstances, take a sleeping pill and a laxative on the same night.... Dennis

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10-13-2005 04:12 PM  13 years agoPost 8
brooksnb

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Sussex , New Brunswick , Canada

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It doesnt have to be tied down for this to happen, but I am betting that it helps..
A bet that you would surely win ...

Never, under any circumstances, take a sleeping pill and a laxative on the same night.... Dennis

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10-13-2005 04:49 PM  13 years agoPost 9
webbhost

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england - Leicester

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now we know where our tax money goes

meh

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10-13-2005 05:23 PM  13 years agoPost 10
J3DI

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Oswestry, Shropshire. UK

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There are chains on the nose and tail but also 2 chains under the centre of the fuselage. I think the centre ones are quite tight and these are the ones preventing the heli from moving much.

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10-13-2005 05:30 PM  13 years agoPost 11
zoom boy

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N.E. Lincolnshire UK

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Not this again, look at navy helicopters, when landing they shoot a harpoon into the deck and are tied down that way and seem to be ok with it

I have pictures of the testing of one of the apache prototypes, totally tied down, if its ok for them then its ok for us

There is an important difference between that chinook and our models (apples and oranges here) first there is the number of blades on each rotor, second there is the rotorhead design (the biggest factor in ground resonance)

I'm sorry but presenting that video as evidence is flawed because of the above reason.

The rotor heads on a model helicopter arnt the right type to allow ground resonance.

Also there is another difference, the landing gear, our helicopters have rather rigid landing gear by design, a chinook has suspension, and therefore its going to be far more likely to go into ground resonance (orders of magnitude here)

I have never ever seen a model helicopter go into ground resonance, and I am sure a lot of people here dont know exactly what ground resonance is, I bet that those that say they have seen ground resonance in a model thats been tied down have only seen "it" when spooling up but before the blades have straightend out, this is NOT ground resonance.

Ground resonance is where the blades are already well beyond the speed to be out straight, and because it only affects fully articulated rotor heads, only happens if the blades lead or lag at full RPM, since we dont have fully articulated rotor heads, people are mistaking pre-fold out vibration, for ground resonance, and this pre-fold out vibration occurs regardless of wether the heli is tied down or not - just watch next time you go flying.

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10-13-2005 05:35 PM  13 years agoPost 12
Leif

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USA

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now we know where our tax money goes
If you read the comments, this heli was already condemned. An uncontrolled input resulted in a full roll in a previous flight. This would de-certify the airframe for ANY future use.

Using the airframe as a test of ground-resonance was a reasonable use of taxpayer money. The heli was already trash before the test.

Leif

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10-13-2005 07:02 PM  13 years agoPost 13
JitsuGuy

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Tulsa, Oklahoma

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If you read the comments, this heli was already condemned. An uncontrolled input resulted in a full roll in a previous flight. This would de-certify the airframe for ANY future use.
Holy crap! That thing did a barrell roll and lived to tell about it?!!!

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10-13-2005 07:42 PM  13 years agoPost 14
Yug

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UK. Herts

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Awesome to see this for real. This is exactly what I have found when running my helis on the bench. I've never had them self destruct because I make sure I spool up rapidly past the resonant band, also with the forces encountered, the carbon models are able to hang together quite happily for the short period in which resonance occurrs.
I am sure I will be shot down for admitting this, but there you go, I'm standing and being counted.

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10-13-2005 07:44 PM  13 years agoPost 15
zoom boy

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N.E. Lincolnshire UK

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Yes, but not independant of each other, a fully articulated rotorhead allows them to move independant of each other, having a solid spindle doesnt allow that, so really our models have semi rigid rotorheads.

Another thing to consider is the surface, if its grass or something, then there is less chance of ground resonance, acts like a natural damper, consider that when looking at that chinook video.

BTW, I mentioned the undercarrage person, where I said about the chinooks suspension.

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10-13-2005 08:02 PM  13 years agoPost 16
GroundPounder

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South Africa, Cape Town

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I have never ever seen a model helicopter go into ground resonance
I have,
A friend has a Rappy 50, and uses rubber skid protecters.
On a hard cement surface he has to spool up quite quickly and lift off, or else that heli shakes itself to bits.
Not so pronounced on grass.

Also, huge movements on a fullsize would be small movements on our helis, so you might just not recognize it.

There are many posts on this subject here, do a search.

GroundPounder

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10-13-2005 08:14 PM  13 years agoPost 17
vaportrail OLD

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Anchorage, Alaska

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The ground shake is well know on raptors and has nothing to do with the blades straightening out. The shake occurs as the head passes through a certain rpm range and stops as soon as you lift off or slow it down. That looks like ground resonance to me. One of the articles referenced says that this cannot occur in a 2 bladed semi rigid head but it also says that the type refered to does not lead/lag but our heads do.


The real point of terrorism is not the act itself, but our reaction to the act.

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10-13-2005 08:15 PM  13 years agoPost 18
zoom boy

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N.E. Lincolnshire UK

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I have,
A friend has a Rappy 50, and uses rubber skid protecters.
On a hard cement surface he has to spool up quite quickly and lift off, or else that heli shakes itself to bits.
Not so pronounced on grass.

Also, huge movements on a fullsize would be small movements on our helis, so you might just not recognize it.

There are many posts on this subject here, do a search.
I know there have been many subjects on it.

I said earlier that that is not ground resonance, what you just described was just because the blades hadnt folded out straight, again unless he has a fully articulated rotorhead on it it cant have been ground resonance.

Too many people with the train of thought here that vibration while on ground = ground resonance.
The ground shake is well know on raptors and has nothing to do with the blades straightening out. The shake occurs as the head passes through a certain rpm range and stops as soon as you lift off or slow it down. That looks like ground resonance to me. One of the articles referenced says that this cannot occur in a 2 bladed semi rigid head but it also says that the type refered to does not lead/lag but our heads do.
Right that isnt ground resonance either, I have already explained that our model helicopters have lead and lag BUT NOT INDEPENDANT OF EACH OTHER, it has to be independant for it to cause ground resonance.

Research lead and lag on rigid, semi-rigid and fully articulated rotorheads, then come back.

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10-13-2005 08:26 PM  13 years agoPost 19
steve9534

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yakima, wa.

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Zoom boy
The blades pivot on the blade bolts independently. I've seen model helis try to shake themselves to bits when tied solidly to a stand. Call this whatever you want, but if it looks like, smells like, and tastes like ... Well it probably is. steve.

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10-13-2005 08:30 PM  13 years agoPost 20
zoom boy

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N.E. Lincolnshire UK

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Yes they do, however that is without a damper in the equasion, if it where a fully articulated rotorhead, both blades would be free to move totally independant of each other, both would have a damper.

But in model helicopters the dampers are on the spindle and not the blade grips.

As for the smells like, looks like, etc

Well it isnt, there are pleanty of things that look like, smell like, but arnt.

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HomeAircraftHelicopterHelicopter Main Discussion › Why we dont tie down our helicopters
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