Hi everyone

Today, on my last flight i was mucking about, going upwind i opened the taps to go vertical and i hear a weird noise. i cut the power and it stoped, i thought it was flutter. however, it also sounded like the big gassers do on low passes and stuf were the prop tips breack the sound barrier. I had a little debate in my mind what it is........as they both happen at high speeds, and they both sounds simular.

My controls have got a bit of slop in them, but what do you recon it is. what are obvious sighns of fluttering??? the plane didnt go out of control either. what shall i check over before i next fly it incase it was flutter?

Thanks
Ian

Ian.
Don't be under the impression that flutter can only occur at high speed. I've experienced it myself whilst test flying a Synergy 3D for a clubmate. Occured at less than half throttle.
Flutter normally is a low pitch noise, but can get very load if you don't "close the taps" and slow the model down.
Things I'd check would be;
Slop in control surfaces
Engine/mount secure
Prop balanced and not damaged, i.e tips
Anything else, like U/C etc. that could resonate.

Good Luck.

Ian.

one thing ian that skeered me about a month ago that ive never seen mentioned here and i searched for it for about a week is every time i would start practiceing my hovering or any type of hard pulling i would get this WIERD NOISE also, and it turned out to be just a small area of my canopy had came unglued and was vibrating a scary noise under the right load so the moral to the story is it might not always be mechanical so look for loose anything!!

Yes. I've also had flying wires on the tail section vibrate like crazy at different rpms. That sounds horible too. Could be one of you main landing gear wheels vibrating or spinning fast in the air. You just never know. I would think if it was flutter and you were going that fast and you heard something that bad. You probably wouldn't have a plane now if it was flutter. Cuz it probably would have blown up.

Hi everyone, thanks for your help. Ill check everything over later, im starting to think its the prop. Im thinking this just because Ian (nice name BTW lol) said it was a low pitch. were this was a faster higer pitch "ripping" noise.

My canopy is all sealed with tape, and i was flying too far away for me to be able to hear my wheels, as i know what this sounds like from other planes.

also, i fogot to mention, when i was flying, i heard it, i idled the engine, it stopped so i pulled up and had the throttle at mid range. surly with flutter i would have ripped the tail off when doign this?????

thanks again
Ian

I get loads of weird noises, I just ignore them for a few flights then everything becomes normal

My airplane powered by a JEN 56 makes a very deep growling sounds very much like a full size Sukhoi, it is very small compared to the other noises but I could swear I could hear it and it was very cool[8D]

Flutter is not always immediatly followed by the destruction of a model. I have experienced flutter in my ultimate biplane. I have since changed all my harware to 4-40 and ball links and now no more flutter. Having said that I suggest if it is flutter you fix it now.
One thing that did strike me when it happened was how loud it was. I could hear it over the engine noise quite far away. It was a low pitch buzzing noise. Prop noise is more of a higher pitch crackle.

Take a look at this short video clip (1.5MB). Near the end, the prop starts ripping on the full throttle pass. Is this what you hear?

http://www.mmrca.org/Taylor2001/movies/ultimate_50.avi

Andy, yes thats what i heard. Im off flying again in a while and ill see (??) if i hear anything. Its making me think that it is props speed and not flutter as everyone says its a low pitch sound, were as this sounded like the video.

Does anyone know a formulea to find out prop tip speed from prop diameter and rpm?????

thanks for your help
Ian

Let's see. Prop-diam * 3.14159 * rpm gives inches per minute. Divide that by 63360 (inches per mile), giving miles per minute... then multiply that by 60 to give MPH. So, a 16" prop spinning at 15,000rpm is moving the tip at ~714mph. The speed of sound is ~740mph, but it varies quite a bit depending on things such as altitude.

Realize the prop tip doesn't have to go supersonic to make that noise. The air getting out of the way of the prop tip can go supersonic without the tip itself doing so.