boingk

Everyone loves a good sounding engine, but most don't like a loud one.

 

I find that many general aviation conventional engines like the venerable Continental A-65 and C-85, turning low rpm with low compression ratios, are some of the best sounding engines out there. Must be something to do with the relatively large displacement cylinders and low comp ratio, kinda like a Harley Davidson I suppose.

 

They're also fairly quiet... had two guys on the ground yesterday who didn't even hear me on final until it was time for me to do an emergency go around! (They were inspecting site of a prop strike I later found out)

 

- boingk

 

 

Big seconding of cficare's post here.

 

I was a kid who went through the whole messy parental situation, and it was enough just to spend time with them and know that they still loved me.

 

Don't let petty stuff get in the way of what really matters. As far as I know you are allowed to undertake almost any recreational activity with your children, provided of course that they want to do it and it isn't likely to cause any harm.

 

- boingk

 

EDIT: I in no way consent to having anything I have written used, in any way, as legal or representative counsel. This includes the aforementioned issue of child custodial proceedings.

 

 

Just saw this and good to hear everyone came out okay, even better that something will be done about it.

 

On radio calls and pilots becoming errant near my location, I generally let them know in a reasonably straightforward kind of way. Nothing offensive, just let them know I've/they've got a problem and try and fix it.

 

eg: Couldn't spot a fellow in a 172 on downwind, despite being apparently right behind him. Got increasingly more alarmed as I couldn't see him after 15sec, so radioed him to confirm position, altitude and runway. He confirmed but still couldn't see him - but now he *knows* I can't see him, too, so was alerted to that. I ended up only seeing him as he turned base - probably 30sec in front of me but flying a polished metal plane on an overcast day, very hard to see!

 

Basically, do exactly what you did - fly the plane first and foremost and try and talk and find a way around the problem secondly. If the pilot continues to fly in a manner dangerous then try and talk with them in person. Failing that, report them. I used to be a postie and often talking to people yeilded a plausible and understandable explanation for their seemingly dangerous actions. Most times they were happy to cooperate. For all you know the guy may have been on his second solo and struggling with flight controls and radio calls - pilot overload during normal flight for an inexperienced pilot.

 

Anyway, congrats on the first solo and hope you have many more enjoyable flying hours ahead!

 

- boingk

 

 

You're probably right... I don't know enough about engine lineage to wade into this one. I do know that there are certain aircraft, though, in which you can easily exceed the speed of sound by using high throttle and rpm settings - Glasairs for example. A Glasair 3 with an IO-540 and 80" prop will cruise very easily at 15,000ft and easily be able to break through the Mach limitation of its prop if you aren't careful. Basically you'll notice increased noise and a lowered speed despite higher rpm setting.

 

What I've always wondered though - all this tipspeed stuff aside - is how slow you can get a prop before it becomes unable to provide meaningful thrust. There must be an optimum 'minimum' speed at which you can operate very efficiently but still maintain useful thrust... does anyone know anything about this side of the equation?

 

- boingk

 

EDIT: Part of the reason I'm asking that is I'm thinking of making my own ultralight aircraft with a reduction-drive engine... or two. Part of the whole 'revitalise 95-10' type movement.

 

 

I believe the R-975, R-1340 and R-1820 are all reduction drive engines, specifically designed as such to gain maximum efficiency from the prop.

 

Very few radial engines are direct drive, I think its something to do with the housing offering a very convenient platform for the reduction gear... not to mention the very high power outputs!

 

Cheers - boingk

 

 

I understand that, but we're back to the same issue.

 

The blades are turned at a maximum power setting of 2250rpm - meaning blade speed of 1500rpm due to the reduction gear - generating Mach .61 tipspeeds. As I also said earlier, anything over mach .70 will generate VERY large amounts of noise as you try and fight transonic buffeting. I have no doubt that the tipspeed would exceed this.

 

I've also no doubt that the things are noisy, but then again a lot of warbirds and vintage aircraft are. Modern prop aerofoils have come a long way since the 1940's, and often generate less noise and more efficiency at higher rotational speeds.

 

- boingk

 

EDIT: If we're talking supersonic tipspeeds, check out the XF-84H 'Thunderscreech' experimental fighter. It drives a prop at supersonic speeds and reportedly made pilots, groundcrew and anyone in the general vincinity violently nauseated due to the continuous sonic shockwaves. Legend has it more than one person voided their bowels when exposed to the noise.

 

 

I don't see how a hard turn would make a difference, unless of course you are operating high throttle/rpm settings during that turn.

 

Mind you if you're breaking Mach with any part of your prop you'll actually be going *slower* than if you were holding a lower throttle setting due to the sonic shockwave seperating the airflow over the prop and reducing its efficiency. Of course if you have specialized laminar-flow props then that may not be of such critical importance... although you will start to reach the mechanical operating limit of your prop, in any case.

 

- boingk

 

 

I'll be there, and I can get as political, jargony and/or irate as everyone deems fit.

 

Maybe I should run for CEO.

 

- boingk

 

 

Thats why I'm leaning toward keeping her...

 

 

Yeah one of the preeminent Russian passenger liners was commissioned by the Japanese I believe... some crazy cruise speed of about Mach .90 at altitude? Insane stuff.

 

- boingk

 

 

Great weather today so went out and got some maintenance done on the Gardan - the Flottorp prop is back on and new W100 in the sump. The new ArkTech prop is great, but I think the spec on the Flottorp is out of whack - they claim it a 72x48 but I reckon its a 72x42. Thus, the new one which was modelled on the old is now a very good cruise prop (90kt @ 12Lph!) but not too flash on climb.

 

After the maintenance was done I took her up and she went nicely indeed... loved every minute of it! The skies were clear, or silent at least, so I did a bit of sightseeing and some nice relaxed turns over Lake Bathurst to get back into the groove of things. I haven't been flying very much lately but it was as if I'd only been up yesterday.

 

Landing was uneventful apart from a change from runway 22 to 26 as the winds had swung and picked up a bit and now favoured 26.

 

 

All in all, I'll really regret selling her... if and when that ends up happening.

 

Cheers all, happy flying!

 

 

Marine propellors also suffer heavily from cavitation, where the low pressure induced by a fast spinning and/or improperly shaped propellor will actually physically erode the prop to the point where it becomes unusable. Many early trans-Atlantic captains succumbed to this due to get-there-itis or wanting to break a new speed record for the crossing.

 

Aviation propellors are a bit different, although somewhat similar in concept. Propellors are generally shaped rather complexly (is that a word?) to give optimum efficiency, and one way of making them both quieter and more efficient is by sculpting them with a scimitar-shaped tip as here:

 

 

The full article is about a Hummel Bird in the US and its extensive modifications undertaken by its builder/owner, David Roe:

 

http://www.eaa.org/experimenter/articles/2010-02_hummel_bird.asp

 

Cheers - boingk

 

 

You need to also factor in the aircraft airspeed on top of the rotational speed of the prop.

True, but as a function of the speed of sound its still nowhere near it. They specifically design propellor driven aircraft so that these situations are avoided, so even at max power rpm giving a tip speed of .61 mach, you'd have to be flying .40 mach to break the sound barrier with the tip of the prop.

 

Don't know about you, but I sure don't know of any AT-6's that fly at 300mph or more, especially given their regular maximum was 200mph and cruise was 145mpH.

 

Then again, I also don't know much about the ones that they race.... although I think they'd try and avoid it even more due to the inherent inefficiency of running a prop above about .70 mach.

 

- boingk

 

 

Thats freaking awesome, esepcially like his Grumman 'Wildcat' F4F flight.

 

Cheers - boingk

 

 

Harvards /Texans produce a lot of noise due to the prop tips breaking the speed of sound. A lot more than the run of the mill Cessna 210 sounds when its prop tips break the speed of sound. I reckon

I wouldn't think so, dazza; unless I'm mistaken the Texans ran an R-1340 Wasp engine rated to 600hp or so at 2250rpm. That turned a 9ft / 108in prop through a 3:2 reduction to give 1500rpm at max power. This would give a tip speed of about .61 mach. If you overrev the engine to 2500rpm you'd be at around 1670rpm at the prop, giving .71 mach for tip speed - that is in the transonic region and would be making prodigious amounts of noise... but nowhere near supersonic.

 

Cheers - boingk

 

 

Dazza - they're offering 10c/L if you spend over $100 at Woollies, excluding liquor.

 

Biggles - sounds bloody good mate! Hope to do this myself but in all honesty will probably stay at Goulburn airport. The fuel I'd spend going out to the farm and back would probably almost equal a weeks rent at the hangar... so may as well stay there.

 

Cheers - boingk

 

 

You going to tack a hangar on as well mate? Gotta have a hangar... maybe even a fuel depot?? You know those woolies vouchers are good for 120L at a time...

 

- boingk

 

 

Yeah was going to suggest the very same - happens if you get it or anything greasy/filmy on smartphones as well.

 

The capacitance sensing screens lock up if they get 'covered' by something which insulates them - such as wondow cleaner, polish or grease.

 

- boingk

 

 

Sorry mate, I didn't' mean to suggest you to try to maximise your safety, disregard what I said and keep doin what your doin, you'll be fine....

Righteo, cheers ma...

 

 

Sorry, couldn't resist.

 

Agree with your point though, I'd rather not work on a fuel vessel where possible. Still, if you're going to, may as well make sure you do it properly.

 

- boingk

 

 

Think people misunderstood my post... I was trying to describe what a grader looks like to somone who asked a question about them.

 

Using a blade will be useless, I'd *Highly* recommend using a grader!

 

Can be as complex as this:

 

 

Or as simple as this:

 

 

- boingk

 

 

Better to use argon from the mig welder gas bottle, it's an inert gas. No wait ..... Better still don't work on them at all.

Better still, lock yourself in a padded room and you'll be completely safe from those loud, noisy, fast things we love.

 

Personally I'm amazed at the amount of complexity people seem to want to incorporate into things... simple things like refuelling. Stepladder plus jerrycan, simple! Multi-switched electrical hydrotransferring duvalacky? Waaay overthinking it I reckon.

 

- boingk

 

 

Bingo, nunas, thats pretty much what I'll be doing if/when I get my rear into gear. Also depends on what I end up with after the minicab and what sort of takeoff performance it has!

 

 

Gentreu - Basically you get a big thing with a tilteds blade on it, a bit like a large razorblade for the ground - and tow it over the ground you need graded with a tractor. It levels out imperfections and provdies a nice even surface to work with.

 

Cheers - boingk

 

 

Aircraft engines are noisy for a few reasons:

 

• High operating rpm
   
   
  
• High continuous power outputs
   
   
  
• Low levels of sound deadening
   
   
  
• Low levels of exhaust muffling
   
   
  

 

 

 

All these contribute to a noisy environment. A car has an effectiv muffling system, layers of sound deadening both inside and outside the engine bay and is running on only a miniscule percentage of what it is capable of operating at. Your typical passenger car will put out 150~200hp but only need 15~20hp to cruise at freeway speeds. Thats a 10% throttle cruise! Imagine doing that in an airplane... it'd be at idle.

 

We cannot afford the luxury of weight and redundance to carry around power we do not use.

 

The propellor also does generate a large amount of noise if tip speed is not kept out of the transonic range over .72 mach. This is the typical loud waaaaaAAAAHHHH! you hear as a warbird or aerobatic plane dives - the blade tips going transonic. For comparison a 72" prop turning 2300rpm will have a tip speed of about .56 mach.

 

Cheers - boingk

 

 

I've been looking into this for some land I own outside of Goulburn.

 

I'd reckon a good moderate grading for a ploughed field would do it, and then plant some hardy grass such as Buffalo... or that matted kinda broadleaf stuff they use on sports ovals thats tough as hell and drought resistant.

 

If you can talk to a local landscaper they would be able to give you a good idea. Essentially you're after a sportsfield surface.

 

Personally, I love those big tyred hoon mobiles that seem so popular in Northern America. Would love to do an RAA version!

 

Cheers - boingk