AHPowelson

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http://www.troybuiltmodels.com/Propeller.htm [8D]


They're very similar to the Mejzlik props, but they're much lighter.

HNPower

My Feedback: (9)

you can also get the PK prop from brison aircraft or Fox manufacturing. I forgot exactly who. But that's the prop I have on my 110. I'm thinking about what silversurfer said about let the engine rev up. I may go back to the bme prop, a 27x10 and narrower than PK.

Tired Old Man

My Feedback: (1)

At rpm levels where the prop is ripping there is no benefit form the higher rpm levels. The prop at that point is basically "cavitating" and not pulling any more at all. My reference to higher rpm levels was simply that it would not hurt the engine, not that it should be run there.

When the propeller is at an rpm where it can no longer sustain an increase in thrust you may actually find that you have a loss of of power. I've seen where a plane equipped with a 115 actually appears to slow down a little when the propeller is being badly ripped. Finding the prop that lets the engine spin in the area of 6,100 to 6,500 without ripping will be the one you want to use. It will keep the engine in an effective power band.

HNPower

My Feedback: (9)

I belived with the bme 27x10 prop and is about 6500rpm (will tach again to make sure). The prop noise is loud but I don't think that the prop is in supersonic. It is still pulling normal. No loss in power.

Tired Old Man

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If the prop made it to a supersonic level you would know it instantly as it exploded. Try a 28-10 and see if you can't drop down to about 62-6,300 rpm. The niose level will drop some and you should note an increase in overall performance. Just don't lug the engine! You can also try some wider blade props in the 27" sizes to see if that helps some. Blade types make a lot of difference in performance and rpm levels.

HNPower

My Feedback: (9)

I came up with a formula to approximate the RPM when the prop reach speed of sound. Assuming the speed of sound is 346m/s at 75 degree temperature. RPM(supersonic)=3304/radius of prop in meter.
So, with the 27 inch prop, the rpm required to make the prop go supersonic is aprox. 9600 rpm.
I calculated with the 27x10 bme prop turning at 6500rpm, the speed at the tip of the prop is around 233m/s which is not even close to 346m/s (speed of sound). But at this speed, the prop noise is lould. But I like it, sounds more like an full scale a/c

Tor

The speed of the air flows faster at the curved side of the prop (which is really why it works for pulling anything ). Thus makes your approximation very inacurate.

HNPower

My Feedback: (9)

The formula calculates the super sonic rpm at a specific radius of the prop. It has nothing to do with airflow. Just put in your radius for the prop you are using, the formula will approx the rpm that is required to go supersonic. This is a simple speed/distance calculation formula which you can easily find in physics text books.

HNPower

My Feedback: (9)

It just occured to me that you misunderstood what I am trying to say. I said the prop going supersonic, not the airplane. If the airplane going supersonic, then it has to do a lot with airflow. Anyway, prop driven a/c can't go supersonic.

Tired Old Man

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Neither can the prop. Actually I did understand what you were referring to.

Ever wonder why turboprop aircraft are always subsonic? The sound barrier was a large part of the development of "scimitar" style propeller blades. Research consistently indicated that the propeller would disintegrate when attempting to pass through the sound barrier so various shapes were designed and tested to make the passage. The evolution of the propeller made tremendous strides in advancement but the end goals did not work out.

HNPower

My Feedback: (9)

exactly, because when the prop is approaching supersonic speed, the air infront of it becomes so thin that it is barely going through the prop. Therefore, the airplane looses speed and eventually stop flying. The engine will overheat because almost no air to cool it.
If you want to understand aerodynamics, understand hydrodynamics. They are the same mostly. When a boat prop spinning so fast, it creates a pocket of air infront of the prop and water couldn't get through.
There was an article in the model airplane news explain how to calculate the velocity of the prop. I believe they have the same formula. If I remember correctly, they used a 32 inch prop and predict the supersonic rpm which came out to be almost identical to my figure.

V(velocity) = rpm*C(cirumference) but remember rpm is in minutes. We need to divide by 60 to convert to rev per sec.
C = distance of prop tip travels in 1 rev in radian.
V = velocity in m/s

HNPower

My Feedback: (9)

Also, this explain why the tip of the prop has less pitch than the middle and at the root. It has a lot to do with the velocity.

Antique

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fastest prop driven airplane ever...The website says the prop was supersonic, apparently the airplane wasn't...F86H powered by a turbine...

HNPower

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With that huge of a prop, I bet the airplane can hover and do vertical takeoff. Looks like a F86 with turbine and they stick a prop up the nose for experiment. How fast was the top speed.

Antique

My Feedback: (4)

Don't know, it was many years ago..the plane was on a stand in front of an airport in Northern California..

Tired Old Man

My Feedback: (1)

Hmmm. Perhaps I'm in error about the abilty of a prop to go trans sonic... I hate it when that happens.

HNPower

My Feedback: (9)

Initially, I said "because when the prop is approaching supersonic speed, the air infront of it becomes so thin that it is barely going through the prop."
You know, I should have said that when the prop spins fast enough. Not when the prop approach supersonic. The bold statement is incorrect. I remember, I read a section on aerodynamics book and it said that the propeller does not provide enough power to break the supersonic shockwave.

Danny Allen

This really is very interesting and I love the looks and highly technical experiment with that plane but I would really like to see us get back on the BME 110 subject. Iv'e learned so much about the BME 110 adjustments so far from all of you and I'm looking forward to more posts on it.

Does anyone know what the ball park figure is for db level of the stock 110 with a 27x10 turning around 6100 RPMs measured on grass? I know there are a lot of variables.

Silversurfer, I wish you and RTK were on my side of town I would get hooked up with you so you could take a look at my setup and give me some more tips. Your posts have been very beneficial though since that's not the case.

Thanks,
Danny

Danny Allen

I'll be leaning low idle needle this weekend (1/16 turn at a time) to get the bottom end smoothed out. I like how the temps came down after readjusting the needles last week.

Hope I can keep them close to that range. I know outside temp also makes a difference.

Danny

Tired Old Man

My Feedback: (1)

We'd love to have ya. Usually it's just him and I flying at one particular site and we get so wrapped up in small talk that having someone else there would be nice so someone would be flying and we would have someone to watch while we yakked

I don't have a clue what the db numbers are. We generally fly at sites where no one cares so we have never measured. The stock mufflers that are obtained from BME are pretty loud though. We're both old enough that any damage to be done to our hearing was done a long time ago. Long before audio regulations were considered, and before residential encroachment became an issue.

F1race79

My Feedback: (6)

More info than you want to know about props.

http://www.supercoolprops.com/

Tired Old Man

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Thanks!! Interesting reading in the articles section.

Tor

While the speed of circumfrence speed may be calculated easily, it doesn't tell now fast the air is moving over the prop. The prop is a wing and the air flowing over the curved side flows faster than the flat side. The air not only has to travel the circumfrence of the prop but also the extra distance caused by the curvature and pitch of the prop. It's in every aerodynamics book

Danny Allen

Well I answered my own question this weekend regarding what the db level was of a stock BME 110 if anyone is interested. If there is not a noise level rule in place at your field there may be one at some point so this may be of interest to you.

I had my BME 110 db level checked this weekend. Here are the results:

With a stock BME 110 and 27x10 BME prop turning at 6050 RPMs the db level was 103 DBs.
I richened top end up a little to 5900 RPMs and the db level went down to 101.
These readings were taken on grass, 25 feet away from the plane, in-line with the prop and 18 inches off the ground. I'm sure there are variables that might cause for someone else to get a different reading but this is what mine read.

Although I do not fly my plane WOT it will fail the 96 db recommended ground test. So for now I will have to fly at another field and work on getting canisters. It's rare that I go to WOT even out of a hover.

Does anyone know how much noise reduction in DBs I could expect with canisters installed?

Thanks,
Danny

Danny Allen

Also, other than the ugly looks, can canisters be mounted on the outside of cowl/fuse instead of having to modify front bottom of fuse to accept the canisters inside of cowl and up under front fuse? I will probably go ahead and modify anyway but just wondering if they could be mouned on the outside. Plane is the 1/3 scale Great Planes CAP 580.

Thanks,
Danny