Pilot Needed.-

Sea Rider

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Was wondering if among fellow boaters there's a pilot that flies planes with radial engine/s. Would like to ask some questions regarding pitch, blade angle of attack and see if there are similarities between plane and boats props when on their way.

Happy Boating
 

Pusher

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I have a private pilot license but I'm not an engineer 😉
Both airplanes and boats have pushing and pulling setups if that helps 😁
 

dwco5051

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Big difference on way prop of plane is designed vs boat prop

An airplane prop is basically a set of spinning airfoils. They create thrust the same way a wing creates lift. A boat prop creates thrust by pushing against the water. They both creates thrust but the design criterias are entirely different.
 

GA_Boater

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Not a whole lot of difference with some boats. :smile:

airboat.jpg

Some are modeled after Bravo 3 or Duo-Props.

tu007sled006.jpg
 

Sea Rider

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Know are different worlds. According to most if not all OB's manufacturers literatures which have read states that the best prop thrust is achieved while boat with well deck weight distribution rides parallel to water level when OB is trimmed to 90?. Under those conditions, prop shaft, anticav plate and hull will ride parallel to water level too. Be aware that we're talking about recreational standard boats driven with standard manual trim OB's usually delivered with 3 blade props.

On that perfect conditions prop angle of attack will receive even (harded) incoming water passing under middle hull. On my last angle transom modification under (I swear...post) have gained 200 rpm reduction at wot with same speed than before while OB was sitting not at ideal 90? due to having factory transom deliverd with a miss shape issue. Now sitting at 90?, with lower leg sittting at the sweet ideal height has contributed too to achieve full prop thrust at full max cowl's HP.

What has prop thrust to do with aviation ? Wanted to ask, know is : when plane has reached its flying level say 15 K feet and plane is fying with artificial horizon indicator right at middle line, would you say that prop is achieving its max air thrust propulsion independently of blade pitch used for that altitude ? In other words, does each balde receives the same amount of incoming air when plane flies horizontal leveled ?

Pusher being a licensed pilot shoud have a proper tech answer for that.

Happy Boating
 

southkogs

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What has prop thrust to do with aviation ? Wanted to ask, know is : when plane has reached its flying level say 15 K feet and plane is fying with artificial horizon indicator right at middle line, would you say that prop is achieving its max air thrust propulsion independently of blade pitch used for that altitude ? In other words, does each balde receives the same amount of incoming air when plane flies horizontal leveled ?
Essentially that's why airplane propellers are thinner and run at higher RPM - they have different work to do on the material they are "screwing" through. Air pressure and wind obviously play a different role for airplanes, but so does water compression for boats/ships. There's another variable for airplanes which is lift - perhaps that's analogous to a boat's freeboard. If you have more lift in a wing configuration, you can generate more thrust with less RPM from the prop.

The principle of airscrew or waterscrew - propellers - is pretty much the same. But the substance they screw their way through is different.
 

Sea Rider

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Would be interesting to know at which rpm is a radial or opossed cylinder engine revving when at best cruising speed for that airplane. A prop gripping on air will need probably more rpm to maintain top blade thrust as opposed to a boat which needs less due to water being 1K times denser than air. A boat prop should grip much better on water being denser than on thin air at lesser rpm.

My question has not beeen answered, does an airplane achieves its top blade thrust when flying perfectly leveled out at its cruising speed.

Happy Boating
 

GA_Boater

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Actually the highest thrust is when flying at or below sea level in the densest air.
 

southkogs

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My question has not beeen answered, does an airplane achieves its top blade thrust when flying perfectly leveled out at its cruising speed.
I think you're into aeronautic engineering theory at this point. From a pure static thrust standpoint, I would suggest that on a shallow climb on takeoff with the throttle firewalled is when you'd get the most "thrust" from the prop. At cruise speed (assuming some bits and pieces about the airplane and the airspace), the airflow over the propeller is probably reducing the "thrust" but boosting the efficiency.
 

bruceb58

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I am a licensed pilot and we all learn about p-factor. Google is your friend.
 

Pusher

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Are you asking for boating purposes cause airplanes have some funny things working on them.

You have gyroscopic prescetion where a force acted upon a plane (the propeller in this case) shows it's opposite and equal reaction 90? from where it was applied. You can spin a cd on a pencil and touch it to see this happen. You also have torque when revving up rpm, P-factor, and you have slip from the propeller airflow. So there's a few different things acting on your effeciency when climbing.

When your engine quits you are supossed to immediately pitch down to keep the propellar free spinning from the force of the wind. You can be at idle (500 RPMish) while pitched down and still be going over your vne (never exceed) speed.

At 15,000 feet you have less dense air and so less friction as stated earlier. It's also (generally) cooler so your engine runs more efficiently, but you would want to lean up for mixture for te leaner air. You would also adjust your prop.

It's been years since I could afford to fly (lived with the parents then) and I only flew in the copilot seat of a Radial Stinson SM8A a few times. This guy says he cruised at 1,800 rpm which sounds about right to me.

I don't think I answered your thrust question but I don't know much about that.

I think someone said more lift from the wings meant more thrust. You'd probably know Bruce. Isn't that why you can make a turn? One aileron goes down (increased angle of attach) and the other goes up.

It's sad how quickly this stuff leaves you.
 

Baylinerchuck

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Highest thrust is achieved at takeoff and certain maneuvers since the aircraft must overcome drag and accelerate. During cruise configuration, (straight and level flight), there needs to be enough thrust to balance drag using the least amount of fuel.

I miss flying and will someday finish my private pilot certificate. I was training on a Piper Cherokee. It had a 74" diameter prop at 60" pitch with a 140 hp engine. Maximum power was achieved at 2500 RPM, best cruise speed was based on several factors but somewhere around 75% of that. I had a lot of fun in that plane, it was the one I soloed in.

Like Pusher said, I forgot so much. Much of the written training I'll have to learn over again.....the thought of p-factor and v-speeds makes my head hurt!! Not to mention dead reckoning navigation......😱
 

Sea Rider

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Thanks guys.
For best prop angle of attack & thrust efficiency with an OB, will boaters agree on this :

90º Trim & Thrust.JPG

Best prop thrust efficiency is achieved when prop shaft or anticav plate runs parallel to water level when combo is on plane while OB sits at 90?on recreational standard boats.

If so, then a propeller engine should achieve best prop angle of attack & thrust efficiency when airplane has reached final straight and level flight (*). Is this condition achieved when imaginary airplane is at middle line of the artificial horizontal indicator? Can someone with flying knowledge confirm or deny (*) this assumption ?

If we talk about best prop angle of attack & thrust efficiency, an airplane flying straight and level while cruising should equate same efficiency to a boat at plane riding parallel to water level when cruising, right ?

Happy Boating
 

Fed

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Mercury say the best attitude for a boat hull is 3-5 degrees, you could check it by getting the keel level on the trailer then marking the hull inside somewhere and using a phone app or even a spirit level & protractor to see what you run at fast cruise.
At the same time you could level your AV plate on the trailer & fit a water level to the motor front to back marking where the motor is level.

Then you would know what the hull & motor are doing in real time as you fly down the river and at the same time it would give you an indication of where to set your trim tab for the best possible result.
 

Pusher

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90? is kind of relative to whether you are in a trough or the peak of a wave. I rarely boat on a glassy day. I believe if you are going for full power in flight then you actually pitch down to compensate for the increased lift at higher speeds. You can't really equate avionics to aquatics... But maybe I'm playing devil's advocate :)
I think ideally (no experiece here) you'd get best performance by focusing on reducing hull drag. Has anyone thought about golf balls and how they are dimpled to reduce drag? I thought about this the other week.
 

Sea Rider

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Forgot a key word "manual trim" OB's, pic corresponds for best angle of attack along best thrust while OB sits at 90?, it's specified on different OB brand Owners's Manual under OB installation/Operation. The issue is that trim holes most times doesn't match boat's transom angle to achieve that cond. Most boaters just sits OB on transom and voil?, few go for boating perfection.

Happy Boating
 

Sea Rider

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Thanks Silvertip, will surely read the article. But boating is my thing, not flying...

Happy Boating
 
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