Improving Thrust

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
WBS
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Re: Would like serious comment on ducted fan airboat experim

Post by WBS »

Check out this Russian video.

https://www.youtube.com/watch?v=TUcxEVrHzWE

Olf Art
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Re: Would like serious comment on ducted fan airboat experim

Post by Olf Art »

In order to continue this discussion I think it's important to note that there's a big time difference between a ducted fan and an actual propeller drive, which is what propels an airboat or an airplane. Ducted fans have their place, but usually in harmony with a plenum like the hull of a hovercraft, or the wind force of a wind tunnel. Propellers are completely different critters.
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WBS
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Re: Would like serious comment on ducted fan airboat experim

Post by WBS »

Thrust, weight, high power requirements, noise, fuel consumption, safety and cost concern a lot of airboaters. There is practical and proven information available to address these issues. Relevant and useful reports listed below may be easily found by a google or other search. There are many others but these are clear and useful. Here are some quotes.

“The static thrust of the shrouded-propeller configuration was approximately 100 percent greater than the static thrust of the equivalent open propeller driven by the same horsepower engine.” “ the static thrust of the ducted propeller driven by 250 hp will be about 1800 lb”. The experimental static thrust results presented in Figure 11, 600 lbs. whereas the predicted result from Figure 5 was 605 pounds. A 7-percent decrease in static thrust was tolerated in order to optimize the propeller blades for the aircraft climb-out conditions. This was done by incorporating the blade twist modifications shown in Figure 23. This modification considerably improved the climb-out characteristics”.” Although the shroud increment of the thrust decreases with an increase in forward velocity the breakeven velocity in this particular configuration was considerably greater than 100 miles per hour.” “..the static thrust of the ducted propeller drive by 250 hp will be around 1800 lb”

A later, cobbled together and un-optimized, hasty 6 month project for a foreign government achieved 5 lbs/hp thrust from 250 to 420 hp, it could have been higher with more time.

Raspet - THE DUCTED PROPELLER FOR STOL AIRPLANES, 1964 - 8 pgs

Raspet - MARVELETTE – tests- quote from conclusion, “AN INVESTIGATION OF THE SHROUDED PROPELLER PROPULSIVE SYSTEM ON THE MARVELETTE AIRCRAFT” 1964- 80 pgs

MARVEL “XV-11A - DESCRIPTION AND PRELIMINARY FLIGHT TEST”, 1967, 105 pgs.
49 test flights of an experimental military STOL aircraft.

I am not concerned whether we should be talking about “ducted fans” or shrouded propellers” or how an airboat should look. That would miss the essential point which is that a relatively uncomplicated aerodynamic ring about 1/5 to 1/4 the prop diameter and weighing 40-50 lb works well for a 66 inch shroud and improves on all initially stated issues. The essential design, construction and cost matters are readily handled.

Current Marine LCAC landing craft use two 12 ft diameter shrouded props with about 14 " wide, 4-5 blade constant chord props driven each by 4000 hp and being upgraded to 5000 hp. They push a 50 to 75 ton hovercraft at 50 mph. And they are as streamlined as a brick. There are many other uses in many countries for high speed ferries, rescue and recreational craft, etc.

Test data show that for airboat speed ranges a shrouded (or ‘ducted”} propeller (or “fan’} thrust drops off similarly to an open propeller. Proper design/construction is needed but this is true for almost all powered machinery. The excellent prop makers could readily adapt their products for use in a shroud. Moderate propeller twist modifications would optimize shrouded prop performance. I do suspect the fan guys could eat the lunch of the prop makers in terms of cost for marine uses.

There are other relevant issues relating to optimization and applications but I feel they are of less importance than those above. If anyone wishes further information, I will try to supply it or sources.

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OneBFC
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Re: Would like serious comment on ducted fan airboat experim

Post by OneBFC »

WBS, sounds like you got it figured out.

Go build it, Noone else is.

Interested to see how it works out for you.

Good luck.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

WBS
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Re: Would like serious comment on ducted fan airboat experim

Post by WBS »

OneBFC - I liked your Youtube “Unstoppable Ecotec” post. Here are some calcs I find interesting.

Re Shrouded Prop calculation, Torque formula T = HP * 5252 / RPM, HP formula HP = T * RPM / 5252
hp = (880 * 5500 / 2.680) / 5252 = 344, 880 lbft/torque ~ 3.15’ = 290 lbft at shaft
880 lbft @ say 5500 rpm = 344 hp, 344 / 31 = 10 hp per sqft
Expected thrust / hp from chart of tests, T = ~ 6.3 lb / hp, Thrust expected from shrouded prop
= 344 hp * 6 = ~ 2100 lb

OneBFC airboat from Youtube, Ecotec Boat Specs, 12x7.6 Diamond Back Deck over
76" 3 Blade WWlkr Maximus Prop, 6.3’ d, = 3.15’radius = ~31 sqft area
6.3’ d =20’ circumference, RPM 2000 Eng 5300 - 5700 RPM max
2.68 Prototype Ox Drive PSRU, 880+ lbft prop shaft torque
Peak thrust: 1145 lb

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glades cat
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Re: Would like serious comment on ducted fan airboat experim

Post by glades cat »

Had a Poker Run on Sat at the AAOF for the annual Corned Beef-n-Cabbage. The water is up south of US41. Needless to say, we rode cross country the whole way…who needs trails. :lol:
A ducted fan would have been full of Sawgrass, Cattails and a few Willow branches. There were sticks and stems all over the place. My full deck was full of vegetation.
A ducted fan would have looked like a salad-shooter and it would have needed a new paint job after we went into the heads where some old camp are.
Sorry dude. Most Gladesmen prefer simple, reliable, tough and cheap airboats that can be fixed with bailing wire, zip ties and duct tape.
I've raced ducted fan hovercrafts and can tell you they don't like anything introduced into them.
You build it…we'll test it and give you an honest review.
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Rigged by Gladescat & sons in 2009

Olf Art
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Re: Would like serious comment on ducted fan airboat experim

Post by Olf Art »

glades cat wrote:Sorry dude. Most Gladesmen prefer simple, reliable, tough and cheap airboats that can be fixed with bailing wire, zip ties and duct tape. I've raced ducted fan hovercrafts and can tell you they don't like anything introduced into them.
You build it…we'll test it and give you an honest review.
That's the plain truth of the matter if it's ever been spoken. Props will take a considerable amount of abuse in dirty air. A ducted fan won't because of tip clearances and the inability to 'eject' debris. Well said.
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WBS
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Re: Would like serious comment on ducted fan airboat experim

Post by WBS »

Recent comments from others have been very practical. The trash in prop one in particular.

I wonder what percentages of the airboat population don’t go deliberately into debris areas or do cross country but I sure agree it sounds a blast. Many videos and posts show a lot of cruising, sight- seeing, racing etc. Also there are mentions of issues like deeper water capability fishing in shallows, river work boats, oil service work, mini airboats and bowfishing. World-wide the shrouded prop is used in many heavy-duty services and info shows craft going over rocks, ice, into major rivers, through brush, over dirt, and so on. This doesn’t need further proof its been done.

It appears the useful applications for now would be in the non big weed and sticks areas. The easiest in minis and bowfishing light boats. The bottom line that got me interested is the world is moving toward needing more bang for the buck and a lot of performance data makes it look like some things need to be worked on.

fireblue
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Re: Would like serious comment on ducted fan airboat experim

Post by fireblue »

Definitely worth trying some scale experiments. Im super interested. I do powered paramotoring, and have read some scale thesis on ducting the prop. ill see if i can find it

fireblue
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Re: Would like serious comment on ducted fan airboat experim

Post by fireblue »

Did some hunting and i found the research. It's quite interesting to read. One of the quoted texts says that a ducted prop can produce twice as much static thrust...
http://docslide.us/documents/drag-reduc ... motor.html
skip to page 37 for the start of the ducted research.

Hardtail
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Re: Would like serious comment on ducted fan airboat experim

Post by Hardtail »

Uhairball wrote:
Olf Art wrote:
Ready to ride wrote:Dude. Really????? Shut up
Vote liberal and move on. No1 is going to buy into this nor do it. Huge waste of your time and mine for even having to comment on this
Stupid is as stupid does. If you're unwilling to make your boat quiet then you'll be one of the first we'll all point to when the fit hits the shan and we lose more access to waterways. And the shame of it is that if you were running a good set of mufflers your engine would run a lot stronger and you could actually put more pitch in your prop. Fact.

I worked in the experimental fabrication shop for a major exhaust manufacturer many years ago. There we had a dyno room and a SBC (we all called Lucy) to test the sound levels and power production of any new muffler they were considering for production. Lucy consistently made more power and more torque (which is what turns a prop) with mufflers than she did with open headers. More, her head temperatures were lower because of something called 'anti-reversion' ..... the exhaust valves weren't sitting in a furnace without a small amount of back pressure to prevent what's called scavenging. Top Fuel dragsters run Zoomy headers because they're supercharged. Anti-reversion to hold a fuel charge in the cylinder isn't an issue, and those engines only need to live for around 5 seconds anyway.

Your attitude, and the attitude of people like you will one day be a big reason why we'll lose access to many of our beautiful waterways. Don''t bring that stuff around me 'Dude' ..... you don't know WTF you're talkin about. Are we clear?
Hey OF, I agree with you 100%. But I am curious. Why don't aircraft use mufflers? And why don't you hear complaints about them?
Aircraft does use mufflers, which is also used for Cabin heat, go figure how unsafe that could be if you had a hole in the muffler when using the cabin heat, FYI

Olf Art
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Re: Would like serious comment on ducted fan airboat experim

Post by Olf Art »

Hardtail wrote:Aircraft does use mufflers, which is also used for Cabin heat, go figure how unsafe that could be if you had a hole in the muffler when using the cabin heat, FYI
Only non-pressurized AC use heat from the mufflers because there is enough residual airflow in the plane to keep the air in the cabin safe. Non-pressurized aircraft also don't operate at altitudes that require much additional heat. Normal drop is two degrees per 1,000 feet. Pressurized aircraft routinely operate in excess of 10,000 ft. so they use something akin to baseboard heaters to keep the cabin comfortable.
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