Raptor NG Discussion

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Malish

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One reason Turbofans are popular is noise reduction. By shrouding the hot gasses coming out of the turbine section in cool air they quiet the rumble a lot. The usual argument in favor of them is fuel economy with improved mass flow. Also, the fan blades in the duct operate at fairly high speeds.
This days turbofan engines have about 70% of thrust coming from the fan at low flying airspeed - that is good for takeoff and climb. At high cruising speed fan don't produce much thrust anymore and most thrust produced by turbine jet. That is why ducted fan aircraft powered by piston or electric engines can't fly fast and at hi altitude! And for PM decision to use ducted fan propulsion system on Raptor NG - was a BIG mistake.
 

Victor Bravo

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It seems that the "NG" designation for the new program stands for "Next Grift" or "Next Graft".

I'm every bit as much in favor of experimentation and innovation as anyone else. Yamaha snowmobile engines... V-twin industrials...Flying Fleas made out of Corroplast...E-AB half-scale replicas of F-104's... if the person is sincere and they want to hash out the concept here with all of our 5000 different opinions - noooo problem.

But for reasons described many times by many people, most of us can't and won't support something that is clearly off in the "nonsense - hype - BS - scam" quadrant. Innovation at the edge of technology is one thing but absolute BS is another.
 

Malish

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-another solution=Ducted Fan optimised for cruise speed
+EJECTION duse for low speed thrust augmentation...?
Ejection effect can be used on turbojet or rocket engines, on ducted fan ejection effect will not work - low airspeed flow and low air pressure difference. It's shouldn't be compereson between turbojet and ducted fan principals of work - they are working by different theories and physics. Same applies for propeller and ducted fan propulsion ;)
For same reason two stage or counter rotating ducted fan units will not do much difference on their performance, best way use single fan and stator straightening airflow after fan - less weight and complexity :)
 
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Malish

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-phisic (nature) is only one...

-I was made simple experiments with EJECTION duse and electric DUCTED FAN=circa 20% more
static thrust (fan power 1 kW)...
I'm will not argument with you on this tread - let PM do his work, but working on our ducted fan aircraft we tried and learned many things!
And just looking at this Raptor NG design, all I can say - Peter is TOTALLY wrong on many things and not only on ducted fan system for this aircraft :oops: raptor2_2.jpg
 

Vigilant1

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I had thought that perhaps a ducted fan designed with an adjustable stator set in front of the fan blades might be useful to reduce the AoA of the blades to the incoming air at low forward speed get them unstalled,, and allow more efficient operation over a larger airspeed range, and easier to implement than variable pitch blades. This wouldn't be practical to implement with a large open prop, but might be practical in a duct. But:

....One thing I can say - Ducted fan is different animal then propeller or turbojet propulsion systems!
On our aircraft two fans(690mm in diameters) turning 7100rpm(engine turning 5000rpm) at takeoff power at "o" airspeed and this rpm's DON'T change up to 200mph airspeed even engine still at takeoff power settings!
If the motor/fan in Malish's setup behaves like this, obviously there's something else going on that makes it behave a lot different than a prop.
Thanks for the information. There's not much ground here that you haven't explored.
 

Flyfalcons

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One reason Turbofans are popular is noise reduction. By shrouding the hot gasses coming out of the turbine section in cool air they quiet the rumble a lot. The usual argument in favor of them is fuel economy with improved mass flow. Also, the fan blades in the duct operate at fairly high speeds. A propeller has size limitations, ground clearance, ( landing gear length & mass ) and when the prop tips go supersonic the power goes into noise.

I'm blanking hard here, There's a high wing airliner made in turboprop & turbofan configurations, ??? Don't remember...
Do-328
 

Vigilant1

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Why do you think that that is true?
Can you provide any data or calculations to support that statement?
Thanks
The diameter of the fan on the GE90 engine is 123 inches. It rotates at 2550 rpm (N1). (All per Google search). The speed of sound under standard conditions is about 1100 fps. The rest is left as an exercise for the reader.
 

Peevee

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PM knows what is important. He's designing a new website. Can't grift without any bait.
 

Malish

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I had thought that perhaps a ducted fan designed with an adjustable stator set in front of the fan blades might be useful to reduce the AoA of the blades to the incoming air at low forward speed get them unstalled,,
It's not will help - stator will deflect airflow to desire angle at any airflow speed and than what? Nothing will change at any airspeed!
Ducted fan has own environment to work with and fan tip blades MUST be working below super sonic speed - at list for low powered(elecric or piston engines) ducted fan system!
 

WonderousMountain

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CR props make sense in this case, you can run two E-motors per duct, and support them with blade shaped spokes. It's not necissary to have gears and other complexities, however, they will have to make very good thrust to match stated objectives.
 

BBerson

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Yes, they do!
But they propelled by THOUSAND HP and have VERY sophisticated fan blades.
Right. The large turbine engine has a thrust to weight ratio about 8 times* more than piston or electric systems, I think.

* quick estimate, based on GE CF6-80E1A3: Weight 8420 pounds. Thrust 72,000 pounds.
(not sure if the above thrust spec is static or at 375 mph where one pound of thrust equals one hp)
 
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Rataplan

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I had thought that perhaps a ducted fan designed with an adjustable stator set in front of the fan blades might be useful to reduce the AoA of the blades to the incoming air at low forward speed get them unstalled,, and allow more efficient operation over a larger airspeed range, and easier to implement than variable pitch blades. This wouldn't be practical to implement with a large open prop, but might be practical in a duct. But:


If the motor/fan in Malish's setup behaves like this, obviously there's something else going on that makes it behave a lot different than a prop.
Thanks for the information. There's not much ground here that you haven't explored.
Something like the drag of the fan blades doesnt alter much with the change of AOA till 200 mph hence the power settong and rpm stays constant.
Doesnt say something about the lift of the fanblades. Might be with vatiable pitch the fan blades would produce more lift and speeds even above 200 mph. Anyway a duct itself is an object and will cause drag. UDF may be more effective also at higher speeds. I just dont know just brainwash about all options and try to use all logic.

Try to design a new concept like PM and be amazed how many ideas already have been tried and used.
IMHO one must know why and what he wants to design.
What is important, what is your goal, which designs are already made and what are their results.
Should I improve an existing design or invent something completely new and futuristic. Do I want to design for fun and for myself or do I want to design for a huge market?
Are the looks important or the goal is more on performance? Take the bede bd4 for example. IMHO not the sexiest plane but very good performance Designed half a century ago !
First time I saw a Decathlon I saw a fat Piper Cub , till you fly one...

All I saw till know (from the raptor) misses all these general design and or invention basics.

Seeing the nice drawing of Raptor NG I immagine the next:

PM showing drawing of Raptor NG to its secret investors. (SI)
SI : what NG , it still looks like a fat velocity.
PM: Well its the engine, i replaced it with an electric one.
SI: we cant sell a fat velocity no matter the engine. Cant you make it look more futuristic, like a space vehicle? Like that space thing of Richard Branson with moving wings?
PM: well moving wings is to much but I can shorten the wingspan and put an extra wing on it, creates a spacy look.
SI: ok, and perhaps some rockets on it.
PM: Well I could bond some ducts on the wing, electric ones. That would give it NG looks.
SI: Mmmm oke we have a deal, start promoting .
PM: Dont you worry about that, thats my profession.
SI: Uhhhh sorry but you are not an aircraft designer ?
PM: Uhhh I am, was just an austrelian joke mate.
 
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