Micro Turbofan manufacturing feedback

[f112owner]

The original WASP used a similar version of this engine...the wr19. It had a 1:1 bpr. Will using this design for a jetpack or my “FlightBike” really suffer with a higher speed/ pressure bass? The SFC would decrease?

[finiteparts]

I'm not sure I understand the target market for this retro-upgraded engine?   I am assuming from your name that this is a F112-WR-100, which was used in the AGM-129A Advanced Cruise Missle (ACM) from back in the mid 1980's. Which means that by copying it, you are still likely covered by US State Dept ITAR regulations, even if it is old and there is already international knowledge of it's construction and technology.

I am assuming that by this, "...as still to date NOTHING has even come close to this engines features and abilities.", you meant in the experimental aircraft or similar market, as the technology in the F107s (and the F112 derivative engine) is rather dated.  I can just go an look at Williams International's website and see how the technology and growth capability has been exploited on top of the basic WR-19 foundation. 

Now, when you throw out ideas such as additive and SPF (I am assuming you are referring to super plastic forming), it doesn't sound very cheap to me...so maybe you are looking to a different market other than experimental light aircraft...??

If I assume that you are looking to break into the experimental aircraft market, there are very few examples using turbojets or turbofans.  The primary one that comes to mind is the Sonex Subsonex:

www.sonexaircraft.com/subsonex/

which uses the PBS TJ100 at about $74k ready to go....so maybe that could be a price point, but PBS has quite a history of producing turbomachinery components and you as a new player might struggle to instill confidence on safety and durability, especially when you are basing the design on a limited life engine.

Also, my guess is that you can't just copy Williams work outright and then sell it without getting a visit from some lawyers.

I am not trying to be a downer, but history is littered with people saying that they are going to make a "cheap" jet engine and then their subsequent business fail.  Maybe, I just don't understand the market that you are going after.

Good luck,

Chris

[racket]

Hi

The engine was originally used by Bell in a "Rocket Belt" , but it was "too heavy" and the fuel burn rate meant short duration flights , so the idea was scrapped .

The modern RC jet engines are light enough and powerful enough to "negate" the need of a fan engine for most applications , a 1:1 bypass is suitable for missiles or very high speed aircraft but pretty much useless for everything else , just too much wasted energy in that "exhaust" for most applications .

Assuming your engine flows 7 lbs/sec of bypass air at a 1 Bar pressure , a 2:1 PR , its going to require ~350 HP to produce it , the exhaust from expanding that 2:1 PR might get us ~1,000 ft/sec and produce ~ 220 lbs of thrust.

220 lbs of thrust in a "vehicle" travelling 550 ft/sec is worth 220 HP , at 1100 ft/sec its worth 440 HP , but at 100 ft/sec its only worth 40 HP , but you've expended 350 HP , .....not a good return :-(

For any use other than extreme speeds you'll need a higher bypass ratio .

Cheers
John

[f112owner]

Chris,

I believe you may be right with ITAR though I have been told it would fall under EAR99 but when I contacted PBS they gave me a clearly bs reason they were not interested so ITAR may still be a restriction 

The market I intend to aim towards is USA only experimental market...at least at the moment.

I do not intend to make a cheap engine....just a better much more fuel efficient engine that will fill the gap that exists.

A little history behind this engine. I spotted it on ebay about 18 years ago. Alerted a friend. He bought it. I bought it from him a short while later. Long story but the FBI ans NCIS seized this engine for 3+ years and returned it to me with a clean and clear bill of ownership...absolutely no competing claims of ownership from government nor private companies..also declared it not contraband nor unlawful for me to own.

I dont expect any williams attorneys to come knocking...ive tried repeatedly to contact them...they refuse to even give me a courtesy reply. Ive onwed it longer than any patent can survive...besides it was made 40+ years ago...under DARPA funded..and I dont intend to direclt copy it...too many advancements in 40 years to ignore. Plus..  Material and process changes count against any patent infringement claims. 

US taxpayers flipped the bill in 1979 to the tune of $250 Milliom dollars...in 1979..thats about a $1 Billion in todays dollars. I want to recycle this investment in R&D. Its time.  Advancements in 3D scanning and printing..plus SPF and other powdered metal processes...its time.  

it wont be easy...wont be cheap but it will be worth it...i have a billion dollar piece of R&D.  Still nothing on the experimental nor civilian GA market even comes close in size and features...esp counter-rotating.   Heres to hoping for success.  

[f112owner]

I do have many ideas for this engine....most wanting to capitalize on the counter-rotating benefit of improved vertical flight....so a bypass ratio change is needed from what im learning. further developments needed...by knowledgeable people....expensive people....I understand this. I like to think of myself as a realists. Im working on putting together a business plan to present to investors. Im here hoping to get feedback and to learn more. Im far from a turbine engineer but i have a dream to build these...I know huge advancements can come from this engine design.

[monty]

Interesting project.

I'll just add some conclusions I came to when researching engines that eventually led me to create my own design. Be careful when looking at specs for non man-rated applications. The impressive numbers are achieved by using very high temp alloys for the turbine and ngv (Mar M etc). The turbine inlet temp is then cranked up to a level where the life is measured in a few hrs, not 1000s. They use special high energy density fuel, not normal jet fuel. The platforms are small, and travel at high subsonic mach #s. Fans are sized accordingly. You will either have to re-design the hot section to power the fan at it's rated power, or lower the TIT and suffer lower performance. Or you could design a new fan to work with the lower hot section output at man rated TIT. But my guess is those components are so optimized for the mission they can't be reused.

For these reasons, I concluded I needed to create a new design. What I arrived at is basically a terrible turboprop engine. However, I don't need the heavy(expensive)gearbox and prop, so it's a wash in my opinion. The engine is going to use a lot fuel compared to a piston engine, and there is nothing I can do about that while keeping cost reasonable. Even if I used the optimum cycle design, the fuel consumption is still not great, and the engine cost is terrible. The physics of the situation dictate this. So I'm just rearranging the compromises to fit my mission. Can't cheat Mother Nature.

Doesn't mean you shouldn't build your engine, just know it's REALLY hard to do better than what's already out there. We are talking about a known mature technology at this point. The only place to make significant advancement is materials and controls. Now if we could come up with a ceramic turbine and NGV that would allow cranking up the TIT, some amazing things could be done. So far all the resources of every government and engine manufacturer have failed to accomplish this. I don't think I'm going to be able to make use of ceramic tech in my garage....

So I'm building a crude thing which may not work, but I'm enjoying the ride ;-).

Monty

[f112owner]

Thank you Monty. I truly appreciate the info and input. Ive gotten a lot of good input and info here....and I thank you all.

I definitely have some challenges ahead. Im learning....and I will keep moving forward.

[f112owner]

Is the LP turbines engineered for the fan speed and/ and or rotational mass?  Can a larger fan with a gear reduction be “simply” added to the front of the engine, IF the original fan was made of a much lighter material such as Titanium or CF?  making it a double by-pass engine?   Would this “slow” the engine down for a slower vehicle?  

[racket]

Hi

Its "complicated" :-(

Everything is connected , you lower the fans pressure ratio by increasing the flow whilst maintaining the same horsepower requirement from its turbine wheel , BUT , because the fan "turbocharges" the core engine the lower fan "boost" will reduce overall engine performance , all the other components within the engine will need to be changed to accomodate that .

Your engine is a "complete package" , it is what it is , a missile engine , as Monty put it so well , easier to start with a clean sheet of paper and design a new engine .

Cheers
John

[f112owner]

Thank you.

[finiteparts]

Mar 14, 2022 15:14:27 GMT -5 f112owner said:

Is the LP turbines engineered for the fan speed and/ and or rotational mass?  Can a larger fan with a gear reduction be “simply” added to the front of the engine, if the original fan was made of a much lighter material such as Titanium or CF?  making it a double by-pass engine?   Would this “slow” the engine down for a slower vehicle?  

Generally, the design point for the LPT will have the stage loading well below ideal because it has to respect the rotational speed limits imposed by the fan tip speed.  So, it is a compromise between the trying to get a higher rotational speed for the LPT, and a lower optimal speed for the fan.  The fan mass comes into play when you are designing to meet mechanical stresses or when you are doing transient performance analysis.  When the fan speeds are higher, you need to have lighter blades to reduce the centrifugal loads which would drive up the stresses at the fan hub.  So, if you are reducing the fan rotational speed with a gearbox, you may not need to reduce the fan mass, depending on the hub/blade stresses.

This is where geared turbofans offer a potential advantage.  You can run the LPT at a higher speed where it runs more efficiently, while the fan can be run at lower speeds to allow larger diameters without pushing extreme tip speeds. Slower fan speeds will help you get the engine better matched to a slower aircraft mission, by pushing more mass at a lower fan exit velocity, you can keep the fan thrust up and get a propulsive efficiency increase at a lower flight speed. The gearbox will be tough to build as reliable and also light, but it really does offer the designers a better ability to match the fan and LPT closer to their respective ideal operating speeds.

The fan of the F112 is a pretty old design and a newer more modern transonic, wide chord fan might gain you a few points in efficiency if designed correctly.  You may be able keep up the fan stage pressure ratio even with the lower fan speed with a more modern fan design also.  Getting the proper matching of the fan and LPT speeds with a properly selected gearbox, could also potentially gain you a few points in efficiency and getting the fan exhaust speed down to get a better propulsive efficiency could also help.  So in general, there is a path to keep a similar core flowpath, but optimize the low pressure system to better align to a lower speed mission.

Now, this is something that will take a huge amount of engineering work and a lot of specialized skills...alot!!!

Good luck,

Chris