What size engine - A poll
 

What size engine would you most prefer to have?

Do you like 'em small or are you a Mega dude? Do you want the whole thing to be blingy or just run-of-the-mill regular.
I've also added an option for the financially challenged (like me :D)


Vote away!

RE: What size engine - A poll
 

You should add the 20 lb & 30 Lb class to your list;)

RE: What size engine - A poll
 

Too many options. Like going into a restaurant and having to spend the next 30 minutes reading the menu :)
I'll add a 33lb option for those who like'm big (but not really).

RE: What size engine - A poll
 

28 to 30 #

RE: What size engine - A poll
 

40lb engine in a 28# case also same weight ;) This type of engine works in any 25lb jets.

RE: What size engine - A poll
 

I like the 40lb thrust class overall, but right now I had to pick mega monster because that's what I'm after!

RE: What size engine - A poll
 

We need a Jet Central Rhino thrust class sized like a Falcon. Kind of like a Rabbit technology based Falcon.

RE: What size engine - A poll
 

You're saying you want more thrust in smaller package, right? Even if the fuel draw is horrible?
Very generally a 40# engine in a 30# case will draw fuel like a 50# engine.

RE: What size engine - A poll
 

PaulD

RE: What size engine - A poll
 

They always say that small ones work fine. Don't let them fool you. They always like the larger ones better.

RE: What size engine - A poll
 

Of course not. Put some compressor technology there man.

RE: What size engine - A poll
 

Well.. A 25lb# engine size in a JL L-39 (Example 40#thrust for a L-39 or a S/M F-18c ) will put your throttle setting above haft the whole flight. But with a bigger engine your throttle just above idle & better fuel consumption.

P.s In my opinion

RE: What size engine - A poll
 

Maybe something like this? http://www.jets-munt.com/pb/M140/M140.html

Gaspar

RE: What size engine - A poll
 

Hehe...
Efficiency doesn't work that way. Consider 2 engines. Both 40# thrust. One has a 120mm dia case and one has 100mm. The larger diameter will have better efficiency. It will use less fuel to push the same thrust.


I can understand why the thrust-to-weight or thrust-to-size numbers produce better sales. But on the efficiency side having a wide and short engine is much better.

RE: What size engine - A poll
 

Good point ;)

RE: What size engine - A poll
 

Actually if you want more thrust.... :eek:

RE: What size engine - A poll
 

Not true as general statements, certainly with the engines I have flown. I have engines in 90mm casings that push out 10kg and are no less fuel efficient than similar thrust engines in 110mm casings. You will find the currently emerging crop of smaller cased/higher thrust engines are just as fuel efficient as their larger cased predecessors.

Better thrust/weight and thrust/size is just evolution, look at how things have progressed in the 110mm class since the KJ66.

You need to add a choice in the poll for those of us who don't have a particular size preference and it does not have to be cheap. :D

Rob.

RE: What size engine - A poll
 

Now thats what im talking about :D

RE: What size engine - A poll
 

I believe that for my budget, cheaper is better, even if that means having to modify the turbine to make more thrust. I Like buying cheap and experimenting, it puts more fun into the hobby.

RE: What size engine - A poll
 

Here's the turbine wheel for the new JetCat....

RE: What size engine - A poll
 

Interesting blade shape. Somebody's spent some time in the test lab.... [8D]

PaulD

RE: What size engine - A poll
 

More taste less filling :)

RE: What size engine - A poll
 

Model Turbine engines have a long way to go before they reach the level of perfomance that can and has already been achieved in 4" diameter sizes. I have seen compression ratios of 6:1 and 300N thrust at FSC of 0.02 g/N/s in KJ sized package, using ceramic NGV and turbine, 600N with 2000 deg EGT.
Mainly the compressors and diffusors are radically different from the current CFD "optimised" designs. Combustors are simple but also very different.
Andre Baird

RE: What size engine - A poll
 

Paul,
The major players are able to invest in R&D effort that is unaffordable by the model engine companies.

That wheel is from a Teledyne Continental 373-8C turbojet (940 Lbs of thrust, using 1980's technology). I was first introduced to this engine in around 1986.

I took the attached launch photo in 2001 at Kom Aushim AFB, (Egyptian Air Force) southwest of Cairo, Egypt.

The booster burns for 4.5 seconds, produces 4550Lbs (nominal) of thrust, when combined with the engine's 940 lbs of thrust, accelerates the UAV from zero airspeed to over 400 Kts at booster burnout and drop-off. The UAV weighs 2356 Lbs. gross.
When the booster ignites, it is Hellfire and Brimstone!!

RE: What size engine - A poll
 

Nice to see some variety here. I was starting to think that the P-200 was the only turbine in existence now. LOL

Eric

RE: What size engine - A poll
 

[/quote]

Model Turbine engines have a long way to go before they reach the level of perfomance that can and has already been achieved in 4'' diameter sizes. I have seen compression ratios of 6:1 and 300N thrust at FSC of 0.02 g/N/s in KJ sized package, using ceramic NGV and turbine, 600N with 2000 deg EGT.
Mainly the compressors and diffusors are radically different from the current CFD ''optimised'' designs. Combustors are simple but also very different.
Andre Baird

[/quote]

Will this technology make its way into model turbines and at what price?

RE: What size engine - A poll
 

Some might and some probably won't. The only ceramic material I'm aware of that has the required strength to withstand the stresses of rotation is carbon-carbon. The same material that makes up the leading edges of the space shuttle. Really expensive stuff.

Supersonic compressors are neat but have their limitations in our use.
Some might

RE: What size engine - A poll
 

Enough said Gaspar, you nailed it. Will Jet Central carry something like that on the other side of the pond? Or is this solely a Jet-munts project?

RE: What size engine - A poll
 

I prefer the teeny ones
You dont see this engines as much as the big ones.

I build two 40rs engines ,they are 65mm o.d and i realy like them.
i think they are much more fun to build then kj66 type

RE: What size engine - A poll
 

I shoulda clued in when the turbine wheel was sitting on top of a manual for a Bandit. That makes it 9-10" in dia as it sticks off one edge of the page.

Turbines of any size are COOL! [8D]

RE: What size engine - A poll
 

A lot of reasearch has been done in the last 5 years which has turned conventional wisdom re compressor difussor design on its head. Some of it was known decades ago in the soviet block and has found its way into small missile engines. There is no reason why a reworked design with the technology we already use cannot produce 240N in a KJ size engine with close to half the fuel consumption. Its a question of know how. Add ceramics and youre talking 600N...
The truth is current compressors barely works as it is. CFD tools available to the public are not good enough to hint at this. Their flow predictions are just way wrong.
Andre

RE: What size engine - A poll
 

I've been tinkering with different diffuser designs and reading a lot of the published literature in the past couple of years.
I agree that there are some really nice innovations in impeller/diffuser designs.

The problem (for us) is the use of ceramics. The current trend for turbines is to use Silicone Nitride and hot press it under high pressure (Hot Isostatic Pressing). While the process itself is not terribly expensive when compared to vacuum casting Inconel the bare materials are still very expensive. Plus any FOD that enters the engine will instantly turn that expensive turbine to dust. All in all the technology has not yet matured to the point we can reliably use ceramic turbines. I'm tinkering with this on-and-off. I promise to tell if I hit on anything :)

As to the thrust figures - we're probably very close to the limit of what you can get in terms of thrust. 240N of thrust from a 70mm impeller will require almost 100% efficiency of the compressor stage. I doubt it's possible but I'd love to be proven wrong. Going to ceramics can increase thrust twofold. 600N from a Kj sized engine is probably not possible.


That's simply not true. I've seen results from OpenFOAM that rivals anything ANSYS can dish out. The real problem is setting up the problem correctly and analyzing the results correctly.

RE: What size engine - A poll
 

Erazz,
Its not a question of being proved wrong, its been done 15 years ago already. Ansys CFD gets it wrong too... New tools being develped right now are improving the situation but advances in laser velocitromy has divulged the true flow problems in non-axial compressors. While is is true that when the problem is set up incorrectly the best CFD fails, predicting initial conditions is very important. I know a lot about the subject, more than most small turbine builders, but it is nowhere near enough to form an opineon of what is possible and what not. So I rely on what has been done as a guide.
I am reminded of the NASA propultion enginners that refused to believe a specification for a rocket motor developed in the 60's in the USSR. When they observed it during tests exceeding the spec they realized they were 40 years behind... Many military /research rockets now use this motor under licence in the USA...
Andre Baird

RE: What size engine - A poll
 

Did you know that the internal of the JetCat P-200 actually is a copy of the legandary first generation AMT NL Olympus?? ;-)

RE: What size engine - A poll
 

Did they copy the reliability as well?

RE: What size engine - A poll
 

:)
Yeah, engineers get stubborn. Good thing I'm not an engineer! :D


BTW. Do you have any link or articles that deal with these new impellers and diffusers? I'd like to read about them.

RE: What size engine - A poll
 

No public info has been released AFAIK from the specific company. I do have the info but I could not release it since it is copyrighted.
I can say that the diffusor has no vanes as we know them. The compressor is mixed flow and has a lot of backsweep right from the inducer end already. It runs at 120K and has a press ratio of 6:1

RE: What size engine - A poll
 

Nothing beats the reliability of AMT NL turbines. ;-)