Theoretical question
 

Hi Folks
Here is a theoretical question for you.
Say you had a twin engined scale jet( eg a yellow F22) that needed 28lb of thrust to fly.
Would you fit one Turbine say a Jetcat 160 with bifurcated pipes
Or twin Wren mk3 or Supersport and straight pipes.
What would you go for and why?

Mike
( potentially mad but what the hell)

RE: Theoretical question
 

I would take the single engine setup.

More room for fuel in the fuselage [8D]
Less cost ?
Easier to start
Half as many potential problems
Better fuel efficiency with one engine.
Save weight

RE: Theoretical question
 

If I could afford it, I'd go with the twin - way cooler. However, I'd go for twin JetCat P-60's - I think hands down, the JetCats are the most reliable engines out there. I don't have any experience with the P-60, but based on the two P-120's and the P-80 I have and the many other Jetcats I've worked with, they are the way to go - but that's a political statement somewhat outside the topic of the thread... sorry.

Bob

RE: Theoretical question
 

I would also go with the single setup, just half the issue's to get lined out, cost is not a factor either way IMHO. I would almost bet money the Y/A F-22 would fly fine, very scale on a P-80 or similar sized engine (ie, Around 20lbs.), I don't see why they are calling for 28lbs sounds a little high...

RE: Theoretical question
 

I think that both solutions works... the twin option is more complex, but I think that is more reliable as long you can bring back the plane with just one engine running...

RE: Theoretical question
 

Hi
If you look at the Yellow advert for the F 22 it says that the plane needs either 2 x KB 82 on Dynamaxes or one 28lb thrust turbine.
A Kb 82 driving a dynamax would give around 12lb or thrust if you are lucky ( perfect duct geometry etc). So two of them would produce 24lb of thrust under ideal conditions. Personnal I think you would be lucky to get 20 lb total out of the pair of them.
So how this equates to a 28lb thrust turbine I dont understand.

I was thinking along the lines of the twin turbines to provide redundancy. A Super sport is capable of 17 to 18 lb thrust. If I could electronically limit it to 13- 14 lb thrust from the tx and then at the flick of a switch get full power back it if I had a one sided flame out I think would be a great idea. (Assuming Asymetric thrust not being too much of a problem.)
The supersports fuel consumption figures are less than half of the Jetcat 160 so fuel would be around the same. What i would lose out on the weight of two sets of ECU, batteries etc. but as I would go for the manual start version it would not be too much

At the moment it is just in the planning stage hence my question.

Mike
PS Safety and reliablity are my profession as you may have already guessed.

RE: Theoretical question
 

From what I have seen, you can't compare DF thrust to turbine thrust. I have seen a BVM F-86 fly with the little GWM 7 pound thrust turbine and it flew every bit as good as one with a Viojett fan with a BVM.91.
If that F-22 will fly on 2 Dynamax fans with K&B .82s, then it would probably fly with 2 MW 44s, but it would not performvery well. For vertical performance similar to the real one, you would need more thrust than the RTF weight of the airframe.

RE: Theoretical question
 

Hi
If i did this, I would use MW54 Super sports ( 18lb thrust)
which would give me a 1 to 1 thrust ratio with interest.

Mike

RE: Theoretical question
 

Ok, cost factor tells me single engine.
BUT:
Twin setup has so many positive sides.
Less loss in thrust, possibility to mount the engines in the nozzles (even more thrust and less fire probability), single engine flying possible in case of flameout.
Besides a lot cooler sound, and the show effect is great also.
As to the room factor: most space i have ever seen in an avonds F-15 was in a twin turbine version with engines mounted right in the nozzles. Awesome sound, enough room in the fuse to mount 3 more turbines and even more or less flyable single engine performance.
If you have the money, go for twin. I'm doing a twin F-15 at the moment....nothing cooler than 2 synced turbines whining ;)

RE: Theoretical question
 

Hi Mike, Personally I am yet to see or hear a twin set up with 2 synced turbines that 'sounds' any better than a single turbine anyway... the bifurcated pipe roar with a single turbine set up sounds great to me!!! defenitely a better sound than even two snyced turbines in my opinion. If you can hear a difference the engines are 'not' synced. One way to really make a twin install sound great is to set one engines idle slightly lower ie 500 rpm, as no difference in residual thrust will be noticed at lower idle rpm's anyway! and they then will sound waaaay!!!!!!! better acoustically when on the ground taxiing etc If indeed snyced correctly you likely will notice little sound difference at all!! IMHO;)

The redundancy question of having two systems is also a mute point for me personally as far as I can see as you need twice the ECU's fuels systems UATs etc etc... more to fail! I would just install one 'well proven' 100% reliable quality turbine along with systems.... that said I have always fancied a large Me 262 or Learjet oneday but thats a different scenario altogether :D

Cheers

RE: Theoretical question
 

Naaaw, bifurcated pipes sound like vaccum cleaners. The sound of two unpiped engines is amazing. As to the "synced": you will always have slight deviation in rpm, therefore having them sing anyway...

Well, you can argue reliability of single engine, but when one goes down, you have yourself a flying rock (remember, gliding distance of your plane is always half of the distance back to the field...). You can turn that argumentation around any way you want it...

There is never a better way, theres always just a bunch of opinions ;)

RE: Theoretical question
 

Hi
Okay forgetting the coolness factor of twin turbines. I am looking at this purely from the point of view of increasing the aeroplanes survivability.
Modern jet equipment is fairly reliable however twin jets where one jet can supply 2/3rds of the required thrust will certainly give me a fighting chance of getting a several thousand pound sterling investment back in one piece.
it will give me a much reduced sink rate and as regards it is twice as much to go wrong is incorrect it is twice as much to keep going.( IMHO)

Mike

RE: Theoretical question
 

Mike,

I agree with the idea that 1 turbine is much less complicated and less expensive and that is how I have set up my F-4 and Rafale. They both sound very authentic/cool and other than perhaps during spoolup it is very difficult to audibly distinguish that they are not twins.

One thing to condsider with a bifurcated pipe is that there is a significant thrust loss, probably in the 10 to 20% range. In your example there is thrust to spare but you would never want to assume that you are achieving close to "rated" thrust with a bifurcated system.

Craig

RE: Theoretical question
 

Mini- :D Vacuum cleaners eh? well guess it depends on which brand turbines and pipe/s you are running????.... In synced turbines 'in fact' will sound as one otherwise they are simply not 'synced' correctly thats the fact. I don't know about unpiped?????? turbines in an F22 or any other internal installation for that matter unless you are suggesting 'very small' light engines are mounted in tail cones????? otherwise your jet would be a fire ball within seconds after start up!
As to reliability again:eek: as a habit I tend not to run my turbine dry of fuel in flight so reliability really then comes down to proper installation I guess, I have never had a turbine reliability problem occur so cannot really see how twice the complexity ie complete and separate duel systems makes for more reliability????[8D]

Mike- Do not worry about the reliability concerns of a single installation honestly!!! as 99.999% of any systems related problems will always occur during the initial installation process and have to be addressed early on before the models maiden flight, this is where manufacturers experience and direct 24/7 customer support is a huge advantage. Most problems are either fuel related ie air leaks, in fuel lines or UAT, or electrical ie wiring and or battery related. These minor issues are part and parcel of many set ups and you will address these as they occur prior to flight as the turbine simply will not perform to spec until these issues are correct IMHO and from my experience with many brands of turbines.
Depending size/type/design of model you choose and field conditions you fly from...its nice to have a bit of reserve thrust if required, plus you will also put less stress on the turbine and extend its service life between major component replacement ie bearings and combustion chamber due to lower operating temps.... ie if you have a Roo or Rookie install a 30 lb thrust turbine and derate to 20-22 lb thrust.


Craig- You are correct with relation to power loss with pipes in general and bi-furcated more so, Iam not sure that 10-20% is really rellevant as there are various manufacturers of pipes and some will vary ie more efficient than others. Also the power loss factor is not necessarily a thing to be concerned about unless installing a lower thrust turbine into a heavier airframe ie 12lb thrust turbine with bifurcated pipe into say an Avonds F15 with an AUW of 18-20 lb. Alternatively if you mount a 30 lb thrust turbine into the same F-15 which may now weigh 22-24 lb AUW you can afford to loose a pound or two of thrust due to bifurcated pipe and still derate turbine slightly and have 1-1 performance....

Hope this helps [8D]

RE: Theoretical question
 

I have to go along with Marty on this one....in the case of twins, you have to install two of everything...two fuel systems, two ecu's, two shut off valves, two battery packs. In other words there are twice as many components, and twice as many components to fail. As an example if the weakest component had MBF of say 1000 cycles, this will be reduced to 500 cycles (approximately) because 2 of them are being used on each flight.

Turbines are utterly reliable as long as they have fuel, no air bubbles, and the ecu keeps ticking. If reliability were the determining factor, a single turbine with a bullet proof system installation would be the way to go (IMO).

However, for separated engines -SU-27, A-10 - etc, twins would be the way to go. Twins also win in the way-cool category as well........

RE: Theoretical question
 

Marty, i was referring to the JetCats in the Avonds F-15 with pipes...that really sounds vaccum-cleanerish. Heard the eurosport with pipe, too....also not convincing, but better.

But why ultra light engines? 2 KJ-66, right back in those nozzles, no pipe, no hassle...put the batteries in the nose and off you go.
See here:
[link=http://www.jo-schaeffler.de/Jetmetting%20Cham/picture-0005.jpg]Twin F-15 no pipes[/link]

PS: twice as many components to fail, but infinetely small probability of a full failure on both systems in 1 flight...

RE: Theoretical question
 

not exactly...there is twice the probability of a single failure, but if both installations are identical, there is no guarantee that the problem wont recreate itself in the running engine soon afterwards.........

RE: Theoretical question
 

Well, that holds true if you mess up the system at installation. But that goes for single as well: bad installation, high failure probability.
Chances for an engine failure are fairly small with a well thought out system. Take "very small" by 2 and you remain somewhere around "very small". However, 2 failures at a time are one in a zillion (unless you fly it dry, which i tend not to try), and you will have that extra safety of bringing it home in one piece. (Basically we are argumenting of single vs twin in the following mannor: small chance of full failure vs twice small chance of a partial failure....)
Then there remains that argument with fire in case of a hot start when using the single on pipe (again, small chance, but it happens)
It all comes down to this: with the great reliability of turbines, it does not really matter if you go twin or single. Either system works, each system has its advantages, and either system can bring trouble. If you can afford a twin then this is probably the way to go. If you can't, single will work fine for you too. If you're in doubt, build something that has single engine anyway ;)

RE: Theoretical question
 

I guess what it comes down to really is whats motivating the dessision either way for single or twin? For me anyway I could never see myself having a twin install set up unless its actually was a model like a Me-262 or Learjet etc. with the obvious separate and scale engine pods.....reliability of my single setups has never been a concern whatsoever to date.
Therefor I cannot agree with there being legitimate concern in regard to safety and the reasoning for twin install alone. The wow! factor between twin v single in say an F-15, F-18 is negligible at best IMHO, I remember seeing Tommy Woods beautiful F-18 twin RAM 750 fly at Superman a few years ago and it flew great but that said you would not have known the difference unless you where actually told or snuck a peek under the hatch that it was a twin... I guess some engines have a better track record than others for consistent reliability and of course none of us have likely first hand experience with 'all' the various turbines that are currently on the market! so therefor we form opinions and base our comments and reasoning on the engines we do fly or have flowen ;)

RE: Theoretical question
 

Agreed. However, I believe the difference between the two is not significant enough to warrant the expense and complexity of a second turbine. Throw other factors in the mix, such as ease of installation (say in an A-6 Intruder), then it is a different ball game altogether.

Miniflyer your arguments are sound, logical, and well constructed...it is an honor matching wits with you!!:D:D