HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 22, 2014, 09:42 PM
Registered User
Joined Oct 2005
59 Posts
The Hawk turbine is NOT centri-flow. It's reverse flow. There was a cutaway some years ago in RCJI I believe. My friend and I studied it for hours to try to understand how it works. The compressor, diffuser, and turbine wheel are within, I would guess, 1.5 inches. It is very different than other turbines. And expensive compared to similar thrust engines.
Jeremy300 is offline Find More Posts by Jeremy300
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 22, 2014, 10:06 PM
Rangers Lead the Way
Joined Mar 2010
1,956 Posts
Yes I see that now. I found a pic of it. Basically uses a turbocharger turbine rather than the usual axial rotor. The compressor runs a higher pressure ratio than normal RC turbines, which enables more efficient combustion (and higher temps). Looking at the pic, they are using an Inconel turbine, which would explain both the price and tolerance for higher temps which provides the better fuel efficiency. It also weighs about 60% more than comparable output JetCentral, but the BSFC is so much lower that you make it back in fuel weight and then some. Probably nets out to .5-.75 Kg less for engine+ fuel for a 100N class. The price point is unfortunate.

I see very few in actual use by RC-ers, and not much data or reviews of actual use. It appears the 100 series had a number of issues when they first came out circa 2007. Not sure if these were resolved. Probably just early production hiccups.

Looking at all this has been fascinating. One thing is for sure: everything is a trade-off. For my purposes, the performance / weight of the JetCentral SB II looks compelling, but the price of a K60 is hard to beat.
TTRotary is offline Find More Posts by TTRotary
Last edited by TTRotary; Jan 23, 2014 at 11:47 AM.
Reply With Quote
Old Jan 23, 2014, 01:29 AM
310mph Kolibri T25 Swist
henke's Avatar
Sverige, Kronobergs Lšn, Ljungby
Joined Jan 2001
4,764 Posts
Good to se you all got the point I tried to make And as some of you already stated, all data must be questioned. The graph posted are pretty much backed up by the Futura video I guess. Looking at the RCJI turbine test, it gives very good info but also laughs where they only read the GSU-display to for example se the EGT and not checking with a calibrated external probe. Eyes open all the time
henke is offline Find More Posts by henke
Reply With Quote
Old Jan 26, 2014, 02:05 AM
Rangers Lead the Way
Joined Mar 2010
1,956 Posts
Well, I certainly am a real noob.

Having crunched some numbers over the last 48hrs, having spoken with some folks, and having rethought certain things, I now realize that, as Dr. Honda and John originally pointed out, I will have to carry A LOT more fuel than I originally thought. Matter of fact, I would need to have at least 72oz on board that 1/8 F-16 in order to come down with about 12-16oz left after a 5mn flight. My K60G choice also will not work in that airframe, unless I want to be white-knuckling it at every phase of flight, from the roll-out to the landing. I would need at least a K80, if not a K100 (these two weigh the same, so why not have the extra thrust margin) to get this thing around the patch with adequate power.

I would appreciate some confirmation of this from you guys. I always set up my warbirds to have at least 1.30x thrust/weight, and I don't suppose turbines are any different, right? I should explain that I have a rather short 500ft "polymer" hardpack runway to work with, so it has to get off the ground pretty quick and land pretty slow.

Also, thanks to Henke for that graph - it is very informative. It is too bad that turbine manufacturers do not provide a fuel graph for their engines (excepting Hawk).
TTRotary is offline Find More Posts by TTRotary
Reply With Quote
Old Jan 26, 2014, 06:54 AM
Registered User
Colchester UK
Joined May 2004
407 Posts
I applaud you for asking these questions before diving in and being disappointed, a little time researching it before you buy will be rewarded.

As to thrust:weight you will get different answers from every person you ask. Many will say you cannot have too much thrust but it can result in a heavy model that is not much fun to fly. In general terms 1:1 is more than enough. The difference between your prop models and jets is that there is no prop to slow it down. The higher the efflux speed of the exhaust the faster you will fly. I have many models that have flown with 1:2 thrust to weight and some with much less. I have a 6 engine Arado that was designed to fly with 43 lbs thrust and it weighs 78 Lbs wet. It takes off quite easily with all engines running. The last time we flew it 2 engines stopped in the takeoff run. Takeoff was a little longer than usual and the flight was fine despite drag of the large multi wheel retracts not going up. When we landed we found we flew most of the flight with only 3 engines running. That was a thrust at takeoff of 1:2.7 and flying at 1:3.7.

If you have a look at this video of my glider it weighs 18 lbs wet and is powered by one of my own engines with a thrust of 7.3 lbs. (1:2.4 thrust weight) A fair bit of the flight is less than full throttle. It takes off grass easily. However the wing has loads of lift and it is very slippery airframe.

swift s1 17 aug (6 min 17 sec)


As another example I have a video of my Dh108 Swallow flying with a JetCentral bee 14 lbs thrust and the plane weighed 30 lbs wet. The thrust/ weight was 1:2.14 and you can see how it flew. In the end I changed the engine for a Merlin 80 and it flew with much more authority.

Dh108 VW120 Swallow Westbury models (4 min 27 sec)


Don't forget any plane that has a bifurcated pipe will lose thrust as the pipes are not as efficient.

John
John Wright is offline Find More Posts by John Wright
Reply With Quote
Old Jan 26, 2014, 09:25 AM
Registered User
Dr Honda's Avatar
Pittsburgh Allegheny, Pennsylvania, United States
Joined May 2004
1,166 Posts
As John was saying... turbine thrust is different.

1) with the smaller engine (p60) you may have a light model, and it will fly well. Depending on lift and drag... that engine may be just fine.

2) on the question of the k80 Vs k100.... since you don't have a prop to slow you down, and that you have to learn to fight residual thrust.... you may want to compare the idle thrust of both. I like a little extra power, but the larger engine will always make it harder to land.

3) also remember... the larger engine will want more fuel. I carry 94 oz of fuel with my "100" sized engine, and sometimes, its not enough.



Oh... one last thing. I know Henke's charts show the fuel as linear, but that's vs thrust. The throttle, and RPM Vs thrust is expo. so... the last 20k rpm can be doubling your thrust, and fuel consumption.
Dr Honda is online now Find More Posts by Dr Honda
Reply With Quote
Old Jan 26, 2014, 12:26 PM
310mph Kolibri T25 Swist
henke's Avatar
Sverige, Kronobergs Lšn, Ljungby
Joined Jan 2001
4,764 Posts
Quote:
Originally Posted by TTRotary View Post
I would appreciate some confirmation of this from you guys. I always set up my warbirds to have at least 1.30x thrust/weight, and I don't suppose turbines are any different, right? I should explain that I have a rather short 500ft "polymer" hardpack runway to work with, so it has to get off the ground pretty quick and land pretty slow.
I know I keep posting about prop/fan vs turbine in terms of thrust. When converting EDF to turbine I get an equal over all performance from a turbine with half the thrust of the EDF. Same or even worse with props.

A turbine jet with 1.3 times the weight in thrust would be like having a prop driven warbird on like 5times the thrust to weight. Only good for 3D no real in flight use.

So you really don't need alot of thrust when you have the efflux. As with electric planes the hunt for more power is on to jets as well. Today most aim for too much power when it's not needed.

The mother of all high performance jets, the Concorde have four afterburning turbojets making a total of 676kN of force. The take off weight is/was up to 190000kg which makes a thrust to weight ratio of 0.35:1 or so. And it will super cruise at mach 2 with no afterburner...

But still choosing the K100 over a K80 is common sense of course.
henke is offline Find More Posts by henke
Reply With Quote
Old Jan 26, 2014, 03:08 PM
Rangers Lead the Way
Joined Mar 2010
1,956 Posts
Thanks gents. Will have to noodle on this some more. I definitely lean towards the "less is more" formula - I'm basically wanting a nice scale jet, nothing that will win a speed contest. My main challenge is the short field I have. The surface is good for about 2/3 of the 500ft, and gets rough thereafter. So the plane needs to get off the deck pretty fast, so I have time to abort and stop if needed, and I need enough power to high-alpha the final approach. It's also a matter of practice, obviously. The best Skymaster F-16 landings I saw both had 60-size engines, but the pilots were both really good. I'd say the rollout was less than 100 ft and the touchdown was greased-in.

Henke, I think I understand what you are saying - the turbine performs better because efflux does not drop off as speed increases, so it is really good at speeding up the airframe versus the EDF. That said, due to my special circumstances above, I actually will need raw thrust performance during certain portions of my flight. Do you agree?

What would you guys suggest for thrust, based on experience: I expect the plane will come in at 18lb wet on startup, and probably closer to 17lb by the time I push the throttle forward for takeoff. This assumes 72oz or 2.5L onboard and the K100. K60 would be 1lb lighter, same fuel load. By the time the plane comes in, it would be about 14lb with 16oz or so left in the tanks, not counting the UAT. As far as aerobatics, going vertical would be nice and scale, as would turn and burn, and I know from EDF that these scale jets need a lot of power in turns to keep the nose up. Not interested in non-scale stuff or doing passes at 300km/h.

Regarding idle/res thrust, the P100 claims 0.5lb and 2oz consumption, while Kingtech claims 1lb and no consumption specification for the K100. I would assume that a 60 class would be about 2/3 of these numbers, although not necessarily.

One of the big challenges seems to be getting specifications. I have yet to find anyone, including the vendors, who can give me specific information on fuel curves for their turbine, or an airframe seller who can give me a simple airframe weight. I find that very odd, considering the very first thing I do is weigh everything. Maybe they know but don't want to say...

I will also try to find some jet guys locally (SoCal) who fly these and watch them. Maybe they'd even let me buddy-box...

Thanks for taking the time on the newbie guys- much appreciated
TTRotary is offline Find More Posts by TTRotary
Last edited by TTRotary; Jan 26, 2014 at 03:16 PM.
Reply With Quote
Old Jan 27, 2014, 12:27 AM
310mph Kolibri T25 Swist
henke's Avatar
Sverige, Kronobergs Lšn, Ljungby
Joined Jan 2001
4,764 Posts
Quote:
Originally Posted by TTRotary View Post
K60 would be 1lb lighter, same fuel load.
I just cut one line to quote at the moment (maybe more later). This is a common thought which in first thought makes sense. But there are more to it.

I fly with the micro turbines. Today there are two options on the market, one is 105grams(3.7oz) heavier then the other. You might think the plane would come in at just 3.7oz more with the heavier engine, but that is not the case.

In a jet you always have the fuel spot on CG, so the engine needs to go behind the CG. The heavier and larger, the further back you get unwanted weight.

I know a couple of examples where the 3.7oz heavier engine makes the AUW a total of 21oz heavier. All things sum up and the result is way over 5times the engines extra weight. That would be like 5lb in your case.

All airframes are diffrent and you might find a way to compensate with moving other stuff forward, but keep it in mind

PS. See the compartion picture, the small K60 can easily be mounted 1"+ further forward too.

henke is offline Find More Posts by henke
Reply With Quote
Old Jan 27, 2014, 10:05 AM
Registered User
United States, TX, Leander
Joined Sep 2003
2,432 Posts
Subscribed, soon to be turbine newbie.
Edwin
edwin1 is offline Find More Posts by edwin1
Reply With Quote
Old Apr 13, 2014, 10:17 AM
Registered User
Joined Jan 2014
12 Posts
RAPTOR F22 jetcat P20 voo de ensaio (3 min 49 sec)


Modelo em EPO comprado na hobbyking que alterei para vers„o combust„o com uma turbina jet cat P20 peso em voo 1670 gramas com um deposito de combustŪvel de 360ml.
Neste primeiro voo o vento soprava na ordem dos 14km/h e no desempenho do modelo notei os batimentos um pouco altos ao qual depois vou ter de reduzir
paulo durao is offline Find More Posts by paulo durao
Reply With Quote
Old Apr 13, 2014, 10:23 AM
Registered User
Joined Jan 2014
12 Posts
RAPTOR F22 jetcat P20

RAPTOR F22 jetcat P20
paulo durao is offline Find More Posts by paulo durao
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale want to trade for turbine or turbine airframe kremecheze Aircraft - Fuel - Jets (FS/W) 2 Mar 15, 2013 09:45 AM
Wanted p20 turbine or the habu 32 turbine conversion houstonderk Aircraft - Fuel - Jets (FS/W) 0 Mar 14, 2013 01:04 AM
Discussion Changing my title from "an intermediate FPV newbie" to "semi-advanced FPV newbie!" Koo FPV Talk 5 Jan 29, 2013 06:45 PM
For Sale NIB JETCAT SPT-5 Turbo Prop Turbine & P-60 Turbine swerd Aircraft - Fuel - Jets (FS/W) 4 Nov 08, 2008 12:33 AM
Discussion Turbine newbie seneka Jet Turbines 3 Jun 20, 2007 08:47 PM