schroedm

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Guys,

I'm planning a few turbine purchases for some new toys and struggling to decide what to go for. It seems that we've got to the point where we have to squeeze the largest turbines possible into models. Recent examples spring to mind of CARF Ultra Lightnings flying fine on 160s but seeing they 'have' to have a 200/Olympus, SM A-10s with 2 p100s through to others with 2 x 170! Mibos with 2 x rabbits or 2x160, ultra flash with P80 - P160...

Purely out of interest, could you post your model, weight (in pounds) , turbine & thrust in pounds and the thrust to weight ratio (thrust/lbs) and if you think you have enough power or not.

E.g. for me...

Airworld Cougar, 44lbs, p160SX, 35lbs, p/w=0.8. Good scale performance. Could maybe do with a little more power when ordnance fitted.
SM Viperjet 39lbs, p160sx, 35lbs, p/w=0.9. Plenty of power, with a little momentum large loops easy. No need for more power

Etc....

powerjets

My Feedback: (1)

I think I have the two that are opposites
Avonds F-15 with jetcentral Superbee, P/W 0.6 , super easy relaxing fun plane , use energy management for manouvres.
Avonds rafale with jetcentral Rabbit, P/W 1.3 , limitless vertical performance, super acc , keep with it at all times.
Both are very much fun in their own way, so I guess it depends on what your looking for.[8D]

Robrow

My maxim is fit the highest thrust engine that will sensibly go. Better to have more power available and not need it than the opposite.

Pro's.....better fuel mileage, less engine stress, more thrust available lower in throttle range. Con's....not come across any yet.

Just my 2p worth.

Rob.

BaldEagel

I have to admit I am with Rob on this one, certainly my Elan was a much more pleasant experience with the 120SE than it was with a P80, no more appreciable weight, but oodles more power to play with and I suppose the P/W ratio changed from below to above 1:1.

Mike

Henke Torphammar

2.8lb AUW, thrust 6.6lb, 2.33:1 thrust to weight ratio = enough I guess.

Robrow

I have been flying my Inspiration with a Merlin 140, it's a P100 size engine but obviously with 31lbs blow available It has very good short field performance still with good fuel economy.

I also know of a Flash fitted with a Merlin 160 reduced to around 28 lbs that the owner flies the a** off and is extremely happy with.

Rob.

basimpsn

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S/M F-18C 34lbs with KT-170 35lbs thrust, Hotspot 18lbs with a Ram 1000 26lbs thrust, E/S 30lbs dry with Rhino 31lbs thrust underpowered .

Dr Honda

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I guess it just depends. If the next size bigger engine isn't Physically heavier... then use it. You can always throttle back. I guess the only down side is that if you get an engine that's too big, and has a lot of residual thrust, and you have it in an air frame that is efficient... you may have a hard time getting it back on the runway.

I'm about ready to stuff a Wren 44 Gold (10 Lbs thrust) into an CMP T-45 with a projected take off weight of 8Lbs or less.

schroedm

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Thanks guys, interesting stuff. I guess as my main interest is scale jets I'm not after endless vertical performance. Having said that, as I fly larger models (160-200size) we hit the airframe size vs inertia issue where the extra power can be used to make it 'appear' you are carrying inertia through manoeuvres.

Take my 1:3.6 scale Airworld MB339, projected all up weight of 44-48lbs. I'm thinking a new P180RX with 39lbs is probably just right as it's a fairly slippery shape. Yes, I could fit a 55lb P200 but that's another 1.2kg in turbine weight plus at least another 1.5-2.5kg in fuel etc. If I wanted Ultra Bandit performance then the 200 is the way to go.

Is there an approximation that can be applied generally do you think? I.e scale models 0.7-0.9 power to weight and sport models 0.9 plus?

Sorry for ramblings, been a slow day....

Nhalyn

I'm also part of anti-overpowered aircrafts !

I've seen two style of overpowering : electric powered guys and jet guys.

For this two style, there's only one thing evident : there is never enough power even if it's 2/1 thrust/weight ratio !

Why ? Because it exist ?

I've seen the birth of electric powered planes, and at first it was real it was not enough ! Now we have lipos and Brushless engines, and as a revenge now we put as more power as we can ! It's just revenge !!!


I think it's the same with jets, after so much time with those poor ducted fans...

My big futura fly with a jetcat p-160, and that's enough for me ! I have lots other things to do with Ã* jet than flying always more than 300 km/h !

Square Nozzle

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Would a P100 in a GJC F4D Skyray scare you? The plane is advertised to take up to 14# thrust. A friend flys his with a Wren SS.

roger.alli

I have two Bandits, nearly identical models, but radically different in construction and power plant.

The first is a Balsa bandit which weighs 24. lbs wet, has a PST 600 with 13 lbs push, 054:1 P/W ratio. Model is a delight to fly, very fast (Bandits are slippery) and very forgiving in the circuit. It does take a little time to get “on the step� but once moving performs extremely well. Operating this model is easy, and it performs like a hot sport jet. Only real down side is it is not suitable for grass unless the surface is manicured.

The New Bandit is fully composite and weighs 28 lbs wet, has a Merlin 140 with 31 lbs push. 1.1:1 P/W ratio. This model requires a LOT more attention to operate. It can be flown stupidly fast, but I have to constantly be careful not to let it out fly me. It is great fun to fly, but requires much more concentration, especially when going very fast, or very slow.

At the moment I probably enjoy the Balsa Bandit more..

Having more power is great, but it does come with a few down sides such as;
More weight. (usually)
More fuel consumption
More residual thrust.
More risk of exceeding the VNE, and blowing your wings off.

In the end all aeroplanes are a compromise.

Roger

funflyerf4

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Hi John I had a p-70 in mine it was a tight fit but the 100 is a little smaller dia.and lighter I believe.

Jame

Il be fitting my Wren SuperSport in my Flash, I also know the Flash owner that Rob has mentioned and was recently watching him fly when he turned the Turbine up to around 35lbs, and to be honest, there didnt seem to be a big difference in either Top End or Vertical, I have no doubt there will have been, but it wasnt noticeable to someone watching him fly it. Im hoping the Wren will provide a thrust ratio of around 0.8 - 1. A similar situation I came across recently that Im sure your aware of, was Dave Wilshere' UF, I havent seen the P80 version fly in the flesh but the video looked as if it was of similar performance to the 120SX, if anything, slightly reduced performance, but not dissapointing by any stretch of the imagination.
On a smaller scale Mark, I made the same choice before I bought the SS, originally for my 1/6 Hawk, my choices lay between P80 and the SuperSport, but the projected Install Weight increase over the Wren, simply didnt warrant the extra 4.5lbs thrust.

Not on the same scale as the Pro's with the Futura's or 1/3 Scale Jets but still the same principle.

Square Nozzle

My Feedback: (1)

The P100 is lighter by a little more than 1/4# but is 0.1" larger in diameter than the P70. I have the engine but the plane has not arrived yet. From pictures, I expect to have some mount plate mods to do. I normally would not go with that much over power but I want to fly this puppy from our club field which is 400' of grass. The extra push should get it out of there with no problems. Then pull the throttle way back.

KC36330

IMO it has more to do with the airframe design/strength then the scale/sport look. a Flash has the integrity to support the stresses of the extreme thrust to weight even with a ham fisted bank and yank flier behind the sticks, other airframes aren't as fortunate to be able to stand up to that abuse.

PaulD

My Feedback: (39)

Comp Arf Flash with Merling 160 - they push out 37 lbs and the airframe was about 28lbs AUW. The speed performance was stunning but thats about it. Flying around at more reasonable speeds meant you were allways in that part of the throttle curve where the response was a little sluggish. Residual thrust was a problem too as the Flash didnt want to land unless it had a good dose of crow and flaps. Had a willing buyer for the airframe so took out the Merlin and cut it loose. Regretted it almost right away.

That Merlin is gonna go in my CT-114 which I THINK will build out around 38-40 lbs so the P/W should be really nice for that airframe. The 114 is a pretty big lump and some extra power and quick throttle response really help.

Boomer Torus with a IQ-Hammer 170 that puts out around 38 lbs. Nice combination for short field/grass plane which is what I built it for as the paved runways around here are 3 hours drive away. I haven't weighed the Torus but my guess is it's in the 32lbs range. It sure acts like it in the veritcals. Added bonus is GPS logger put the top speed around 189 mph.

Currently waiting on an Ultra Flash and a Hammer 170 is going in it. I think the P/W ratio will be perfect and I agree that it doesn't need a P200 esp with the slipperier Ultra wing. Also not going to stick a lot of extras like a cockpit kit or smoke in it either to keep the weight as low as possible.

PaulD

Veritech

Boomerang Nano and a Jet Central Rabbit. Originally designed for the MW 44 at 8 pounds of thrust and the Rabbit is putting out 21 pounds of thrust.

I originally set out to put a Bee II in there at 15#'s but the Rabbit is more useful in more airframes then the Bee is.

The first two dozen flights were set at 15#'s but at Route 66 jets this year I turned it up all the way for a few flights, what a blast. Not as fast as my old Ram 1000 Roo but still was was moving pretty good. It was keeping up with Chris Tuckers P80SE powered Falcon 120. Problem is that this airframe is NOT designed for all that power and after a few flights the booms were loose on the anti rotation pins...So it's back on the bench getting repaired and next year it with either get a 12-15# engine or i will dial down the Rabbit.


-Randy

Veritech

I couldn't agree more, the Flash is built like a tank. I have seen them get yanked and banked with P120's and up and they always seem to hold together. I have also seen them get bounced hard on landing and it is not even fazed by it. Compared to my balsa boomer nano, which is NOT designed for the thrust I have in it, it is a real durable jet. Not to say that the nano is not a great jet because it is but jets like the Flash and Bandit are much more durable for high speed and high G Flight loads.

-Randy

KC36330

i wouldn't put the Bandit in the brute strength category with the Flash, it simply won't hold up to the same abuse.

David Gladwin

How do you define "that will sensibly go "?

Cons: The possibility that you will precipitate structural failure by going outside the (undefined) flight envelope.

After the Reno accident the air racing world is taking a long hard look at what they do and how they do it. The findings and recommendations of the NTSB will make interesting reading.

Are we just going to continue stuffing bigger and bigger engines into airframes some of which (ARTFs) are of questionable structural integrity and flown by people who do not really understand what they are doing ? If we do my guess is that sooner or later we will suffer what Violett calls our "big black eye" .

Regards,

David.

Robrow

I think what I have said has been misunderstood, I do not subscribe to using any more thrust than a particular airframe is designed for. So if it is designed for say 120N then use that as a max. The point I was trying to get across was that fitting a higher thrust engine does give you advantages.

As an example my Graupner Inspiration is designed for 80-100N but is fitted with a 140N engine which comes in useful for my local grass strip, particularly during the winter months. I would say I am careful with throttle management and do not put the airframe under any more stress than a 100N engine would.

When it comes to safety I'm right behind you David.

Rob.