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Turbine model construction - can a normal balsa/ply model work as a Jet?

Started by FlyinBrian, January 05, 2014, 07:03:53 am

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FlyinBrian

This may be something already asked on here but I can not find the relevant post so I'll start from scratch

I am tempted by the idea of a Turbine powered model, the effortless ease with which they fly, the sound and the smell are so tempting it hurts. Now - just say that I wanted to "do turbines"

Please answer only if you have relevant experience, I can do without further confusion. Sure I can go and talk to a model shop but their primary aim will be to sell me an ARTF with all the goodies, I want independent advice
Can a self built model of standard, albeit substantial and careful, construction work well as a jet?,  I know "Fighter Aces" produce a kit of mainly ply construction and the various Boomerangs contain a lot of wood. But they are to my mind blumming expensive for what they are. I am a pretty adept builder of standard models and it seems to me that it should be possible to build something to suit a modest sized turbine engine (say 15lb thrust) for a reasonable price.

Our flying site strip is c100M x 40M with a clear approach one end and somewhat less so from the other end with some trees and bushes, the terrain around the site is farm land with a sports ground behind the pilot area. On weekdays we have access by arrangement to the sports fields which total aprox 500M long by 100M wide, naturally a good lookout would need to be kept while flying and especially landing and turbine flying would not be allowed when flammable crops are standing in the fields.

My thoughts re the model are:

Probably a twin boom layout similar to the Boomerangs for practicality and easy access to the innards and to avoid the need for a tailpipe.

AUW under 7Kg inc fuel.

Wing loading -  30ozs / sq ft - Wing fitted with flaps to allow a slow(ish) landing approach
so I need a wing area of close to 8 sq feet say 7.5 sq ft

Thick wing to support booms and for strength, probably foam, skinned with balsa and glass fibre. say 21/4" - 21/2" thick and using 25mm Carbon tubes thro the fuz and to attach the booms.

Span  65"- 70" for practicality with an average aspect ratio of 5ish so about 15";-  therefore a swept LE with 18" root and 13"  tip gives c 1000 sq inches or c 7.2 sq ft and looks "jetish"

Turbine size smallish around 4" diameter either  Jetcat, or Wren as service is obtainable easily via Als Hobbies or Wren directly (Als Jet centre is about 18 miles from home) I would hopefully obtain a used in good nick turbine unit with a 1:1 power ratio so the engine needs to generate 15lbs ish of thrust.

All ply and balsa construction with glass and carbon reinforcement as needed.

Booms need to be light and strong, possibly balsa with ply sides and carbon rod, carbon strip or carbon wrap reinforcement for stiffness. Or just Carbon Tubes but that gives fixing problems for the wing, fin and tailplane.


I have other ideas which I am cogitating over but the specific turbine related questions I have are:

Modern turbines a pretty self contained, start and run on Kerosene have little need for ancillary items! - I am working on the basis that if it all goes wrong I can survive financially - I have determined that I cannot afford one of these modern kero start units.

Is the older, gas start, turbine still fairly easy to operate?, How can I gain experience of using a turbine - that is start up, running and shut down without buying, trying and probably bu99ering one up. What should I expect to pay for a used but good gas start turbine which still has many hours of life left in it, I would use either Jetcat or Wren. Is a
"Jet day" or Wren Experience day a good idea, has anyone done one?
Does the aeroplane need a gas tank as well as a fuel tank or do you start with an external gas tank?

What is a FADEC, What is a data terminal for? I have my own ideas based on reading bits on line and I have started reading Al's articles in Model Flying, but when I want to learn about something and am interested I want to know everything now!

Please feel free to shoot me down or offer advice, I am not going to do this tomorrow - if ever. Please see my motto at under this post

Brian




Basic Research is what I do - when I don't know what I'm doing!.

THE BLACKBIRD

Hi Brian I have just built a Hawker Hunter from scratch using balsa an ply, from a Traplet plan and it fly's great using a Jetcat 100RX
Just got to fit proper retracts and paint her



Tony[attachimg=1][attachimg=2]
The man that never made a mistake
Never made anything

Thommo

Quote from: FlyinBrian on January 05, 2014, 07:03:53 am


  I know "Fighter Aces" produce a kit of mainly ply construction and the various Boomerangs contain a lot of wood. But they are to my mind blumming expensive for what they are. I am a pretty adept builder of standard models and it seems to me that it should be possible to build something to suit a modest sized turbine engine (say 15lb thrust) for a


Brian


Having just built a Fighter Aces Valkyrie I can tell you that they are NOT blumming expensive in fact they are excellent value and great pleasure to build, however would be too big for your needs, mine weighs 27lbs dry, including 3lbs of nose weight...  :''

Have you considered MR Super Reaper? Ideal for small field use with large wing area.

nickr100

Get in touch with alasdair sutherland (Wetjet on here). his OD JayTee flys really well, has acrowot like flight envelope which can be extended to acrowot on crack if required. with a wren 54, it can take off in about 30yrd and land in less with its flaps down. i also know he is designing a low wing version too which i think is planned to be more sporty

jetster

Have a look at the Ripmax Xcalibur for an artf jet it is very good value for money at around a grand with retracts and brakes that are made especially for this plane,it may suit your needs

The Saint. (Owen)

The Mick Reeves Super Reaper is an excelent model, may not be the best looking model but it flies good on just a 12lb turbine and will fly great on the Wren 100 (I love Wrens) and at £295, it's a bargain.  :af :af :af
Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

Turbine Tinkerer

I built a ziroli turbinator (all balsa and ply) flys great. I think 7kg auw is a little optimistic.

xairflyer

To answer your initial question, yes of course conventional construction works as a jet, many of the jet trainer kits are simply balsa and ply (boomerang)

There are many ways you can go, you seem to have the knowledge so why not just design your own copying the proportions/wing section from the boomerang intro to give you a start and help you along.

Look for many of the plans that are out there, they don't have to be turbine only, lots of the 91 size ducted fan plans suit perfect for a 60-80 size turbine.

Buy something second hand there are lots of boomerangs etc ready to go for between 800-1200 coming up regular on BMFA classifieds

The cheapest and best value jet which fly excellent and land very slow are the falcon 120/navycat/tornado/kestrel models, the falcon 120 is the cheapest in the range but requires a little more mods than the navycat (£250 colchester models) etc are coming more turbine ready.

Yellow one is my navycat with a P60 one behind is a Falcon 120 built for a friend with a wren 54.

trebor

Just to follow on from what Xairflyer is saying, I bought a set of Boomerang Intro wings and using my Intro as a pattern have made my own fuselage and tail feathers , everything on the plane is in the same place as an Intro other than the elevator/stabiliser is a bit lower.
It's waiting a test flight when the weather improves.
I'm hoping that the flight  characteristics should be very similar to the Intro which I like but at least to my eyes looks better , oh and it doesn't cost the sort of money that other sport models do.
Weight has come out at 18 lb with painting to go which is 1lb more than my Intro, so I think you may struggle to get near 7kg with fuel as the fuel weighs 2 kg alone.

Rob

xairflyer

Rob love it,  I had the same idea but so far only got as as drawing up some plans and was hoping to build it over this winter but other builds will delay it now.

I have the same using the boomerang wings with their great flight characteristics and keeping the undercarriage on the main fuselage, which looks like what you have done as well, what did you do in regard to flaps

trebor

Started this about a year ago so nice to get nearly finished, I'll leave painting until I know it flies ;). I bought the inner wing as well so the flaps are as on the Intro, I also got the Sprint air scoops it was easier than trying to make some that looked good. The only weight penalty was having a thrust tube which meant a bit extra weight up front. C of G as per Intro  :xx

Rob

sticky

If you are an adept builder and flyer then I would skip the boomerang trainer jet.  I built the Jetlegend f15 kit version as my first jet and its a pussy cat...not a floater though as I guess a boomerang would be, but I hate the ARTF looking boomerangs...my opinion though.

I am now building Tony Nijhuis Vampire which is all balsa and lite ply and will take a 60 to 80 size.  As for not affording a kero start look at the new Kingtech turbines.  Mine is a 140G and starts and runs faultlessly.  Mind you I am very tempted by the Wren Jubilee 80 for the vampire although I can get an 80G 30% cheaper than you can in the UK so that could be the decider.  Even so a new Kingtech 80 can be had for the used price of a jetcat/wren etc.

Have a look at used planes on BMFA site.   Some very cheap complete models keep cropping up.

Pete
Beer is proof there is a god who loves us and wants us to be happy.

FlyinBrian

Quote from: jetster on January 05, 2014, 11:02:08 am
Have a look at the Ripmax Xcalibur for an artf jet it is very good value for money at around a grand with retracts and brakes that are made especially for this plane,it may suit your needs


Look, I am Yorkshire born and  Geordie bred so I am afraid "a grand" is too blumming expensive as is the Valkyrie which lets face it is just a big plywood jigsaw puzzle. - Sorry Mr Clarke!
Basic Research is what I do - when I don't know what I'm doing!.

FlyinBrian

Quote from: xairflyer on January 05, 2014, 12:56:13 pm
To answer your initial question, yes of course conventional construction works as a jet, many of the jet trainer kits are simply balsa and ply (boomerang)

There are many ways you can go, you seem to have the knowledge so why not just design your own copying the proportions/wing section from the boomerang intro to give you a start and help you along.

Look for many of the plans that are out there, they don't have to be turbine only, lots of the 91 size ducted fan plans suit perfect for a 60-80 size turbine.

Buy something second hand there are lots of boomerangs etc ready to go for between 800-1200 coming up regular on BMFA classifieds

The cheapest and best value jet which fly excellent and land very slow are the falcon 120/navycat/tornado/kestrel models, the falcon 120 is the cheapest in the range but requires a little more mods the navycat (£250 colchester models) etc are coming more turbine ready.

Yellow one is my navycat with a P60 one behind is a Falcon 120 built for a friend with a wren 54.


They look quite promising! and affordable.

My first jet will not  have retracts at least not  at first as its less of a learning curve and less initial expense.
Basic Research is what I do - when I don't know what I'm doing!.

FlyinBrian

Quote from: THE BLACKBIRD on January 05, 2014, 08:03:00 am
Hi Brian I have just built a Hawker Hunter from scratch using balsa an ply, from a Traplet plan and it fly's great using a Jetcat 100RX
Just got to fit proper retracts and paint her



Tony[attachimg=1][attachimg=2]


The Blackbird, very nice model, I hope it proves to fly as well as it looks.
Basic Research is what I do - when I don't know what I'm doing!.

rogerandout

Quote from: FlyinBrian on January 05, 2014, 23:02:39 pm
Look, I am Yorkshire born and  Geordie bred so I am afraid "a grand" is too blumming expensive as is the Valkyrie which lets face it is just a big plywood jigsaw puzzle. - Sorry Mr Clarke!


S/H Reaper on BMFA at the moment for £100 I doubt you will get cheaper.i

FlyinBrian

Quote from: rogerandout on January 06, 2014, 04:25:07 am
S/H Reaper on BMFA at the moment for £100 I doubt you will get cheaper.i


Sorry I hate the look of that thing but it is cheap mmmmmm.
Basic Research is what I do - when I don't know what I'm doing!.

THE BLACKBIRD

Hi Xairflyer I have just bought a Navy Cat and im interested in what modifications need to be made to it
The model shop never said anything about any mods

Thank you
Tony
The man that never made a mistake
Never made anything

xairflyer

I was referring more to the Falcon 120 the NavyCat comes more turbine ready
If you look at this thread from post below you will see what I did to mine, might be of some use.  You will need to scroll down through thread to find more of the posts.

http://www.rcuniverse.com/forum/rc-jets-120/5913492-bob-cat-copy-falcon-120-jet-176.html#post11191509

wetjet

Quote from: nickr100 on January 05, 2014, 10:07:32 am
Get in touch with alasdair sutherland (Wetjet on here). his OD JayTee flys really well, has acrowot like flight envelope which can be extended to acrowot on crack if required. with a wren 54, it can take off in about 30yrd and land in less with its flaps down. i also know he is designing a low wing version too which i think is planned to be more sporty.   


Thanks for the plug, Nick100!!
I still have not got around to drawing up the plans for the magazine (promised to Model World years ago, but still waiting for the round tuit), but JayTee does sound the ideal model for FlyinBrian

others I could suggest are the aforementioned Falcon 120 and Super Reaper. Not sure of the weight of a Super Reaper tho.

My JayTee is ply and balsa with a foam/veneered wing and weighs about 6 kg (13 lb).  The significance is in the legislation. Above 7 kg you need to adhere to more regulations, including the failsafe (essential anyway) and a height limit of 400 feet. That is useless for a jet, as a tight loop is bigger than that.  I fly my heavier jets only on airfields with ATC permission, or at events with permission and NOTAM for operation to 1000 or 1500 feet AGL (that covers the legality).
I have flown the JayTee on a Wren 54 Mk3 (14 lb thrust, 63N) using trike fixed gear or floats. It flew well even on a Wren 54 turned down to the power of a Wren 44 (10 lb thrust) but my next one (some time this year) will have an 80N  Wren.

The Saint. (Owen)

Quote from: wetjet on January 08, 2014, 21:54:12 pmNot sure of the weight of a Super Reaper tho.




I have a Super Reaper fitted with a Wren Supersport and fixed u/c and it weighs in at 7kg.   :uk:
Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

FlyinBrian

Basic Research is what I do - when I don't know what I'm doing!.

The Saint. (Owen)

Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

xairflyer

Quote from: wetjet on January 08, 2014, 21:54:12 pm
Thanks for the plug, Nick100!!
I still have not got around to drawing up the plans for the magazine (promised to Model World years ago, but still waiting for the round tuit), but JayTee does sound the ideal model for FlyinBrian

others I could suggest are the aforementioned Falcon 120 and Super Reaper. Not sure of the weight of a Super Reaper tho.

My JayTee is ply and balsa with a foam/veneered wing and weighs about 6 kg (13 lb).  The significance is in the legislation. Above 7 kg you need to adhere to more regulations, including the failsafe (essential anyway) and a height limit of 400 feet. That is useless for a jet, as a tight loop is bigger than that.  I fly my heavier jets only on airfields with ATC permission, or at events with permission and NOTAM for operation to 1000 or 1500 feet AGL (that covers the legality).
I have flown the JayTee on a Wren 54 Mk3 (14 lb thrust, 63N) using trike fixed gear or floats. It flew well even on a Wren 54 turned down to the power of a Wren 44 (10 lb thrust) but my next one (some time this year) will have an 80N  Wren.


Tell me more about this JayTee I'm excited, when I see it on floats!

wetjet

thank you xairflyer.
The mark 1 JayTee succumbed to brownout on the then brand new Spektrum DX7 in June 2007 on its second flight.
After a year I built the improved mark 2 which was extensively flown, on fixed gear and the floats in the photo. After another prang (my fault) I built a new fuselage, redesigned a bit for easier building with laser cut parts and a much bigger canopy/hatch, and that's in the top photo, with wheels. It has been flying since Oct ’12.
Span is 80" or so, and it flies better than my Boomerang or Falcon, it is easy to transport and quick to assemble on the field. The wing has 2 veneered foam panels that slide onto a metal wing tube. The tail on the mark 2 was removable but, since I never removed it in 3 years of flying, it is now glued on the latest version.

wetjet

Quote from: FlyinBrian on January 08, 2014, 23:22:34 pm
Look what I found:- can I keep it mum, can I eh pleeeeease


Go for it, they fly very well. I have flown one for a while, on a Wren 54, built with fixed gear on the KISS principle
[attach=1]

They do have a reputation for poor build quality (maybe just because they are cheap), but mine was fine as far as I could see. I strengthened it in a couple of places and made my own moulded fuel tank to fit the space. I always flew it gently and did not over-power it – just in case.

The only thing about them is they are awkward to transport.  I have a big van (VW transporter) and it fitted in one piece but was awkward to get in through the doors.  Taking it apart would have meant disconnecting so many wires that I never dismantled it.

I damaged it recently, when I clipped the fence around the strip when attempting a touch and go on wet winter grass.

JohnMac

Hi Brian,
To answer your original question, yes of course it is possible for an experienced and  competent builder like you, to sucessfully design and build a jet using traditional methods. I currently have a plan for a Sea Vixen which if I had the free time I would start to build now. Your starting idea is a good one in my opinion. Keeping the model light is important if you wish to fly from a small strip. Make the flaps quite large, as the residual thrust is a factor during landing.
Make the landing gear and its mountings strong, prefeably tied maechanically into the spar. High landing speeds, and wing loading give the gear on jets a hammering.
Go and hang out with jet flyers, pick their brains. One of the biggest challenges is to learn the lttle tricks of the trade that experience jet pilots take for granted.
If you fancy it go for it. Plan carefully, think a lot. If in doubt ask, and come and wow us all. Good luck Brian,
John

ThrottleBender

HobbyKing are probably already working on upscalling some of their 90mm EDF jets ready for turbine use.  :xx
blobbygate scandal
firefox AdBlockPlus

The Saint. (Owen)

One possible problem could be accomodating a 2 litre fuel tank.  :-\
Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

FlyinBrian

OK

Just the Slightish deviation from the original idea -
I am buying the model shown, no servos or rx but with turbine (Wren ECOstart 70 and tank, plumbing etc)
Also included is 20 litres of ready mixed fuel, and cannister of starting gas .
With the servos I plan to use and the JR921RX which I have allready It will cost me just about a grand in total to actually get into the air.

So, I now have time to plan jet number 2 which will be the self build one, I plan to change from a twin boom to possibly a shoulder wing or mid wing layout and traditional style fus using a jet  pipe.

I'll update when the model shown has flown.
Basic Research is what I do - when I don't know what I'm doing!.

djay

How about looking at the Tony Nijhuis Retro jet.
I built one powered by a really ancient 18lb thrust turbine,, which in reallity was giving about 12lb of thrust.
It is a heavy plane but it taskes off in about 10 meteres and lands real slow.
It comes as plan only, or you can buy the cnc cut wood and extra wood pack.
This way you could modify it as you want, redesign it, rebuild it etc to suit.
It has fixed gear, no fancy equipment and is high wing.
the wing is one piece but it is easy to buy a set of wing tubes and make it two piece.
Also most importantly it is cheap, about 300 pounds all in, and uses  basic shop or spares box hardware.

[attach=1]

Darryl
I used to land in English cow poo, now I land in Camel poo, but the plane still smells the same thou

The Saint. (Owen)

Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

djay

I had a 32oz (think it is 32, the biggest Dubro do) a 28 oz tank underneath that  and a Hansen bubble trap fitted, but after a 7 min flight only half the big tank was used, so I removed the 28oz tank to save weight.
masses of room inside to fit what you want.
Darryl
I used to land in English cow poo, now I land in Camel poo, but the plane still smells the same thou

The Saint. (Owen)

Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

djay

Yes you are right, it is 50oz thought 32 was a bit small,  did not know they sold a 100 otherwise I would have fitted one, but as it turns out a 32 will probably be right for most smaller turbines, but 50oz is perfect.
Darryl
I used to land in English cow poo, now I land in Camel poo, but the plane still smells the same thou

wetjet

The 50 oz (1500 ml) used to be the biggest Dubro made, and I used one in my first jet, the Baby Boomerang (Intro). I also fitted a BVM airtrap header and my Wren 54 and I set my timer for 6 mins from takeoff, and aimed to land within 1 min (6 to 7 min flight).
Now Dubro make bigger tanks, but I don't know the size to check if they fit.

I designed my JayTee (photos above) to take either a 50 oz Dubro or a 2 litre cider bottle.  The cider bottle, used without a header, gave me longer flights. I set my timer to 6 minutes anyway out of habit, but had 2 or 3 min to shoot a couple of practice circuits before landing.

P.S. the Retro Jet (review by Dave Swarbrick) is a bit ugly with its straight wing, turns out well over 7 kg as it needs lots of noseweight, so is limited to 400 feet AGL unless you have special arrangements. Flies well though apparently!

Beereycalfs

the retro jet is so damn ugly though, my own personal opinion is that a jet should look like a jet not a shopping trolley or a pram, i really did not want a boomerang, but i was advised to not be silly and get a good cheap second hand one to cut my teeth on, and it was the best bit of advice i have had for a long time, the old intro is a wonderful flier and has been great for me, however i am now building a fighter aces Valkyrie, and it is not an expensive jigsaw puzzle, if you actually look into the kit it represents amazing value for money, so maybe you can stop slagging something off you have no experience of!! i wanted a sports jet that looked different, and if i have to build one then so be it, Phil should be applauded for the quality of this kit, it really is world class quality

THE BLACKBIRD

Just flown my Falcon this weekend managed to knock the nose wheel leg off, found there was not much holding the supports in place only four joints and one of them had no glue in it, so worth beefing them up a bit
Found it flew very well but a bit fast for me being fairly new to jets, but I do have a Jet Cat 100RX in it  :ev :ev :''
Then again I have a throttle  ;) ;)
The man that never made a mistake
Never made anything

xairflyer

Its one of the things you have to do with the falcon 120 is re glue everything.  On one I built I was able to snap out all the formers clean then hysol them back in.  In china they use flour and water for glue  :)

THE BLACKBIRD

I keep my Navy Cat fully assembled and transport it on top of my car, I made a roof rack to transport my SR71 so I utilised part of that works a treat, the big box you see in the background is what I carried the SR71 in as I kept it in one piece
The man that never made a mistake
Never made anything