Topic: hawker harrier jump jet ( large size )

Fantastic! Reminds me of my Hang gliding days!

hi pdr, this is getting far to technical for me i think need to get a book
and start reading up on all this.
can you recamend a book to get started with ?
planeking-robin

hi yoyo, your on will let you know when i have one read to go,
planeking-robin

Robin, I suspect a slope soarer version will glide further than a breeze block but not by much!
To start with the wing sweep works against you, I don't know what the sweep is on the Harrier but say 25 degrees (I am sure Pete can tell us the correct angle) so the effective speed of the air across the wing is 0.9 whatever the true airspeed is and lift is the square of the airspeed so the lift is 0.81 times whatever it would be for an equivalent unswept wing.  That starts to destroy the lift/drag ratio from the lift side. (Airflow over a swept wing is a mixture of flow at right angles from leading to trailing edge, and flow from root to tip.  At the extreme, 90 degrees of sweep, the flow would be all from root to tip creating no lift, (yes I know a flat plate effect would create some lift!) and none from leading to trailing edge.  Airspeed at right angles to the wing, which is what creates lift from the wing section, is airspeed times cosine of the angle of sweep)
Then there is the drag, gliders have pencil thin fuselages to minimise drag, your harrier model not only has a chunky fuz which isn't too bad but those air intakes with no flow through them are a barn door for drag.  So that's the drag side of the L/D ratio destroyed.
The result will be a glide angle that is very steep (glide angle being the same as the L/D ratio).
Therefore I don't feel that anything worthwhile can be learned from all the extra effort it would take to make a glider version.

Surely the wing lift section is parallel to the airflow and not at right angles to the leading edge, which, I would have thought, means there is no effective change in the speed of the air over the wing.

  Tom

You can look at it in either way. Either look at the section as drawn at right angles to the quarter-chord line and use an airspeed/Re number based on v.Cos(quarter-chord sweep), or draw the section parallel to the aircraft axis (which will be thinner, and will have less camber) and use the airspeed/Re numbers directly.

The prefered practice is the former, because the SPANWISE component of airflow will essentially follow the quarter-chord line, and it's much easier to analyse if the spanwise and chordwise components are taken to be at right-angles to eachother so they don't interact.

The actual airflow over the wing obeys *neither* rule, of course - because it unco-operatively leans inwards on the upper surface and outwards on the lower surface even when we tell it to stop. This is being raised with its boss as a disciplinary matter.

PDR

hi mpx ,you lost me with all the tec/stuff, but i think i get the drift of what
you are talking about  .
it is like any thing you try for the first time if you don't know what you are
doing, it is trial and era.
just like when i first got my laser i had no one to help me , with in 2 to 3
months i had cracked it, now i can do almost every thing i need to do
with it.
one thing i do know is how to build planes  .
planeking-robin

Came across an article about Mike Koskelas' Harrier experiments back in 1993, have scanned the relevant pages and should be attached below:

Therefore I don't feel that anything worthwhile can be learned from all the extra effort it would take to make a glider version.

If you have the fuse mould and skills to turn out a light one, you can fit it out with pretty much a hole right through the middle to reduce the drag.

As for a fat fuse and small wings, the wind rider BD5J flies pretty well and is exactly that (although admittedly smaller).



It's not at all unusual to boost the wing size for PSS gliders as well - if they are finished in the right colours it doesn't stand out. Possibly a different wing section too.

Let's see it fly as a jet first though!

Popped over to Planeking's this morning, It was a bit of a shock when I stepped inside his Garage! Laser cutter in the corner, Printer, Rack upon Rack of aircraft, spares, you name it, He's got it, I thought I knew a thing or two but my tail was literally between my legs with Robin's knowledge, Top bloke,
With regards to the Harrier, it's huge! You can see that the guy who made it had thought it out quite well, twin fans with a very good duct design whereby the front 2 nozzles get the same amount of thrust as the rear, I really can't wait when Robin lays up the first Fuselage, I'll be waiting to get my hands on one of my own!!
Robin, I'll pop over tomorrow evening

As for a fat fuse and small wings, the wind rider BD5J flies pretty well and is exactly that (although admittedly smaller).

I did say the fat fuz wasn't too much of a problem but the air intakes are, nor is it the small wing but the sweep that makes it inefficient.  And yes it can have a massive duct right through it or just a semi-ring to simulate an air intake but either would require complete different fuselage mouldings which means new plugs etc, hence it just isn't worth the effort as far as the jet model is concerned.  A glider version could be made but will be so different that it will tell you nothing about the jet version.

...but either would require complete different fuselage mouldings which means new plugs etc,..

 A glider version could be made but will be so different that it will tell you nothing about the jet version.

For my own selfish needs I don't care what the jet does, I want to see a big PSS Harrier!

I would have thought the moulds were of the outer shell with maybe another mould for the internal mounts and ducting, is that not the case?

Nope, just the external moulds, the internals were all done by hand by the look of it, it all needs gutting so Robin can make a clone of the ducting as it's quite a special idea internally,

For my own selfish needs I don't care what the jet does, I want to see a big PSS Harrier!

So would I so let me know if and when you ever get to fly it!

Hehe :-D
It won't be long, Hopefully Robin can build a flyable version by january! I'll give him a hand

Thommo, That Article is fantastic, I had a few ideas about the stabilisation etc and that should do the trick, Hopefully in theory, the size should aid itself as smaller planes suffer with more environmental problems i.e. WIND

At this rate, I'm not gonna get my P61 in the Air as i'll be around Robins!

hi thommo , once again many thanks for the new info  .
i did go to the link you posted, it made interesting reading not just the piece on mike koskelas.
the other posts .
i ment to back to you on it , but working night never seem to have the time to get round toevery thing .
but still it's only till jan 2012 .
please keep the info coming .
planeking-robin

So would I so let me know if and when you ever get to fly it!

Flying a huge PSS Harrier?

It'll be on here, and Vimeo, and rcg, and....

From the sound of it, it would be quicker to make a hollow glider version than to remould the ducts   

hi mpx and yoyo , let's get one thing straight we will get a jet harrier flying even if i have get the
bigest firework rocket i can find and strap it to the back  .
now now guy's let's keep it friendly  .
all joke's aside i fully intend to have one flying as soon as pos. ..
planeking-robin

hi mpx and yoyo , let's get one thing straight we will get a jet harrier flying even if i have get the
bigest firework rocket i can find and strap it to the back  .
now now guy's let's keep it friendly  .
all joke's aside i fully intend to have one flying as soon as pos. ..
planeking-robin

You go for it Robin, this is definitely all friendly, we're all right behind you. 

Now get that thing up there!

hi pdr , are you any where close andover hant's , as i would love for you to have a look over
this harrier before i start putting one together .
as any info you can give me will stop any misstakes .
planeking-robin

hi yoyo , many thanks  for your support most welcome.
i did think of the hollow duct through the fuz, after mpx said b/block
i don't think i will need to change the fuz just the internals what do you think.?
planeking-robin

hi yoyo , many thanks  for your support most welcome.
i did think of the hollow duct through the fuz, after mpx said b/block
i don't think i will need to change the fuz just the internals what do you think.?
planeking-robin

I guess the important thing for a glider version is to minimise drag - weight doesn't matter so much as long as the wing loading stays reasonable.

If the air has a big hole through it with not many corners and dead ends that should be fine - although maybe a smooth tube or two to guide the air through it would help?

What are you doing for the wings? Built up, foam, moulded?

But anyway, I don't want to distract you from the ducted fan version, get that one going first! I know how easy it is to spread yourself too thin and never finish anything...

hi yoyo , at first i will make a fome wing to get the project started and get one flying.
i have a lot of ideas for a built up wings but i need to draw them out and work things out.
planeking-robin

Robin, Are you in on sunday mate, I've now got to teach someone to fly a TREX450 tomorrow unfortunately!!!

Reply #103
 warbird_fanatic wrote Re: hawker harrier jump jet ( large size ) on Today at 22:59:14
Robin, Are you in on sunday mate, I've now got to teach someone to fly a TREX450 tomorrow unfortunately!!

hi dave,yse that ok.
planeking-robin

Brilliant, I'll give you a bell on sunday morning beforehand!

I have just been remembering another reason why a model Harrier may be very difficult to slow down towards the hover and accelerate away from it.  In John Farley's book "A view from the Hover" he describes how intake momentum drag at high throttle becomes more powerful than than tail fin at low airspeeds.  The intake momentum drag is destabilising in yaw so as speed is reduced there comes a point at which, if a yaw is allowed to build up, the sideways force from the intake trying to increase the yaw can overcome the fin trying to decrease the yaw, yaw rapidly increases and due to a high yaw-roll coupling the Harrier will flip inverted and the controls and puffer jets do not have enough power to stop it.  It is not a problem at the hover, just at low forward airspeeds, anything below 70kts for the full size.  The solution is the weathervane ahead of the cockpit for the pilot to see the amount of airflow yaw present.  A model pilot will not have that and it will be easier for the model to gain a lot of yaw at low speeds before the flier realises it.  It is not something a yaw gyro can deal with as the problem is related to yaw relative to the airflow, not a rate of rotation.

It is not something a yaw gyro can deal with as the problem is related to yaw relative to the airflow, not a rate of rotation.

It doesn't sound like it would be impossible to add a sensor for that, but to have somewhere to plug the sensor into you would need a flexible quad copter setup rather than just off the shelf heli gyros.

Having said that, if there are two fans in two ducts could they counter rotate to avoid it? I can't remember now if robins harrier has two fans or just the one?

2 fans, only problem is, they're both turning in the same direction, contra-rotating them would be a good idea to remove any centrifugal forces (like a flywheel forcing an engine to lean to the left or right under power) Was also thinking of maybe modding spoiler brakes into the flaps and maybe the tail like on a buccaneer to reduce airspeed but maybe i'm thinking too much, PDR should be able to help?

Having said that, if there are two fans in two ducts could they counter rotate to avoid it? I can't remember now if robins harrier has two fans or just the one?

It's not a gyroscopic effect, so counter rotating fans won't fix it - remember the full size has counter rotating shafts to avoid gyroscopic effects.  It's caused by a side force from the airflow going into the intakes, that causes an aerodynamic side force that pushes in the direction of the yaw that has already started, and being ahead of the CG it acts to increase rather than decrease the yaw.  It's not as simple as making an airflow weather vane.  A Harrier can fly sideways in the hover, at which point the weather vane points out to the side, and that is allowed because there is no forward air speed, or if there is then a limited sideways speed can still be used as long as you keep within the airflow yaw limit.  A simple weather vane control would block that from happening by always yawing the plane into the sideways flight, so it would always fly pointing forwards and could never translate sideways in the hover, or be able to hover in a sidewind for it would immediately yaw to point into wind.  If it was that simple to fix, it would have been done on the full-size. The problem only occurs, and thus the solution is only needed, when some forward airspeed is present and until the more recent fly by wire became available, that understanding had to be done by the human pilot.

I have just been remembering another reason why a model Harrier may be very difficult to slow down towards the hover and accelerate away from it.  In John Farley's book "A view from the Hover" he describes how intake momentum drag at high throttle becomes more powerful than than tail fin at low airspeeds.  The intake momentum drag is destabilising in yaw so as speed is reduced there comes a point at which, if a yaw is allowed to build up, the sideways force from the intake trying to increase the yaw can overcome the fin trying to decrease the yaw, yaw rapidly increases and due to a high yaw-roll coupling the Harrier will flip inverted and the controls and puffer jets do not have enough power to stop it.  It is not a problem at the hover, just at low forward airspeeds, anything below 70kts for the full size.  The solution is the weathervane ahead of the cockpit for the pilot to see the amount of airflow yaw present.  A model pilot will not have that and it will be easier for the model to gain a lot of yaw at low speeds before the flier realises it.  It is not something a yaw gyro can deal with as the problem is related to yaw relative to the airflow, not a rate of rotation.

You're (or he's) conflating two seperate issues here.

1. There IS a directional instability between about 85 and 65kts when decelerating into the hover. It's not intake inertia drag (see below) - it's simply (or more probably "complexly") something that crops up in the way the resultant forces, degree of damping and inertia distribution work out. It is critical to keep the yaw axis under control duing this phase because it takes less than two seconds to get to the point where the only option is the martin-baker let-down. But it's a straight aerodynamic vs kinematic issue and is easily understood, and more to the point can be nailed completely with a simple yaw gyro (because the unstable term is yaw *rate* not yaw *position*).

2. "Intake inertia drag" is the name given to a curious effect that is unique to jet-driven VTOL aircraft. It's easy to explain with a few scribbles on a whiteboard, but I'll have a go at describing it in words. At the hover air is pulled into the engine intakes, accelerated through the fans, turned through 90 degrees and allowed to exit through the nozzles. Now remember your basic Newton's laws and think of it in those terms. You see that the aeroplane applies a "force" to the air that turns it through 90 degrees - there must be an "equal and opposite reaction" and it's this reaction which actually causes the airplane to sit motionless in the air in precisely the same way bricks don't. Please read that but until it clicks, because it's important!

We're now looking at it as the aeroplane  acting on the air, not the air acting on the aeroplane. OK, so we're sitting in the Harrier hovering over the pan at RAF Cottesmore with absolute zero groundspeed in all three dimensions (because we arte ace harrier pilots who can walk on water at a single bound). The aeroplane is JETborne, not WINGborne, so it's affected differently by wind and gusts that other, more primitive aeroplanes. Suddenly the wind (into which we were hovering) switches direction by 60 degrees. This makes two things happen:

a)The intake on the "downwind" side of the aeroplane now gets partially blanked, so that side of the LP fan sees less air and the front (cold) nozzle on that side develops less thrust. This makes for a roll, pitch and thrust trim change. This isn't "intake inertia drag" but is a related effect.

b) The air coming into the intakes has a velocity and an inertia which is in a direction that is 60 degrees different to the axis of the engine, and as this air enters the engine this is "corrected" by the ducts, stators, engine casing etc. Now remember that Newton's Laws stuff? There must be an equal and opposite reaction, and that is seen in the form of a yaw departure. It's powerful because at zero airspeed there is no aerodynamic damping. and it essentially means that any time the aeroplane isn't hovering PRECISELY into wind it experiences forces to push it even further out-of-wind - this is "intake inertia drag". It's highly unstable because the initial force makes the aeroplane move in usch a way that the force increases, and as such it can't really be left to a gyro. In the full sized it's left to the driver, who is provided with a small weathervane just in front of the windscreen on which he must concentrate when hovering so that he can anticipate the gusts.  The only way I can think of dealing with this in the model is with an extremely yaw reaction control, possibly "tamed" with a heading-hold gyro (which is the approach we take with modern helis). This is the main reason why I keep emphasising the need for a LOT of reaction control capacity.

So that's the basics. There are some other effects if you actually do try to run a lot of sideslip on a harrier, some related to the differential intake effect and others related to the anhederal on the wings and tailplane, but they are minor issues which are easily handled by the simple practice of not letting the aeroplane get away from you (definitely the driver's job).

HTH,

PDR

So that's the basics...

Nicely done. That all made sense (or at least I think I understood it...)

So when in a stationary hover (for 15 seconds before the water runs out, was it?  ) the wind effect is subject to positive feedback, not just blowing you to one side. I can see how that would be something you'd need to keep on top of...

Nicely done. That all made sense (or at least I think I understood it...)

So when in a stationary hover (for 15 seconds before the water runs out, was it?  )

The water lasts rather longer than that (just as well, or those 10-minute hover sections at airshows would be a bit of a problem) and its also only needed at high all-up weights and in hot/high conditions. The warning caption lights up at "15 secs remaining". It's only needed at all because the equipment weight and cleared operational flying weights have risen somewhat, from the 9,800lb of the original P1127 to the 34,000lbs of a GR9A. Max VTO weight is a smidge over 20,000lbs, but max vertical landing weight is a couple of thousand pounds higher (depending on density altitude and air temp). Of course the landing weight is less of a problem because they'd generally be looking to have minimal fuel remaining at that stage of the sortie!

A typical GR9A in UK/North-Europe conditions (other than the hottest month of the summer) would use water for vertical take off, but probably wouldn't use it at all for vertical landing or hovering.

the wind effect is subject to positive feedback, not just blowing you to one side. I can see how that would be something you'd need to keep on top of...

Yes, it's a positive feedback condition, but it's also a non-linear one with quite an abrupt ramp-up for relatively small amounts of sideslip.

PDR

? I can't remember now if robins harrier has two fans or just the one?

hi yoyo , yes it has got 2 fans and they are 280mm apart, as warbird_fanatic said
and they are both on the same shaft,
sorry i did not get back to you before now but i have just got back from CHELTENHAM
as it was my gradsons birthday.
planeking-robin

hi yoyo , yes it has got 2 fans and they are 280mm apart, as warbird_fanatic said
and they are both on the same shaft,

Tricky to get them to counter-rotate then

 Yoyo wrote Re: hawker harrier jump jet ( large size ) on Today at 20:00:10 Quote from: planeking on Today at 19:28:57

Tricky to get them to counter-rotate then

hi yoyo, that's not so much of a problem.
the problem will be in getting a fan with the blades the opposite hand i think ?
do you think ?
planeking-robin

hi all , just to show you the kind of building that i do to a very hi speck.
some pic's of a plane from a plan from the 1960's this is a1/4 scale plane.
no prizes for what it is, i have redesign it to the latest build speck .
hope you like it, and it is all cut out on my laser. .
planeking-robin

That's gorgeous Robin, it always seems a shame to cover over such lovely structures.

mode=AOL

Me Two!

/mode

PDR

 Mpx wrote Re: hawker harrier jump jet ( large size ) on Today at 06:13:23
That's gorgeous Robin, it always seems a shame to cover over such lovely structures.

hi mpx, many thanks for kind comments , i posted the pic's just to show that i am no
fly by night, when i take on a project i give 100 per cent.
by the way your lightning is looking the biz , keep it up.
if you need any bit's cut out give me a shout and i will cut them out on the laser.
planeking-robin