And now for something completely different....in Depron

[Simon Chaddock]

Erfolg

Having looked at a couple of the guides that can be down loaded I am not sure how accurate (or even applicable) they would be for the tiny ducts (3/4x3/4inch) and relatively high velocities used in an EDF.

[Erfolg]

Simon, having being involved in my early years as a designer, of a high velocity air curtain, using small ducts, they are not pessimistic. The losses are far higher, the faster and the smaller the ducts become. The worst scenario is as has been suggested is where sharp turns are made and significant changes in size occur. Turning vanes reduce losses, the losses are still there.

It seems a fact of life that DF use and loose a lot of power, certainly the faster you want to go and the more air you are trying to shift.

As one who has been deliberating for a long time now if I should try a DF and just cannot bring myself to try, as either the ducts are to long or the fan to small or the model becomes to large I do admire your can do approach.

[Erfolg]

Neth

That is certainly some achievement. Particularly the control. The power used is also enormous with 2 *60 ESCs and 2 *40 Escs. The Lipo is also of high discharge one is at 60C. Also a 3700 Lipo is mentioned. The flight time always seems to be about 1 minute one near to 2 minutes. The system is using 2 lift fans, and 2 aileron fans. Also auto stabilisation is mentioned.

To date the project has lasted 2 years, all apparently hovering flight.

I know I could not carried out the project however hard I would try.

The one thing that has bothered me, is that one of the ducts seems to be the product of a machining operation, from solid. I wonder has he also done that?

What ever, a tremendous achievement.

Also the video of the early VTOL aircraft is interesting, although, as you would expect, not exhaustative of all that have been built and flown. It did strike me that the Ryan, would not be the same challenge today, when taking of or landing with all the electronic systems available. Just as it is with air sea rescue helicopters in the hover, once very difficult, now pick your reference point, the system takes care of everything else.

[Delta Foxtrot]

Great to see something different being attempted. Here are my thoughts based on what I can surmise from the photos:

The amount of turning you can achieve from a cascade is a function of diffusion, turning and the space to chord ratio of the vanes. In this case the diffusion or staic pressure rise in the cascade can be neglected as the area at cascade inlet and exit look similar so the vanes are just deflecting the flow through very large angles.

There is a parameter called the leiblien diffusion factor that is used in cascade design to ensure that the blades have sensible loadings and do not stall. A design value might be around 0.4. If I assume that your vane spacing is approx the same as the chord and that your duct areas are not contracting across the vanes then to run the flow through 90 degrees would imply a DF = 0.5. I think that you are trying to turn the flow more so the DF may be > 0.5. Given that you also are operating at low reynolds numbers (small chord) your cascade will be stalled and will not turn the flow as much as you want and wil generate high losses. That is the science bit, if you want to ignore all of this then that is fine.

So I think that your first row of vanes will be stalled creating high loss and not delivering the flow onto the second row at the correct angle therby causing more loss. You could maybe do some experiments to look at this by tring to attach tufts or streamers to the suction surface of the first row of vanes and if you have line of sight up the exit nozzle shine some light in there and perhaps video it too see what happens as you run up in power. If you do not have line of sight then you could try some flow viz by painting some coloured oil mixture on the vanes and run, shut down and look for flow separation, which I am sure you will see.

You could maybe improve the design by adding vanes, increasing the chord, adding contraction, to reduce loading. You could also perhaps back off the turning as the second row of vanes is doing the opposite turning to the first.

good luck

[Delta Foxtrot]

http://navier.stanford.edu/bradshaw/tunnel/cornervane.html

have a look at the above web page which talks about corner vanes in wind tunnels. These are usually turning the flow through 90 degrees, similar to yours and the space to chord ratio is around 1/4. You can see straight through your vanes and so can the air.

It would be better if you could design the duct corners as smoothed curved surfaces rather than tight corners. Indeed if you make the duct more of an S shaped duct with some contraction like a curved nozzle that would help. You could maybe do this internally and keep the external shape if that is important to you.

[Erfolg]

I have been thinking about the project in the USA that Neath has brought to our attention.

One fan is direct acting, the second lift fan is both short and large dia relative to duct length. There was much discussion on how to reduce losses from this item.

The roll fans 2 off seemed to consume a disproportionate amount of power due to the ducts. There did seem to be one set up where these were direct acting units, that is without any ducting. A later set up?

[Chuck Plains]

David took some of the words right out of my mouth.

Shirley leaving the scale touches to the outside and gleaning best efficiency internally would have benefits.

As mentioned by more than one other, shallow angles improve flow.

Ask me to build you a custom QUIET water system in your house and I would use angled joiners that favour the direction of the flow by reducing turbulence/drag.

[eflightray]

Neth ?, who's that.

First, it's actually eflightray in Neath, (that's near Swansea) , I screwed up when signing in. . Not a problem some Americans even called me Tray. Doh!.

Second, please excuse me for pointing to another forum, but if you want more information on Vtols, this one has a load of info on all type of Vtols.

**LINK**

For specific threads on EDFs, use the Search this Forum, (upper right), and type EDF, make sure it also has Show Threads set.

Ray in Neath, who does eflight.

[Delta Foxtrot]

http://upload.wikimedia.org/wikipedia/commons/8/82/Pegasus-engine-diagram.svg

also have a look at the above for a sketch showing the Pegasus plenum and single row cascade vanes arrangement. The large plenum will create a reservoir of low velocity high pressure air to feed the thrust nozzles and only a single cascade is required to achieve the flow deflection in the nozzle.

[eflightray]

Just to show what an awkward sort of modeler I am, I don't do EDF, but EDP is interesting, (and uses a lot less power).

EDPropeller ?, Ok so you need a bigger plane.

Sorry for taking up space in this thread, but props still work even when hidden.

You just need a darn sight bigger Harrier.

Ray.

[Delta Foxtrot]

Ray,

you have some really nice models on your web site

dave

[Simon Chaddock]

Ray

No worries. I think I have seen a video of it on You Tube.

Yes I have done EDP as well but to scale. Well everything but the inlet and exhaust..

And not that big either at 36" span.

But in this case the prop is right at the back and as a pusher.

However for the modest power involved it is not that quiet!

[Simon Chaddock]

The next issue is to convert the flow from the top and bottom quadrants into a rectangle to feed the inlet for the rear nozzles. Had to think a bit about the best shape for this.

When enclosed and the rear duct added you end up with an EDF Pegasus!

It fits on the same test stand

And gives 11.9oz thrust.

This is really quite close to the thrust achieved by this long duct in my V-1

This does seem to suggest that the extra losses of the complex airflow path tend to be offset by its much shorter length.

The thrust achieved should be quite sufficient to fly a lightweight test plane, maybe a simple 'profile' Harrier, just to find out how the duct performs at speed.

[Chuck Plains]

Are you sure you don't have a secondary, smaller, EDF hidden in there? But that's a very peasant increase! It seems like you're way ahead of our suggestions anyway.

Hmm, could a secondary, higher rpm or pitch ratio fan improve it further? The Pegasus is effectively 3 groups of fans after all.

[Simon Chaddock]

Chuck

As I understand it for a given static thrust a single fan is always more efficient than multiples in series but this assumes the airframe can accept the large diameter it requires.

 

A simple(?) profile Harrier fuselage under construction.

The two skins of 2mm Depron will be 15mm apart to give sufficient bending stiffness.

The 4 nozzle unit glued into the completed fuselage.

The fuselage is brought to a fine edge in front of the fan inlet.

It looks like the only place for the battery to achieve a suitable CofG will be in between the front and rear ducts, probably in a 'saddle' arrangement one each side.

It will make a very compact layout.

 

Edited By Simon Chaddock on 07/07/2014 00:16:56

[Martian]

coming along nicely Simon

[Chuck Plains]

If it works, it works! It certainly has a very 'bird like' profile at the moment. That has to be a good sign.

[Josip Vrandecic -Mes]

Mr. Ray ,hats off , hope it will reach the Spit 72..

[Roy Mundy]

Blimey Simon you do like a challenge mate

I will watch and learn with interest, you certainly take things to another level I admire your enthusiasm .

keep up the good work

regards

Roy M

[Simon Chaddock]

The 850 mAh 3s 30C batteries in panniers either side between the nozzles.

The ducts require careful fairing to reduce the drag of the high speed airflow on the fuselage.

The front fairing.

I am waiting for a 30A ESC before I work out the best way to connect it all up!

[Colin Leighfield]

Very, very interesting!

[Simon Chaddock]

The Harrier has pretty small wings. At the scale of the fuselage they would be just 17" span. In order to keep the speed down I have simply stretched the span to 26" but kept the same root chord so they have a higher aspect ratio.

Still quite small and I want to keep the weight down so another all Depron design with multiple shear webs and no spar.

Pretty thin so the 3.7g micro aileron servo is flush with the under surface.

The full size has 'inset' ailerons to allow the tip wheels to retract backwards. To keep things simple I have run the aileron right out to the tip.

It has a scale all moving tail with the correct anhedral and uses a glass fibre cross tube.

Probably not necessary but just in case it is also mass balanced with 0.8g of lead in the leading edge of each half..

The wing will also have anhedral but it will be a bit less than the scale angle due to the extra span.

I have a suspicion it will end up more stable inverted than the right way up!

[Stefan Hafner]

Looks interesting Simon, I've been tempted to do something similar but bigger, when my wallet allows me

Regarding stability, what about simply having the batteries mounted lower down the fuselage if you have any problems, may improve things somewhat?

Interestingly, I read somewhere that the reason for the anhedral was that the original design was too stable so to compensate they added the anhedral.

[Simon Chaddock]

The just wing placed on the fuselage to give an idea of what it will look like.

The wing will only be fixed on permanently once all the electrics are installed and tested.

The servo for the All Moving Tail is mounted below and linked directly to the leading edge.

So far it looks like it will weigh only just a little bit more than the measured static thrust.

[Simon Chaddock]

At last the ESC has arrived.

This is a very compact installation so I needed all the bit to hand to work out exactly how it would all fit.

The saddle batteries each with there own connector.

They run down to the ESC underneath.

The ESC takes the motor wires forward to the EDF.

To get it all to fit all the wires have had to be cut and soldered to exactly the right length.

It looks like it is going to weigh almost exactly 12oz (340g) which is very close to the measured static thrust. Hopefully this should mean it will fly well enough - but then I am not trying for a hover - yet!!