Hamilcar - a rebuild.

[Erfolg]

I had thought I had seen the Hamlicar somewhere. Although apparently not as accurate as some later, perhaps better researched publicans, for us modellers, more than good enough.

So I have had a look at p25, of vol 7, in my book.

As suggested the airfoils shown is almost symmetrical. You can see that the wing was set at a very high AoA according to the drawing. The LE radius shown is of a very large radius. The wing section at the root is suitably impressive. The reality with the real aircraft, the wing will have been very cambered when operating.

I had not realised how tapered the wing is, at scale. If the model replicates this, the taper itself will be enough to make the wing prone to tip stalling. As been suggested, washout is a must.

From reviewing the detail of the design, it is apparent that the real aircraft was always intended to be a slow flier, with the wing always at a high AoA.

I still see a very boxy fuselage, coupled with a wing planform, that most manufacturers would avoid, as they will want all round handling, which is forgiving. It seems that the Hamilcar was conceived as a straight flyer, with one mission, carrying a heavy load, at the expense of good, forgiving handling characteristics.

I am now convinced it is an issue of a lack of power, combined with a less than ideal wing, needing washout. Unfortunately, setting the ailerons at reflex, does not work that well, as a washout substitute.

[Simon Chaddock]

As the two flap sections on each wing have a slightly different hinge line the single servo requires a double link.

A short test of the flaps.

Flap test from Quorneng on Vimeo.

I doubt they will actually be needed!

[Simon Chaddock]

Slow progress but the flaps are now complete.

I had forgotten just how big they are, broad and covering 2/3 of the span!

A video of them on automatic cycle.

Full Flap Test from Quorneng on Vimeo.

Next is to organise where to put the ESCs.

[Erfolg]

Simon

With those flaps deployed, you would need a lot of power, just to overcome the drag from the flaps.

I was thinking about the fin, and have convinced myself that the fin is not the issue, in that if the spiral instability was caused by the fin, your RC inputs would correct the issue. Further to that, my suggestion that more fin/rudder area would be beneficial, is clearly nonsense.

However, I am still convinced that more power will solve the launch issues.

[Simon Chaddock]

Erfolg

My intention in building scale flaps was not to 'fly' with them but hopefully to emulate the very steep approach of the full size. They are however fully proportional so they can be tested at any angle.

You may be right about the fin but I am concerned that at high angles of attack the it (and the rudder) may be rather blanketed by the broad wing root and the wide flat rear fuselage deck.

This original colour picture does rather show the substantail area involved.

[Simon Chaddock]

Two build posts in one day!

At some stage in its many rebuilds the wing has lost its dihedral. In the flap video above you can see there really is none at all, so I thought I would put it back.

To do this requires the spar join braces to be separated with a thin knife and the whole wing join cut, taking care not to sever the aileron servo cables!

The end of the wing then has to be 'packed' to give the required dihedral angle and the whole thing glued back together again - then do the same for the other side.

The more I do the more I think I should have scrapped it!

 

Edited By Simon Chaddock on 06/01/2013 22:06:57

[Erfolg]

It would not surprise me that the very high aspect ratio fin/rudder was to ensure that under the most unfavourable circumstances, the rudder/fin would operate to some extent, as a glider and tug combination.

Looking at the X, I would be very surprised if the AoA ever got above 12 degrees, without the wing stalling. If this assumption is correct, the tail will never be blanketed.

As bungee glider guiders, we will have been used to very steep climbs, where the model acts like a kite, and the rudder/fin can be blanketed. Well that is what some say, I have never experienced it, but then, my models seldom just kited up the line.

I think we both have had experiences where models have been a handful, as we have struggled for height. Just as we think we are getting away, the model tip stalls, and the struggle starts all over again. All because we are on the limit of the power available, relative to the power needed to keep the model flying.

I think that the Hamilcar is an example of this scenario, albeit, with less than the margin for even level flight..

[Colin Leighfield]

Simon/Erfolg. The Hamilcar didn't have any dihedral and I doubt if it will matter very much. I know that doubt has been cast on the quality of the drawings in Aircraft of the Fighting Powers and it is certainly true of some of the more "secret" types, but I think that most of them are of quite a high standard and I consider the Hamilcar to be in this category.

Some attention had to be paid to aerodynamic efficiency at the designed operating speeds because these things had to be towable and the Hamilcar was pulled along well enough by a Halifax. As far as angle of attack is concerned, high angles would be very unlikely, in the tow position the glider is positioned well above the tow plane and the nose is level, not raised.

There's no doubt that the huge flaps are designed to enable a rapid descent in a fairly sharp nose down position at a controlled air speed and giving the pilot maximum view of the landing area. Once Simon has got it flying, it should be great fun to try this out and find out how much elevator trim has to be dialled in!

Tailplane blanketing at different angles of attack is one of those varying things. To me, the tailplane on he Hamilcar is on the low side for minimisation of interference effects at normal angles of attack, perhaps it would have been better higher or lower, but we need to be careful in thinking that our judgement is better than that of the guys who designed these things. As far as the wing section is concerned on the Hamilcar, the RAF 34 doesn't look very different from the NACA section on the Hawker Typhoon and it's worth remembering that the thickness/chord ratio of that at the root was over 16%, almost as thick as the Hamilcar!

Stored in my garage loft I still have my Cambria Slingsby Eagle, 70" span, built in the 70s. It was good on bungee or the slope, but if you pulled too sharp an angle on the bungee at high speed, it would stall vioelently, with sharp wing drop and corkscrew. I had to rebuild the wing twice because of this and consequent violent contact with the ground at full catapult speed!

Flying the HamilcarX will most likely need to be undertaken in scale fashion, allowing time to build up flying speed on the ground, followed by a natural lift off and climb without inducing a sharp angle of attack. Fine pitch props are bound to be helpful with flying speeds not greatly above the stall. In other words, just like the real thing. I don't see any reason why this model shouldn't fly very well. It's a great project.

Finally with nostalgia, I have strong memories as a small boy in the early fifties being taken frequently to Whitton Barracks in Birmingham by my dad when he was in the Parachute Regiment and playing in the Airspeed Horsa that was parked in the parade ground there. Sadly a few years later they burned it. Very sad.

[Erfolg]

Colin

I think Simon hand launches.

I would be very surprised if the playing field he flies of is smooth enough for a conventional take off, without a lot more power.

I am not sure about the Typhoon though, as an example of good airfoil selection. According to the Putnam book Hawkers were a sort of pressurised into the wing section used. Even with all the massive power available from the Napier engine, speed was a bit of a struggle.

[Colin Leighfield]

I chose the Typhoon deliberately Erfolg. Although Camm didn't grasp until years after Mitchell the importance of wing thickness in controlling compressibility at high Mach numbers, the one thing that the Typhoon wing was good for was load lugging at speeds far higher than the Hamilcar ever approached. To me the Hamilcar wing is an efficient design for it's purpose. It's got an aspect ratio of 8 to 1 with a wing section .that was as good as you'd get at the time, operating at speeds where the relative drag of the fuselage wouldn't have been critical. I agree with you that the tall fin is almost certainly perfectly adequate, for modelling purposes it wouldn't hurt to enlarge the tailplane and having enough thrust at take off and normal flying speeds is crucial. None of these are too difficult, this should be a good flyer. I wouldn't like to have to get my hands around it for a hand launch though, good luck Simon.

[Erfolg]

I have not been much of a fan of Sidney Camm, in the past. All the aircraft seemingly been less than cutting edge. Although the same is not true of the engines.

However in more recent times I have become aware of more of the whys. As a designer, I would suggest that he was less than brilliant. Although portrayed as the designer of Hawkers, his role was far more complex.

Essentially Camm was the interface with the various interests in the MOD, both instigating specifications/orders, and the sounding board what was acceptable to the customer. This role included sitting on committees, when he could get his feet under the table, more frequently wooing the officials in Whitehall.

Some of the designs also stemmed from self interests in the method of construction and the investments in tooling systems.

Above all he won contracts and kept them. There are many examples of more advanced aircraft, which were never built, or just a prototype, or the order cancelled. Camm on the other hand won and kept his orders generally.

His project leaders were to most peoples minds, those who gave physical form and capability of the actual airframes.

From reading the Putnam book on Hawkers, it appears that Hawkers were pushed towards the airfoil initially used. The tails falling off was all hawkers doing. It is easy to be critical of there lack of understanding of fatigue. Particular;ly as every school boy has observed it, when bending cans etc. Students being familiar with S-N curves and Grithiths Crack Propagation Theory. The trouble a lot of these things were still waiting to be formulated and receive broad acceptance in the 50's.

I used to thing he was a total numpty for dismissing the swept back wing as a means of minimising the effects of criticality nearing the regions of compressibility. This Christmas I discovered that the original wing for the Me 262, was indeed a straight wing, until the engines came in heavier than envisaged. This needing the wing moving or sweeping. Sweeping killing two birds with one stone. I feel a little humbler now. Perhaps he did not know about compressibility and wing sweep, though he was correct in why it came to be swept. The incident also shows the extent and much effectiveness of UK spies.

Most people accept though, that thick wings, with a lot camber (which will be true at high AoA for the Hamlicar) will generate a lot of drag. For ease of handling the 1/3 -1/2 tip chord is not good for low speed handling (particular without washout).

[Simon Chaddock]

Colin

The Hamicar did have some dihedral but I agree 'not a lot'!

The top of the spar was flat but tapered up on the underside which would I think gives a degree of positive aerodynamic dihedral?

My wing was actually flat on the underside which gave it an anhedral appearance so it now has a small positive dihedral.

Unless I can find a nice smooth surface it was, and will be, hand launched but with a wing loading of less than 8oz/sqft it is no big deal.

[Erfolg]

Simon, this could a whopps moment.

I think you were correct first time round, if scale fidelity in an absolute sense is sought.

Looking at the drawing in chapter 7, of Aip power etc. of the Hamilicar the wing is drawn with the Neutral Axis, on the centre line of the wing ribs. Dependant on the angle viewed giving the impression of slight anhedral or dihedral. The text states no dihedral.

The text also states that the wing is set at 5 degrees 30 minutes, seems a bit precise to me.

The drawing is large scale, and quite detailed, but does that make it accurate I do not know.

Almost certainly better than a plastic kit or thumbnail sketch though.

[Colin Leighfield]

Simon.

You're quite right, when I said that there was no dihedral I was referring to the top of the wing, in fact the upward taper of the wing underside does give a degree of dihedral, I hadn't envisaged that you'd got it the other way around!

I appreciate that you've achieved amazing lightness in creating this and that certainly eases hand launching, (which I'm hopeless at), but personally for that first flight I'd definitely be looking for a smooth surface to get a gentle R.O.G. and gingerly sort out any detail trimming issues.

I've got total confidence that you will make this work and have a good flyer, which is more than I can say about my own confidence in the Wellesley, without even mentioning the 70" Westland Welkin waiting for the cg to be finalised. (Another story).

[Colin Leighfield]

Erfolg.

You're quite right about the Me.262, the wing sweep was a solution to a cg problem and nothing to do with compressibility issues. In fact it's critical Mach number was lower than that of a Spitfire anyway, regardless of it's top speed in level flight. It wasn't much quicker either than the Heinkel 280 with similar engines and a straight wing. (It did look nicer though).

Sadly the acquisition of German data on swept wings and compressibility was used as an excuse by Sir Ben Lockspeiser's committee to cancel the Miles M.52, when it was almost ready for it's first flight. They said that this information had made the M.52 obsolete and irrelevant before it flew. Complete stupidity, I don't think there's any doubt that it would have been the first aircraft to go supersonic in level flight, look at the F.104 and F.16 as evidence that there's nothing essential about swept wings!

What is more the M.52 had been designed in a way that different wings could easily be adapted to the fuselage because the attachment was to a circumferential beam in the fuselage, which meant that different wings could be almost bolted on and off.

I'm digressing and revealing things that make me bitter. Winkle Brown's analysis is bang on for me!

Cheers!

[Simon Chaddock]

I find it amazing that Miles, a well established but small manufacturer, actually got it so right!

They even built the 'Gilette' Falcon to test the slow speed characteristics of the M52 supersonic wing.

I am not sure it would have gone transonic as expected with the limited thrust of the Power Jets W2/700 and I expect its afterburner system for supersonic flight would have taken rather more development than anticipated but the M52 did after all achieve a sustained Mach 1.38 in rocket powered model form although the RC system lost control and it was last seen heading out over the Atlantic!

Not much to show for several hours work joining the wings back together, putting in lots of patches and filling and sanding the surface.

Nearly ready to start rebuilding the engine nacelles.

[Erfolg]

I would expect most British people will have regrets with respect to the M52. Partly it was so much money wasted. It seemed to be another case of the UK being unable to finish a project.

Now we can see what the issues were and to some extent are still with us.

The first, was a country that had a Empire mentality, we can do anything. The we will do what is necessary to be ahead of the game, as a first line power.

The second, was the country was essentially bankrupt, from WW1 & WW2. The latter prising the hand of power from the colonies, who were now increasingly seeking independence and breaking favourable trading arrangements with the UK.

The third, where evidence of the practice can be glimpsed from time to time, even now, some projects are favoured by the civil service for a multitude of reasons, other than what they may deliver.

I also suspect from what I have read that the Whittle engine was up to the job. I did read, so I though, that it was some form of early by pass engine.

I guess the real monetary disaster, that more money was spent in testing rocket models than was estimated was needed to complete the test programme with the M52.

I think one of the reasons given that the authorities did not want to risk lives in the test programmes. Particularly when conscripts were forced to experience Nuclear bomb testing, with no care to their well being.

I was recently tempted to buy a book via Amazon about the M52. With a view of better understanding what really did happen.

I have got a packet of unopened Polyfilla Simon, if you need some more.

[Colin Leighfield]

Both the plane and the Whittle by-pass engine would have been world leading. Cancellation was utter stupidity and, much as I admire him, Barnes-Wallis didn't help. The definitive work on this is the recently published "Miles M.52 - Gateway to Supersonic Flight", written by Eric Brown and co-authors. It's a compelling read.

[Simon Chaddock]

The RH nacelle rebuilt with temporary electrics ready for test with its 9x4.5 LH prop.

When I originally built the Hamilcar it was only my second Depron structure of any sort and by far the largest.

As a result the wing surface in particular was made up of many pieces so had a lot of false 'panel lines'. The full size was virtually all a fabric covered plywood skin so had a particularly bland smooth surface.

In this rework I am determined to better replicate the scale finish hence all the filling and sanding!

Edited By Simon Chaddock on 08/01/2013 12:08:19

[Colin Leighfield]

I congratulate you Simon for achieving so much with Depron! A couple of years back I had a go at making a ducted fan Hawker Hunter out of Depron. There was quite a lot of sanding to shape. I confess that I gave up and binned it. The thought of Depron puts my teeth on edge, lord knows why. At some point I must stop being silly and have another go. Seeing what you've done with it makes me think and the weight advantage is obvious!

[Erfolg]

Colin that is the very book I was considering.

Again I am no great fan of Barnes Wallis, yet he was doing exactly the same as many leading figures, looking after his own self interests and the company that employed him.

Now it is easy to very critical of what was done. Yet when put into a historical context, it becomes easier to understand what happened and why.

WW2 had just ended, the UK had incurred massive debts, the economy was based on arms production and many of the colonies were seeking independence from the UK, in addition the returning soldiers were in no mood to return to the conditions of the 1930's.

In this climate a Labour government was elected to power. The weapons production needed to be stopped, yet this would mean mass unemployment, just at the need level. Given the large national debt, there was an economic rational to stop all production of this type. Yet the levels of unemployment would have soared and the consequences which may have arisen.

The Government of Atlee, reduced many contracts and tried to keep employment across the UK reasonably even.

Is it any surprise that the M52 was cancelled, when it appears that Miles was not a company as politically connected to Whitehall, and Westminster as Vickers, Hawker and AVRO etc.

Barnes Wallis appears to be extremely good at self promotion, in a similar vain as Isambard. Others were solid engineers, who listened to customers, ingratiating there companies with the client.

There were other disastrous consequences from the general policies, ranging from rationing being in place longer than all other countries, exports of a couple of jet engines to the USSR, a lack of investment in new plant and machinery, as confiscated patterns and machinery were used to underpin the struggling UK economy. Overseas sales becoming increasingly difficult to obtain, as countries went their own way and allegiances disappeared. Only the USA would take our goods, and we soon made a mess of that market to.

Yet with the high debts and poor balance of payments, governments for years felt unable to stimulate internal UK demand.

Simon, I was joking about the filler. Better to have the model fly well, than look good, yet not struggle into the air?

[Simon Chaddock]

My own take on surface mounted components!

The MOSFET side of the ESC heatsink is flush with the wing surface.

Actually cooling is probably not necessary as the 30A ESC is only running at 50% even at WOT.

Now I have just got to bring the other wing up to the same standard.

[Simon Chaddock]

The LH motor installed and on test with temporary electrics - to make sure it both works and goes round the right way!

A servo tester is being used to control the ESC.

The RH wing is painted and virtually complete.

[Simon Chaddock]

Not very exciting, only duplicating the modifications but LH wing atlast complete.

Just need to work out how best to install the radio.

Then just the cockpit canopy to do.

[Simon Chaddock]

The wing painted.

Just a few days ago it was full off holes!