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Author Topic: Hawker Tempest II, 1/24 scale rubber power.  (Read 9338 times)
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OZPAF
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« Reply #150 on: April 21, 2015, 04:03:36 AM »

Ah what a pain- it looks like Mr Reynolds wins at last Grin Your Spiteful should prove it one way or the other, Stephen.

So I guess its back to the podium position on the shelf for your Tempest.
John
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DHnut
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« Reply #151 on: April 21, 2015, 06:13:08 AM »

This is facinating. Last weekend I finally managed to fly the 1/24 Hurricane in the Doug McHard series. It has been converted to CO2 from rubber and in the process has become some 10 grams lighter balacing at 25% with no ballast. The weight all up is now 45 grams with an empty tank. The glide was defintely better and the behaviour under power was transformed with a nice initial climb to the left ( once a bit more tab had been added ) followed by a good transition to the glide. I suspect the tank being right behind the Telco motor is helping control the power burst by moving the CG forward when charged. It may be a little under elevated as the glide is fast and a little steep. The tail was built as per the plan with a 1/16" frame capped with 1/16" strips sanded to a symetrical section. I have not measured the thickness but would estimate I have last 1/16" in sanding making it 1/8" thick. The thick wing will clearly not help the glide and a tab was needed to keep the inside wing up. When it was rubber powered the weight was 55 + grams and the model was clearly in need of more rubber and the weight was climbing all the time. I wonder if you are reaching a point of the wing loading becoming to great for the model. By the way the model has a full airbrushed finish and will now be completed with markings and a spinner.
The use of a pendulum clearly has possibilities and I wondered if some form of damping may be beneficial ( dont ask how it is to be achieved ) to reduce the overshoot of the control surfaces. I look forward to hearing of the further adventures with pendulums.
Ricky
     
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Pat D
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« Reply #152 on: April 21, 2015, 06:57:34 AM »

This is facinating. Last weekend I finally managed to fly the 1/24 Hurricane in the Doug McHard series. It has been converted to CO2 from rubber
     

Ricky

would love to see a photo of this CO2 hurri - what size motor did you use?
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Prosper
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« Reply #153 on: April 21, 2015, 12:01:43 PM »

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- it looks like Mr Reynolds wins at last Grin
Yeahhh? I'm just lulling him into a false sense of security.

Hi Ricky, thanks for the useful comparison. I measured the root thickness of the Tempest tailplane and it's 8.3mm. That's a bit more than 1/8" but it's interesting to hear that a reasonably thick tailplane can work - you don't know your Hurricane tailplane area as a percentage of wing area by any chance?

Wow - I didn't realise CO2 conferred such a weight advantage Shocked.  Mind you, I don't think the Tempest wing loading is the problem - the model as flying in the video clips in replies no.146 and 148  was 43g which isn't toooo bad for 486cm2 wing area. The wing is plenty thinner than the Hurricane wing (I'm assuming yours is scale thickness) and has an almost symmetrical section which should reduce pitching moments. I expect the problem is a result of some particular quirk of the Tempest II layout, perhaps combined with the prop.

It's good to know that the Hurricane will fly at 1/24 scale as it's always high on my list.

Stephen.

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« Reply #154 on: November 30, 2019, 11:49:31 AM »

A new Tempest model - only this Tempest II is a Tempest V. . .

I got some way with this second project way back in 2016 or somesuch but shelved it - can't recall why. Now it's about ready for initial flight tests, after a recent fever of building work. There's a lot of finishing and painting undone, but no point in doing that until I see whether it can fly with a scale tail (it was this - the thickness more than the area I think - that killed off the Tempest II model).

The main improvement I felt confident of achieving was to build a lighter tail. The tail of the first model was a separate unit, so it needed a weight of timber to attach it to the rear fuselage. What's more there was provision for a balanced, floating rudder. This proved unnecessary, but carried its legacy round as dead weight.

The reason I felt a Mk.V might just work with a scale tailplane is as follows: the Mk.V has a slightly shorter nose than the Mk II, meaning more noseweight would be needed if the tail weighed the same. I hoped that if the whole tail of a new model was lighter, it might balance with the same amount of noseweight despite the shorter nose. This lighter tail, plus noseweight slightly closer to the CG, would reduce pitch and yaw inertia overall. That means the tailplane (and fin) would have less work to do, so it could afford to be smaller.

Furthermore the shorter nose reduces the destabilising effect of the prop, further reducing the workload of the tail. These effects are small, I'm sure, but perhaps enough to make the difference needed.

Well, the new model has come out several grams lighter than the original one. The model is built using the same methods as the first one, but has less internal structure, and the pendulum system is much lighter.

I took no photos during construction except the two of the outer wing panel shown here. I took those as a memo to myself, showing how I installed the whole pendulum system in the lower wing and then attached the top wing skin, aileron surface and all. This is a bold move because it means that once the top wing skin is fixed there is no access whatsoever to the pendulum system, other than the pendulum itself on the fuselage centreline. Everything has to work perfectly first time, without any testing having been possible. Once the wing panel is complete, the ailerons are carefully cut free of the wing and the aileron can (one fervently hopes) be separated from its actuator for final finishing and painting. This idea worked, and was worth the fairly extreme anxiety engendered, because it's considerably more simple to make an installation this way, and because if the wing has any washout (this wing doesn't) the aileron T.E. will automatically have the correct washout built in. At this scale, fitting a pendulum system after the wing is built is fiddly, no question, and making an aileron with the exact T.E. washout to match the wing panel is tricky too. Hawkeyed observers will spot that the aileron skin is obviously separate from the wing skin - the grain is in a different direction. . .that's quite right, but the wing skin blanks were made back in 2016 or thereabouts, and I only had the 'pre-installation' idea a few months ago. The aileron skins were tacked to the wing skins during assembly, and the aileron cut free later.

Even less-than hawkeyed observers will spot that spar 5 goes all wobbly inboard of the aileron. None of the spars had had their final gluing and shaping at the time the pic was taken. The white dome is the landing light reflector. the little block fixed behind spar 5 further out is just a mounting block for the pitot tube.

The propeller blades are from the Tempest II model. The model as pictured weighs 39g. That includes noseweight to balance the model at an admittedly rather far-aft point; and a 22" long motor of 7/32" rubber (two loops of 1/16" and one of 3/32") which weighs 6.5g. Looking back thru the thread I believe that the original model in the same state only minus canopy, weighed about 43 grams.

I'm estimating paint at 2g and that will require more noseweight to balance. We'll see. When test chucks might take place I dunno: the weather where I am has been lousy. An almost wholly wretched, anti-model-flying summer has been followed by maybe? the wettest autumn on record, and cold too. Everything is waterlogged. There has actually been some sunshine today, hence the outdoor photos. The one of the tail was sposed to show the internal structure (as in: there isn't much) but the sun didn't co-operate just then.

The two whole-model photos are intended to illustrate what a handsome beast the Tempest was, even the chinny one.

Stephen.

Attached files Thumbnail(s):
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
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OZPAF
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« Reply #155 on: November 30, 2019, 07:16:11 PM »

Fascinating monocoque artistry as per your usual efforts Stephen. Good luck with this one - tell Reynolds to take a holiday Smiley That is quite a motion reduction on your aileron pendulum linkage.

John
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Don McLellan
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« Reply #156 on: November 30, 2019, 08:27:11 PM »

Beautiful and exceptionally interesting work Stephen!  Is that a 'rest' for the wire leading out to the aileron? 
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MKelly
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« Reply #157 on: November 30, 2019, 10:17:22 PM »

That really captures the Tempest's shape, and you're going to be quite a bit lighter than my leaden West-Wings-derived Tempest.  Very much look forward to seeing how it flies compared to your Tempest II.

Mike
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Prosper
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« Reply #158 on: December 01, 2019, 06:12:16 AM »

Hi fellas, thanks for the comments. Yes the reduction is considerable, and gives enough leverage that a 0.3g pendulum bob moves the ailerons such that, if I blow like billyo over the outer wing, the aileron isn't budged, whether deflected fully up or fully down. One difficulty with the Tempest is that the bottom surface of the aileron has a much greater chord than the top (a deep-Frise aileron?). This means - see diagram - that the aileron has only to pivot down a small amount before the upgoing nose of the aileron, far ahead of the hinge line, starts interfering with the actuator. In the diagram I guess it looks like there's quite a ot of room available but remember this is a 2D sketch and the real actuator has depth and width. This is an example of how all installations are different, and an example of why I sweated having chosen to 'pre-install' the setup and hide it away forever without even having tested it.

The 'rest' Don mentions is another example, because it's the first time I've used 'em (well spotted Don). I've been reluctant to use these in the past because of the friction created, but in this case the weight of the spanwise bar running from pendulum to crank can bow the long crank arm slightly. The crank is made of 0.38mm piano wire. The 'rest' is a balsa strip with a 0.28mm piano wire slide, just visible in the pic I think. In reality the crank arm barely kisses the slide, and there's no noticeable friction.

I'd actually meant to post a snap of the pendulum itself yesterday but forgot. Pic 1 is the pendulum and hanger which links the spanwise crossbars to the pin halfway down the pendulum. Pic 2 shows the pocket on the front spar into which the pendulum assy slides, and 4 shows the lot together. Note that there's a vertical slot in the hanger and in pic 4 the pendulum pin is right at the top - the hanger and crossbars are literally hanging from the pin. This is unintended (the hanger was nicked from a previous project, not tailormade). The slot should extend above and below the pin so that the pin exerts only sideways forces on the hanger (friction again) but since the system works I've ignored that for now.

The system - excluding the ailerons - weighs just under 1g. I made a very brief video clip of the ailerons working, which I meant to append to a flight video, but since it mightn't fly for some long time and I'm gassing about the pendulum anyway, I've uploaded it today:

https://youtu.be/4O6SGN07wok

Stephen.
Attached files Thumbnail(s):
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
Re: Hawker Tempest II, 1/24 scale rubber power.
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Prosper
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« Reply #159 on: December 12, 2019, 04:24:58 AM »

I had a nerve-wracking morning last Saturday, flying the model.

It soon became clear that the model has no static pitch stability worth a damn. Man that model took some thumps. Sometimes the particular noise of the impact made me sure the nose must be smashed or the fuselage split or the wing wrenched off, and I could hardly bear to go up to the model - but nope, it remained undamaged. Most of the nosedives were onto bouncy grass, but not all, and once the model dived into bare mud (soft, thankfully). So the airframe's strength and resilience is encouraging. All four blades had chunks bitten out of them by the chin intake, but no more blade breakages, which was encouraging as well.

The tailplane situation was very disappointing though. There was just no elevator position that gave any balance, it was either zooming up to a full stop and flipping into a vertical power dive to the ground, or diving in right from launch. I taped 2g of lead inside the chin and incidentally blanked off the chin intake, which I'd forgotten to do previously.

The pitch behaviour with more noseweight was possibly better, but it certainly wasn't adequate. A few more hefty thumps. The pic shows a typical 'after landing' scene, on bouncy grass this time. I taped yet more weight to the nose and in a couple of lulls in the breeze got an indication of improved flights. But the noseweight is now over 6g - that's putting the model into lead-sled territory even without paint and final details. I'll continue experiments when weather allows.

Stephen.


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Re: Hawker Tempest II, 1/24 scale rubber power.
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« Reply #160 on: December 12, 2019, 04:54:27 AM »

Stephen I love these all sheet builds of yours and this one is no exception.  This one has the added interest of your pendulum system.  I wonder whether the next time you try it you should make up a thin sleeve to slip over the existing tailplane to increase the area. This will tell you the story and if that is what it needs you can work out a permanent alteration
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Indoorflyer
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« Reply #161 on: December 12, 2019, 11:38:25 AM »

I know you're not fond of "Tail volume calculations", but it would be interesting to know where the calculated c.g. position is, based on scale stab area Smiley
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« Reply #162 on: December 13, 2019, 06:45:42 AM »

Ta Mike, that's not a bad idea. In this case the tailplane isn't fixed yet so it's about as easy to make another one as to make ultra-light sleeves which accomodate elevator adjustment. One thing that's niggled me is that I think the Bentley drawings may have the tailplane outline slightly wrong - in the few photos and video I've seen which allow a fair 'plan-view approximation', the outline looks more symmetrical and a bit rounder-tipped than the drawings suggest. Since the last model I've found info giving the true tailplane span and area (15% of wing area). I'll try adding more-more noseweight first, but I honestly think a bigger tailplane will be necessary. The model would be several grams lighter probably, and better-behaved. Just look wrong.

Quote from: Indoorflyer
. . .not fond of "Tail volume calculations",
Grin Indoor, I'm glad you've noted my negative feelings towards 'tail volume' calcs, but I don't really think you've grasped the true depth of my contempt for them! It's deep! Really deep!

I'm sure this very matter was discussed on Mike's Lysander thread just recently. It's possible that once you're up to Mike's Lysander's 50" wingspan these calculations are of some use.

Stephen
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tom arnold
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« Reply #163 on: December 13, 2019, 08:33:48 PM »

I have really stood in amazement at the sheet balsa skin you can work with as it is really hard as I found in my exuberant youth. Since I have a Tempest on my "To-Do" list and inspired by your build, I thought I would do my usual calculations for my efforts. I found that the scale CG drop line touches the back edge of the tire (aircraft being level) and that is logical for any tail wheel aircraft. That is also at the 25.6% point of the centerline chord. As for an enlarged stab (which I do) of 126% I can move the CG back to 34% of the centerline chord. Of course, to a modeler's eye you can notice the enlarged stab but it is interesting to see the comparison between stab area and CG movement. Good luck in any case on your flights.
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« Reply #164 on: December 14, 2019, 03:03:14 AM »

I was going to ask if tail ballast would be out of the question. A larger stab would do that. Whatever, I love the idea of the pendulum control, and can't wait to see it in action once the perplexing tail issue is sorted out.
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« Reply #165 on: December 14, 2019, 03:25:22 AM »

Thanks Tom.  ". . .interesting to see the comparison between stab area and CG movement. " Yes, that's what's keeping me engaged with this project at the mo. I want to keep the root of the tailplane very close to the original otherwise it will mean re-making the fixed, paper fairings which in the original held the rudder actuator and the tail position lights. I can't recall the CG I used on my first Tempest, after putting a temporary flat-plate tail on it. It's probably written in this thread somewhere but this model's a bit different in terms of leverages so stability will be different too.

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. . .as it is really hard as I found in my exuberant youth.
Ah! But were you using sheet that was coated with some glue or other? That's the thing that makes it workable, and amenable to forming using moisture and heat. I know I've posted this picture before (perhaps more than once Wink ) but I like it so here goes again. . .

Stephen. P.S. thanks Crabby, you posted while I was writing. I don't know about tail ballast - I'll be hoping to save weight at the nose, which amounts to the same thing maybe?

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« Reply #166 on: December 14, 2019, 12:45:26 PM »

Stephen,

Thanks for sharing your build, very entertaining.

Re. pendulums and getting a pendulum to work.

I'm wondering if a pendulum equipped model should not have aileron differential, i.e. more up than down?  Maybe try to avoid the balanced turn? It could be worth trying more down than up to keep the model side-slipping in the turn to let the bob-weight see some gravity?

Definitely not a case of Straighten up and fly right!

Steve



 
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« Reply #167 on: December 15, 2019, 04:26:05 AM »

Hi Steve, I think I see what you're getting at but let me work this through:

Differential aileron is intended to reduce adverse yaw, and if Frise ailerons are used this reduction is greater yet. Without yaw there can be no sideslip and without sideslip wing dihedral doesn't work. Thus it makes sense to allow sideslip, and to set up a pendulum system to allow sideslip. Is that your point? Please forgive me if I've misunderstood.

Against this is that sideslip = height loss,* so is best avoided, esp. since the less dihedral the longer the slip before the low wing picks up. My intention from early days investigating pendulum ailerons has been to act fast and hard - a low-friction system with minimal play, that moves the ailerons a lot per pendulum movement. The idea is that the ailerons should be acting correctively even as a roll is taking place, and before a sideslip has set in (inertia means there's a finite time before the sink and slip develop). I can't say whether I've ever achieved this though, because I don't know what's going on in flight.

A sideslip can be defined as too much bank angle per turn rate, and a skid (flat turn) as too little bank per turn rate. The first means a lack of the centrifugal force necessary to provide a balanced turn, and the second an excess of centrifugal force. Centrifugal force is the only thing the pendulum reacts to**; at all other times it simply points to the centre of the Earth. In a sideslip the pendulum droops to the inside of the turn, which moves the ailerons to pick the lower wing up. In a skid the pendulum is flung to the outside of the turn, which shifts the ailerons to increase bank angle. The pendulum is always seeking a balanced turn.

Whether it can achieve a balanced turn I can't say; it's working with or against the prop torque and the fixed trim of a freeflight model as well as the basic aerodynamic properties of any given layout, and of course it's being bullied by wind and turbulence. I've sometimes seen my pendulum models perform nice flat turns - which shouldn't be possible.

I worried a lot about the vertical tail of a Fairey Battle model I made as well as the first Tempest model. They both have lots of fin area. This prevents sideslip and reduces dihedral effectiveness, so with both these models I went to lengths to install floating, mass-balanced rudders with servo tabs [ground adjustable only]. This effort proved unnecessary, and introduced a 'woozy' look to the flight pattern.

*This may not be apparent: a model with inadequate dihedral might be climbing nicely under power - but it would be climbing more if it wasn't sideslipping. It might be losing height imperceptibly more in the glide. Excess dihedral is not just a stability enhancer but a duration enhancer.

**Yes, I know there are other things that will upset the pendulum - jus' trying to keep it simple.

Stephen.
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« Reply #168 on: December 15, 2019, 05:40:23 PM »

Stephen,

Thanks for your detailed reply.  Very interesting, your ideas of correcting the roll before sideslip develops and the resultant height lost in a sideslip.

Steve
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« Reply #169 on: December 15, 2019, 07:22:31 PM »

It really looks as Mr Reynolds doesn't want to take a holiday Smiley it's nice to know I suppose that your sheet construction can take a lot of punishment though. I'm afraid that the thinner and slightly larger tail plane will be necessary.

It's interesting to see how small a tail can work when it and the wing are both thin. I use a 13.4% tail on my small CLG's - the tail being 4.5% thick on an average(thinner at the tip) and the wing around 6% at the root , 3.5% mid span and thinner at the tip.

Merry Christmas

John

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