Seagull Hurricane Laser

[ASH.]

Your post made me laugh Jon.. It seems your Hurri is a bit of a wild thing when it comes for her to settle down. Taming her is the challenge - one that will give you much satisfaction when you finally make her succumb..

I have a similar problem with a high wing sports model where rudder becomes quite ineffective at low speed. It frustrates me as I keep forgetting to blip the throttle, not that it would make much difference that quickly.

Another thought - on a seperate switch have just elevator on high rates and opposite expo so sensitivity is increased and activate few feet off the ground.

[Jesus Cardin]

Jut one question: Are you keeping with the instruction manual C.G.?

I have not read the entire thread but I know well the model from a good friend here in Spain. When he maidened his Hurricane he found it to be too sensitive on elevator just from the take off and, in fact, he damaged the model trying to land it!

He asked me to check the manual C.G. and propose other postion if I found it wrong. What I discovered is Seagull C.G. is calculated at 33% MAC, which is common to my own Seagull models (Gipsy Moth and Bucker Jungmeister) and, which for me is too far back for scale models maidens.

In my own models I switched to 25% and only the on the sweet Moth I have finnally left it at 28% but seeing your problems with your Hurricanes I strongly suggest trying with a 25% MAC C.G . for your next flights.

I do not know if I keep my calculations on the Seagull Hurricane C.G. but I will check and, if so, I will publish them here for your reference.

[Nigel R]

I watched a few hurricane videos on youtube earlier. Quite a number have landing approaches consisting of lots of nervous looking ups and downs, and a good proportion seems to end in a less than successful arrival. Lots of damage ranging from noseovers to U/C out to cartwheel with wing ripped off. I've so far found no, zero, none, perfect mains and tail greasers, all the successful landings are flying the thing in on the mains. The worst ones are up and down like a roo, with luck the pilot catches the thing at the right point. Even the abnormally talented Deano stacked a DB Hurricane.

Some things that occur to me;

The Hurri doesn't have a very big tailplane, especially when kept to scale proportions.

The above suggests it requires a fairly forward CoG for tailplane to exert adequate pitch control. The 33% of MAC figure sounds fine - providing you have a nice 0% camber section and around 20% or so wing area on the tailplane, not so good if you only have 15% with a cambered foil (like Clark YH or Y, I forget what the full size uses).

Big flaps, pitching moment changes, CoP movement (as already pointed out) - more work for that small tailplane.

Big flaps, fair amount of extra turbulent air, and, that tailplane is likely sitting right in the rough air at landing AoA - that tailplane now only has bad air to work with.

It's a complete 'gut feel' but I think the Hurricane just suffers a perfect storm of the above factors.

See also, assorted full size designs with high mounted tailplanes, the high mounting being used to correct this sort of thing, Whirlwind, 109, I'm sure there are many more.

Not sure what the best answer is for us. On the full size, the tailplane is likely adequate. Maybe the aerodynamics changes because of scale factorrs, and we simply need "a bit more" area to maintain proper authority.

[Denis Watkins]

Gut feeling again here with me, but I agree with Nigel, it is the Tailplane/airspeed

Half the tailplane is Elevator

At low speed I imagine use of the Elevator leaves only Half the Horizontal Stabiliser to do its work?

Using the Elevator is like a Half lift switch to the Horizontal stabiliser catching us out

This is just my feeling

[Jon H]

Andrew, i think we tried flapless and it was impossible to slow down. At 80 inch they just have too much momentum.

ASH these Hurricanes arent even mine! They both belong to customers and i put my hand up as test pilot. Im not complaining, its an interesting challenge.

Jesus, it might be worth reading through the thread as we discussed the various traits of the model and their causes in detail. The short version is that the c/g on the models 'feels' correct. I didnt measure it myself as they arent mine, but just picking the model up the model feels right. This is backed up by good manners in the air at normal flying speed with a fairly neutral trim.

warbirds and scale models are often quoted as being tail heavy when in fact they just have too much elevator travel.

Nigel, my little 63 inch Hurricane displays many of the traits seen here with the seagull version but my old mick reeves example never did. The common theme between the seagull version and my little one is the wing is extremely thick, more so than scale, and i think this could be part of the problem as there is so much lift you cant bring the nose up to 3 point it.

Smaller tails on scale models are often promoted as a problem but we are in the situation where the model is over sensitive in pitch in normal flight, so a bigger tail with bigger elevators would not be very helpful.

In fact on my little hurricane i shrunk the tail to scale proportions and its easier to land than an earlier version i had with a bigger tail.

[Nigel R]

"we are in the situation where the model is over sensitive in pitch in normal flight"

I'd contend that indicates the tailplane may not be large enough to properly control pitching.

The thicker-than-scale wing section will make things worse. It will have more camber (assuming it is still flat bottom) and thus high pitching moment.

If the full size is "only just" large enough to control a normal sort of WW2 thickness wing (very thin tip up to, what, standard 12% ish root section) then a girt big thick section might push things too far for a scale taiplane.

[Jon H]

Posted by Nigel R on 12/02/2020 09:35:21:

"we are in the situation where the model is over sensitive in pitch in normal flight"

I'd contend that indicates the tailplane may not be large enough to properly control pitching.

If you fly the model hands off, its totally stable, but the elevator is very sensitive so rates are very low. Flying around the model is lovely, its easy to takeoff, does the best scale rolls i have ever seen and is generally very nice to fly. The elevator/pitch sensitivity is not any worse in real terms than my other big warbirds.

The only one of my models which gave me similar trouble is my P39. It too has a very thick wing and will fly insanely slowly if you let it but it becomes unstable, even with its oversize tail. It also gave me trouble with pitch instability on approach and, like the hurricane, seems to have an airspeed below which the trim changes significantly. I have resolved this by setting an elevator flap mix essentially as a trim offset and this allows the model to remain below its critical trim speed all the way down the approach. As a result it remains controllable.

I tried this on Chris's Hurricane but it just stopped moving. Honestly it was like a hurricane shaped cloud and just floated there which still remaining unstable in all 3 axes and virtually uncontrollable. This is what is leading us towards adding weight as my P39 is 21lbs and the Hurricane 17.

The size of the tail is not the problem, its an aerodynamic issue moving the centre of lift i am quite sure. The best example of why think this is a loop.

Run into the loop, small up elevator input gets you to the 45 nose up. As you come to vertical speed bleeds off and you need progressively more and more elevator. This is because the model wants to dive when slow so it starts to tuck out of the loop. Eventually you will have the elevator full up, but if you didnt time it right the model will then bunt out of the loop as you pull the stick off the tx trying to raise the nose. Once the speed rises the elevator bites and you have to let it off very quickly to prevent it pulling up exponentially and flicking.

My small hurricane did exactly this as well, made worse by incorrect incidence..which is something else we could investigate.

[Nigel R]

Interesting stuff Jon. Does appear to be a common theme to your experiences. I just had a quick look on the data on airfoiltools.com for Clark YH rendered at different thicknesses. Interesting because it goes a long way to backing up what you say.

Several things I noticed -

The 18% YH section stalls out much earlier than the regular 12% thickness section at low reynolds - the 18% section turns into a low lift airbrake (presumably generating lots of lovely turbulent air to blank off the tailplane).

The pitching moment behaviour for the thick section is highly inconsistent across different reynolds, whereas a regular thickness section behaves quite similarly across airspeeds. The thick section, at low speed, stops trying to pitch the thing forward (contributing to ballooning up) - thus completely altering the trim needed from the elevator.

But. At full size sorts of reynolds, none of this would be experienced, it would be travelling fast enough to avoid the change in behaviour as speed dropped off.

A very similar comparisons can be made between thick and regular NACA sections say 2412 and 2419.

"This is what is leading us towards adding weight as my P39 is 21lbs and the Hurricane 17."

Also leans toward the above; a heavier model would need to come in a bit quicker, and it would thus show less of the above effect?

Edited By Nigel R on 12/02/2020 10:19:56

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

While I agree that the wake diverges downwards - the primary reason that the wing produces lift, after all - the air that the tail encounters must be influenced by this flow as the wing has just passed through the same bit of airspace - whether it is turbulent or relatively smooth air being drawn in the replace that deflected air.

Looking at some of the videos, it appears that the nice stable approach is interrupted by sudden ballooning as the speed is being reduced - of course, by increasing the angle of attack. This seems consistent with the tailplane encountering turbulent air or airflow at a different angle, reducing its up force which is balancing the lift moment, at a critical angle of attack. The fact that this does not appear to happen with small flap angles or with a clean wing may support this supposition as there is less disruption to the airflow.

Edited By Martin Harris on 12/02/2020 11:29:53

[Jon H]

Seagull Hurricane Tim was just here at the factory collecting fuel and we were discussing this. A few internet searches later revealed the clark yh section has some reflex in the trailing edge to aid longitudinal stability. Neither my little Hurricane or the SG Hurricane have any reflex as far as i can see. Perhaps this is also contributory.

One thing i mentioned before but not in this recent thread is that lowering the undercarriage makes both the SG and my little hurri want to bury themselves in the ground. Very large amount of trim are required to hold the nose up and we have mixes in place to cover this on both models.

Lowering the flaps results in a nose down attitude in level flight making 3 point landing very difficult due to the previously mentioned tendency to balloon. Add to that the thing being divergent in pitch, and its all very exciting :D

One other thing to consider is that the outer wings of model hurricanes tend to be even thicker than the roots when compared to scale. Full size hurricane tips come down quite thin, but models tend to keep the thick wing over the entire span. 

Edited By Jon - Laser Engines on 12/02/2020 11:52:35

[Outrunner]

Interesting reading if your trials and tribulations of Hurricane models. I had the privilege to watch 7 full size Hurricanes last year at Old Warden, the take off, flight and landings were a joy to watch. Granted these were pampered extremely rare aircraft with the best pilots flying them, but they did not look a handful on landing.

I'm intrigued to what causes the problems described but I can't help wondering if anyone tried any one tried a gyro?

Phil.

[Nigel R]

"A few internet searches later revealed the clark yh section has some reflex in the trailing edge to aid longitudinal stability. Neither my little Hurricane or the SG Hurricane have any reflex as far as i can see. Perhaps this is also contributory."

Undoubtedly.

The YH with its reflex has much less pitching moment - thus the tailplane to do less to stabilise the thing.

Going with the vanilla Clark Y section won't help matters.

[Jon H]

Posted by Outrunner on 12/02/2020 13:45:15:

 

I'm intrigued to what causes the problems described but I can't help wondering if anyone tried any one tried a gyro?

Phil.

Wash your mouth out, gyro's are for sissies

But, no so far we have not tried that as strictly speaking it should not be required and i will hang my head in shame if we are forced to go that route. 

I was also at the old warden show. It was awesome to see so many Hurricanes together and they put on a really great display.

Nigel im not sure what section SG are using but its maximum thickness point is really far forward if i recall. Chris if you get time could to whip a wing off and get a photo of the root rib section?

Edited By Jon - Laser Engines on 12/02/2020 14:32:25

[Nigel R]

I suspect the lack of reflex might be the straw, here.

I know that pitching moment of the wing is quite a large determinant when figuring out the size of a tailplane.

I am however, only an armchair amateur.

[Jon H]

I think its a combination of the reflex, the overall thickness, and the fact that the section used reaches maximum thickness very early. This all means the centre of pressure is moving all over the show which is what makes the thing divergent at certain airspeeds.

Still, its all interesting stuff and im keen to try out some things in an effort to tame the beast

[John Stainforth]

The fullsize Hurricane did not have a standard 12%-ish thick wing section at the root, but a whopping 18%. This was one of the main reasons it was 40 mph slower than the Spitfire. This is how the wing sections compare:

Hurricane ClarkYH cambered 18% root 12% tip

Bf 109 NACA 23 cambered 14.8% root  10.5% tip

Spitfire NACA 22 cambered 13%  root  6% tip

The drag coefficents of the Hurricane's wing section were much higher than the Spitfire at low Reynolds Numbers, so a thick wing model Hurricane would be particularly bad in this respect.

Overall the Spitfire's wing had a quite extraordinary performance, a late model in 1944 achieving the highest speed of any piston engined aircraft, I think. I also remember reading somewhere that Sir Sidney Camm regarded putting such a thick wing on the Hurricane a his "biggest mistake".

Edited By John Stainforth on 12/02/2020 17:36:08

[Nigel R]

Crikey, that is thick for a full size. Wonder if the original wooden wing construction factored into that.

[Tim Flyer]

Here is a picture of the Seagull Hurricane hanging in my garage revealing the thick wing section with no reflex .

Edited By Tim Flyer on 12/02/2020 18:05:12

[Jon H]

Full size for comparison. It looks to me like the thickest part of the wing is further forward on the model and tapers away faster. Also, unless i am going cross eye it looks like an under camber on the model around the flap area?

Edited By Jon - Laser Engines on 12/02/2020 18:29:26

[Martin Harris - Moderator]

Posted by Tim Flyer on 12/02/2020 18:03:47:

Here is a picture of the Seagull Hurricane hanging in my garage revealing the thick wing section with no reflex .

Edited By Tim Flyer on 12/02/2020 18:05:12

The undercarriage is a bit smaller than scale...

[Tim Flyer]

Tee hee Martin , that’s why it keeps digging in 😉😉😉... (that’s my old Acrowot behind it .. just for those that didn’t get it ).

Yes it’s very slight but the thickness of flaps give it a very slight undercamber 

Edited By Tim Flyer on 12/02/2020 19:56:39

[Outrunner]

Posted by Jon - Laser Engines on 12/02/2020 18:28:08:

Full size for comparison. It looks to me like the thickest part of the wing is further forward on the model and tapers away faster. Also, unless i am going cross eye it looks like an under camber on the model around the flap area?

Edited By Jon - Laser Engines on 12/02/2020 18:29:26

I can see the problem now, those wheels are far too small for a decent landing!

[Outrunner]

Posted by Jon - Laser Engines on 12/02/2020 18:28:08:

Full size for comparison. It looks to me like the thickest part of the wing is further forward on the model and tapers away faster. Also, unless i am going cross eye it looks like an under camber on the model around the flap area?

Edited By Jon - Laser Engines on 12/02/2020 18:29:26

I can see the problem now, those wheels are far too small for a decent landing!

[Nigel R]

"It looks to me like the thickest part of the wing is further forward on the model and tapers away faster. Also, unless i am going cross eye it looks like an under camber on the model around the flap area?"

Concur. It's an odd choice of section. I wonder on what basis that change was made.

Myself, knowing as little as I do, I would have chosen a standard, well behaved, well proven in our sizes, low reynolds section, NACA 2412 or very similar, or gone with (nearly) the full size choice of Clark YH - but at a more useful 12% thickness.

That said, I'm not a believer in the usefulness of thick sections, I build everything with a 12% section.