TN Hurricane

[Bill Frost]

OK, well here we are! Interesting that until Allan just now, there'd been no other postings on this thread since my flight pictures from April 2014 - I was quite surprised when I saw that. A small claim to fame, perhaps? Anyway, the aircraft still flies, although not as often as I'd like, for relevant reasons I'll describe below.

Hi Allan, good luck. In response to your queries. Nose-weight - I can't remember the details now, but - we are flying our electric on one half of an F3a 10 cell, ie a 5 cell pack because of availability. It was always planned that way. I've got that up as far forward as possible (ie just clearing the back end of the motor's shaft, so that doesn't drill into the battery). My building techniques were very basic, so I'm sure I built everything heavy, including the back end, hence still needing more nose weight. From memory and for redundancy, I used two separate receiver batteries one for radio/servos, the other for retracts and landing lights. Those two batteries are strapped to top and bottom of the motor mount (ie inside the cowl), so that helps. Think I still had to add a little lead. Result - its a heavy model,

Because of the taper, the inside of the cowl isn't very spacious.

Our airfield uses a tarmac runway (you can see it in one of the pix), not a square patch. Therefore you have to cope with whatever the wind direction is, ie crosswinds etc. Because of its weight, unless there's a stiff-ish headwind coming straight down the runway to land in, its a very fast landing event, with little margin for error. For that reason, if I was building again, yes I'd definitely go for flaps, so at least there's that option too, although obviously I don't know if they'd be effective and how much they'd reduce aileron authority etc. Yes, photos from Shuttleworth/Old Warden will show you the amount they can droop.

For that combination of reasons (chiefly the need for stiffish breeze straight down the runway, combining with availability etc), it doesn't fly often. The fast landing speed tends to show up the lack of sturdiness of the landing gear due to the retracts - I'm always bothered that during landing, the struts could rotate in their sockets in the retract units, with cartwheel results on hard tarmac.....

The other design mod that I would definitely do now, but didn't have the experience to do at the time, would be to make the main flight battery accessible without having to take the wing off - ie a fuselage hatch, but obviously extra strengthening would be needed as the hatch would be quite large in the Fus top.

Enough for now, but feel free to ask. I'm currently slowly building a 72" wingspan Stuka - partly chosen because it has a longer nose, for balance!

Kind Regards,

Bill

[Allan Bennett]

Thanks for those replies Chris and Bill.

I'll go ahead and make the battery bay through the firewall now; seems like it could save me a bit of weight by minimising the amount of ballast. I'm thinking I might even cut the protruding shaft off the back of the motor as well, to give me that extra 1/2" to get the battery forward. I already have 6S 2600mAh and 6S 3900mAh LiPos for other models, so I plan to use them with the recommended motor instead of 5S, with a suitable adjustment in prop size. I too don't like the idea of having to take the wing off to change the battery, so I've already made a removable cockpit/canopy unit as a battery hatch. No strengthening required since nothing's been removed. My main receiver power will be from a stand-alone BEC, with the BEC in the ESC being used for the retracts.

I'm lucky enough to live close to Old Warden, and in fact I went there last weekend to see their Sea Hurricane in the workshop, and to take photos of interesting bits such as landing lights, wingtip lights, radiator, and exhaust stubs.

Lack of space inside the cowl is also noted: My normal method is to make a fibreglass cowl, so its thinness compared with one carved from balsa blocks as per the plans gives me a bit of extra space inside to install a lead lining if necessary.

Edited By Allan Bennett on 05/01/2019 21:04:18

[Allan Bennett]

Hurricane is progressing slowly, due to other distractions, but I have one query at the moment: Because the retracts are fitted into the wing at an angle, the wheels need to be fixed at a corresponding angle on the legs to avoid having massive toe-out when the gear is down. That's not a problem except that I'll have to relieve formers W2 a little bit to accommodate the 'twisted' wheel.

But the wheel bay covers that are attached to the u/c legs need to be flat to the wing surface when retracted, so they will be angled out significantly when the gear is down. Is that correct, or am I missing a trick?

[Ron Gray]

Yes they will be angled (toe in) when down. If you look on the Mick Reeves ‘site you will see that he has a cunning way to get round this problem.

[Allan Bennett]

Ok, I think I see it Ron, in this video. That hefty cranked arm is twisting the strut as it raises it. But that won't work with the simple electric retracts I've got. His model is almost twice the size of TN's, so he has plenty of space for some clever mechanism.

The twisted wheel when stowed is not a problem, but I'm now thinking that maybe I can attach the wheel bay covers to the struts by sprung hinges of some kind, instead of rigidly, so that their normal position will be in line with the wheel but they'll be pushed flat against the fuselage underside, and hence twisted from their normal position, when wheels are up.

On the other hand, maybe simplest is best -- rigid fixing, and live with the covers being out of line.

[SR 71]

Mould the wheel covers from fibre glass and attach with silicon they will move into position when they retract and bac9k when open
Tony

[Allan Bennett]

That sounds like a possibility SR 71

While at Old Warden the other week they did a demo of the landing gear lowering and retracting on their Sea Hurricane. I remember them saying how the wheel covers were profiled in such a way that the slipstream acting on them would force the u/c to lock in position in case of hydraulic failure.

[Allan Bennett]

Canopy size question.

Things have been going slowly due to other commitments, but I'm back on the job now. What's been puzzling me for some time is the fact that the moulded canopy is longer than the cockpit, as shown on the plans. But the full-size isn't like that -- it doesn't overhang the back of the cockpit as shown in the TN plans.

So what have you guys done about that? I could cut the canopy to the right length for the cockpit, and use a thin strip of plastic to form the rear frame, but then the two intermediate frames wouldn't be equally spaced as they should be.

[Martin McIntosh]

I am about to do a little work on mine due to a flap servo failure at the RCM&E fly in so while I am at it may take some pics. I may well have done a build blog here a long time ago and there should be pics in my album. My 5S pack is up against the firewall, not flat.

[Allan Bennett]

Thanks Martin, I've checked your photo albums and see nothing for the Hurricane, so a photo of your canopy would be appreciated when you have time. I see in your albums that you have a vaccuum-former -- you didn't make your own canopy did you, instead of using the TN one?

[Martin McIntosh]

Looks like I omitted an album for this one because it has been done before. I used the TN one here because vac forming is a very hit and miss affair for me. You can easily make a Hurricane canopy in two parts if you make up a balsa plug. Form the rear by using a heat gun then the front as a separate piece and glue them together.

Just about to look at the wayward servo so will get a couple of pics later.

[Martin McIntosh]

Here is the battery compartment. The gubbins other than the Rx amongst the spider`s nest of wiring is a sound unit.

The batteries are a very tight fit.

The canopy fits like this:

[Allan Bennett]

Thanks for taking the trouble Martin. I visited Shuttleworth a while back and took many photos of their Hurricane but, because the canopy was open, I never noticed that it actually overlapped the fuselage behind the cockpit when shut -- as you have modeled and TN's plan shows.

On closer inspection of a blow-up of one of my Shuttleworth photos I see that in fact the fuselage behind the cockpit is recessed slightly to accommodate the rear of the canopy when closed and, in another photo I found on the internet the recessed portion seems to be painted a much lighter colour than the brown/green camouflage. The cockpit on my model is removable, as a battery access hatch, and the battery will slide forward to right behind the motor.

What sound unit are you using? I've got Benedinis in my Flair Magnatilla and SE5A -- with 4" speakers in the Maggie and transducers in the SE5A. Lovely sounds!

[Martin McIntosh]

Without removing the sound unit I can`t remember the make but it is small and light. Only really effective on the ground at start up and shut down.

I originally tried mounting the pack flat as per plan but the cg was way too far back.

[Allan Bennett]

OK, my battery goes through F1 to the back of the motor, so I hope I don't need too much lead. Just starting painting now, so I should be in a position to find out around Xmas!

[Martin McIntosh]

My pack is 5s 5000mA/hr, (2s + 3s) so would not fit through F1.

I seem to recall that this simple build model only took about three weeks!

[Allan Bennett]

I plan to use two 4S 3200mAh in parallel, which do fit easily.

I think the only model I've 'built' in 3 weeks is my Multiplex TwinStar

[Allan Bennett]

I think I need some flying lessons

A couple of months ago, as lockdown was relaxed, we finally got a day that I was happy to maiden my Hurricane. The result was not good. Take off was quick and straight, as was climb out to about (I guesstimate) 100ft. At that point I throttled back a bit to level off, and retracted the undercarriage. A couple of seconds later, turning slightly left to join the circuit, the Hurrican dipped its left wing and became uncontrollable, ending up nose-first in a neigbouring field.

It really was a bin-liner job; no hope of repairing it. The good news is that all the electric and electronic bits survived, and tested out okay. Also the canopy, cowl, retracts, and the exhaust stubs that Gary Clark 1 printed for me all survived. Since I had plenty of wood left over from the original build and previous models, I decided to start again with another CNC pack from TN, and the new build is now well under way.

In the meantime the receiver from the Hurricane (FrSky R6XR with v2.1.0 firmware) is installed in a small depron model to see if it exhibits any nasty traits -- two flights so far without issue. The retracts share the ESC's 10A BEC with only the lights, with the Rx and servos using its own stand-alone 20A BEC, so the fact that I'd just actuated them before the crash is probably just a conincidence.

So it must have been pilot error

[Chris Walby]

Allan,

I have a theory so probably wrong but here goes....its that electric thing

If it was Ic you would be listening every second just in case it dead sticked on you + you would make sure there would be a generous amount of revs on to make sure the engine was running well, hence you would be flying with plenty of airspeed and a draggy airframe.

Electric is near silent at almost all throttle settings, IMHO its very easy to let the airspeed drop off and not notice, then add a turn in and the warbird is going to bite.

I have watched plenty of videos and experienced the problem of judging the airspeed of an electric model to the point of tip stall

Well done for taking on the challenge of building another and all the best with that one.

[Allan Bennett]

Thanks Chris. Having, I think, ruled out component failure -- especially the coincidence between gear up and the onset of my problem -- I came to the same conclusion, that I had throttled back too far. But I've flown a Spitfire without any issue, so I was surprised that the Hurricane would experience tip stall so easily.

With all the other bits to hand, paying for the CNC kit to rebuild was really a no-brainer. It's cheaper than any other kit I could have bought.

[Martin McIntosh]

I think Chris is correct there. I need to be very careful not to reduce the power too much, especially on landing. This is one of the main reasons I favour i/c if possible. It would appear that some TN Mossies have come to grief due to throttling back too much without realising. I tried a sound system which helped a little but was pretty poor.

One other thing, the cg was not even slightly rearward of the position shown, was it?

[Danny Fenton]

I have to agree with you guys, the electric models are very quiet and easily drowned out by an IC. It isn't helped by many of the lesser quality ESC's not giving a very linear throttle, you may think you are at half, but often the motor doesn't even start to spin until a third. Some of the cheaper ones only really give 1/3 to 2/3 as actual travel.

I have switched to the FRSky Neuron esc's and they are really nice, the full travel gives nice linear control, however that has caused me grief as it took some getting used too. Half throttle is not the same power. So landing at third is now landing at half..... but you do have to be careful.....

Cheers

Danny

[Jon H]

Does the Hurricane have any washout? im told TN never uses any and i have to confess i think that is a mistake. If it has none add 2 degrees.

[Allan Bennett]

Thanks for all the comments. As for the c of g, I'm pretty sure I had that right. There's quite a bit of lead in the cowl to achieve it.

There's no washout and, unfortunately, I've just finished sheeting the wings so can't add any now. I wonder if a bit of 'up' on each aileron would help. Or maybe I could build some washout into the ailerons themselves and then adjust the wingtip blocks to match.

For my next maiden (not anytime soon!) I guess I really need to keep power on until I get to a much greater height, and then check out the result of reduced throttle -- presumably increasing airspeed is part of the method of getting out of the spiral dive that's started with the wingtip stall?

[Jon H]

Knowing spin recovery is advantageous, but its probably better to not spin in the first place. I know that is pretty obvious, but with all my warbirds i do everything i can to fly around the stall and not up to it.

Again, i know that is easier said than done, especially with a new model but getting it up and away before trying some stalls is a really good plan. Get the gear away as well (i know you did that) as it gets rid of a whole bunch of drag. I cannot understand people flying around with their gear down.

Also did it spin left? if so torque could also be a factor and some right rudder in left turns might be needed to keep the yaw in check. I use my rudder as much as the elevator and aileron when flying my warbirds and its so 2nd nature now i cant actually remember how much my 60 inch hurricane needs. I know its a fair bit