Cambrian Spitfire Mk IX Build Log

[Geoff Gardiner]

Next job - CofG.

according to the plan, it should be 90mm behind the leading edge of the wing.

In order to achieve this I have had to add 150g of weight in the nose:

This gives me this:

The total flying weight is now...................... wait for it.............

3210g or 7lb 1oz

Should make a dent when it hits the ground

Just need to set up the control throws and program the Taranis - then see if it will fly.

[Jon H]

That all seems reasonable. I would not be too worried about it. I would practice a few stalls at high altitude first just to get a feel for how it reacts at the stall.

[Cuban8]

What a fantastic finish to your model - lovely job, I hope my BT Spit just looks half as good.

What scares me is the weight. A tad over 7lbs on a 55" Spit (and no flaps!) is a tip stall and flick just waiting to catch you out. Airspeed is your friend so keep it flying all the time and don't skimp on nose weight to get the CG a little forward on the first few flights. Hopefully, you'll have a head wind of around 10 mph or so to help with the landings.

Just beware on the stall tests - not sure about the value of these IMHO - the machine will stall one way or another, all aircraft do, but this one might bite and could be unrecoverable - a shame on a maiden voyage. I had a 68" Slingsby Firefly that came out very over weight many years ago and it spun itself into the deck after a flick and stall after pulling out a bit hard after a loop with no time to initiate recovery action - not good!

Very best of luck, I hope she turns out to be a great success.

Just curious, but have you done a static thrust test?

C8

Edited By Cuban8 on 13/05/2016 10:05:26

[Jon H]

I have never known a correctly balanced model be unrecoverable from a stall. The only time i have seen people crash a model following a stall/spin was through holding full up elevator and yelling 'it wont pull out'. The issue here was incorrect stall recovery not the stall itself.

Stall testing at altitude is not exactly the same as in landing approach but knowing if the model will violently snap onto its back or just mush is very helpful. You can also get a feel for where your elevator stick is at the point of the stall and this can also be helpful on landing. If the model does stall violently at a high ish speed testing at altitude will give you this information and give you time to recover. learning the hard way on a landing approach 4ft off the deck wont give you anything other than a pile of bits.

7lbs is not too bad though. The Yaks my club mates have built are about 6.5lbs and with flaps they almost stop moving before they touch down. I think you will be ok with this but the model needs to be flown to touchdown. Dont chop the power and glide in, warbirds dont normally like this! Also make sure your elevator rate is set for about half the movement you think you need as spits are normally very pitch sensitive. if there is a recommendation in the kit i would set the rates 10% above and 10% below this figure to give you all the options and no expo as this can induce pilot induced oscillation if your rates are also high.

[Cuban8]

Agree with spin recovery..............providing you have enough height.............providing you don't freeze.............providing you know what you're doing

Let's be careful out there.

Edited By Cuban8 on 13/05/2016 12:20:34

[Jon H]

If its all gone spinny and panic sets in just let go of the sticks! Most of the time that will sort it a treat

I do agree however that spin recovery is often not taught very well. I teach stalling and spinning to my students before their A as frankly you cant really land without understanding a stall!

[Geoff Gardiner]

One last finishing touch - painting the tips of the prop yellow.

Just waiting for some dry weather for the maiden.

[Jon H]

Looking very lovely!

[Cuban8]

Superb looking job - hope the maiden goes well.

No10 in the pilots' ten commandments................"Thou shalt confirm often thine airspeed on finals, lest the earth rise up and smite thee"

 

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Edited By Cuban8 on 13/06/2016 11:58:28

[Jack Banner]

Posted by Jon Harper - Laser Engines on 13/05/2016 10:54:36:

..but the model needs to be flown to touchdown. Dont chop the power and glide in, warbirds dont normally like this!...

Jon, this isn't a challenge (as you are far more experienced than me) but rather an attempt to understand something I may be doing wrong before it results in a crash.

I have an irvine .39 powered Cambrian funfighter p-51 that I fly regularly. It is heavy, over-powered, needs a damn good javelin launch and likes to be flown fast. It also has to be landed dead stick because of the lack of undercarriage. I always chop the power just after turning to finals and glide it in. I have never had an issue with this approach.

Should I be doing it differently?

[Jon H]

Hi Jack

For your model what you are doing is fine, my comments are aimed at bigger models with wheels.

The funfighter series are not scale in the strictest sense and given their small size and strong construction you can more or less slam them into the floor and they will just bounce.

Bigger models dont bounce and retracts will not take the degree of abuse that a fixed (or no!) undercarriage will take. Flaps will also add drag and any attempt to cut and glide will usually end up with a stall and a pile of bits. My new seafury has been a wonderful example of this principal to me as with gear and flaps down i need 1/4-1/3 throttle to keep the thing in the air. If i throttle back it slows down very fast.

to demonstrate this check out the videos below (start at 6mins 10 for the landing part on the first one). I have shared these videos before to demonstrate landing technique. It shows me landing my 80'' La7 and as you can see the decent to land is more or less constant and i still have power on.

Now, the reason i have power on and always keep the nose flat or slightly down is shown below. This is same model, very similar final turn and similar flying weight etc but this chap pulls his nose up a fraction without power on and the result is self explanatory. If we ignore for a moment that he was 40ft in the air and assume he did the same as he came to flare the model, it would behave exactly the same and still end up quite broken.

Warbirds are draggy things that dont like to glide, so come in with a gently curved decending approach and only level off when close to the runway. A long flat approach will make speed control more difficult and could lead to you hanging on the elevator stick trying to keep the nose up, which is not where it wants to be.

[Tim Flyer]

Good lesson! Thanks Jon. Last Sunday on my second landing after a great flight I bounced my Spit and sustained minor damage. I will reduce my elevator travel a bit more to stop landing up and down wobble and make sure power stays on. I had come in too flat rather then your recommended gentle curve.

[Geoff Gardiner]

Well, it's been about 2 years in the making (I said I was a slow builder) and I have finally got around to flying my Spitfire.

The field that I flew from was a little smaller than my other club field (with some trees that like to catch unwary planes) but the advantage being, not too many people around to witness the possible carnage!

It took me a while to get used to the ground handling as it wanted to pull to the left quite a bit. Once in the air, it was a treat. No trim was needed and power about right. I was worried about the weight and kept the speed up for this first flight. This made the landing a bit tricky as the strip is quite a small target to hit, and hit it I did.

I think I may have got away with the hard landing if it wasn't for the fact that both wheels turned 90 degree's on contact with the grass, causing a nose over. This, I have realised, was because I forgot to file some flat spots on the undercarriage legs. Still, no real damage done. I will chalk this up as a success.

Here's the video:

Next up on the building board is the Tony Nijhuis Mosquito.

Geoff...

[Danny Fenton]

Well done Geoff looks ace
Cheers
Danny

[Concorde Speedbird]

Well done, very nice job. These are good fun in the air.

CS

[Jon H]

A great start Geoff and for a first warbird landing that was not a bad effort.

I do have a few suggestions that might make your next flight easier.

The first is right thrust on your motor. watching your flight all the way through, especially when you have a low airspeed/high power combination like your takeoff, go around and the top of your wingovers, the nose of the model is pulled very strongly to the left. It also shows when you were banked steeply as the model would fall into left turns and knife edge (slightly) through right. You could trim with rudder, but you will then probably end up out of trim at high speed or when off throttle. I would suggest a few degrees right thrust on the mount and to have another go.

I would also suggest you bring your rates down a touch, especially the elevator as it looks quite aggressive. I don't know if you have any expo in but if you do knock that off and reduce the rate by at least 10%. You could leave your current setting on one switch position and set the new one on another so you can always go back to the tested setting if you need to.

The final comment is that it looked a shade tail heavy so perhaps shove the battery forward a little for the next one, but you will have to experiment as it might not be required with the lower control rates.

It might sound like I am splitting hairs, but you will be astonished by the difference these changes can make and will give you much greater confidence and more enjoyment from the model

 

Edited By Jon Harper - Laser Engines on 27/07/2016 20:47:42

[Geoff Gardiner]

Thanks for your comments chaps.

Jon, that sounds like really good advice, which I will definitely act upon. Many thanks.

PS. I didn't set any Expo but I did set up normal, high and low rates for the elevator. In my excitement, I only used the normal (as per plan) setting and forgot the others!

Geoff...

[Josip Vrandecic -Mes]

Dear Geoff, after more than two years of your precise work came well-deserved reward to you .... Congrats from my heart because, I am a fan of every Spitfire in the whole world
If you don't mind a small note: Following your Spitfire project should have flaps ... you already know why.....

A lot of health, happiness and enoy  in flying ,
Jo

Edited By Josip Vrandecic -Mes on 27/07/2016 21:43:57

[Geoff Gardiner]

Had a second flight of the Spitfire today. Having adjusted the thrust angle of the motor (to give more right thrust) the take off was a lot easier. I also remembered to try the low rates that I had set up on the Taranis.

I had also filed some flats on the retract legs so the wheels remained pointing in the correct direction when landing.

I am very pleased with how this model has turned out and hope for many more flights. The only problem today was that one of my e-flite retract units has failed. I will have a look on the bench but I fear it is dead.

Thanks to everyone who has given me advice on this thread.

Geoff...

[Jon H]

Glad to hear the mods have helped. The next part is just to fly the model as often as you can and if you visit an airshow or see a video of a spitfire, remember how the full size aircraft behaves and then try your best to copy it. You will find quite quickly that you can use much smaller control inputs to get a scale result.

[Geoff Gardiner]

It's still flying!

[Don Fry]

.

Edited By Don Fry on 03/12/2017 19:46:57

[Rob Ashley]

Superb Geoff well done mate.

[Phil Curtis 1]

Geoff
Your logo sheet is great but I am having trouble finding the exact logo positions and the words for the first aid and ballast box on the side of the fuse, also any other words used eg the fuel detail on the top of the fuse large.
Any help greatly appreciated