Brian Taylor Spitfire Mk 1 C of G

[Tim Cheal]

Hi All

I have just about finished my Brain Taylor Mk 1 Spitfire, but a couple of things surprised me. First, the model needed about 1 1/2 pounds of lead in the nose to get it to balance at the CofG on the plans. The other thing that has caught me out is the tendency to tip on its nose during my initial taxi trials. The grass is really soggy at the moment, but if anybody has any experience of the CofG of this BT Spitfire Mk 1 I would be really grateful.

I am tempted to ease it back a bit, but don't want to do that until after a successful maiden!

Comments grateful received.

Tim

[Jon H]

most warbirds need a fair bit of beef in the cowling but if its really tippy, and you have decent size wheels (about 4 inch?) then you might have over done it a touch, which engine do you have in there and what is your total weight? That said, most warbirds are not fond of soggy grass. My little hurricane spends quite a bit of time on its face due to the long/wet grass at our patch. I look forward to the summer.

When you did your c/g did you do it gear up with an empty tank? that's how I do mine. Some guys suggest doing it with the model inverted to make it less tippy when trying to narrow it down. I have tried it but didn't find it made any real difference.

[Chris Freeman 3]

Do Not move the CG back, a Spitfire has very sensitive elevators due to the small taiplane size which was also evident on the full size. A Spitfire will need a lot of lead to get the CG correct so do not worry about that. You can try to rake the unercarraige forward a bit more to improve the ground handling. Take time to set up your control movements correctly and ensure that you do not have too much elevator movement. I set up the dual rates so I can reduce the movement once in the air and even land on reduced rates. If you have retracts you will find the Spitfire will drop the nose a little when the retracts are lowered and also more when flaps are used. Due to the nose over issues and nose down pitch with retracts, I have also found that expo can be an issue as about 10% is all that is needed as it will work against you when trying to get the nose up in certain situations. My Spitfires needed very little elevator movement and once set up correctly are very smooth flying aircraft.

Another trait of the Spitfire is that when you do a loop you need to increase the up at the top of a loop and not reduce it like most other aircraft, as a Spitfire will try fly out inverted and you will need to pull it around. Many Spitfire models have been lost due to a spin fron the top of a loop.

[Jon H]

cant agree more regarding elevator rates. All warbirds should have very small elevator rates and i dont recommend expo either.

I cant say i have noticed the other traits you mention in spits i have flown but each model is different. I have had a P40 and a Hurricane that behaved as you describe though

[Tim Cheal]

Thank you Chris and Jon, I really appreciate your replies.

I did the CofG with an empty tank and the wheels down (well actually up as like you suggest I balanced the CofG with the aircarft inverted!). I shall have another go with them retracted.

Caution noted about the CofG, and I dont think I can angle the retracts forward any more and them still etract into the wheel wells, so I will have to wait for the ground to be firmer!

Picture of the landing gear below with refernece to the plan, in case anybody has any other trhoughts?

Tim

[Jon H]

looks good to me but those wire legs are naff as they will bend and move the wheel back. oleos will be better but will be less forgiving of a bad landing

[Denis Watkins]

This view at Manston may help the "nose over" discussion of setting mounts to track the wheels to the leading edge.

[Chris Freeman 3]

Pleasure Tim, on the YT models Spitfire they add a packer of ply onder the rear mount to get more forward rake. I have found that all my Spitfires that I have built and flown have had very few nose overs on take off as the thrust of the motor and wind over the elevators prevent it. The challange is to hold enough up to keep the tail down but not to take off without enough airspeed. Landings are the hard one, I try to land in a tail low attitude but not 3 point. I also tend to use the scale curved approuch as it is easier to control the speed and height. A long approach can be very tiring with a warbird as the elevator is very sensitive. Once down you need to hold all the up you can but with a grass runway you should not damage the plane if it does nose over. I am sure that once you are used to the flying you will see that the nose overs will be few and far between. You can see from the above picture that even the fullsize was not great at taxing around.

[Tim Flyer]

I notice Jon's good comments on the wire legs. I have just the same problem on my World Models 60 Spitfire. Jon also pointed it out to me. When I land the wire legs spring back unless the ground is firm and billiard board smooth (and I make a perfect landing!!) We also have grass runways I am going to upgrade to oleos and will probably fit HK electric retracts while I'm doing that. Good luck for the maiden ! Best to wait for firmer ground though.

[Jon H]

Chris makes excellent points about how to land a warbird. Long straight runs to the runway are not going to help you at all and i favour the curved approach for the reasons he describes. It also looks awesome!

[Martin McIntosh]

Good advice above. My current Spit. is a 1:6 TN design. It has never nosed over on take off but once rolling elevator control needs to be precise since the nose will try to bob down on full power. Don`t use flaps on take off because they will push up the rear of the wing and make matters worse. I try to retract them on touch down for the same reason but landing is normally a doddle.

My wheels are as far forward as possible, using blocks to angle the retracts. Whatever you do, don`t try moving the CG back. On my second test flight the lousy Traplet (weighted) spinner flew off. The model was virtually uncontrollable.

I have tried high rate elevator on Spits but it is counter productive. Lots of expo is much better.

[Jon H]

I wouldn't recommend any expo at all at it usually leads to porpoising and stall on approach. Low rates are the way to go for sure and there will be a balance between c/g, undercarriage rake and elevator rate that will bring it together.

[Chris Freeman 3]

2 Sundays ago a club member brought his new Seagull PT 19 to test fly. Nice looking aircraft that was powered by a Saito 180. I watched the flight that started with a take off run that was very short as the aicraft almost nosed over on take off and when up was given it lept into the air, lucky the power was enough to drag it to a safe altitude. The landing was a porpoise approach ending in a nose over. Later the owner asked my son to help trim it out but I saw the take off was another leap into the air and the landing was good but not the normal smooth approach that Byron does. I asked Byron if the elevator was not too sensitive and he replied that it was. Whilst reducing the elevator movement they also found that 40% expo was used so it was reduced to 10%. The aircraft was flown again and the owner could not beleive how much better it flew.

[Denis Watkins]

Exactly Chris, there is a time for Expo,

And as Jon highlights, a Warbird elevator is not the place on maiden flights or learning a new model

Expert flyers can dial Expo in with their judgement,

But Expo " cart blanc " can play havoc while familiarising with a new venture

[Jon H]

Chris, i had the exact same experience with a friend's hangar 9 spitfire which should by all accounts be a pussycat....but not when you have 70% rates and 65% expo on elevator! I ditched all the expo and whittled the rates down to 30% before i handed it back to him. He was utterly astonished by the change and after 3 years of struggle finally was able to enjoy a flight with the model. I dont know why he didnt ask for help earlier as it was the work of a moment to sort out.

[Tim Cheal]

Thnaks for the heads up on the 'naff' wire. I did think it might be thick enough (and the maximum thickness for the EFlite retracts). Ill give it a go, and hope its not too much of a problem.

I had forgotten about people on the tail, and it reminded me of the story of the WAAF that clung on for a circuit:

Tim

[Jon H]

I think the aircraft that happened to was MH434 and its still airworthy at Duxford. Not sure if it was that aircraft but that is what i was told once

[Martin McIntosh]

Chris F., it sounds to me like a classic case of entering expo the wrong way for the type of gear used. I got caught out myself at the R/C hotel a couple of years ago. I use mainly JR, which has +ve expo. The twitchy model I was trying to tame was on Futaba. I kept increasing the expo and it got worse each time, not realising that Futaba needs -ve. (I think that is the right way round for these).

Any new model I am test flying gets +30% low rate, +40% high rate initially. Most are scale warbirds.

No point in buying a fancy radio if you do not use it to full potential. In my aerobatics flying days I would almost have given my right arm for expo on at least rudder.

[Jon H]

If you are using that much expo then to be honest the rates are just too high. most of my models use none and if I do use any 10% is all they get. My stampe is an example with 10% on aileron as the deflection needed for a scale rate of roll makes the model sensitive on slow flybys. 10% expo sorted it out.

I would never recommend anyone start with a load of expo on a model.