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Got away with it!


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I've had an interesting time with the Double Size Tomboy over the last few days. It has been fine in the air but it has squirreled all over the place on take off, so much so that on Sunday it looked as if it was going to clout a group of pilots in the pits so I deliberately put it in, damaging the undercarriage mountings in the process and losing a couple of cross members from the wing mounting. Part of the reason for the problem is that the undercarriage is just one piece of 6mm wire so it flexes easily and the wheels are also very loose on the spindles. I tried to remove the wheels but the grub screws have seized in the collets, but I did manage to solder a brace to stiffen up the undercarriage and I replaced the cross members with larger section balsa.

completed job (1).jpg

I took it to the flying field yesterday afternoon. I am a club level instructor and have just acquired a new pupil, a 71 year-old Belgian called Franz to add to my 60 year-old Englishman Andy, and my 50 something Frenchman Eric. We are getting very international at our club! Franz is making all the usual beginners' mistakes with an electric four channel foamy trainer but I have long held the view that elderly beginners are better off with a vintage model because they are based on free flight technology and are much more stable than any modern ARTF trainers. After a couple of flights with the foamy trainer I offered Franz a go on the buddy box with the Tomboy.

The model still went all over the place on the ground but at the second attempt I got it into the air. I climbed to altitude then gave Franz control. He did alright at first then things seemed to go haywire. I regained control and was immediaterly aware that something was wrong. The model would not turn to the right. There was very little wind but it was sufficient to send the model slowly further and further away. I still had control of the electric motor so could gain height but it was impossible to keep the model on a constant heading steering into into the breeze. Consequently it was reaching the limit of my vision and perhaps I was getting disoriented, whatever the reason the model went into a spiral dive which I thought was terminal but suddenly I had full control again so I flew it back and landed safely. My colleagues had been sitting in the shade drinking beer. After getting the model back, that's what I needed too!

It was only when I was packing the model away that I found a possible cause. Inside the cockpit was one of the old wing seat cross members which I had not noticed before. Had this lodged in the rudder servo preventing me from using right rudder? Had it become displaced in that seemingly terminal spiral dive so that I had control back again?

Two things are for sure. I am going to put the servo through a thorough testing with the servo tester and I'm going to grind off the collets and either fit better fitting wheels or bush out the old ones.

Happy landings gentlemen!

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A lot of old style former free-flight designs seem to have difficulty on the ground. I think the reason is that the undercarriage is very far forward. They were designed to hand launch (as free flight) and the gear was there just for the landing and far forward to protect the propeller.

We've had several members in the past with this type of model who would chase the model round our (tarmac) runway in a sometimes a thwarted attempt to get them airborne. I think the real answer is to locate the undercarriage further back, under the wing leading edge.

Geoff

Edited By Geoff S on 10/09/2020 12:05:00

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I agree with Geoff. I fly in Summer a venerable Super Scorpion. It must be directly into wind on take off, also normal practice of opening the throttle slowly must be discarded. Half to thee quarter throttle ( model being held back) is the order of the day to get some wind to operate the rudder. Any slight deviation and I am running around. LoL

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Many an aircraft has been brought down by a wayward object in the control system. Friend who was serving in the RAF at the time was part of a team sent to recover the remains of a Canberra that had gone straight in.

After two days digging they got to the cockpit remains and found at the base of the control column a 2 BA nut.

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Thank you for all of your advice gentlemen.

The wheels on the Tomboy hang straight down from the firewall. On my Tomboy they are raked forward slightly and they were toed in from the outset. I added a brace last week to the single wire undercarriage leg which stiffened it considerably but the holes in the wheels were too big for the axle resulting in considerable play and a less than satisfactory performance on take off.

I spent yesterday morning checking the servo by connecting it up to a battery and servo tester, switching it to "automatic" and leaving it to oscillate for over 15 minutes. That proved that there was nothing wrong with the servo, a Hitec HS311.

I then squirted WD 40 onto the collets and went for lunch. I tried to slacken off the grub screws without success so gripped the collets with a pair of pliers and pulled them off the axles with main force. I tried bushing out the existing wheels but as I only had plastic tube and no drill stand, that was not too successful. I found a nice pair of wheels with aluminium hubs, drilled them out to match the undercarriage wire and then found out that the hubs were too wide, so there was no chance of retaining them even with a soldered on washer! Finally I found a pair of cheap and cheerful foam wheels which I fitted to the undercarriage, then I drove the 4kms to the flying field and tried a couple of test flights.

Much better! The wind blew from the north and our tarmac runway runs east to west. I could have taken off into wind from the grass but I would not be allowed to do that on club days because I would be flying towards the flight line and the pits so I took off towards the east. The model did not track like a three channel trainer, with all that dihedral and no ailerons a cross wind take off is not easy but at least the model is more controllable now and less dangerous on take off to assembled clubmates.

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Yes - I agree with FB3 - into wind and enough oompah get her off the ground in as few feet as possible - apart from anything else - most of these elderly beauties have no tail wheel to steer them, they were designed to fly ( and don't they do it so beautifully ) not to be taxied around. My Scorpion with a 30 year old OS MAX25 turning a 10" prop is off the ground in 10 feet in still air, 6 feet if there's a light breeze ( or when it had a slightly less well used OS 25FP, with the same prop, on the front.).

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After I converted my old Veron Sopwith 1 1/2 Strutter to 3S electric power I found that the biggest problem with take-offs was that opening the throttle too quickly caused an instant 90 degree turn to the left, opening too slowly allowed for ground loops to develop. If kept straight it would float off the ground in a few feet, maybe 5 yards on a flat calm day, but the challenge was in keeping it straight long enough for the rudder to become effective. Tailskids are a real pain! At least it flies well enough once it's up, it must do as it reached 40 years old this year cake

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I had a similar problem when I modified my Super 60 by replacing the rear tail wheel to a steerable tail wheel. Due to the design of the SS60 I had to move the tail wheel further forward to the leading edge of the horizontal stabilizer.

In this case when I applied power the rear of the plane would lift straight away hence as the tail wheel was no longer on the ground there was no directional control as there was not sufficient air speed for the rudder to become effective. Hence the plane would shoot of to either the left or right.

The only way I can overcome this is to hold full up elevator as I gently apply power. This keeps the tail wheel on the ground. As the plane builds up speed the rudder become effective and I reduce the up elevator as the plane takes off..

.

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Posted by Bob Cotsford on 11/09/2020 12:00:36:

After I converted my old Veron Sopwith 1 1/2 Strutter to 3S electric power I found that the biggest problem with take-offs was that opening the throttle too quickly caused an instant 90 degree turn to the left, opening too slowly allowed for ground loops to develop. If kept straight it would float off the ground in a few feet, maybe 5 yards on a flat calm day, but the challenge was in keeping it straight long enough for the rudder to become effective. Tailskids are a real pain! At least it flies well enough once it's up, it must do as it reached 40 years old this year cake

Interesting. Did the model exhibit the same characteristics when it was powered by an i/cengine Bob?

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I don't remember it being so wayward David, but then again my thumbs were much younger back when it was IC powered. Certainly IC engines don't typically accelerate as quickly as electric motors and as long as I don't flick the throttle to full it doesn't do the 90 degree turn and it's wayward tendencies are manageable more often than not.

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