TD .049 Scratch Build

Thanks Baloug..!
With the price of what a NIB Cox .049 engine is...I wish there was a way to tell that you are buying an engine from the proper time period...[?]

An idea is to make a tapered hone and try to custom fit a .051 piston into a .049 cylinder...?
I'm not a machinist..but I like to day dream.

If the TeeDee has a thin wall, or, stepped wall cylinder, that will have tapered bore....meaning, all thin wall cylinders, and most stepped wall cylinders on TeeDees had taper bore...E.g the replacement stock step walled cylinders came already without taper bore, I have a few (in original blister pack ) stepped wall replacement cylinders with the piston hanging out from the cylinder top.


None of the later, thick wall cylinders on my TeeDee-s have taper bore, though..so the type of cylinder is an indication.
I doubt a 051 piston could be grinded to match a tapered 049 cylinder..the piston wall near the piston crown would become too thin and may lead to splitting the piston..
I think something similar occured with the Venom pistons that self destroyed themselves due to insufficient wall thickness.

balogh wrote:If the TeeDee has a thin wall, or, stepped wall cylinder, that will have tapered bore....meaning, all thin wall cylinders, and most stepped wall cylinders on TeeDees had taper bore...E.g the replacement stock step walled cylinders came already without taper bore, I have a few (in original blister pack ) stepped wall replacement cylinders with the piston hanging out from the cylinder top.


None of the later, thick wall cylinders on my TeeDee-s have taper bore, though..so the type of cylinder is an indication.
I doubt a 051 piston could be grinded to match a tapered 049 cylinder..the piston wall near the piston crown would become too thin and may lead to splitting the piston..
I think something similar occured with the Venom pistons that self destroyed themselves due to insufficient wall thickness.

What I want to do is to machine a .049 cylinder for a .051 piston...but do it with a tapered bore.

The bell crank, center section sheeting, lead outs and bladder compartment details are done. I wont commit to lead out placement at the wing tip until the plane is all assembled and I can judge how much line rack looks about right.

Ken Cook wrote:                    Certainly not a amateur. That looks like a Texas combat build by Dawson.

Thanks...I've been borrowing ideas from better builders for about 40 years now...

Ken Cook wrote:          I just highly modified a Driskill Litehawk. I clipped the span down to 31" total span vs 36. I sunk the noseblock back into the leading edge a bit as well. I shortened the tail moment. I was never impressed by the turn as I found it to be mashmellowy. That's the best way I can describe it. I cut the wing panels at the root and put some leading edge sweep in it. I also put trailing edge sweep into it. I now have a plane which I can use a AME .049 on and have it as fast as my .061 powered stuff and turn on itself.

 

I'd be curious to know how many Litehawks Mr. Driskill has sold.
Must be in the 100s maybe pushing 1000...?
They made good planes for RC conversion too.
Larry published an article about how to prep a Cox TD for combat and also a 1/2A Combat construction article..I think that plane was called the Halflite.

Here it is almost ready to fly at 6 7/8 ozs.
It's covered with tinted cellophane that was misted with 3M 77 adhesive.
The bladder holder looks like a gutted plastic fuel tank..but I made it out of 2 layers of 2 ox cloth and medium CA. I coated it with a smear of epoxy inside and out. I was afraid the fuel cell in the wing was going to doom the plane to having way too long of a nose. The nose ended up long enough as it is [I'd like to move the engine back after some flight tests.]
Still needs the fuselage fuel proofed and a nickle taped to the outboard wing tip.
The span is 30 inches not counting the wing tips.
This is the most extreme control line thing I've built for the .049 TD.
I'll want to see it fly on 40 foot Spiderline if it passes the test on 35 foot lines.

Nice work TD with innovative features….. Can you share a little more about using cellophane for covering?…..

rdw777 wrote:Nice work TD with innovative features….. Can you share a little more about using cellophane for covering?…..

Craft store / Dollar Store cellophane was in the gift section of some stores or sold as "floral wrap".
50 cents to a dollar for a roll big enough to cover most 1/12 scale 1/2A wings.
It is clear cellophane with colored ink on one side. [be sure to verify which side has the ink before using it]
I lay out some newspaper, then lay the ink side up on the newspaper, then spray on a light coat of 3M77
Wait for the 3M 77 to "tack up"...then do a nice job of positioning it on your wing.
With the iron set at about 11 o'clock [should be too hot to hold] start getting the perimeter of this stuff stuck to the LE, then the TE and every chance you get trim the excess material away.
This stuff is very easy to melt so keep your eye on the temperature.
It has great shrinkability.
It weighs NOTHING
It is less durable than the stuff that was made for our hobby, but I've covered lots of 1/2A projects with this stuff.
If you want to make a covering job last longer use Scotch tape over the seams..or else there is a clear surgical tape I've heard of for doing that .

Do not buy metallic rolls of this stuff because it doesn't shrink. I think if it doesn't say CELLOPHANE on the package it's probably the wrong stuff.

Here she is at 7 1/8 ozs RTF on 35 foot long steel
The engine only puts out 18500 with a 5x3 instead of the normal 22,000 output we would expect to see back when a Cox TD .049 was REALLY a Cox TD .049.
I used .055" wire  to connect the bell crank to the elevator which is much lighter than using 2-56 wire that is already threaded.
The drawback is that it is much more difficult to adjust the control response with the .055" wire. because you only adjustment is to use pliers to re-bend the control  wire until it is just the perfect length.
Line tension was pretty good for this low revving TD. I used "leadout rake", some engine out-thrust and a tiny bit of right rudder to enhance the line tension.
I used a nickle for wingtip weight




https://youtu.be/t0yRxGGVSEg

Good looking build and the flight was pretty good too LOL I love the way you get it back to the truck every time You keep looking and will find a good running TD .049 just know what to look for the mounting platform show a lot of what the engine has been doing for the last 50 yrs.
Thats good we keep finding new stuff to cover with , I have some of this paper in colors from Christmas packing , was wondering if it could bee done and now you show it can . Thanks

getback wrote:Good looking build and the flight was pretty good too LOL I love the way you get it back to the truck every time  You keep looking and will find a good running TD .049 just know what to look for the mounting platform show a lot of what the engine has been doing for the last 50 yrs.
Thats good we keep finding new stuff to cover with , I have some of this paper in colors from Christmas packing , was wondering if it could bee done and now you show it can . Thanks

Thanks for the kind words.!
I found a couple more TDs in the attic still bolted to RC planes.
One of them had the most slop in the ball socket I've ever seen.
It is all cleaned up, reset and ready for a test flight today.
Today I'd like to work on getting the plane adjusted well enough so I can try flying square maneuvers.
That's something I've never spent much time trying to do.

Sounds like a plan , hopefully one of the TD s will work better ?!? Slop will effect the SPI pretty bad can rob some RPMs .. What RCs do you have them on ?

getback wrote:Sounds like a plan , hopefully one of the TD s will work better ?!? Slop will effect the SPI pretty bad can rob some RPMs .. What RCs do you have them on ?

I was following Amp Abuser's guidance and built a couple small and light RC speed planes. I think the smallest has 65 sq inches of wing area and weighed less than 10 ounces. Anyway, the TD's I used for this project were not the greatest specimens I've ever had but pretty good.
They were revving in the 28,000 range [in flight rpm] with APC 4.2 x 4 props
Anyway, this project "hit a wall" at 100 plus MPH and by now buying replacement TDs had already become too expensive for this "Cox TD Racing Program"........to continue. I had also just lost the last open field to land development.

I love the tinkering that needs to be done to keep Cox TDs screaming but the cost and lack of good P/L sets has spoiled the fun.
It's so much easier to bolt on a Cyclon .049 and get 100s of absolutely thrilling runs with nothing more than glow plugs changes to do

This morning I put a Product Engine P/L set on one of my mediocre TDs and it responded with 19,500 rpm with a 5x3 prop. The plane is a lot more fun and the line tension is pretty good now.

Thanks for the info on the cellophane TD…. I may have to give it a try…… Enjoy practicing those squares!!

Yesterday I was practicing my squares with my  .049 powered "stunt pattern plane"..... but it also  did a FIGURE 9 too...!

It hit the ground so hard that the engine got remounted closer to the wing and the tail turned into just a flap of wood hanging off the trailing edge of the wing..!!

So here is what the remodeled wing flies like now with a pretty healthy TD.....

I thought I lucked out with no engine damage after the crash until I noticed that a hunk of the crankcase is missing.
The reconfigured plane weighs just over 6 ounces and as you can see is much larger than the little 26 incher parked next to it. The wing is pretty weak thanks to the flexible 3/8" square leading edge and no spars.
It's just barely strong enough for the forces of flight and not having to use a pair of spars saved me about $100 worth of wood at todays prices too...!

Youza! You really put that plane through its paces. Most amazing is how consistent the engine run was, constant throaty note through its flight except for the single tiny burp near flight's end. You definitely lived up to your moniker, @TD ABUSER.

GallopingGhostler wrote: amazing is how consistent the engine run was,  

Now that you mention it I'm not sure if that run was with the big venturi or the stock one.
Years ago when I was first learning about Cox TD combat everyone was drilling out the stock venturi to 5/32"..so that's what I did to all of mine. In recent years I thought it would be nice to have a stock venturi and so now I need to go see which one I was running this morning.
I can't honestly say that I've ever done a side by side comparison to see what the rpm difference is.
The other thing to note is that this was a Product Engine P/L...not TD.
I seem to recall TDs going rich on outside maneuvers
Many engines have a tendency to go rich while doing outside maneuvers. The Fox Combat Specials do this...[which is exactly the last thing you expect a "Combat Special" with many years of design development to do.
I think the theory is puddles of fuel in the lower crankcase get sent up the boost or transfer ports due to the way G Force is felt by the puddles of fuel...?

TD ABUSER wrote:Now that you mention it I'm not sure if that run was with the big venturi or the stock one. Years ago when I was first learning about Cox TD combat everyone was drilling out the stock venturi to 5/32"..so that's what I did to all of mine. In recent years I thought it would be nice to have a stock venturi and so now I need to go see which one I was running this morning. I can't honestly say that I've ever done a side by side comparison to see what the rpm difference is.

I'm a casual observer and certainly not up-to-speed on TD .049's. I purchased my first maybe 6 - 8 months ago, when Bernie offered his new production to those who contacted him as he requested a year ago at a slight discount.

I plan to leave mine unmodified. The originators of the TD had designed the opening to suit most users. I gather it to have sufficient suction to work with natural unpressurized fuel systems.

TD ABUSER wrote:The other thing to note is that this was a Product Engine P/L...not TD.

I noticed that although RPMs were consistent, did seem a little less whine, which explains with the slightly lower performance non-SPI cylinder. However, appears you had a good propeller match to take advantage of the TD's torque characteristics, plane most certainly was not underpowered.

TD ABUSER wrote:I seem to recall TDs going rich on outside maneuvers. Many  engines have a tendency to go rich while doing outside maneuvers. The Fox Combat Specials do this...[which is exactly the last thing you expect a "Combat Special" with many years of design development to do. I think the theory is puddles of fuel in the lower crankcase get sent up the boost or transfer ports due to the way G Force is felt by the puddles of fuel...?

I really can't comment, but relay what I've gleened from discussions on Stunt Hangar.

They speak of the venerable Fox .35 Stunt engine, which when installed pancake (horizontal) in say a profile fuselage plane, had a problem of a stutter called "burp" in certain locations during stunt maneuvers.

Solution was to epoxy a flat stick of wood in the crankcase bypass, which reduced the cross sectional area, which in turn accelerated the mixture velocity, which prevented Castor oil droplettes from puddling in the bypass. Apparently the bypass was oversized to what was necessary for stunt.

This is why it is preferred to mount the Fox .35 Stunt in the upright position. I guess the same would go true to mount it inverted. It was only a problem with mounting the engine sideways.

I don't have any Fox .35 engines, only a .25 R/C, a few .15's and a Fox .09 Rocket side port, all non-Schneurle standard older cross scavenge engines. So, the discussion is academic.