Tee Dee Performance Crank

Great looking plane Kris well done!
What is the all up weight without a cowl, do you have a pic of the underside?
When ready post a videooO

One thing to note with APC is the white stress marks that can form on the blades. I've seen this on high powered engines but never on Cox related items. As far as bushings are concerned, a piece of fuel tubing is all that's needed. I had designed APC bushings that Mike Parkin was selling on Ebay. These work very well, but prior to that, all of our high performance engines were utilizing tubing on the prop screw which was all on Cyclon's, Fora's and Profi's. Ken

I see the vid was posted back in 2009 back when the 5 x 3 props with the safety tips where marked
Cox Hobbies. Seems like a past issue yes? These days Im sure Bernie has his efforts checked. I did a flex check just now with 2 props bought under Bernies watch a black 5 x 4 and a yellow 4.5 x 4 flexed just fine no signs of brittle plastic.

Kris I remember this pic posted back in August I had zoomed in on it appears to be painted? What type of paint did you use in regards to protecting the plane from nitro? There is a special epoxy paint sold in the US for cooking ovens it only comes in a few colors I have had great success with high nitro use, very tough finish.

Surfer_kris wrote:Here is a link to the reported problems on the 5x3 props; RCU thread

The test is easy but destructive...

Shown here is a safety tip 5x3 black nylon prop of which I bought a few from COX Int'l a couple years ago. They were dead on arrival, I have never used them since I noted the fine tangential cracks on the blade.



The 5x4 black nylons, except from the mishap yesterday, never broke, when spinning 24k unloaded.

Surfer_kris wrote:The new production black cox props have had some problems, the 5x3 ones can also shred their blades around 20000rpm.

The APC props can be bought directly from APC, and the 4.75x4 is a very good prop. They need to be protected at landings though. The Norvel .049RC will spin these at around 20500rpm (10% nitro and stock muffler), while the .061 will give you an additional 2000rpm (approximately).

Here is my little speed plane, also made from sheet balsa, it just needs an engine cowl before I maiden it;

Beautiful plane, Kris..looking forward to seein a vid on the maiden..weather permitting, I guess? How much does it weigh? Do you have dihedral in the wings?

I dug through my cox props and found a 5x3 with safety tips I had bought 2 by mistake this year. It says Cox Hobbies Inc. and bent it over stress cracks appeared on the skin right away then bent some more and it snapped right in half what a waste of money. Good job I never used them, could have taken out an eye out!!

Has anyone had a response from Cox why they still sell these??

Here is a picture of the bottom side too. The wing has a square carbon fibre wing spar for strength, so no di-headral in the wing, only wash-out at the wing tips.

The weight ready to fly (but without engine cowl) is around 8.5oz. That's with a clunk tank and regular 400mAh NiMh battery, I'm a little tempted to try a balloon tank and a lighter battery though (e.g. a 500 mAh smart Lipo). That could save another oz or more of the weight I think.

The colour is a regular spray paint for cars, I have used that in the past and it has been okay with low nitro fuels, the paint will mostly see exhaust residue too. I have even once painted a plane with regular, oil-based, indoor paint. Still looks okay about 30 years later...

Should do just fine landing on grass the underside will slide to a stop. I have tried car paint it has worked for me too, long curing time before flying is the key.

Yes the smart lipo is the way to go massive weight savings!
I have posted some very new 400mah 2/3rd AAA nimh fresh on the scene a simple 4 cell pack would weigh in much less than standard AA.


The trick with the smart lipo is you need to rig up a switch bypass to the battery with a charger port as an option on the other end where the arming shunt is or you will have to open up the plane each time to arm and charge. I have to rig up mine and will post a pic. This will allow external charging and switching on and off. So its always armed but switched off at the battery. I bought a 250mah version only weighs 11g. The circuit board can be used with any lipo so change outs are easy if you need to up the mah. Note 250mah will feed 3 HS 45HB (bearings / karbonite gears) servos for 4 flight 6 - 7mins/ea. Nice thing is you can field charge direct with any voltage source up to a limit can't recall off hand. I plan to have a 2 cell lipo in the field jacked in to the charging port when not armed, should allow flying at an all day event or extend at normal pace another 3 to 4 flights.

Surfer_kris wrote:

The weight ready to fly (but without engine cowl) is around 8.5oz. That's with a clunk tank and regular 400mAh NiMh battery, I'm a little tempted to try a balloon tank and a lighter battery though (e.g. a 500 mAh smart Lipo). That could save another oz or more of the weight I think.

Wow that is pretty light, my Skortch is around 16 oz with empty balloon tank.  The battery pack is a soldered set of 4 pcs of AAA batteries providing around 800mAh.




I at least once had a low battery situation mid-air and lost the 010 driven Roaring 20...that was the green NiMH 300mAh set sold by COX Int'l and Bernie said some of those batteries had had reliability issues.

Ever since then I tend to add redundancy in RX batteries.

I might be a little obsessive with weight, but it usually makes for a much better flying plane.

Here is a size comparison to a "Yellow Jacket" from Morris hobbies, it weighs about 10oz and has unlimited vertical on the Norvel .061RC. Big loops at full throttle are a great fun.

It is the only plane that I might have made too light, so far, as it is a little hard to get it back if the fuel runs out downwind from the field...

Small price to pay for performance, plus it looks cool.

My 5 channel Skorch has a current weight less two 9g carbon geared servo's 263g / 9.27oz ready to fly with wing covering should be around 10.5 oz

Wow...I seem to be the only fat guy here with my 16 oz???

Any idea how much your 4cell pack of 800mah cells weigh?

Sanik Ni-MH 2/3AAA 1.2V 400mAh 10*30mm

http://www.ebay.com/itm/4-SANIK-iDEC...#ht_2089wt_998

Here is a major weight savor a swap out for any .020 size plane 33.9g with modified spinner and cut down steel and aluminum fins. At 1.19oz the power to weight ratio is excellent.
For use with small / low load speed props perfect for the APC 4.2 x 4.
TD .049 cylinder SPI

1/2A Nut wrote:I dug through my cox props and found a 5x3 with safety tips I had bought 2 by mistake this year. It says Cox Hobbies Inc. and bent it over stress cracks appeared on the skin right away then bent some more and it snapped right in half what a waste of money. Good job I never used them, could have taken out an eye out!!

Has anyone had a response from Cox why they still sell these??

Bernie has recommended right from the start to boil these props before use.  I have still noticed the surface cracks on a couple, but have never had one break apart from heavy impact with the ground.  I did originally mention to Bernie that I thought the prop snapped a little too easily and he was happy to send me replacements, with a reminder to boil them.  I've used a number of similar old black nylon K&B props and have never noticed any surface cracks.  I would suggest the current production Cox props shouldn't suffer the same problem.  Bernie must have had a million of the safety tip props as he happily gave them away with other orders as a bonus.

We used to boil the old topflite nylon props, but that was because they were made from pure nylon (not composite) and that goes brittle when/if it dries out.

I thought the soft cox props were made from a different material?

I have a bunch of old TF 1/2a props that I re-boil every other year and keep in a zip lock with a bit of moisture...these are purely for nostalgic period correct use. I have not had one fail when run up. The note to immerse in hot water (or boil) was because the nylon would would loose elasticity if you let them sit and dry out.

I think the note to "boil" the rubber/resin newer blades may provide some additional heat cycled stress relief and lower the depth of bend induced stress cracks...I have used all of Bernie's different variations and see no real world difference in the "as delivered" condition or any of the ones I "boiled"

My world famous figure 9 escape maneuver frequently has the prop surviving well especially with the free Yellow props Bernie gave away some while back. ( I was ordering so many must have things because of CEF postings that as a frequent buyer the yellow props soon filled one of my cigar boxes)

FYI almost ready to test out the 1/2A Skorch will post a vid when the deed is done.
Ode to the .049 engine with the race number 49





May attempt to razor blade a sticker logo of this for the wing

Congrats 1/2A Nut, a beautifully slender Skorch I am sure this will be a helluva racer. Mine that I made based on your advice flies like hell.
The postman has just delivered to me 3 NIB TD 049 thin-walled stepped cylinders crispy and fresh from the 70'-s, and I seem to be already well furnished to continue my experience with TD powered craft for many yeards to come (I only have to survive).




All the Best Wishes for a Happy new Year.

Thank you András,

Im glad to hear yours has been keeping you happy = ) Let me know if you should capture any new video.

Nice collection of the vintage thin walled cylinders!
They should be well matched cylinders to pistons and are of the day when the founder Leroy was still influencing the product line.

If these are indeed the thin walled versions be careful with them not to push too much rpm as Cox made a purpose move to thicker walled cylinders to avoid cracks that would sometime appear around between the exhaust ports. The competition guys had pushed them to failure.

Again these will be very well matched and yield fantastic duty life for flying most likely to 23k. Perhaps Medium compression glow plugs with 2 shims will allow the rpm to exceed expectations by keeping the pressure down.
For sure use 2 to 3 shims with a high compression glow plug if  using 20 to 30% nitro. If with 10 to 15% you may do just fine on 1 shim with a high compression plug. Big props will lag the combustion cycle and extend the peak stress time on the cylinder walls as you can imagine. The thin walled version really had to be pushed hard to cause them to crack perhaps up to a 10% chance and that was enough to prompt change. Maybe someone has some further insights and can chime in.

Thanks 1/2 A Nut. I have very positive experience with thin wall cylinders retaining excellent compression even after 100+ hours runtime.

Contrary to my expectation based on old-stock thin wall stepped No 4 and No 5 cylinders that came mounted on my NIB engines, these spare cylinders do not seem to have tapered bore. (I checked on all my old-stock 049 and 051 TD-s with stepped cylinders the TDC pinch is there).

These 3 sets may originate from times when COX, in an effort to cut costs, may have given up tapering but the thin wall cylinder (a further cost cut with reduced machiuning time) was not yet introduced.

I will just let them spin at whatever speed they can develop with the 5x4 Thimble Drome props. My old 051 that you also tached on the video as running 22-24k unloaded does not really seem to recognize that in principle an engine is supposed to wear off with time...this one just does not.