Tee Dee Performance Crank

Ah, those are even higher in compresion than the regular TD ones.

At 20% you could well run the regular BabeBee heads, that's what the enignes came with. I have used that on 10% nitro but then it was a little under compressed. The best one, for me, has been a head that takes a turbo plug (hot OS plug).

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How about these ones?



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Very nice, photo's looks GREAT you should be proud of your efforts and enjoy!!!

How did the CG work out empty weight vs fueled? If at 17.5K rpm should unload tad over 20k -95 to 110 kmh.

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Very nice, photo's looks GREAT you should be proud of your efforts and enjoy!!!

How did the CG work out empty weight vs fueled?  If at 17.5K rpm should unload tad over 20k -95 to 110 kmh. [/quote]

Much to my surprise it is a bit tail-heavy when empty but sets the CG at about 1 inch behind the trail edge of the wind when fueled.

Yes the wider ply rather than tapered tail has added additional rearward weight and if the servo layout , rx and batteries are fixed you should still be ok. The landings should still be smooth and you will have to be light on the sticks /controls with no fuel as it will be more nimble at that stage.

Do you have a pic of the underside ?

balogh, Your airplane is looking great And can wait to see the vid of your median flight been keeping up some what with this post / there still working on the Tach race rules ... https://www.coxengineforum.com/t7382-tach-race-2015january-24th-25th  Hope it flys as good as it looks it will be dangerous    Eric

getback wrote:balogh, Your airplane is looking great And can wait to see the vid of your median flight been keeping up some what with this post / there still working on the Tach race rules ... https://www.coxengineforum.com/t7382-tach-race-2015january-24th-25th  Hope it flys as good as it looks it will be dangerous    Eric

Thanks getback, once i have a vid I will post it.

Shipping COX engines between the USA and here takes a good 2 weks or so, and if I participate in the tach race I will have to send in my engine way before. BTW I saw it is mainly reedies that are in the race? Ain't it unjust to throw in a TD whose speed is inherently above those of the reedies?

1/2A Nut wrote:Do you have a pic of the underside ?

Here you are, 1/2A Nut:




The one-cent taped to the underside of the wing is an attempt to statically balance the plane but this is before the maiden flight so I may remove that once I am through the first flight, or dig airgun pellets in the wingtip if needed at all.



The close-up from the guts is a bit disillusioning, a mess of cables that I cannot prevail upon myself to shorten because the one thing I hate is fiddling with soldering...the details of my rough craftsmanship on the woodwork is also unveiled here. I feel a bit ashamed when I think of the nice details of the planes you posted, but I have limited space and tools to work on my birds, and as said, with the manual skills of a caveman.

At this stage in the build I wouldn't worry about the details more so consistency with the planes function and if lucky some grand flying fun enjoyed! I have been designing and constructing RC crafts since 1974 so some aspects tend to be intentionally more in depth as I'm use to it.

Yes we all want to see a video if willing / able. I would suggest you take a bit of sandpaper and round off the sharp edges of the carbon tube hold downs to avoid wing damage should the rubber bands release the wing on a hard landing. I dab a bit of CA to harden the soft sanded carbon. I use 3mm wide rubber bands a set of 4 and take spares to the field. For me carbon tubes are a tad long and will inhibit the release function in a crash.


Best wishes on the flight tests.

It's looking pretty good! Your CG was about an inch back from leading edge? Also, I wanted to suggest you put some color (stripes, decals,etc.) On top or bottom of plane, fast little airplanes are easy to get disoriented. I once built a Sig Hummer in light blue...the maiden flight didn't go very well!

Yes Mark is right even if you throttle down to gain perspective sometimes the lil fast ones can get away from you. I used a large bold number 34 on one wing tip a cockpit using black sticky back trim for the Lil Speedy and red checkerboard pattern on the rudder to help determine orientation. Of course once you know your plane while flying up close can be easy enough and helps keep the plane in the comfort zone. I have ordered some transparent monokote that I may use this time around otherwise I'm still on the fence with the color scheme of the Skorch.

Mark this vid was about 14 flights under the belt, smaller size than than the 1/2A version tricky to keep up with at times.  
You can set to watch in HD 1080p to help follow along.

Mark, 1/A Nut,


thanks for the advice on decoration...you know the feeling when you are almost done with  your plane and you cannot wait anymore and go to the field...my patience is that of a taxman so I decided I would give the decorations only after the plane has survived the maiden flight ...not that I kill virgin planes too frequently but this one was built based on  dimension estimates I snatched from the pics of 1/2 A Nut, and on his remote advise blended with my gut feelings.



Here it comes already with the well deserved decorations after the maiden flight, that was recoreded on a short vid.



My wife used her tablet to shoot the vid and given the speed and the weather conditions, not too much is visible. I could only post in on youtube, have no idea how to upload a 150MB vid here...

https://youtu.be/WxebGv0EVwI

The plane was a bit tail-heavy as said, despite the near 2 oz fuel  (50 ml) it carried in its nose, so I had to push the elevator down a bit thru its 8minutes flight.

When the fuel was spent, I wanted to see how it glides...but it dropped from the sky in a nose.down spiral without reacting to the elevator and rudder moves I transmitted.

It thumped into deep grass and survived without a scratch thanks to the massive fuselage too.

I often experienced with small low-wing planes the same instability in gliding. I assume with the elevator trimmed a bit down the tail-weighted CG will be compensated...I know the elevator impact grows with the speed, but I just do not want to add balance to the nose.

Otherwise the wing bottom cord  is parallel with the horizontal stabilizer so I do not suppose the reason for the instability is aerodynamics like an offset stab or wing. As said, had the elevator been trimmed a bit down before the flight, it would have flown smooth. It flew quite well with the elevator constantly pushed down. It was just too fast to trim it mid-air.

With the elevator constantly pushed down and using the rudder and the throttle, the overcharged 300mAh RX battery had its voltage dropped from 5,2 to 5 volts during the 8 minutes run. Meaning that the esimate by 1/2A Nut the battery will sustain 6-8 flights before its voltage drops below 3,8volts was correct.

Did you ever experience something similar to the plane going spiral instead of gliding, and how did you cure that (assuming the plane survived and there was something left to cure)

I will replace the TD050 R/C - whose rpm I tached this time from the vid with my smartphone app at 16,5-17,5k so not quite bombastic - with a naked TD 049 or 051 to add more power, but before that I would like to sort out the instability in gliding. Any advice will be highly appreciated.

 

Perhaps you have room to move the battery forward and sort out the CG issue so when the power is off and the fuel has run out its not so tail heavy to flounder into a death spiral. Yes by nature of the design unlike a balsa fuselage this one one won't break in half if smacked into the ground the ply is a big plus!



Yes you always must post on You Tube then you can paste the link using the You tube tab in the posting tools.

Im happy you held it together the imbalance is difficult to deal with on a first flight, with throttle you could have backed off to 60% power and dialed in some trim just to fly with less trouble till some CG shifting can be accomplished.

After watching the vid a few times now it turns well the wing has a lot of lift and grabs air when the nose is up. There is enough rudder the tail does not wiggle or wag at speed. It appears to want to track well. The engine is running strong in dives you went over 19.6k. Once you have it trimmed out well you can make some great diving low passes and climb outs with good authority. With throttle control you and tic overhead and do nice slow fly bys and circle around up close for nice nostalgic grace. Well done I am happy for your success!

Well, the wing saddle area of the fuse is already so darn crowded and the battery is already right behind the wing saddle front former, that I do not really have too much room the reshuffle the guts so as to change the centerline. (The balloon tank is in front of the saddle former and I do not want to jam the battery here--would take up useful space of the tank and kinda bizarre setup to have the fuel and the battery share the same compartment...)

The one-cent coin from the left wing bottom was already removed and replaced by 3 airgun pelletts that I embedded in the thicker part of the wingtip near where the spar would lie. (I did not shoot them in !!! )

I wil try to trim it out with the elevator and hope that it will cure the spiral-happy instability in gliding. Did you have any experience like that with low-wingers?

This happens do to the CG being too far back during glide mode the engine running helps to control tracking. The plane stalls and the wing blankets the stabs some during glide there is less airflow over the tail surfaces CG fix should help the plane maintain forward speed and solid control.

Here is a pic showing the planes condition at launch. Slight positive wing incidence is good, the horizontal stab is in line with the thrust line this is ok as there appears to be no down thrust preset with the engine mounting. The elevator appears to have up trim.
You may need to consider leaving the TD .051 RC on the nose the weight of the muffler helps. You can add some lead on the inside up front, puddle some CA and drop the lead in the puddle to hold it in place if unable to reach into place.  Adjust it into position with a small stick.



The plane lifted up and out with ease you could tell it was going to climb out fast do to elvator position and wing attack.

Congratulations on the maiden!

The "spiraling" sounds more like a tip stall to me?
The remedy for that would be to add more wash-out to the wings.

A too rearward CG will give a plane that is very sencitive to the elevator input, but the wing should not stall at the tips due to that.

To test for CG position you can go inverted and check where the elevator needs to be. It doesn't have to be completely neutral here, a little bit of down on the elevator stick is usually good (during inverted flight).

The wing insidence might be too high, the line shown in picture above is not the interesting one. The center line of the wing goes from the forwardmost portion of the leading edge to trailing edge. I.e. the true wing incidence is higher than simply what you get from the flat underside of a wing.

I'm surpriced that it is tail heavy, it indicates that there are too heavy things behind the wing (as the nose certainly looks long enough). Perhaps the metallic pushrods and guides are too heavy. The Cox 05RC is quite heavy (perhaps the most heavy .049 there is), a TD will be much lighter so be careful with the CG position if you are changing the engine.

A rearward CG can induce a wing to stall and when this happens it will force the wing to tip off in the direction of the most stalled wing panel or weighted.

Its like flying on a ball bearing able to roll off in any direction at anytime. Wing washout forces the stalled wing to stall forward rather than off to the side avoiding a induced spiral dive which blankets the tail surfaces even further and makes it harder to recover.
A forward CG will always improve tracking in a glide, glider pilots use this to provide motive force and extend there glides as they can afford to do this having plenty of wing span to work with. All wings should have some washout. If not you must have a forward or solid CG no further back than 30% of the cord to play it safe.

[quote="Surfer_kris"]Congratulations on the maiden!

Thanks, Surfer Kris, so it looks like you and 1/2A Nut agree the plane geometry is more or less in line with the fundamentals, a downward trim on the elevator plus some relocation of the CG forward may help sort out the spiralling misbehavior?

There is not too much behind the tail, only the thin pushrods in light plastic conduits, so I cannot really relocate anything from there to the front. Maybe I wil add some weight to the nose as 1/2A Nut suggested. Or try to jam the battery in the fuel compartment...though a bit bizarre to have them sit together...

My battery is in the nose but I use a hard plastic tank. = )

1/2A Nut wrote:My battery is in the nose but I use a hard plastic tank. = )

I managed to rearrange that mess in the belly and now the battery is a bit more forward than before...

BTW a quicky to show what one can do when in a dilemma how to change out the TD 050 R/C with a TD 049/051 the latter having exhaust throttle, without modifying the throttle pushrod location in the plane:


You want to have the linkage point on the exhaust throttle barrel level with the linkage point  on the TD050 R/C arm:



The barrel has a circlip on its top which is higher than the linkage on the throttle arm.So you may want to bend an extension from a music wire that comes down from the circlip on the exhaust throttle barrel to near the engine mounting lug.

Mine was bent with the toolmaking skills of  a Cro-Magnon pre-homo sapiens, so once I have the time I will re-bend a new one to live up at least to those of a Neander-Valley caveman.,.

But  at least the idea works well on my previous R/C planes...

balogh wrote:
Thanks, Surfer Kris, so it looks like you and 1/2A Nut agree the plane geometry is more or less in line with the fundamentals, a downward trim on the elevator plus some relocation of the CG forward may help sort out the spiralling misbehavior?

There is not too much behind the tail, only the thin pushrods in light plastic conduits, so I cannot really relocate anything from there to the front. Maybe I wil add some weight to the nose as 1/2A Nut suggested. Or try to jam the battery in the fuel compartment...though a bit bizarre to have them sit together...

I'm still not sure what you mean with a spiraling behaviour, is it at low speed or high speed?

A too reward CG will give you a very sencitive elevator, but the plane will not spiral in any way.

Regarding battery placement I have once placed the battery in front of the tank, directly behind the firewall. This way the tank comes closer to the CG point and the tank level matters less.

I did a weigh in on the TDRC vs a TD throttle sleeve both had props it was just a fast weigh in the TDRC was 15.5g more.

You could add a pressure tap to increase rpm.




Just remember different CG positions will have their own effects on stall/spin behaviour was yours flat or nose down?
- rearward CG will result in a flatter spin and much more difficulty with recovery.
- forward CG makes spin entry a more difficult to induce and the nose will be lower during spin yet recovery is much easier to achieve.




Some further food for thought in lieu of a wing with dihedral.

Spiral Instability:

An aircraft with positive spiral stability tends to roll out of a turn by itself if the controls are centred. Some light aircraft with little or no wing dihedral and a large fin tend to have strong static directional stability but are not so stable laterally. If a sideslip is introduced by turbulence – and left to their own devices – such aircraft will gradually start to bank and turn, with increasing slip and hence increasing turn rate and rapid increase in height loss. The condition is spiral instability and the process is spiral divergence which, if allowed to continue and given sufficient height, will turn into a high speed spiral dive. Neutral spiral stability is the usual aim of any aircraft design.

There are several design features that stop that slip and level the wings thus promoting lateral stability, for instance placing the wing as high as possible above the cg promotes 'pendulum' stability; the feature usually employed with low wing monoplanes is wing dihedral, where the wings are tilted up from the wing root a few degrees known as angle of incidence.

Angle of incidence:

Angle of incidence is a term which is sometimes confusingly used as being synonymous with wing angle of attack, however the former cannot be altered in flight. Angle of incidence, usually just expressed as incidence, is within the province of the aircraft designer who calculates the wing aoa to be employed in the main role for which the aircraft is being designed, probably the aoa in performance cruise mode. The designer might then plan the fuselage wing mounting so that the fuselage is aligned to produce the least drag when the wing is flying at the cruise aoa. Wings which incorporate washout will have differing angles of incidence at the wing root and at the outer section. Again, the spin is a stalled condition of the aircraft. Unintentional spins can be avoided by not allowing the aircraft to stall (take immediate action to recover) and by avoiding uncoordinated flight which leads to autorotation when flying close to the stalling AOA with a rearward CG.