Odd Job

[Graham Davies 3]

Looks great Nigel.

Drop Peter Miller a line regarding the magazine submission; I am sure he will be able to advise. I think it would be a very worthy design and I'm up for it!

Graham

[Nigel R]

Thanks Graham, DaveyP

The foamboard I used is the stuff available from Hobbycraft, four A1 sheets for a tenner.

I used medium cyano on any foamboard to balsa joins. The really thin stuff gets a bit too hot when it cures and the heat seems to melt the foam, but slower stuff seems to work ok. For wing sheeting you need PVA I guess, or a foam friendly contact adhesive like copydex (i.e. not evo stik).

I'll hold fire on any plan submission until she is flight proven!

---

A brief update:

The good:

I've run the motor up. Nice lumps, the old Surpasses. Fired straight up (after removing the flat glow stick and using my old power panel), good throttling, steady idle, all good.

However, the bad:

In the process I discover that the battery has a bad connection somewhere. I tried plugging it straight in to the RX and still found issues when waggling the wire, so either the plug, or the wire, or maybe even a connection inside the battery is flaky. Not something I want to chance. A new battery is in the post...

And the ugly:

I made pushrods using standard M2 rods & metal clevises (clevii???). The rudder and elevator pushrods are too long, and will easily bend. I will need to reinforce them. I guess the lesson is thicker rods are needed for that amount of unsupported pushrod. My (ugly) fix will be to bind some dowel or hard balsa strip to the metal and splash some fuelproofer on it.

Ah well. Best to discover these things on Terror Firmer.

Edited By Nigel R on 08/12/2020 17:40:09

[kc]

Good luck with the test flights and lets hope you can get the design published. It's always been said that to get your design published you need to have a photo of the model in flight. I don't know why they cannot just take the pilots word for it! So make sure you get some photos done by someone with enough expertise with a camera whilst the model is still pristine without oil residue or hanger rash.

Edited By kc on 08/12/2020 17:53:59

[Dwain Dibley.]

Good luck with the maiden flight, I am sure it will be a success Nigel.

I am also sure that it would be a successful/popular design/kit too.

D.D.

[Gary Manuel]

First time I've visited this thread. I must say that for an odd job made from leftover scraps, that looks really good. I hope it lives up to the design brief.

[Geoff S]

Posted by Nigel R on 08/12/2020 17:39:15:

And the ugly:

I made pushrods using standard M2 rods & metal clevises (clevii???). The rudder and elevator pushrods are too long, and will easily bend. I will need to reinforce them. I guess the lesson is thicker rods are needed for that amount of unsupported pushrod. My (ugly) fix will be to bind some dowel or hard balsa strip to the metal and splash some fuelproofer on it.

Ah well. Best to discover these things on Terror Firmer.

I use 3mm carbon tube, which has a 2mm hole. Then glue in 2mm threaded rod at each end with either epoxy, or, I think better, JB Weld Kwik. I use a standard s/s clevis at one end (at the control surface) and a ball joint at the servo end. That's so that it's very unlikely to unscrew as the plastic ball joint is very stiff on the threaded rod. They're surprisingly stiff even with no further support.

Note that if the rod should turn and both ends have fairly free threads the adjustment stays perfect right up to the point it falls off with obvious consequences.

Geoff

[Nigel R]

Thanks for the kind words gents.

Geoff I've never tried the carbon rod, where do you source it?

[Piers Bowlan]

Excellent job Nigel, looking forward to news of the maiden and subsequent plan.

[Jonathan M]

Nigel

Hyperflight are a good source for carbon rod, tubing etc: **LINK**

Odd Job looks really fabby!

[Nigel R]

A quick update. Sorry no photos - maiden day was busy enough.

 

Noise check was first order of business yesterday. The engine was wearing an APC 14x4W. I was a little surprised at this - she failed.

 

The reading from front, behind and right were all several dB over. Exhaust noise is high and the prop tips could be heard just starting to rip at full bore. Whilst it was over the 82db limit, it was not far over and I was allowed to retry with the exhaust pointed downward (grass is beautifully absorbative) and with a limited throttle opening to keep RPM down to approx 8.5k. It was then on the limit from both front and rear, so I did at least get to test fly.

 

This means I must come back next time with something changed. The silencer I fitted was the standard OS item, which a single chamber job. As I have a baffled unit from an 81-alpha which is currently spare, that will be first thing to swap, the second being a different prop. In the pocket I will keep some an exhaust extension as well.

 

The advice I have seen around noise testing suggested 350mph as a limit (although that was for conventional shaped tip props, not the nice scimitar APC). The 14x4 prop at 10k has tip speed of approx 420mph. However. The wide blade APC is, well, wide, and the tip shape is different to most APC. More akin to one of the old Graupner grey props. I know that the APC 13x6 spins at the same rpm; if I move to that prop, it has the more normal APC tip shape and the tip is moving 30mph slower at the same rpm. I also have a 14x6 handy - this would be far slower turning. I am going to try the 13x6 first; it would be nice to maintain throttle response with the lighter, smaller prop.

Following that drama, the test flight was generally drama free really - and a lot of fun ?

 

A few circuits to get the trim correct (just one or two clicks needed) and it was on to some more fun stuff. Lots of power available ("you've fitted an engine which is far too big, it should have a 40" was the comment... opinions vary). Loops are as tight as you would expect, with a dab of power to blast air over the control surfaces she can be persuaded to pull a very tight maneuver; rolls are as quick as the aileron size suggests. Hovers are quite easy (compared to my - twitchier, smaller - foamy) with half throttle, and harriers are held steady with a little juggling of throttle around the one third point. Torque roll in a hover happens quickly if ailerons are not used to hold her in place, that big prop showing its weight. She floats along at a snails pace. On-the-spot turns and in place spins are easy - to the left (torque, I guess), to the right, not so easy. Lovely.

 

I had the engine idling a touch high for the day, even a few rpm was nearly keeping her aloft, and a conventional landing actually needed a fairly long approach. In a harrier I am sure she could be brought in on the spot but that's not for the maiden.

 

There is some opposite coupling from the rudder. I didn't try much knife edge for this reason. A TX mix from rudder to aileron will be needed to remove most (or all, hopefully) of that effect in flight.

Will report back when the next noise check is done.

[Graham Davies 3]

Congratulations Nigel. Been watching with interest!

 

So, this means you can publish the plan?

 

?

 

[Jonathan M]

?  Well done!

[Nigel R]

Noise check #2 - pass. 13x6 apc and baffled silencer borrowed from os81 came several db under the limit. 

 

Sadly on flight #3 I suffered an engine cut at around 50ft whilst pointing upwards. My own fault. I ran out off talent while getting it pointing downward and moving fast enough to recover... although pulled off an absolute greaser of a landing... at altitude minus five feet.

 

Damage is repairable in short order. Prop, cowl cheeks and uc took most of the damage. Most awkward bit will be replacing the tailskid.

 

Hey ho. That'll learn me to be clever too low. Plus combination of minor engine errors, idle a bit low, needle a bit lean for throttling while pointing upward. 

Edited May 1, 2021 by Nigel R