Easy Built Hellcat

[Piecost]

8 May 2026

My first outdoor flying session of the year was under stormy clouds, but light winds. This was a couple of hours before sunset so coincided with the reduction in breeze strength and reduced the risk of strong thermals beneith the towering cumulous clouds.

I had intended to confirm that the trim was unchanged from last summer, then to trim the tips of the original propeller to enable a thinner motor to be used. As usual, my plan did not survive long and differed from reality.

I had found a graph of typical motor width versus total model mass [see attached] Considering the total mass of just under 100g, the graph suggested a motor width of just over 1 inch, whereas I have employed 8 strands of 3/16 which is 1.5 inches. This confirms calgoddard's employment of 8 strands of 1/8" as being about right.

For this evening; I installed the last used 25g motor of 8 strands of 3/16" with the original 35 degree pitch propeller.

I employed my new torque meter as a replacement for the spacer with my blast tube. This worked very well and I was very pleased with it.

I started very conservatively at 50 turns to get a powered glide. Even with the Gurney replaced; the model often turned right under power and left on the glide.

I did not realise that the LH yaw rudder Gurney had fallen off. Its replacement did not prevent the model turning right under power.

I tried reducing the right thrust, but I was at the extreme limit of the adjustment, so inadvertantly reduced down thrust as well. This caused a zoom climb and a stall into a turn.

I tried launching left wing low to force the turn direction but it caused a tight left turn and spiral dive.So, I reverted  to wings level launches.

I packed 1/16" under the tailplane leading edge in a desperate attempt to kill the zoom. This seemed to help and since the model landed with some turns remaining; the glide was not compromised.

I worked up to 260 turns and 450 g.cm torque. The model gently climbed up to a dozen feet with a right turn; transitioning to a slight left as the power came off. It coped well with the turbulance; demonstrating ample stability.

I was a little frustrated that I had lost the trim from last year, but was happy that the model still worked and I finished the session without damage.

I think that it is not worth spending more time getting the old trim back with the too chunky motor. So, I will switch to the 32.5 degree propeller and revert to the 8 strand of 1/8" motor. If that is still underpowered then I will switch to the 30 degree propeller.

I will also remove some noseweight to achieve the Deloach/McCombs recommended CG position. I hope that this needs a more moderate thrustline adjustments.

[Jmk89]

I employed my new torque meter as a replacement for the spacer with my blast tube. This worked very well and I was very pleased with it.

Is the torque meter home made or bought in? Either way, I'm interested in some details, if you would give them.

[Crabby]

I made a torque meter and bought one. My reason was it's a way more accurate way to get repeat results than counting winds. My home-made torque meter was very good but it broke because of ham-fisted soldering. The bought one serves me well.

 Piecost,Great patience is exhibited in your trimming. Frustrations lead to a knit brow but stiff upper lip and one muddles on as they must.

I love the Hellcat, the real one almost as much as the model.

[OZPAF]

Even with the Gurney replaced; the model often turned right under power and left on the glide.

I wonder if the right wing is twisting under power and generating excessive washout?

John

[Piecost]

Jeremy,

Find below a link to my homemade torque meter.

https://hpa.aeromodelling.gr/index.php?topic=337.0#new

[Piecost]

28 July 2026

I took advantage of the ongoing fantastic weather to have a flying session with the Hellcat.

I had constructed two new propellers; with 32.5 and 30 degrees pitch at 50% radius. The original had copied the 35 degree pitch seen on a Maxfliart video. I speculated that the plastic used to construct my propeller was too flexible and was increasing pitch in flight. Thus too thick a motor was needed.

I chose the new 30 degree propeller since I had made the Reverse S hook the wrong way round on the other new propeller!

I made up an 8 strand motor of 1/8" weighing 25g (strip length of 316") However; even after significant pre-tensioning turns the motor was still double  the prop to peg length. This might cuase catastrophic bunching in flight.

So, I made up a 20g motor of 8 strands of 1/8" . (Strip length 240") This was 30" long without pretensioning turns and 11" with 800 Pre-tensioning turns. This sounds a lot; they were applied to the single 120" loop; before it was doubled and then doubled again to form 8 strands. Does this make the effective pretensioning turns only 400? I am not sure how this works on an 8 strand motor.

I adjusted the noseweight to achieve the CG at the Deloach/McCombs recommended location (30% amc). This corresponded to 7mm forward of the front spar. I was hoping that this would reduce the thrust line adjustments needed. I was to be disapointed.

The model was still equipped with a massive LH yaw Gurney but none on the (warped) wings.

I spent many flights increasing the turns and adjusting the thrustline, untill I reached very little RH thrust and the maximum down thrust available. I was disapointed in, again, maxing out the downthrust adjustment and still getting zoom climbs and stalls.

A consistent pattern, over the range of turns, was a straight, steep climb to a stall or two followed by a lovely, floating LH turn as the turns ran down. I resorted to launching with the LH wing 30 to 45 degrees low to kill the climb/stall and force the turn. This was not consistantly successful and I want to remove the nessesity for this unelegant expediant. I did not want to compromise the nice glide by adding roll Gurneys.I was pleased in not needing any packing under the tailplane

I worked up to 800 turns and 440g.cm (6.1oz.in) which is only about 60% of the linear cruise range of the motor. I was only achieving under 20 seconds duration with about 60% cruise turns. Whilst, the stalls were wasting much energy; perhaps the model was still over-propped.

I had reached the limit of the thrust adjustment before reaching the full potential if the motor.

Going forward; I see that I have 2 options.
1. Perform surgary on the nose block to allow slight LH thrust. Sounds odd to need LH thrust at all. Any thoughts anyone?
2. Progressively trim the propeller tips, by 1/4" each time, say, to reduce the diameter. This should reduce the destabalising effect of the prop and thus the thrust line adjustments required. It will bring it closer to the 9" Gizmogeeza prop used by calgoddard on his nice model, and follows his reccomendation.

The flexible neoprene O-Ring on the propeller end of the motor worked ok; except that on high torque the Ring twisted, itself, a few turns and motor tended to climb the hook at 90 degrees to the prop shaft.  The resulting vibration caused the tailplane flap in sympathy. It was also a handful on high torque; much care needed to not let the slimey twisty O-Ring escape my grasp.

I attach a dramatic photo of the model trying to screw itself into the dry grass.

[OZPAF]

Hmm! I think it is possible that the fuselage may be twisting with motor torque generating washout in the right wing and washin on the left. This would account for the strong right turns with a fair bit of power.

As for the Zoom on launch - my feeling is that the decalage may be too much for the power that it is flying with. Perhaps raising the LE of the stab and moving the CG back to regain the power off glide, may help.

I hope this helps.

I'm surprised the Deloach settings didn't work , but this may also relate to the power loading.

Good luck
John

[billdennis747]

20g in a 60g model? "Most scale rubber models are overpowered and underwound."
J O'Donnell