Rubber Powered Model Aircraft Build and Fly - The Vintage Model Co. Sparrowhawk, 20" Wingspan
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- Опубліковано 27 жов 2024
- Building and flying a vintage model company, Sparrowhawk, balsa, tissue and dope, rubber powered, free-flight, model aeroplane.
First flight and trimming flights.
Longest duration flight (so far) flight was 29 seconds on 1000 turns on a 19" long 3/16" rubber loop motor and a 7" prop.
Winding rubber is an art. When you break a motor, record the dimensions and the number of turns. Then you can calculate a turns coefficient and calculate breaking turns for other motor dimensions. You should stretch wind the motor.
Winding may be rapid at first, but you must slow as you get higher on the torque curve. Winding heats the rubber and heat increases the tension. If you wind fast, the heat can make it exceed the breaking point too soon. It is necessary to let the rubber cool as you get close to maximum turns. The last turns must be put in slowly to let the heat dissipate. More torque produces more heat per revolution.
Also, check your winder counter. I find that mine are skipping counts. This could lead to you over winding. Set to zero and count manually to 100 cranks. What does the counter say? I find that rapid winding leads to errors. The counter is accurate when cranked slowly.
Good advice.
Well done and welcome back to free flight, enjoy it before it's banned.
Honest! - It was an act of God that caused my free flight glider to exceed 400'
Ah so you know about all that, don't let it stop you building more models and I hope to see the videos
Hi Steve, Yes, I have checked the new CAA regulations and my planes/flying is exempt from the requirements to have Flyer ID or Operator ID as my planes are classed under " Toys, Small Drones and Small Model Aircraft".
The planes being: "Below 250g with no class mark and no camera. Toy or not."
It’s quite easy to build as I’m 11and I’m currently building this model
Nearly done
Post a video when you have finished the model. I'd love to see it flying. Doug
Am just about to build a Sparrowhawk also, so enjoyed watching your video, Doug. Interested in what you did with the rubber. My first build, a Vintage Models/KK Elf, nigh on exploded when I tried to give it a mere (?) 300 turns. More rubber, more lube, I guess...
Hi Michael, I have exploded a few rubber motors a well! It certainly makes a mess of the fuselage, I've had to recover the fuselage a couple of times already. I changed to a double loop of 1/8" FAI rubber rather than the 3/16" supplied in the kit. I'm still using a fairly short rubber motor and winding to about 800 turns. Tried various lubricants - everything from castor oil (messy) to silicone grease.
@@DougsShed Thanks, Doug, that’s really useful. Forgive me if you already mentioned it in the video but what did you end up finding best to use?
I've still not found a totally successful rubber lubricant - which reminds me, I must go and replace the tissue paper on the fuselage again!
There is a formula for ESTIMATING the maximum turns a motor will take before breaking.
T = LKt/sqrt(S)
T - turns
L - length of motor
Kt - empirical turns coefficient
/ - divide
sqrt(x) - square root of x
S - cross section of motor
Cross section of motor is the product of number of strands, strand width and strand thickness.
S = nwt
n - number of strands
w - width of strand
t - thickness of strand (Modern Super Sport rubber nominal thickness is 0.042″)
Kt will be different for different batches of rubber. It can vary some within a batch. It will vary with temperature. It will vary with your lubrication and winding practices. It is established through testing. Make up and wind test motors in your usual way at standard temperature, record the breaking turns and calculate values of Kt from Kt= Tsqrt(S)/L. With lengths in inches, a value of 10.5 is a safe default for modern Tan rubber. You may find values as low as 9 or as high as 13. If you need a more precise value, you must test your own rubber.
You should not use this number to decide when to stop winding your motor. It is an ESTIMATE to be used as a guide for when to pay close attention to the motor. As the motor approaches its maximum torque it will become less flexible. You can sense this by stopping your winding, letting the motor cool and giving gentle tugs on the motor. When the motor becomes very stiff it is time to stop winding. Knowing when to stop winding is a matter of judgement borne of experience. Motors that have been used may break sooner than expected. Motors that are wound fast will break sooner than expected. Motors that are allowed to cool by slowing the winding, especially at the high end, will take more turns.
Now my brain hurts!
@@DougsShed Use a pocket calculator.
sound is dreadful
Aye right pal! That is my Scottish accent.
@@DougsShed True!