PeterF
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Posts posted by PeterF
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This is an outcome of fluid flow dynamics, for a specified thrust it takes less power to move a large mass of air slowly (prop) than a small mass of air rapidly (ducted fan).
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4 hours ago, Rich Griff said:
I haven't read the above but was the nitro content dropped to 15 percent, from memory.
IIRC the government wanted to reduce it to 15%, held a consultation and got pushback from BMFA and probably the RC car fraternity and probably other users/ producers and it was set at 30% so ready mixed high nitro fuels did not get included. Can not remember the exact details.
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I am guessing you mean Tayna batteries and auto correct has changed it. They have a very good reputation.
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Richard, I have been away for a few days and missed these recent updates. I am glad you have got back to your Moth. Excellent modelling, puts some of my work in the shade, especially the slats, I simply screwed mine in place. I look forward to seeing your ongoing work and the plane flying.
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If the model needs me to cut out the formers and ribs then getting started is the rate limiting step, I do not like cutting parts, I find that I am less than accurate. Once over this stage I am OK. If it is a ready cut kit, no issues, straight in and through the build.
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Spent a lifetime designing methanol production plants, they typically produce 3,000 to 6,000 tonnes per day, but the minimum order quantity needs a small tanker (ship tanker not lorry tanker) to collect it with if you order direct.
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I have had it once on a NiCad Rx set many years ago. Someone recommended running a dehumidifier in my garage workshop to keep it drier, only run it for 2-3 hours twice a day. I have not had black wire since then, but not sure if that is due to the dehumidifier or the move away from NiCad Rx batteries.
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On 27/03/2024 at 21:05, Peter Miller said:
GReat to see Miss Lizzy. You will love her I am sure.
Yes the weight is without fuel.
ENJOY!!!!
First flights today, what a lovely plane, flew on rails straight away and inspired a lot of confidence in the first couple of minutes, well balanced, positive controls and responsive so I put it straight through most of the B test on the maiden flight without any issue. Why have I waited so long to get around to building it!!!!.
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Just completed this and ready for maiden at the weekend as weather looks more promising here in the north east.
It is Miss Lizzy, a Peter Miller plan from RCME September 2005. I am surprised how long I have had this squirrelled away, I always liked the look of it as well as the earlier smaller Tequila Sunrise. Since stashing the plan away I have swapped to electric only so I have converted this by making the space between F1 and F3 into a battery bay which has plenty of room for a 3S 5000mAh battery and cut a hatch into the top of the sheeting. Other changes are swapping the u/c to a small carbon fibre unit, 3D printing the cowl and moving the tailplane servos to the rear to offset the battery weight. The pilot and windscreen are also 3D printed. It all comes out to 4lbs 1oz including the battery and with 525W of power it should have good flight performance.
ps, I have just gone back and checked Peter's build article (RCME Miss Lizzy build article) for the weight and that states 4lb 1oz, exactly the same as I have achieved with my electric conversion. Just curious if the quoted weight is with or without fuel, mine is in flying condition including the battery weight (13oz).
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Are the ailerons the same thickness, are the control horns on the ailerons set the same distance back from the hinge line. Otherwise as per Martin, it depends how you have generated 4 servo outputs from the Tx / Rx and if all channels have the dame end points / mix.
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Here is the best one I have seen so far. I was looking at ornithopters a bit just before this topic came up. Very few commercial kits available and lots of impressive solo development that does become available. I would consider building one of these if plans were available.
https://m.youtube.com/watch?v=fBADJ7-elHQ
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One model I use an APC IC prop on is my Ripmax Rapier which runs a 9x7 at >16,000rpm in a full power dive as the motor unloads. This is on the APC limit for E props (150,000/9 = 16,700rpm) but IC at this diameter is good to higher rpm (190,000/9 = 21,100rpm).
In terms of relative performance of IC and E props, APC publish information on each prop for thrust and power at APC Performance Data.
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Here is a jointed wing ornithopter
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I use it on rudder, elevator and ailerons.
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If you swapped the gimbal leads over what about the trim switches, they will still be in the current locations. Can you get a manual for your tx.
As an aside, this is the first time that I have heard of a club specifying what mode you must fly.
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Presuming you have a hand launch Spitfire, I have a Ripmax one with 12" diameter prop and have not had any issues breaking props over 15-20 years, just make sure power is off before touching down. I do not have the brake set on the ESC so the prop is windmilling on touch down and it stops on first contact. If the brake is set and the prop stops with a blade pointing down then that can lead to breaking a blade as the brake tries to hold the blade in position.
As noted above, with the shape on the bottom of the spitfire nose, a folding prop will still sit proud if it stops when pointing down.
As you will need a larger than typical spinner, you may need a slightly smaller prop because setting 12x6 blades on a 60mm hub will give you a prop disc more than 12" .
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Just done the account update from the email, password input and all past orders and addresses are on the new system.
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Got the email, tried to log into my account last night, account not recognised, thought it was a glitch and was going to email them today. I will likewise leave them be to sort it.
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I believed the hype on Poly-C from RC World stating that it was fuel proof, I used it on a plane and ended up with a sticky mess.
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We are getting some answers here. As stated above fsa is fan swept area, i.e. the area that the fan blades sweep, the annulus between the ID of the shroud and the OD of the motor housing and to get a 100% fsa exhaust the diameter of the exhaust duct MUST be smaller than the fan shroud, i.e. the exhaust duct is always a cone reducing to the outlet to compensate for the motor. Keeping the exhaust duct at the same diameter as the fan shroud is bad news because it reduces the thrust because the air slows down. I noted above that I did some detailed thrust checks on some 55mm fans and I also looked at the effect of different sized exhaust ducts and a parallel exhaust duct with 127% fsa reduced the thrust from 825g to 739g but reduced the power as there was some energy recovery as the air velocity decreased. See the table below.
Duct type FSA, % rpm Thrust, g Power, W g/W Vel m/s No duct 100% 55260 825 492 1.68 60.5 Round 127% 55380 739 461 1.60 50.8 Oval 100% 54120 833 503 1.66 60.8 Round 100% 54300 823 504 1.63 60.5 Round 95% 53700 823 499 1.65 62.0 Round 90% 53580 820 509 1.61 63.6 Round 85% 53400 836 517 1.62 66.1 Round 80% 53040 829 523 1.59 67.9 -
I carried out some proper static thrust tests on Vasa 55mm fans with Tenshock motors (high quality gear) and at 490W I could only get 820g thrust bare fan from a 55mm fan. I find the claimed >1000g thrust at 480W to be too high, getting 20% more thrust from a fan with an FSA that is 20% smaller is just not realistic. Reducing fan size means that to get the same thrust you need a higher velocity because you have less flow area. Moving a smaller mass flow to a higher velocity is always more energy intensive which is inherent in fans, thrust is proportional to velocity^2 and power is proportional to velocity^3, ye can't break the laws of physics.
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10 hours ago, Duncan Disorderly said:
PeterF - yes I nearly jumped in with those huge Multistar LiPos and that's a really good price for all those mAhs! However, it was still a LiPo fuelling a LiPo, so I was still caught in the discharge cycle and having to second guess if tomorrow would be a good flying day. Substituting Li-ions for LiPos was the final piece of the jigsaw, as it means they can stay permanently charged (they settle down to about 4.16), seemingly without issue**, so are always ready to go. That was the bit that changed the way I went flying because it's much more like having an IC plane (or "one of the very few advantages of having an IC plane", but let's not go there...)
You must have some absolutely MASSIVE planes!
**mine are new. I'm going on Russ's version using the 18650 cells (all 120 of 'em) which is now 4 years old, so roughly 3000-3500 LiPos charged with that box.
Well the strategy is that I keep them at storage charge and at that charge I can take them to the field and use them for a flying session using my normal sized planes. However, if I go with a larger plane (largest is Tony Nijhuis Vulcan using 2 x 8S 6,250mAh) I charge the field pack up in the morning. I have a 40A charger so I can get it from storage to full in less than 1 hour at the same time as charging the batteries to take with me, load the car etc etc.
LiFePO4 is the way to go but at the time the cost of the end of line Multistar packs was much lower than an equivalent LiFePO4 pack. You can get LiFePO4 leisure batteries, 12V 100Ah for about £350 now with a built in BMS for charging and discharging as others have mentioned. You could even get bare prismatic cells and build your own, I would certainly consider this if I was doing it now and not multiple years ago.
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I put together a field pack of HobbyKing 6 parallel 6S 16,000mAh cells, these were the green 10C packs for multiro that were not sold for long as they did not appear very popular. This gives me a wapping 96Ah at nominal 24V. HK were selling these off cheaply so a good bargain for <£300 and much more capacity than a lead acid leisure battery for less weight. All day flying with some large models. It is the way to go.
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I agree with you, it is the wrong way around. Here is an extract from my go to for trimming, "Get in trim!", Bob Wasson, RCME, Aug 2008
Adjust the engine down-thrust to ensure that the model neither zooms nor dives on changing throttle settings. If it climbs after throttling back in level flight this is
symptomatic of too much down thrust, if it dives steeply, this is symptomatic of too little.
Twin EDF Lipo quandry?
in Electric Ducted Fan
Posted
Thst sounds like much to much fan for a 2700mAh battery, that size battery is typically running 55mm fans, it.might do 2 55mm fans but not 2 70mm fans. I have a model with twin 70mm fans on 4S, it pulls 105A and I use a 62500mAh battery. Your may not be that high powered but as said above, you should always have a Watt meter to check.