Peter Jenkins

No, the Red Kite has a forked tail whereas the buzzard has a triangular one. That's the main distinguishing feature. The Red kite is on the left in the photo. They are very similar in other respects. I know this because I was trying to identify whether it was a Red Kite or Buzzard flying over the house a couple of days ago so did a Google Search and got the gen!

Love the buzzard photo Kevin!

I'll have to bring mine along for some formation flying Ron!

You said it Paul!😉

Hi GG, I was just making the point that when you draw a surge of power from a battery, in this case my pack powering the motor, then there is a drop in voltage. The same holds true of a Rx pack that is independent of the Motor pack. Since Adrian is using an Opto isolated ESC then his Rx power comes from a separate battery. Perhaps I didn't explain it as well as I could have!

When I look at the power draw on the motor on my electric F3A machine, there is a significant voltage drop when a lot of power is demanded. I wonder if what you are seeing is just that. You must remember that voltage drops when there is a significant power draw from a battery. If you find that you don't have any servos hitting the stops then my observation would be that it's probably nothing to worry about. It's the issue of looking at something that we couldn't access before and being taken aback at what is happening. Remember that the IR of the battery or the BEC will have a say in what the voltage drops looks like as you draw a surge of power.

That's fine Learner. Just thought I'd throw in my penny's worth.

Hi Chris The prop hang is done at less than WOT unless you are right on the limit of 1 to 1 power to weight ratio. I am not talking about that situation. On the ground, with the aircraft restrained you place a brake on the ability of the aircraft to start moving and thus to reduce the load on the prop. For electric motors, where if you over load them they will eventually burn out trying to overcome the load on them. An IC engine will just slow down and stop in the same situation. The two power units are fundamentally different in their characteristics. For an aerobatic aircraft, whether 3D or precision aerobatics, you want more far better than 1 to 1 power to weight ratio. In the case of precision aerobatics, as opposed to 3D, you are looking to fly the aircraft at the same speed throughout the manoeuvre. So, in a large loop, you are looking for power on the way up and drag on the way down. The modern F3A machine is built to be draggy to help in this respect and the use of electric motors with ESCs that provide proportional braking is a great help. The introduction of contras and now governor ESCs moves us to a very different way of increasing drag when you want it and power when you want that. I would suggest that your experience may not have included how to set up a modern aerobatic aircraft where drag is actually quite a good thing as you are trying to operate in quite a narrow speed range. The excess power needed in precision aerobatics and the airframe drag and prop drag a way of combating the effect of gravity on up and down lines. The old F3A models were the other way around where engine power gave speed and that was needed to produce the large vertical manoeuvres since the engines were limited to 10 cc. This then evolved into todays' situation where we no longer have really fast aerobatic aircraft. In general, they look, and are, relatively slow. Next time we're up at the field I can show you what I mean. Peter

Hi Learner Good bit of data there. What I found that the figures obtained on the ground with the aircraft tethered is up to 20% higher than achieved in flight. The problem is the prop is more highly loading the motor when tethered and that will make the motor draw a higher current and therefore power. It slso means you will have less power available once airborne. I found that out with on-board telemetry! On the ground, my setup (2 mtr F3A with a 10S pack) drew 3,600 W and 99 A! I closed the throttle pdq! In the air, with the aircraft flying very slowly, I pulled to the vertical while applying full throttle and recorded just under 2,800 W and 80 A. I use a sensor called the UnisenusE. It's very light and can easily be moved from model to model. In addition to V and A it slso provides rpm and height data. The UnisensE can be set to communicate with slmost all current radio brands. I wouldn't be without it!

Hi Folks I recently received a request for help from Martin Dilly whom I met when was a member of the BMFA Council. I remember Martin being a regular contributor to Model Aircraft magazine when I first started buying it back in 1963! He was, and still is, a great free flight enthusiast and flew in many competitions representing the UK. Martin is after input on RC contest Classes and aerobatics in particular. Please read his message to me below (pdf attached) and the attached document which is where he currently is with his drafting. If you are able to fill in even a small part of the picture, please will you get in touch with me? Here’s what he sent me: Hi Peter, Some time ago I wrote a history of model flying, which was included in the earlier version of the the BMFA website. It lacks much coverage of RC contest classes and I wondered if you might be able to remedy this lack. I've attached what we have already, along with a few memory nudges to me at the end, suggesting what else might be needed. It does seem to me that there needs to be some sort of overview of the whole of model flying, so people can see what else is going on apart from what they fly themselves, as well as how we got to where we are now. Having it on the website seems the best place to make it accessible. Best regards, Martin Many thanks Peter HISTORY OF MODEL FLYING.pdf

Good choice of car Paul! I can get 2 x 2 mtr models and a 70 size model in mine and the front passenger seat can still be used!

Nutters, flying that close to themselves at that speed!

Just one more point Birgir, if you are taking off in a cross wind, as soon as the aircraft starts to move, and sometimes before if its a strong wind, the model will act like a weather cock and the fin/rudder will yaw the aircraft into wind. If you had a wind coming from the left when you take off then that will also have added to the yaw to the left. I always think to myself before I start the take off, which way will the wind swing the aircraft so which rudder to apply, left or right? On a strong wind day, you might start with rudder deflected, in the correct direction, before you apply power and then adjust with the rudder to keep the aircraft straight. Remember also that applying, say, right rudder will also cause the aircraft to roll to the right as airspeed rises so be prepared for a touch of opposite aileron to the rudder to keep the wings level - it won't be much aileron but it might stop the wing being tipped over. Also at no/low speed, especially for a high wing model, the wind can "get under" the wing and blow the model over as well. So, thinking about what the aircraft can do before you apply power will help to prevent situations like this occurring. Also, if you need to land on a runway as opposed to into wind, the cross wind take off will help you to remember that on approach the aircraft's track should be along the runway heading but the aircraft's heading will be to the windward side of the runway. As you round out to land, you will need to squeeze on enough rudder to align the aircraft's axis with the runway and the direction to move the rudder will be the same as you used for take off. Again, be ready for some opposite aileron to prevent a roll in the direction you have applied rudder. There is a lot going on when taking off and landing and indeed flying a good circuit to give a good stabilised approach path is the precursor to a good landing.

Hi Colin, quite understand. It's a shame you don't have the space to fly a schedule. I think Miss Wind is an earlier design compared with the Axiome 70 bipe. I've been flying designs from BJ Craft and each new model has benefitted from lessons learned and design changes. I started with the Agenda, then Element and now Anthem. Each has been better by small but noticeable amounts than its predecessor. However, setting up and trimming play major roles as you no doubt know. There is a 70 size bipe offered by BJ Craft that will be a more advanced design than either the Axiom or Miss Wind. This is what it looks like: https://www.bondaero.co.uk/BJ_Encourage_70/p1085152_20098103.aspx# I'm sure there will be second hand versions available at a more attractive price.

Do you fly in aerobatic competitions Colin?

Well done Simon. Look forward to seeing it in action at Knettishall.

John A wing with low torsional stiffness is a disaster waiting to go into flutter. Avoid building such wings. The best way is to use a wing box arrangement i.e. a closed tube. All aeronautical structures are like closed tubes. You are right that in the early days of trying to break the sound barrier designers did not build sufficiently stiff structures. So you got control reversal which was just the effect you mention. Once they realised that, the structure was beefed up and it didn't recur. If you do have a model with a wing of very low torsional stiffness I would suggest you don't fly it as it could end in tears!

I'd put the trim tab on the warped panel to try and unwarp the effect. You don't want to add wash in on the other wing. Why? The way a wing stalls determines how it acts when it stalls. The correct stalling sequence, for non-aerobatic aircraft, is wing root and then tips. If the tips stall first, which is what wash in will induce i.e. the wing tip is at a higher angle of attack than the wing root, the wing tips will drop and the effect will be far more dramatic than a root stall first.

Try moving the CG forward a tad. Sounds like you are close to a neutral CG with your current set up.

Simon Unfortunately, just having a single motor with a contra does not eliminate the torque effect. Yes, the propeller effects are cancelled out but the single motor still has a load to turn. The Adverrun I currently use suffers from torque effect but the TRMC, with 2 motors independently driving the props does completely eliminate the torque effect. What I have observed is that the prop effects are of a higher order of magnitude than the torque effect.

Thanks for the info Chris. That is heavy!

Hi Roy Thanks for the information. I've attached a photo of the Debowski Twin Motor Contra Rotating (TMCR) powerplant. The motors have a kv of 120 so with a 10S pack had a max rpm of around 4,800 swinging a 23x20 props front and rear. The great attraction of this setup was with 2 outrunners cooling was good and there was no maintenance of belts or gears. You did need 2 ESCs though but I found that controlling them using a Y lead to connect them to the Rx was perfectly acceptable. If my memory serves me correctly they weighed in at around 600 g. Sadly, following a failure of the JR X-bus converter board that froze the elevator and rudder control on the aircraft, terra firma put an end to its flying days. I was going to point you at his website but when I looked he seems to have taken the TMCR off it. Whether that means he's stopped making it or is about to launch a new version I shall have to wait and see. I have no idea how much the TMCR costs to make but they are selling, or were, for around £1,600 including the 2 ESCs, spinner and a toolkit. A good deal more than you spent if you exclude your time. I suspect if you include your time, depending on how you value it(!), you might be in excess of the TMCR acquisition cost! These days, there seems to be a move away from epicyclic gearboxes towards a belt and direct drive gear drive and replacing in-runners with outrunners. Most continue to cost in the £1,000 to £1,500 range though. They do not take kindly to nose overs though! I'm currently using an Adverrun V1 that is a belt and pinion drive. The early Adverruns had straight cut gears but they were soon replaced by bevel teeth that made far less noise. In fact, most of the noise is generated by the props and they do sound almost like a well silenced four stroke.

As a mztter of interest, how much has it cost to make your contra excluding the cost of the props? Be good to knos the weight as well. Commercial units for F3A are between £1,000 to £1,300. Designed for 10S and produce up to 3,600 W at around 4,000 rpm and 22 to 23 inch props. Some have 3 blade props but thd majority run 2 bladers.

I have to say that I use the UnisensE telemetry module in all my electric powered aircraft on their first flights. Ground testing is not terribly helpful. As an example, the Hacker Q80 in my Citrin pulled 3,400 W at full throttle tethered on the ground. As the motor is rated at 2,800 W I closed the throttle pdq! In the air, only once did I see more than 2,800 W and most of the time I never saw more than 2,750 W.

Hi Adrian On my F3A setup - 10S usually 5,000 mAh pack - the usual max current draw is between 80 - 84 amps with max power drawn between 2,800 W and 3,100 W. You are running 12S so I would expect that like for like current draw would be down by 20% for the same power - based on W = V x A. I would expect with the larger heavier airframe you would be back up to my sort of figures. My aircraft's AUW is a 5,150 g with the heaviest pack. What's your aircraft's AUW? I once saw a current draw of 99A but that was with my larger prop set (23 in as opposed to 22 in) and with a different motor (the TMCR as opposed to the Adverrun I'm currently using) and that was obtained by slowing the aircraft down right after take off with a fresh pack and then pulling to the vertical with full power applied immediately i.e. with maximum loading on the prop. That produced a reading of 3,600 W and 99A.