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Member postings for Peter Jenkins

Here is a list of all the postings Peter Jenkins has made in our forums. Click on a thread name to jump to the thread.

Thread: Electric powering a Biplane or twin
31/07/2019 00:31:44
Posted by i12fly on 30/07/2019 23:13:51:

We generally accept that the power required for a moderately aerobatic monoplane is 100 W/lb.

Depends what you mean by moderately aerobatic. A competition aerobatic model (F3A) has around 250 W/Lb or more. Like I say, it depends on what you mean by moderately aerobatic but I would not consider 100 W/Lb adequate for even moderate aerobatics.

Thread: Battery
27/07/2019 09:49:40

Hi Kim, the noise of a petrol genny, particularly a Honda, is pretty low, and is at ground level. A petrol engine in flight, unless properly silenced, or a glow will have the ability to spread the noise a considerable distance. Remember, people are happy to put up with the noise of their neighbour spending 2 or more hours with a much noisier petrol lawn mower but immediately complain if they can hear a much lower noise that comes from the air.

As has been said above, high revving electric motors, particularly ducted fan, do emit a particularly annoying noise but, being high frequency get attenuated more than lower frequency sound. I do know that none of my 2 mtr electric aerobatic machines can pass the 82 db sound check. Does this matter? No, because in the air they are never stationary when full power is demanded. That is the biggest problem with the niise test but that's off topic!

So, yes, it could be just you 😎

24/07/2019 23:42:05

My experience with field charging with a 110 Ah leisure battery was not good. I use a 2 x 5S 5000 mah packs connected as 10S but charged as 2 x 5S so 10000 mah. The battery, new and fully charged managed not quite 3 charges of the 2 x 5S packs. As mentioned above, the battery is very heavy and after several experiences of not quite 3 charges in the field before the battery was down to just under 12 volts. I decided that the cost of a new Leisure Battery was balanced by buying 3 more flight packs. I now take 6 flight packs with me and bring them home to charge them. I should explain that I fly F3A aerobatics so flying 6 schedules in a session, usually half a day, is about all I can cope with.

A genny was something I also considered but then you have to add in the weight of the genny and the space needed in the car for it plus the need to carry petroil (OK you probably don't need to take any with you provided you remember to fill the tank before leaving home).

Thread: CofG
21/07/2019 21:49:40

Good luck Martin. Be interesting to hear how things pan out. Another learning opportunity.

21/07/2019 09:17:22

Well Martin, I am still more inclined to a thrust line issue than CG issue. By the way, does operating the u/c cause any significant CG change?

20/07/2019 22:56:21

0.8 deg on wing incidence is quite a lot Martin. I would consider reducing that and see if that helps.

Thread: Model vs Trees
20/07/2019 22:11:05

Quite right Terry.

Thread: Who says flying thermal soarers is boring?
20/07/2019 00:09:51

FilmBuff - the heading says thermal soarers and yet you have a hot liner in your video. Rather different don't you think? Don't get me wrong, I used to fly full size thermal soarers and it was a fantastic sport but have yet to fly model ones.

Thread: Model vs Trees
19/07/2019 23:57:14

Hi Levanter

I think you'll find that the pitch down is due to the thrust being pulled back to idle which is what you want. Once the required rate of descent is reached that's when the elevator is used to nail the descent speed which will not be Vne - velocity never to be exceeded. That is the edge of the flight envelope and airlines don't normally like to have their aircraft at that speed since the slightest turbulence will most likely push you into an overspeed or overstress situation. The acronym is PAT, power, attitude and trim, in order, to move from any trimmed condition to another.

If an automatic approach is flown it is always much smoother than a manually flown one where the auto throttle is disengaged as well. We looked at engine usage in auto throttle and manual throttle cases and found that there were many more throttle movements and larger ones at that, when the aircrew were flying the aircraft fully in manual. This is a function of human time constant not being able to keep up with the machine! That's why you will find that most airlines encourage the use of the autopilot to fly the aircraft down to almost touchdown since the amount of airframe and engine life used is minimised.

Thread: CofG
19/07/2019 23:42:11

Be interesting to hear how you get on with the incidence check Martin.

Thread: Saito 62 in a Gangster lite?
19/07/2019 23:40:06

If you liked the Gangster lite, you might like to see if there are any unstarted Gangster 75 kits around. I was lucky enough to get one and it flies very nicely. Unfortunately, it's a bit on the heavy side even with a ST 90 on a pipe!

Gangster 87.jpg

Thread: Model vs Trees
19/07/2019 18:45:01

Hi Rob and Martin

Well, I was taught elevator for speed and throttle for altitude on full size. Worked well for me on Cessna 150, 172 and Piper Cub. I also flew and instructed on gliders and again the airbrakes were always the go to for adjusting the aiming point with the elevator used for speed control. Clearly, as you closed the airbrakes the speed went up unless you applied aft stick. Having sat next to the pilot in a Hunter on approach it also looked like, once established on approach, height control was from the throttle. Pilots were taught not to allow too high a nose angle on landing as the tail bumper arrived first and put the aircraft into Cat 3 damage territory!

I suspect that the issue of where the aircraft sits on the drag curve on approach also has a bearing on the way you handle airspeed and altitude adjustment. I know that for delta wings it is possible to get into a position where even full power will still not accelerate the aircraft and you must lower the AoA to get your speed up since deltas do not exhibit the normal behaviour of straight wings. Indeed, I once had a delta wing at around 80 deg in a smoke tunnel with both vortices functioning perfectly. The slightest yaw destroyed the vortex on the less swept leading edge. The power needed to maintain an 80 deg AoA would have been phenomenal and the pilot would have just been looking at blue sky!

I have always used the elevator controls speed, throttle controls height on approach with models. My experience has been that you get into a lot of porpoising with the opposite technique and lots of bent aircraft.

I have zero experience of flying heavy aircraft and so Rob your experience speaks for itself. However, I watch lots of pilots flying F3A (competition aerobatics) and by listening to the motor usage on approach, they all use the technique that I have mentioned above. F3A undercarriages are not the most robust and yet you hardly ever see any landing accidents or incidents with these 2 mtr aerobatic birds. Landing in high cross winds, i.e. 20 kt 90 deg cross wind, is another story however!

Perhaps this is an issue that needs to be addressed when flying high wing loaded aircraft that are operating on the wrong side of the drag curve.

Peter

Thread: CofG
19/07/2019 18:26:37

Hi Martin

If t/l is OK then the usual other suspect is wing incidence. I presume you have checked this but if not worth doing. I would not have thought that moving CG will have too much effect on the tendency to climb as it's primarily stability that you are affecting. Would the wing fairings be contributing to the problem? Not easy to fix if they were mind you!

Having said that, is it worth trying to engineer some downthrust into the setup to try out the effect it has on the problem? Appreciate that the spinner alignment will be ugly but worth trying. I cannot think of anything else that would solve the problem you have.

Good luck.

Peter

Thread: Model vs Trees
19/07/2019 00:21:57

Hi John, well I hope those who are training your new pilots impress on them not to make tight turns in the circuit. Provided they are encouraged to maintain a constant descent using the throttle to control the rate of descent and not the elevator then they should avoid the problem you describe. There is a lot going on during the base and final leg of a circuit but that's why it's usually taught at the end of learning how to fly. The other thing that helps is not have too much control movement as that can lead to pilot induced oscillation and eventually a hard arrival.

18/07/2019 19:12:48
Posted by J D 8 on 18/07/2019 17:55:21:

One feature of model flying I have never been keen on which is often taught is the square circuit / approach, downwind leg, 90 degree turn onto base leg, 90 degree turn onto final approach.

Usually fine with trainer and lightly loaded types but when pilots move on to more advanced types the extra gee in those turns can provoke a stall more so if the downwind turn problem is factored in.

I prefer a more oval descending turn starting at the end of the downwind leg.

JD8, I cannot agree that flying a square circuit with a non trainer is any more likely to provoke a stall. Provided you keep your bank angle to not more than 45 deg and you can also add a whiff of power, as we were taught in full size, you are quite safe. I fly both types and have never experienced a stall in the turn - to date at any rate! Provided you are following a descending path and have a good idea of what your aircraft feels like as she gets slow you should not have any difficulty, If you do, then the answer is to practice some more and not shy away from a standard manoeuvre. Why else would the requirement exist for a rectangular circuit if it were more dangerous. I think this is another myth that needs to be challenged.

18/07/2019 12:24:36

I heartily concur with Martin Harris. All I would add is that if you need to commence your descent on the downwind leg then reducing the throttle in order to commence the descent is fine. Many pilots tend to close the throttle completely and just use the elevator until they land. Unless you are high, this is poor practice as the elevator controls speed and throttle controls height. Too high an approach speed will mean the aircraft will float a long way and may still have flying speed at the end of the strip. Too low a flying speed and you run the danger of stalling. Practice the right speed at a safe height - generally speaking a shallow descent with 1/4 throttle is good. If you are in danger of undershooting add sufficient power to flatten the flight path so you can reach tge strip and then return to 1/4 throttle or less. Maintain the attitude of the aircraft with the elevator so speed remains constant. As you begin the round out close the throttle. It is worth spending time on getting landing in the right place at the right speed right as it helps to reduce damage. Always overshoot if things start to go wrong and have another attempt.

16/07/2019 23:53:09
Posted by Sam Longley on 16/07/2019 18:50:43:
Posted by Levanter on 25/01/2019 07:38:08:

Taken to extreme and the windspeed is greater than the airspeed and the aircraft can appear to stand still or even go backwards! But we all know that is "impossible" in aerodynamic terms zo we readily accept the concept of a headwind. . It also explains the common and infamous stall on the downwind turn.

I suppose it would be too much of a thread drift to ask for you to elucidate a bit more on that onewink

The infamous stall on the downwind leg is caused by pilots thinking that a high downwind ground speed can be reduced by reducing airspeed! The result, is the infamous stall on the downwind leg.

It is quire surprising how many experienced pilots, and even an examiner on one occasion, do not understand the vital difference between air speed and ground speed.

An earlier comment by Simon Cragg falls into that category.

Where things do get confused is when you are descending through a wind gradient (that is wind speed reducing as you approach the ground - exactly like the boundary layer on the wing). In this case, you need to increase your approach speed when landing otherwise as you descend your airspeed will drop away as the speed of the block of air reduces. That is unless you have a very light foamy that immediately reacts to the change in airspeed.

Aerodynamics is not something most model pilots have studied. Where they have it tends to be at a very basic level. Some of us who post on here actually have studied aerodynamics to degree level, have done flight test courses and flew full size power and gliders. It's up to you if you wish to ignore the advice but don't complain when you end up with a broken aeroplane because you ignored the advice.

Thread: CofG
08/07/2019 00:17:10

And the real ones didn't have side thrust as far as I'm aware so double jeopardy! Alternatively, you could resort to using a gyro in pitch to look after the problem for you.

07/07/2019 01:20:06

Martin, as you will know from your F3A days, if thrust line is wrong, tinkering with a mix will only work at one speed. I would think that your best bet is to bite the bullet and fix the thrustline mechanically.

Thread: Beginner to telemetry
07/07/2019 01:16:34

The SM ModelBau Unisens-E is worth considering. Check out the English translation of the manual .

The Unisens-E can be hooked up to Futaba as well as 6 other radio brands. I use it on my JR Rx/Tx and it provides me with a wide range of telemetry from one small sensor package. While this is primarily aimed at electric propulsion, you could also use it for gliders and IC aircraft. At around Euro 65 or so plus p&P, it is quite competitive if you want to have several areas monitored.

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