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Panther Trainer Autogyro

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Panther Autogyro

Panther Autogyro

info for builders of RCM&E's March 2013 free plan

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Second Time Around

Second Time Around

Colin Budds rediscovers his love of autogyros

Big T02/06/2016 09:38:49
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214 forum posts
202 photos

I get all of my alloy sheet and strip from http://www.mallardmetals.co.uk. He is a very friendly man, if you ring him and have a chat he will send you exactly the dimension you need. As far as a steerable tail wheel, in my opinion it's not needed, I just put in a skid. The rudder is plenty big enough to swing the tail and in any case you will need a more forward cg at first but that depends on the size of lipo, or are you going glow? BTW rumour has it that coolwinds have a limited supply of ready made blades in stock.

Richard Harris02/06/2016 09:51:32
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2033 forum posts
1865 photos

Tim,

Thanks for that I will give them a bell, they are in Birmingham so not that far away, what grade alloy have you used?

This version will be electric and has a slightly longer nose as per the original.

Rich

Richard Harris02/06/2016 09:51:35
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2033 forum posts
1865 photos

'fat fingers' = double post!

Edited By Richard Harris on 02/06/2016 09:52:15

Big T02/06/2016 10:31:36
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214 forum posts
202 photos

HE 30 now called 6082.

Richard Harris08/06/2016 19:03:42
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2033 forum posts
1865 photos

Had a ride over to Mallard metals this afternoon and it is a very nice and helpful gent working from his garage! He had me sorted with the 1/8" x 3/4" x 1metre long length of 6082 aluminium, with minimal overheads it cost me a mere £3.50! I explained the needs of us modellers and he is quite happy to help any requests, I will certainly be using him again.

Thanks for the link Tim

Rich

Erfolg08/06/2016 20:38:13
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11211 forum posts
1118 photos

I am not familiar with 6082, although i understand that it does not work harden. Yet it can be heat treated, to make a strong UC ?

I understand that 6061 can be precipitation hardened. I believe that 7005 can be hardened by heating and cooling in air.

Yet the reality seems to be that where i live, getting my hands on any quality aluminium will not happen. Even though just a few miles away is a BAE aircraft site.

In fact I gave the scrap man a sheet of silicon aluminium, as it is useless for modelling. May be the most affordable aluminium for making electric/control cabinets, yet is a waste of space for UC legs.

I am so envious. crying 2

Richard Harris08/06/2016 22:46:23
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2033 forum posts
1865 photos

Carl,

The material is the same as on my original Panther and that has been flying for a good few years now, despite a few heavy landings I have only needed to straighten it once.

No need to be envious,they have a mail order service, what the postage cost are I have no idea but there is an online enquiry form, or just ring them and get a quotation.

Rich

don cardy06/01/2017 17:19:38
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19 forum posts
37 photos

Having just built a Panther and completing a maiden flight I thought it would be worthwhile recording some of my experiences. My Panther uses all the electrics from a crashed ARF autogyro from which I was trying to gain easy experience before launching out on a large Cierva C30A project! I'm glad I've changed. The plan and the laser-cut parts arrived in good time and I started construction. The plans were very clear and I made rapid progress but soon realised that they said nothing about the initial settings of the direct control head. This detail was probably set out in the RCME articles of March and April 2013 and I had neither of these editions. The "modelflying" website list reprints but a click on the lead only came up with "page not found". Physical copies of these editions are no longer available so having considered the digital archive I took the easy way out and found copies of back numbers on ebay. At last I could get things set up and ensure that the neutral positions of the gymbal and its travel were correct. It was at this point that I noticed that the motor needed side-thrust (not noted on the plan) so this required some corrective work to the motor mounting and the cowling. Then there was the issue of the undercarriage. Nothing ready made could be found so like others I was into sourcing a suitable.supply of alloy bar. I found a helpful local supplier of non-ferrous metals and bought some 1" x 1/8" 6082 T6 bar. This was immensely tough but I managed to bend it well enough making sure I got it right first time using a cardboard template. I found that the fixing hole centres given on the plan at 2x35mm = 70mm apart were wrong and needed to be 60mm if captive nuts on the floor of the fuselage were to be used (ought the plan to be corrected?). When making the blades my previous experience with Morley helicopters back in the 1970s proved to be invaluable. There were quite wide differences in the weights of the three blades according to our kitchen scales and I corrected this with quite large panel pins which I buried in the underside of the balsa part of the blades secured with epoxy in positions along the blades which ensured that the balance point of all the blades was identical. The rotor ran very smoothly on a little motor driven test rig which I have and did so in flight too. The use of shims to give negative blade incidence turned out to be problematic if the blades moved in the lead-lag direction because the amount of contact with the rotor's triangular plate was minimal and they would pop out at its edge. Originally the rotor would not spin up well on my initial take-off hop tests and so I increased the negative incidence. After a successful hop I measured the negative incidence of the flat underside of the blades relative to the triangular plate at 2 degrees and then added an extra bit of ply to thicken the reinforcement plates on the underside of the blades before sanding these to give the required relative negative incidence. The blades now move very smoothly in the lead-lag direction and there are no shims to pop out. All in all I think the design of Panther is brilliant. However, perhaps after three plus years the publishers of the plan could arrange for an issue 2 with corrections and with notes about side-thrust and the gymbal set-up?

Don

Richard Harris06/01/2017 18:14:29
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2033 forum posts
1865 photos

Hi Don,

As you are aware the Panther was covered over two issues and soon became sold out, I believe that RCM&E don't reprint but certainly offered a digital issues soon after. It was re printed in the Model flying .co.uk workshop special which included all of the write up of the first two original issues about 12-18 months later but I think that this is now sold out.

Failing all of that the Panther has been covered in great detail on this very thread by myself and some very experienced builders who have all added some great ideas along the way.

There are many gyronuts out there who, like me, are more than willing to give our help and advice, the only daft question is the one that is never asked and we have all been there smile

As it happens I am just finishing my 4th Panther for a friend, I can pop up a few photos up if you think this would helps in any way?

Thanks for the complements on the Panther, always good to hear as a designer thumbs up, has your flown yet? Any photos?

I do keep thinking of drawing up a slightly larger version for a 60, though not right now. Interest in this would certainly light the Panther fuse again?

Rich

don cardy06/01/2017 20:06:13
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19 forum posts
37 photos

Hi Rich,

Thanks for your comments. Yes, it has flown. It's maiden flight was yesterday and it landed in one piece despite this pilot having had no previous experience of autogyros. It was here that I found your videos particularly valuable in the run-up to the maiden flight. Although I do a bit of fixed wing flying much of my time had been spend in model helicopter development where gentle realistic flying is my interest, not aerobatics. Over the last two years I've perfected a NOTAR model using an EDF to power the tail boom. The April 2015 edition of Model Helicopter World in "Scale by Scale" had my article on the early "proof of concept" experiments. Sadly with the cessation of MHW I haven't been able to do a part 2 update, but an article is with a Traplet stablemate and I'm hoping will see the light of day soon.

I've long been interested in the history of helicopter development and was aware of the significance of the autogiro development in the 1920/30s. Your history article in the February 2013 RCME (also bought over ebay) covers it very well. It's for this reason I decided to have a go, as a new project, at a stand-off scale Cierva C30A from scratch with a 6 ft rotor. I have much background material from when I used to do talks and demos locally on the subject. This includes stuff relating to Hafner's work as well as Cierva's. Maybe we'll even get round to jumping take-off?

I hope this explains why, when I decided to order a Panther plan, I had no awareness of the background material you refer too. I was busy doing other things. And I guess this will apply more and more as time passes and other modellers decide to have a go at something new. The club members who witnessed my flight yesterday were "tickled pink" with the "swooshing" noise Panther made and perhaps now someone else in the club will have a go?

The only pics I have were taken indoors but when I've some taken outdoors and mastered how to attach them to a reply I'll send you something. My Facebook page has a couple of pics.

Don

 

Edited By don cardy on 06/01/2017 20:10:20

don cardy16/01/2017 12:49:00
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19 forum posts
37 photos

Hi Rich,

At last some pictures taken outside. This first one now includes a pre-rotation system based on one obtained from the far-east which I had fitted to my ARF model before its early demise and which then provided the mechanical parts for Panther. Thus this Panther uses the main motor (a prop adapter was needed), the servos and push-rods, the wheels, the gymbal control arms (as axles for the under-carriage), and the LiPo from the crash site. It was after my Panther's maiden flight that I decided to fit the pre-rotation system. My club's take-off and landing area is virtually square and works well for fixed wing and helicopter model but in calm weather the available length of take-off run seemed very marginal on my Panther's maiden flight. My pre-rotation system has been re-engineered to use the bearings, main shaft (cut-down), main gear and one-way bearing from a mini-Titan helicopter. The bearing block is made from four pieces of MDF glued together rather like your head-set system, and then turned on a small lathe to tidy it up and house the ball races. A long 2mm pin (instead of bolt) acts to link the one-way bearing sleeve with the main shaft and with the triangular rotor plate. The design is quite compact with the rotor plate being only about 5mm higher than on the original head-set with plain bearings.

Don

p1080545.jpg

don cardy16/01/2017 14:42:57
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19 forum posts
37 photos

To additional pictures.

The first is a close-up of the Panther's pre-rotation system; the second has my NOTAR helicopter in the background. This project has occupied me for the last two years and has fully working Coanda-slots in the EDF powered tailboom. Panther and what follows are expected to provide new challenges.

Don

p1080546.jpg

p1080548.jpg

BILL PETTIT16/01/2017 15:01:27
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230 forum posts
75 photos

Oh baby Don I am so looking forward to seeing a short video of the rotor in action, I have been struggling with my version. Your panther looks AWSOME! Bill

Richard Harris17/01/2017 19:43:50
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2033 forum posts
1865 photos

I will second that , it's a Sterling job Don thumbs up

Your spindle and pre-rotator look to be well thought out, do you know the ratio between the gears and the KV of the motor?

Though not my thing the helicopter looks like it has raised some interesting engineering challenges, interestingly I have found that the majority of gyronuts have a fixed wing background.

It would be interesting to know your thoughts on how flying your Panther compares to your helicopters?

It does need someone in the office mind wink 2

Rich

don cardy17/01/2017 20:53:15
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19 forum posts
37 photos

Rich,

The motor for the pre-rotator is 820KV, the pinion is 12T and the main gear 150T. The motor is really only for 2 or 3 cells and I'm running the Panther on 4 cells so have to keep the power to the pre-rotator turned down a bit. I ran the pre-rotator up with Panther sitting on the bed in our spare bedroom a couple of days ago and at half throttle on the TX slider control it was running smoothly at 500 rpm according to my tachometer. This seemed quite good to me as one of the contributors to this thread had, I think, measured about 700 rpm using a data logger in flight. Clearly a bit more throttle on the TX would probably have got to 700 rpm, but not indoors!

Now I hadn't done the calculation before but if we say that half throttle is equivalent to 2 cells then the formula, ignoring any efficiency factors, gives 2 cells x 3.7 v x 820 KV x 12 T / 150T = 485 rpm. Wow, what a surprise when theory works out as close as that!

I took Panther out this morning. There was hardly any wind. I first flew my small Stearman biplane and its take off run on our grass strip, muddy with worm casts, was at least 10 metres. I then switched to Panther and ran the rotor up using the prerotator, probably to a bit beyond 500 rpm. Leaving the rotor at its neutral pitch position (+ 6 degrees), I shut down the pre-rotator and at the same time gently opened up the main motor. The take off run was less than for the Stearman , I'd say 6 or 7 metres. and Panther climbed gently away. I completed several LH circuits and then noticed at the end of an up-wind leg that the aileron control was getting sluggish. I decided it was time to land but half-way down the down wind leg couldn't prevent Panther spiraling in. Damage wasn't that bad, one broken rotor blade; the pre-rotator had a very slightly bent shaft which I have since straightened (helicopter experience) so it's prefect again; and the main motor, firewall and cowling ripped out of the fuselage. Nothing else. I shall now repair the front with a longer bay for the battery etc, and a shorter motor compartment. I'm also swapping the servos for new ones whose spec I know and replacing the ESC / BEC too.

Reminds me of my early days with Morley helicopters when I had to teach myself to fly and had to put the tail boom back together nearly every week. I also had to make rotor blades too!

Will keep you posted about how it compares with helicopters.

Don

don cardy24/01/2017 16:47:43
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19 forum posts
37 photos

Hi Rich,

An update on my progress with a re-build after the crash reported on 17th Jan.

The re-build has been completed as shown in the pics. The firewall bulkhead has been moved forward by 3 cm to make more room for the battery and the motor cowling, yet to be completed, will therefore be shorter. I'd run out of my original red covering material and have had to settle for a slightly different red to cover the repairs. The broken blade I've repaired by splicing in new material, and here my belt and disk sander helped me to produce really good quality joints such that the repaired blade appears to be is at least as strong as the original. Other crash damage to my Panther was superficial, the odd crack being repaired using cyano. Panther seems to be immensely strong.

As far as the electrics are concerned the original unbranded servos I've replaced with Savox SC-0252MGs and I've fitted new heavy-duty push-rods too. This part of the system now seems to respond to inputs much better. Some research on the ESC identified it as having a 3 amp BEC which may have been one of my problems. I've now fitted an ESC (left over from my NOTAR EDF experiments) with a 4 amp BEC and hope this will be adequate for its principal load of just two Savox servos. The motor I was using was unbranded but I believe was a 650KV 60 amp unit. Although immediately after the crash it seemed to be ok, when I fitted it in my re-build it wouldn't start properly. I therefore replaced it with a Ripmax Quantum 40 of 800KV and 60 amps. When I ran this up with the 4 cell battery and the 13 x 6.5E inch prop I had been using previously, but with the new ESC, the maximum power consumption was around 750 W - I actually got up to 950 W on one occasion! With no more props readily to hand I found that a swap to 3 cells gave me a maximum power consumption of 370 W to bring me into line with Richard's early guidance on the choice of motor and prop. More experimentation with other props is on the cards. One last point on the electrics. I had made up a bifurcated deans connector to connect the battery with the main ESC and the pre-rotator ESC. The connector to the main ESC was found to make intermittent contact on tests with the re-build and so was replaced. I'm therefore left with the possibility (slight?) that the crash wasn't due to pilot error but to possibly an over-loaded ESC or an intermittent deans plug contact. We shall never know for sure!

I took Panther for flight testing this afternoon. In absolutely calm conditions and using the pre-rotator it took off easily and smoothly but when I opened the throttle it seemed to want to go very much nose up. Reducing the throttle it was fine and I felt I was completely in control when landing. For my second flight I tried reducing the head pitch angle but things were much the same so I again landed and decided to ground Panther to give time for thought.

I suspect the answer may be more down-thrust. With my pre-rotator fitted I have added 84 grams to the top of the pylon and have therefore moved the cg up a bit. Having said that the cg is now on the button as shown in the plan. In such a position the thrust line of the motor passes below the cg which is contrary to the guidance shown in Richard's drawing (382977.jpg) of 15th Feb 2013 which shows that the thrust line should be through or above the cg. Another factor may be that my 3 cell battery is 50 gm lighter than the 4 cell it has replaced although this is nothing like as significant as 84 gm at the mast head.

Suggestions from experienced pilots would be welcome.

Don

p1080558.jpg

p1080551.jpg

Richard Harris24/01/2017 18:16:33
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2033 forum posts
1865 photos

Don,

Nice repair work, just wish I could repair that quickly!

Your Panther flew perfectly fine before its bump, so I would be looking at what has been altered.

You mentioned you have changed your servos and push rods? could it be that it simply needs extra rearward tilt, a few hops would soon give you the answer to this.

The extra nose length and heavier battery will certainly bring the CG more forward , an easy fix without adding extra weight to the tail end is to move your rotor spindle forwards and see what difference this makes?

Because you have moved the motor forwards and kept it at the same height the thrust line is vertically further away from the CG point, this could possibly act on the model. The Panther blades,area of the tail plane and long moment arm are designed to reduce this effect. There is no reason why you couldn't drop the motor to try but prop to ground clearance may become an issue.

If the blades have been repaired has the repair had any negative twist? this would greatly reduce the lift/drag highlighting the down thrust 3 fold. Again an easy check is to the blades on a flat surface and seeing if there is any twist by pressing down in different places and watching for any blade lifting. If they are fine have you any negative shim? could this be reduced?

For me my money is on moving the spindle forwards as I have seen this done many times.

Hope this helps and please let us know how it goes?

Rich

You mentioned you

don cardy24/01/2017 19:31:54
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19 forum posts
37 photos

Rich,

Thanks for your prompt response. Rapid repairs come from a combination of not wanting to be beaten by the technological challenge and from being retired!

Just a few observations to identify what hasn't changed. The motor bay has been shortened to adjust for the longer battery bay so the motor itself is in exactly the same position as on the plan and before the crash.. After the servos and push-rods were replaced I set up the angles for the rotor head relative to the tail-plane exactly as before so there should be no change there. I used a helicopter digital pitch gauge for this purpose both times. The repaired blade is absolutely flat underneath so there is no twist but there may be a some variation in blade section at the point of the repair.

At present the blades have a negative pitch (equivalent to the use of shims) of 2 degrees measuring the relative angle between the flat underside of the blades and the rotor plate. I set this angle after hop tests with the original model when with zero degrees as defined above there was no lift off but the addition of shims made it much better. (I then fitted tapered plates under the blades to give the same amount of negative incidence. From what you say one option may be to try reducing my amount of negative incidence by using positive shims.

Your suggestion to move the spindle forward is very interesting and another option.

Finally coming back to down thrust. I've been looking at the photos in your RCME article and their prop angles and cowling profiles and, whilst it's difficult to judge, I'm left wondering whether extra down thrust, over and above that given by the angle of the firewall/bulkhead as specified in the plan, has often been used? With the extra down thrust I'm now considering, the motor axis will be horizontal when Panther is resting on its two wheels and tail skid. I would be really interested in your observations on this please. I'm also glad I haven't completed the motor cowling yet because the motor may be moving!

Don

Edited By don cardy on 24/01/2017 19:33:30

don cardy25/01/2017 22:54:39
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19 forum posts
37 photos

Rich,

Some further thoughts on my problem and the motor thrust line.

It was only on reading through the many posts that I discovered that the CG shown on the plan is not to be taken too literally. It is correct in the horizontal direction only, not vertically. One contributor had drawn attention to the motor thrust line on the plan passing 22 mm under the CG shown. The response was that the downthrust incorporated in the plan (I measure this as 5.5 degrees) is about right for most Panthers which therefore suggests that the actual CG will usually be around 22 mm below the position shown on the plan.

My CG will be higher than normal because of the extra weight of the pre-rotator which adds an extra 84 gm at the mast head. I calculate that this has had the effect of raising my CG by 11 mm.

I have determined the CG position, both horizontally and vertically, of my Panther by conducting two hanging tests, one from the mast head and the other from the spinner nut. The photographs show that my CG is almost exactly in the position shown on the plan, both horizontally and vertically. This means that it is 22 mm above the normal motor thrustline and since my pre-rotator accounts for 11 mm of this, I must previously have been 11 mm above the thrustline.

To bring my thrustline to pass through my CG, as recommended in Richard's diagram of15 Feb 2013, I need to double the downthrust to 11 degrees. This I'm going to do without changing anything else for the moment to see whether it eliminates the nose up tendency at high throttle settings. Will keep you posted but unfortunately the weather forecast is not promising just now.

Don.

Trevor26/01/2017 08:37:43
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355 forum posts
51 photos

Unlike Rich, my sole autogyro experience is from building a Panther a while back, so please don't give my views equal weight to those of the designer chappie!

Anyway, my contribution is just to say that the performance of my Panther was much improved when I took out the shims so that the underside of the blades was flat on the head plate. As I understand it, the shims are only required if you don't profile the blades as per the drawing on the plan. In particular, if you don't keep the leading edge low, you need the shims to offset the positive incidence that results. The downside of taking the shims out can be that spinning up is harder but, since you have the luxury of the pre-rotator, this shouldn't be a worry for you.

Anyway, just something else to think about if the thrust line mod doesn't do the trick.

Good Luck,

Trevor

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