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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

Richard Harris28/01/2017 16:44:32
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1902 forum posts
1721 photos

Don,

Please ignore my last reply as I read your post wrong! my time is limited on the net at the moment so it was a little bit rushed.

Your Panther will climb under power, if you think its too much and your CG is correct just add a little extra shim under each blade. You will be surprised at just how little you will need to bring down the nose, maybe even a piece the thickness of a piece of paper.

Rich

don cardy12/02/2017 17:44:46
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19 forum posts
26 photos

Hi,

EUREKA - with brief details.

As promised earlier I increased the down-thrust to 11 degrees so that the prop thrust-line passed exactly through the vertical CG position. After one aborted take-off (made difficult by all the worm-casts on our take-off and landing square) I achieved lift-off. Panther flew like a pylon racer, very fast and neutrally stable. If the nose dropped a quick nudge of "up" would put it right and vice versa. It sure made me concentrate and I managed a safe landing at the second attempt. Phew!

Back to the drawing board to do what we are told not to do and change three things at once. I reduced the down-thrust (to about 8 degrees), the negative incidence of the blades (by 1 degree using less shimming), and the gimbal neutral pitch (by 1 degree).. I was again back to Panther tending to hang on its prop, but because there was a 6mph breeze it was more difficult to land this time and Panther collapsed on its tail from about 5 ft up and needed a little remedial work.

Back again to the drawing board for a through review of what had gone before and of the advice received via postings. It was clear that the "hanging on the prop" problem had only occurred after I had changed the motor and the battery after the major crash reported earlier. The motor was 34 gms lighter and the battery 54 gms lighter than before. Had my recent check of the horizontal CG position been right? NO IT HADN'T - how embarrassing! I found that 125 gms of lead positioned between the under-carriage and the fuselage and secured by the fixing bolts would put this right. I left the blade incidence where it was and increased the gimbal neutral pitch back to 5 degrees. At last Panther flew like a dream - patience was rewarded! There were problems taking-off because of the worm-casts making it necessary to using a bit more throttle than usual but landings were no problem at all.

Back to the drawing board - hopefully for the last time! To eliminate the lead I had to move the motor and battery forward by at least 2.5 cms and probably reduce the inherent weight of the tail sections. A major re-fit was needed so the whole frame was stripped back and the motor mounted on the 2.5 cm extensions I had used previously but then discarded when I extended the battery compartment by 2.5 cm after the big crash. The battery would be capable of being moved well forward into the motor bay. A hole was cut into the rudder to lighten it and eight holes in the tailplane. The fin would use an open framework instead of being sheeted and the stern post be one piece instead of being cut at the tailplane. The fuselage was also lightened (see pic). These changes took at least 20 gms off Panther's back end. Finally, to cope with the worm-casts, the spats would have to come off to make room for larger wheels and the tail-skid be replaced by a small wheel to give the rudder more ground-clearance. After all these changes and then re-covering the CG came out dead-on with an all-up-weight of 4 lb 11 oz.

I'm looking forward now to an improvement in the weather and am confident enough to give the pilot a ride!

Don

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Edited By don cardy on 12/02/2017 17:49:01

Trevor12/02/2017 19:52:18
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170 forum posts
16 photos

Ah, so the fundamental problem was a rearward cg. Glad you got it sorted. I flew my Panther last wek for the first time this year. It's always a somewhat tense affair because of the constant fear of disorientation. We had next to no wind so I was envying you our prerotator. However after a steady J shaped take-off run it lifted off smoothly and I enjoyed a short but reasonably comfortable flight and a slow, safe landing. As always, very rewarding.

Good luck with the next phase of the flight trials.

Trevor

don cardy12/02/2017 20:26:35
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19 forum posts
26 photos

Trevor,

Yes I've been pleased to benefit from the prerotator. Am about to start making another with a 6 mm main shaft. I've had no problem with disorientation because the spats seem to help so much - but now I've removed them who knows? Just for the record the balance point, both horizontally and vertically, is exactly where it's shown on the plan. I've put a spike through the pylon in order to check this very carefully. This means that my present down-thrust setting gives a thrust-line passing about 15 mm below the CG. Am checking with Rich whether the note on his diagram about the thrust-line needing to be through or above the CG is correct.

Don

Richard Harris17/02/2017 18:42:27
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1902 forum posts
1721 photos

Don,

I have just replied to your PM, hope all your modifications work out ok. I will be test flying a new one this coming weekend that I have built for a friend. Photos and video will hopefully be taken if all goes well , but for now a 'before' photo. Not my choice of colours may I add smile

 

Rich

 

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Edited By Richard Harris on 17/02/2017 18:54:23

Richard Harris19/02/2017 21:44:02
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1902 forum posts
1721 photos

Maiden was undertaken yesterday with 3 more flights today, the newly finished pea green Panther was passed on to its new owner today.

I managed to take a few snaps and a video off my phone yesterday. The flight in the video is its 3rd and was the final trimming flight of the day, trims ending up pretty much the same as my last two which is always reassuring.

And a few more snaps
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Rich
Daniel Johnson 120/02/2017 22:13:00
1 forum posts

Nice build and flight Rich. I really like the colour.

Richard Elliot24/02/2017 20:57:32
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175 forum posts
115 photos

Nice job Rich, that flies eally well. Any reason why the roll and pitch servos are on the right on this one?

Rich

Richard Harris25/02/2017 10:48:02
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1902 forum posts
1721 photos

Rich,

No reason other than I glued the roll control arm on the opposite side and didn't notice embarrassed

Rich

don cardy28/02/2017 10:02:30
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19 forum posts
26 photos

A link to a Facebook video of my Panther rotor on test up to 750 rpm to test balance and tracking.

Soon I'll post details of my second pre-rotator, including a linked video, which on test at 600 rpm indicated that the motor was using under 50 Watts.

Don

**LINK**

Edited By don cardy on 28/02/2017 10:04:55

don cardy01/03/2017 12:30:41
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19 forum posts
26 photos

As promised a report on my second pre-rotator.

My first was based on one I had bought from the far east to fit an ARF autogyro which had then suffered an early demise. My first pre-rotator features in pics in earlier posts; the main points about it were that it used a mini-Titan main gear, one-way bearing, and 5mm dia main shaft, and that the XA2212 820KV motor was a helicopter variant. My Panther, on its first flight with the pre-rotator, took off easily but then met terra firma in a vertical dive which I'm increasingly inclined to think was a system malfunction, not pilot error (but then I would wouldn't I ?). That was the only occasion when the 5mm dia main shaft bent, but then only slightly and therefore was easily straightened.

My second pre-rotator dispenses with the normal sleeve used with one-way bearings and instead the mini-Titan main gear and one-way bearing runs directly on the 6mm dia silver steel main shaft. The main shaft runs in a bearing block made from several layers of fibre board which machine easily on a Unimat lathe. The ballraces are 12x6x4mm. The only work required on the main shaft after cutting it to length is a 3mm tapped hole at bearing block end and a 2mm hole through it at the rotor plate position to take what I shall call a "Jesus pin". This fits in a slot in the plate and serves to secure the plate to the main shaft and also transmit the pre-rotator drive to the rotor. The rotor plate fits between two disks made from 6mm five ply. This also machines very easily and the ply I used drilled very cleanly with the 6 mm holes being a snug fit on the main shaft and therefore the rotor plate runs very true. It appears that the only XA2212 motors on offer are the plane/quadcopter variant so this motor required a fixing plate at the bottom and therefore remote from the pinion. This is not ideal because the pinion can tend to move out of alignment under load but in practice this seems not to be a problem. Another slight problem is that the XA2212 motor has a 3mm shaft whereas the mini-Titan pinion is for a 3.17 mm shaft. I used a couple of wraps of cooking foil round the motor shaft and this has worked well. Remember that the pre-rotator only works for a few seconds each flight so the motor doesn't have the arduous duty it would have in a helicopter. It also doesn't matter if it fails; the rotor can still free wheel round!

I hope that the sequence of pictures will help fill in the detail. A video of the pre-rotator under test can be found using the link in my previous post.

Whilst I now have two pre-rotators which work and which I must use if I am to be able to take off cleanly on my club's mowed square, there are still some issues to be resolved. Whilst my maiden flight without the pre-rotator went well, I can't say that this has been the case since fitting the pre-rotator as detailed in my earlier posts. The standard Panther rotor complete with its shaft etc weighs about 300 gms and my pre-rotator adds 80 gms (25%) to this. This clearly has the effect of raising the CG of the model as a whole quite significantly. I'm still struggling with the issue of whether the main motor thrust line needs to be changed to counter this. To add to this I have just removed the spats so that I can cope better with the worm casts on our take off square and these weigh about 40 gms so the CG has been raised even more! My experiments will continue as winds permit.

One last point. In my tests of my second pre-rotator I've achieved 650 rpm at a motor consumption of just 52 watts. Using a battery discharged down to 3.4 v per cell I still managed to achieve 560 rpm at just 34 watts. With power consumptions at such a low level the wiring to the motor ans the connections can be quite light weight.

Don

 

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Edited By don cardy on 01/03/2017 12:32:55

Edited By don cardy on 01/03/2017 12:36:59

don cardy06/03/2017 19:24:45
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19 forum posts
26 photos

Well the wind eventually abated and I was able to make a test flight in a 6 to 8mph breeze. The pre-rotator was the original, but upgraded to have a 6mm shaft identical to the second pre-rotator described in the previous post. A fellow club member filmed the take-off using his smart phone and the video can be found using the previous link. There was no problem with the take-off but Panther did get knocked about a bit a few seconds later. Whilst the top of the pylon snapped off, I'm pleased to report that the pre-rotator survived unscathed. Panther is now back together again but the pilot is finding it difficult to plead guilty! Horizontally the CG was slightly ahead of the position shown in the plan so I'm still chasing the issue of the vertical positioning of the CG. Now have lead weights on the undercart to compensate for the missing wheel spats and the extra pre-rotator mass at the top of the pylon. Let's see what happens!

Don

Richard Harris07/03/2017 20:22:37
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1902 forum posts
1721 photos

Don,

I have just viewed your take off video via Facebook, may well be worth while if your friend could upload to Youtube as more folk would be able to view it.

It looks to be a really good spin up speed and was off in no time, any idea how many amps its pulling at full RPM?

Rich

don cardy07/03/2017 21:09:45
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19 forum posts
26 photos

Rich,

In my post of 1st March I record that on test the pre-rotator achieved 650 rpm at 52 watts using a 3 cell battery. This works out (and I measured it too) at a current in the range 4 to 5 amps. This led me to get an ESC with a 12 amp max rating which was much smaller that the ESC I was using and this new ESC slips out of the way under the battery tray thus tidying up the battery compartment a great deal. I've set it at the slowest possible spin up rate. The revised design of pre-rotator seems to be immensely strong and having a spare means I can also test rotors for balance and tracking on a test rig in my garage before they are fitted to Panther. This seems to work well and I've put a video of this on my Facebook page too.

Whilst the pre-rotator works fine this doesn't mean I'm out of the woods yet. After the take-off which you've seen, Panther went into a spiral dive to the left which left me having to fit a spare rotor and put new cheeks at the top of the pylon. Minimal damage really. Today I tried again although the breeze was again marginal at 6 mph plus. The new rotor had clearly changed the flight dynamics and I should have tried a few hops first but Panther tended to hang on the prop quite a bit which in a wind is hard to deal with and I had another spiral prang. Not so serious this time so I'm virtually ready to have another go. I'm now going to put the CG well forward of the position on the plan and try a few hops first. Hopefully this will bring some encouragement. Funny really that after the maiden flight when all went well, it seems to have been downhill since the fitting of the pre-rotator. That's except for the occasion which led me to make my "EUREKA" post. However, the major re-fit sadly failed to replicate the encouraging flights immediately before that. There must be something I'm missing and we have to find it!!

We have a club member who does regular videos for youtube and when I'm properly sorted I'll get him to do one of Panther with the pre-rotator in operation.

Don

Trevor07/03/2017 21:51:24
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170 forum posts
16 photos

Sorry to hear about the prangs Don. Just to check the obvious - are you absolutely sure the spiral dives aren't caused by orientation confusion, or even a reversed 'aileron' servo? In my limited experience, the Panther is very stable so spiralling in does suggest that something fundamental is wrong.

Richard Harris13/03/2017 20:22:01
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1902 forum posts
1721 photos

Don,

I 100% agree with Trevor, orientation can get the better of all of us. Those RPM figures are pretty impressive, in fact, are getting close jump take off speeds which is something that I have always wanted to try. Something like this:

Don't forget, we have several get togethers during the year, I'm not sure where abouts you are in the UK ?but there is bound to be one within driving distance. You'd be more than welcome, gyronuts are a decent bunch, always willing to share their experiences to help like minded folk thumbs up
Rich

don cardy13/03/2017 21:41:03
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19 forum posts
26 photos

Rich,

Thanks for your encouragement; I shall persevere and get there. I can vouch for the robustness of your Panther design, the damage is never as great as I expect it to be. And, by the way my later version of pre-rotator with a 6mm shaft has never been bent or damaged.

I think there is a problem with the Panther rotor as far as jumping take-off is concerned, that's apart from it being fixed pitch etc. It is that the rotor has a very low inertia such that when I shut down the pre-rotator the rotor quickly starts to slow down as.it's rotational energy is absorbed in overcoming the rotor drag. In practice I'm keeping the pre-rotator powered up as I start the take off run and then shut it down a few seconds later.as the normal air flow through the rotor takes over. I'm not having any problems with take-offs at all - that is apart from the worm-casts which cause Panther to dart about a bit on its take-off run.

The solution to this is to increase the inertia of the rotor by using tip weights or whatever. This will get more stored energy into the rotor although of course it will take longer to get up to speed. I'm not sure what the effect of an increased rotor inertia will be on Panthers flight dynamics. With helicopters using a 3 axis gyro (SAS) blades of different weights can be used to fine tune flight behaviour. I loved my mini-Titan with heavy blades as it was so stable.

In one example of a modern autogyro with a very spectacular jumping take-off I believe the blades used depleted uranium in order to significantly increase the stored energy available for take off.

I'm quite enjoying setting up a my rotors for Panther using my second pre-rotator in a test rig in the garage. I've evolved a way of replicating the shimming too and matching the three blades for negative incidence. I've discovered that differences between bought-in delta plates suggest that having balanced the blades individually it is worthwhile balancing the assembled rotor, making sure that each blade is labelled along with its position on the plate so that if it's taken apart for any reason it can be reassembled without the need for more balancing.

By the way I live near Colchester.

Don

 

 

 

Edited By don cardy on 13/03/2017 21:41:55

Leif Scott28/03/2017 01:53:28
3 forum posts
5 photos

Hi Richard,

Thank you for the panther design. After wanting to get to the build for a few years (life sure gets in the way), I have finally started construction. I looked through many pages of this thread but alas, no luck finding clarification. Regarding the c of g indicated on the plan, should the model sit level with it balanced at this point or should it stay in any position around this point, much like balancing a propeller?

Thanks for all your guidance and knowledge shared with all,

Leif

Richard Harris28/03/2017 22:50:21
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1902 forum posts
1721 photos

Hi Leif,

Glad to hear you are making a start on a Panther. Yes, the model should balance horizontally from the point shown on the drawings. You can get away with a little nose down attitude but not the tail down.

Let us know how you progress?

Rich

Steve Jones 229/03/2017 06:18:30
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464 forum posts
346 photos

My 2 Panthers have Servo Brass ferrules at the indicated balance point then the full model is suspended on a wire passed through the ferrule. They balance slightly nose down

Steve

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