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The Ohmen

My first electric powered aerobatic model

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Martin McIntosh10/06/2020 12:39:44
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Got it in the air today, albeit with the motor needing attention, probably just a new plug. Very pleased with it, just a bit of up trim to compensate for the slightly forward cg. I would say that I am much happier flying it now because it grooves as I would expect an i/c to and easier to land since I can actually hear what the motor is doing.

Managed one tumble even with the cg as it is.

Nigel R10/06/2020 13:16:24
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"Lomcevak"

they're fun smiley

basic lomcevak is:

fly up at 45 degrees, with decent speed, throttle to half or two thirds

left positive snap

after a rotation (ish)

move elevator to full down, retain left rudder & aileron

after another rotation (ish)

centralise aileron, throttle may need to go to maximum

if the timing is right for the airframe, you will end up rotating around the wing axis in this third phase

experiment with entry speed, angle, and timing for each phase

the first snap initiates things, it must be stalled, then the transition to down eventually rotates you to a point where torque can take over (when you go to just down elevator and left rudder)

torque works in your favour when rolling left, rolling right will not work (unless you have a clockwise prop)

**LINK**

26 seconds, perfectly executed, all three phases visible at a slow speed, this is as good as it gets

and a number of examples here:

**LINK**

at start of vid, very quickly straight into third phase, but already stalled & moving slowly

0:30 from vertically up, almost flat spins before winding into lomcevak

0:50 lots of rotations!

1:50 is a good one with standard 45 deg up / snap/forward elevator/neutralise aileron sequence... ignore the quick quarter roll popped in before the lomcevak sequence starts.

2:13 standard sequence from 45 deg upline

Peter Miller10/06/2020 13:37:48
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And I think that this is a partial Lomcevac in a microlight aircraft. Later in the video it does a great rolling circle.

And YES! it is a Rotax poweredmicrolight stressed to+9 and -6 G

And yes. I have almost finished my plan for it!!!

Peter Miller10/06/2020 14:43:37
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OI forgot to put the link in my last post

**LINK**

Martin McIntosh10/06/2020 15:04:16
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3471 forum posts
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Great videos, but where is the microlight one Pete?

In the Neil Williams book he describes variations of this maneouvre; there is more than one type. Very similar to the spectacular knife edge spin where the aeroplane rotates about its horizontal axis with a wing tip pointing vertically downwards. When I had a Cap 21 I could do it if I fitted a small battery to shift the cg rearwards.

The entry for any of these is hit and miss evidently.

As an aside, when I took up the hobby again after a long layoff and joined my local club, I stated that I had a `B` but did not have the certificate and the SMAE had lost all of my records so elected to do it again using a very light o/d fun fly in lousy conditions which surprised the examiners. I also had with me an o/d Dalotel, OS 25FX powered and only about 44" span which they thought was an awful design. I took it up and did my party piece of the time, only possible with that model. Vertical climb, flick to the right with rudder then on full power apply opposite rudder. It would then do 2 1/2 rotations about the longitudinal axis culminating in an inverted spin close to the ground so bicycle clips at the ready. The examiners reckoned that I had been wasting their time taking a `B` again. Still have the thing somewhere in the loft in a rather dilapidated condition.

Nigel R10/06/2020 16:03:58
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Pete yes it looks like the Rans can't quite develop the end over end rotation at the end of the maneuver. Maybe not quite enough torque or thrust perhaps.

Peter Miller10/06/2020 18:29:15
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Posted by Nigel R on 10/06/2020 16:03:58:

Pete yes it looks like the Rans can't quite develop the end over end rotation at the end of the maneuver. Maybe not quite enough torque or thrust perhaps.

Well it does have rather a small engine!!!

Martin Harris15/06/2020 17:21:52
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Another club mass build Ohmen takes to the sky - maidened this afternoon by the builder, Derek.

whatsapp image 2020-06-15 at 14.47.21.jpeg

As with several of our builds, he put his own stamp on your design, Peter. Apart from the obvious deviation from your plan with the single cockpit, he made his with detachable separate wings sliding on to a tube joiner - for no particular reason other than thinking it would be fun to try.

Peter Miller15/06/2020 18:28:09
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THat is great and looks really good.

I never mind what modifications people do. I always say that it is the first step to designing their own.

My current design is scale but it is a home built with a great many variations on undercarriages, rear turtle deck and colour schemes. This will give people plenty of choices for variations.

Just Google Rans S-9 Chaos images.

Because it is a fully aerobatic microlight (+9 -6G) it is builtlike a model.Even the huge canopy is flat sheet.There is even an open cockpit version!!

 

Edited By Peter Miller on 15/06/2020 18:30:30

Martin Harris18/06/2020 23:03:28
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...and another for you Peter. This one from James, whose son Harry built the Dusty version - and flies it very enthusiastically.

whatsapp image 2020-06-18 at 22.47.03.jpeg

Martin Harris18/06/2020 23:25:34
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9405 forum posts
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...and a couple more photos have come my way:

whatsapp image 2020-06-16 at 19.36.59.jpeg

Mick's [built without dihedral]

and:

whatsapp image 2020-06-16 at 19.36.17.jpeg

Dave's Magister/Ohmen

Peter Miller19/06/2020 08:22:06
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11211 forum posts
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THose look really good too.

OH Yes! THey ask to be flown very enthusiastically.As I have said,mine only flies straight andlevel while it is inverted!!

Martin Harris23/06/2020 20:21:33
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9405 forum posts
255 photos
Posted by Martin McIntosh on 05/11/2018 14:07:39:

This is it with the cockpits now populated.

Tried moving the cg back by by about 10mm, don`t do it.

I would concur.

Maidened one today for a friend [sorry, his camera didn't play ball so no picture] but I didn't have a copy of the plan to hand and went by the builder's assurance that he'd checked it - after all, they are all pussycats and it was visually forwards of 30%...

It was horrible - nervous in roll and very sensitive in pitch - had to nurse it in to land. We moved the battery forward - better, but I don't think he would have enjoyed flying it and the third attempt with the battery even further forward transformed it into a pleasant flying machine.

I flew my 85% glow powered version afterwards and discovered it does the quickest flick rolls I've ever encountered! Great fun.

Edited By Martin Harris on 23/06/2020 20:23:36

Peter Miller23/06/2020 21:04:57
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I do like my CG at 25%!!

I was flying mine todayand,following someones instructions I was able to do fantastic Lomevaks Great end over end tumbles.

Funnily enough it was doing them best on low rates.When I went to high rates it wouldn't do them properly.

The instructions I got were: Left hand vertical roll and then put the two sticks in the top left hand corners. WOW!!!

Peter Miller24/06/2020 10:12:01
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Just a further comment on my choice of CG location.

I tend to use small tailplanes. Typically 15% of the wing area.THis is the reason for my CG locationat 25% of the chord

Martin Harris24/06/2020 17:47:33
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9405 forum posts
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And from my experience yesterday, a recommendation to be adhered to!

David Clark 1810/07/2020 03:14:10
11 forum posts

Do you think the Ohmen would make a good model for the transition from high to low wing flying.

Chris Walby10/07/2020 06:21:51
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1275 forum posts
315 photos

David, I don't see why not and for me the sign of a "good" design is a wide flight envelope with well mannered stall characteristics.

  • Control throws change it from quite benign to very lively
  • Good low speed performance
  • Seems to be robust design that will take a few knocks (simple UC design that will stand a few less than perfect landings)
  • Runs of the common and cheap 3S200 lipo
  • Designed for electric so battery access is quick and easy

So IMHO if you want you first low winger on the sporty side its the Ohmen...but if you want something larger and with slightly less aerobatic (and only slightly) performance and equal or better stall characteristics then Lindsey Todd's Renaissance is a nice build and great flyer although the pilot is a right animal!

Ohmen

20200516_100836.jpg

Renaissance

20190801_182212.jpg

If the weather is nice I'll fly them back to back and see if I can split the difference wink

PS - for windier conditions I give the Renaissance the edge due to increased mass and wingspan.

Edited By Chris Walby on 10/07/2020 06:27:09

Low pass Pete10/07/2020 06:54:53
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Posted by David Clark 18 on 10/07/2020 03:14:10:

Do you think the Ohmen would make a good model for the transition from high to low wing flying.

Agree with Chris that Renaissance would be a good choice. Here is mine. She really is nice to flyimg_6593.jpg

Or if you want a kit build then how about a SLEC Fun Fly. Not low wing but mid wing. This has been my lockdown model build. Flys well and can be IC or electric.rmac 2020 058.jpg

Or perhaps Ballerina from Pete Millers fold.img_5283.jpg

David Clark 1810/07/2020 08:50:32
11 forum posts

Thanks for the reply and your suggestions. They are all of interest, is the Renaissance designed for electric, I have a number of 3s 2200 and 3700 batteries which made the ohmen very attractive.

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