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MU 28

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Peter Balcombe
Posts: 1359
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: MU 28

Post by Peter Balcombe »

Well done Brian :)

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B Sharp
Posts: 817
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: MU 28

Post by B Sharp »

Today I eventually got reasonable conditions to maiden the rebuilt MU28. When I got to the top of my westerly slope the wind was blowing 18 to 22mph and it was quite warm for this time of the year.

The MU was launched and rapidly gained height almost directly overhead followed by me inputting a shed-load of down trim. (It was my fault as I had been very conservative with the longitudinal dihedral) An additional couple of beeps of left trim had the MU flying around quite happily.
My initial response was that the model was flying way, way, way better than in it’s previous existence. A dive test showed that it was still a little nose heavy. A couple of rolls show the model is much more responsive, even when just using the ailerons without the flaps coupled in. Loops were big and open mainly due to a soft elevator and I will reduce the exponential and increase the movement. Stalls were a non-event with no sign of wing drop or spin. Just so much better than before!

After 10 minutes I landed to remove some nose weight and adjust trims and throws. The landing was another non event, however a massive gust of wind lifted the model before I could get to it, turned it upside down and slammed it back into the ground. I thought that I had managed to escape any damage but closer inspection showed that the servo mounting tray had broken loose as had the battery tray. Oh golly gosh I said!
It won’t take long to fix and I will be back up the hill as soon as possible.

Brian. :) :D :D :oops:
Attachments
The MU28 rairing to go!
The MU28 rairing to go!

Jolly Roger
Posts: 445
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: MU 28

Post by Jolly Roger »

Well done on its first flight Brian and sorry about the mishap - these things happen. It sounds like its performance is transformed - ample reward for all your meticulous work.

I seem to think the original Mu28 had some kind of automatic flap system driven by a pendulum in the fuselage. I'll have to dig out the relevant Martin Simons book.

Best wishes,
Rog

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Peter Balcombe
Posts: 1359
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: MU 28

Post by Peter Balcombe »

Your memory serves you well Roger.
There is a diagram of the weighted swinging lever (in horizontal plane to react to ‘G’ forces) & damper (to prevent unwanted oscillations) connected to the pilot’s manual flap control.
The swinging lever could be locked to allow the pilot full manual control for take-off & landings plus tail slides (in order to allow the pilot to choose which way to recover).
The combination of symmetrical wing profile with automatic camber change made it easier to perform negative loops, Cuban eights and rolling circles.

It’s described on pages 54 & 55 of the Martin Simons Sailplanes 1965-2000 book.

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B Sharp
Posts: 817
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: MU 28

Post by B Sharp »

MU28 update.
I have now managed a couple more flying sessions on my local slope with the MU and all the basic trims and flight modes have been established. I will do fine trimming of control throws and mixes over the next months to get it just the way I want.
The rebuild of the model has been totally justified as the MU is now a pleasure to fly and all the nasty tendencies have disappeared. The choice of RG15 with the CG set at 34% root chord (9% static margin) is perfect and has resulted in a fast flying and buoyant aircraft. There are no more flick rolls when up elevator is applied; to the point that consecutive square loops are a dawdle. Rolls are now a lot quicker and they stop where requested due no doubt to the much lighter wing panels (especially out at the tips). Inverted flight requires a small amount of down elevator but that is to be expected. Landings are very easy and predictable which is a good thing as landing on my postage stamp patch of grass in a sea of heather can be challenging at times. All manoeuvres that I am capable off should now be easily achieved with the MU. On its last flight I managed to gain enough height to try my favourite manoeuvre; a horizontal square 8 with half rolls in the down-lines, and was quite pleased with the result. :) :) :)

As a by-line to this rebuild, I have been watching Mike F’s build of the Phase 5 aerobatic slope soarer. It has been a while since I had one of these in my collection of models and I quite fancied something similar. It would have been way too simple to build my own Phase 5 so I sat down with my drawing pens and a roll of paper to design something similar, but different! I ended up drawing a “cartoon” scale MU28 with a span of 2.00 metres which makes it 1:6.5 scale. The side elevation is pretty much to scale and so is the plan view except that the fuselage has been put on a severe diet and is only wide enough to house the radio. I have used foam/veneer wings with a root section of MH32 and a tip using RAF27. The fuselage is mainly 1/32 ply sides with balsa top and bottom to achieve a more pleasing shape. The model is finished but is awaiting suitable weather for it’s maiden flight. I now have two MU28s. :D
Brian.
Attachments
MU28 to 1:6.5 scale.
MU28 to 1:6.5 scale.
MU 28 small 1.jpg

Mike F
Posts: 65
Joined: 18 Mar 2015, 14:08
Location: Gloucestershire

Re: MU 28

Post by Mike F »

Hi Brian

Please to hear that you are very happy with the refurbished Mu28.

Your mini version has worked out well too, looking forward to reading about its first flights. What is its unballasted flying weight?

Regards
Mike

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B Sharp
Posts: 817
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: MU 28

Post by B Sharp »

Here is an update on the little 1:6.5 MU28.
The final weight is 1.46kg or 3lb 3oz in old money. I reckon that this is quite light.
The first flights were yesterday afternoon in a 10mph wind and onto a less than spectacular slope. I managed five 10 minute flights with landings inbetween to make changes.
Although the wind was lighter than I would have wished the little MU performed very well. It is very buoyant and gained height easily. I initially had to rack in a whole pile of down on the all moving tail as I had too much longitudinal dihedral wound in. I was able to remove a chunk of lead from the nose to bring the CG back to the 10% static margin point.
After a bit of trimming and adjustment the final flight was really good with lots of aerobatics which it handled with ease. The stall/spin is very benign and it can be rotated very quickly in all axis.
I think this is going to be a fun machine, especially when I let it loose on a good slope in a decent wind.
Brian. :D :D :D

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