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M-Tee Plate (scratch build)

hart

Aussie in Belfast
#1
After browsing around for a few ideas on scratch building my first foam board plane, I decided to build something called an M-Tee Plate - not sure why it is called that, but anyway, it looked like fun, so I grabbed some foam board from the Belfast Hobby Shop and got to it.

The foam is not the cheapest, at nearly £9 per large sheet, but I didn't want to bulk order the cheaper stuff from the mainland just yet.

I downloaded the plans from rcgroups.com and printed them out on A4. I had to cut and tape the pages together carefully to get a larger sized plan as I didn't want to pay for A3 or larger printing. It wasn't that hard and before long I had all the pieces cut out from the template:







I finally got around to getting some coloured spray paints and tested them on some offcuts of foam board to make sure paint didn't cause the paper didn't lift off; eat the foam; or cause the foam to warp. Great result first time!



The black is very nice - one light coat gets a mirror finish - almost good enough to not bother with a second coat!



The red needed two coats to get this finish, it will either need a thicker application or three coats to get a nice even finish - but red is always bad for that.



Despite the orange hue in the next picture, under direct sunlight this is a bright yellow like the lid. One coat to get this finish.



Satisfied with my testers, I gave one side of each component a light coat of white as a primer and after an hour of drying in my nice warm shed, I applied the first red coat on the wing, front skid and elevons:



Then changed colours for the "fuse" and vertical stabiliser:





Looking forward to getting the electronics in this one in time for summer. I'm looking at the following gear but I am mostly guessing at the figures. I am, of course, aiming for low cost and reasonable performance:


With 357g of thrust produced from 2S @19340rpm, I am guessing 20-30% more thrust from 3S, but less thrust based on using a 4.75/4.75 prop instead of the tested 5x3. Again, I'm new at this, so not really sure :)

I may also look at adding a KF airfoil after looking at a few threads here.

Motor 37g
Prop 9g (guess)
Servos 18g
RX 5g
Battery 47g
ESC 24g
Wires, glue, tape, velcro: 10g

Total:150g plus the foam board and paint - which I have no idea on yet.

Comments welcome!
 

hart

Aussie in Belfast
#2
I ended up ordering the electronic parts locally and got the following components to try on this mad creation:

  • pair of E-Power 8.5g Micro Servo (EMZ ES08A)
  • pair of Corona CS-929MG Anolog Servo (CS-929MG (BLUE))
  • Gens Ace 1000mAh 3S 20C Lipo
  • HobbyWing Brushless Motor ESC 30A
  • 4.5x4.5E TGS Sport Propeller
  • A2208/8 20A 2600KV Outrunner Brushless motor (2208/8 Motor RCM)
  • FlySky 2.4Ghz 6 channel receiver FS-R6B (R6B)

I'm using the E-Power servos for now, they seem strong enough and are not too chatty. The Corona MG are a backup in case. I've also got an alloy stick motor mount and used spruce to sandwitch the wing for the mount.

I picked up some control horns, piano wire and pushrod connectors from Icarus, should have got a battery strap... :roll:

After some careful planning it came together rather nicely - getting the CG right was going to be difficult with the servos in the recommended position so I opted to put them right back near the elevons. Throws are generous so no real issue with that.



I'm not happy with the battery mounting solution - I don't think the velcro will hold up to the forces that will act upon it mounted there - the last thing I'd like to see is a fully charged 3S go flying back into a prop on a climb or roll... I will use a velcro strap instead with something on the bottom side to keep it safe.

Delta mix was relatively easy to setup on er9x, I've gone with 60% expo to keep the movement subtle until I get a better idea of how much throw is needed to manouver.

The thrust this setup produces is, well, ballistic - the watt meter test confirmed my PeakEff calcs: 22A 250W using 4.5x4.5 TGS prop. Niiiiice. It will probably fall apart the first time I go full throttle though - but it will be fun either way!
 

hart

Aussie in Belfast
#4
Spent a few hours at the field today, sadly the wind was too gusty for any flying - so I made a cuppa and had a nanna-nap in the club house. Visited our club secretary on the way home, borrowed his scales and learned that the AUW is exactly 350g - so I have a 1:1 weight-to-static-thrust ratio. Now if only I knew what that actually meant!

According to John P. Fielding, Introduction to Aircraft Design, Section 3.1 (p.21) (thanks, WikiPedia), the quoted thrust-to-weight ratio for aircraft is often the maximum static thrust at sea-level divided by the maximum takeoff weight. Daniel P. Raymer, Aircraft Design: A Conceptual Approach, Equation 5.2 says: in cruising flight, the thrust-to-weight ratio of an aircraft is the inverse of the lift-to-drag ratio because thrust is equal to drag, and weight is equal to lift.

Then there's power to weight - I've read articles which say anything over 50W/lb will usually fly reasonably well, in which case, 350W/lb (250/0.771618) would be somewhat insane, I would imagine.

Now if someone could explain that to me in layman's terms, I'd appreciate it! Meanwhile, if the wind drops to a reasonable or consistent level tomorrow, Il'l find out first hand :)

Cheers

Leigh
 

earthsciteach

Moderator
Moderator
#5
Anything above 1:1 thrust to weight ratio means you have more power than any well behaved aircraft needs. Here's to aircraft that aren't well behaved!
 

hart

Aussie in Belfast
#6
Back at the field today, hoping for a lull in the wind. After 2 hours it finally dropped below 10mph for a while so I had a crack at getting this thing in the air.

I was hoping for something like this:


but sadly, what I got was this:


First attempt she rolled around and flopped rather un-gracefully onto the ground and hopped a bit in protest.

Second and third attempts were equally ugly.

Fourth attempt would have been fine, had I not panicked and pulled back on the throttle. ARGH!

The prop came loose and fell off that time, so after a quick break, I was back out for the fifth and final attempt - where much the same happened as before, only this time she hit a bit harder and losened the motor mount from the foam - time for a reglue and re-think of how this thing will fly... we'll see how the wind is next weekend!
 
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hart

Aussie in Belfast
#9
Anything above 1:1 thrust to weight ratio means you have more power than any well behaved aircraft needs. Here's to aircraft that aren't well behaved!
Well as can be seen in the video - it is anything but well behaved :) I'll have another go next weekend if the wind has died down to something sensible...
 

earthsciteach

Moderator
Moderator
#10
It was hard to see in the video, but are you mounting the battery on the left hand side of the plane? If so, that is likely contributing to the roll. Can you center it through the fuselage to balance the weight?
 
#11
That just doesn't look right to me. You have a huge battery, decent sized motor and esc on a small disc. I would expect a 2 cell, 200-300 size pack and a much smaller motor esc combo with micro receiver. I'd really expect about twice the diameter for the hardware that you have on your plane. Just wondering if there isn't something lost in translation.

Flight path looked like something that was just getting torqued/pushed over by a high power, high thrustline. Of course a lot can be added by a less then perfect launch and when your doing your own test flight launch, that can really add to the problems of a new design. That's not 24 inches in diameter like a Snowball or is it?
 

hart

Aussie in Belfast
#12
It was hard to see in the video, but are you mounting the battery on the left hand side of the plane? If so, that is likely contributing to the roll. Can you center it through the fuselage to balance the weight?
That just doesn't look right to me. You have a huge battery, decent sized motor and esc on a small disc. I would expect a 2 cell, 200-300 size pack and a much smaller motor esc combo with micro receiver. I'd really expect about twice the diameter for the hardware that you have on your plane. Just wondering if there isn't something lost in translation.

Flight path looked like something that was just getting torqued/pushed over by a high power, high thrustline. Of course a lot can be added by a less then perfect launch and when your doing your own test flight launch, that can really add to the problems of a new design. That's not 24 inches in diameter like a Snowball or is it?
100% correct on both counts. The battery was way too far out on the left of the wing - when centered the balance was perfect (in my hands) - the torque was still there after moving the battery. The model was also way too small. I'm starting a new build today with between 22-28" WS and leaving a lot more room for centered electronics and will add symmetrical KF airfoil steps as well as a centered motor mount.

Scratch building is a learning experience and I certainly have learned a lot from this one. I've enjoyed the process and the test flights (if you can call them that) were a lot of fun - despite the frustration :) No electronics were harmed, so my total outlay for the experiment was around £10 in foam, glue and paint. No great loss!

I'll update on my progress!

Cheers and thanks for the feedback / comments!

Leigh
 

hart

Aussie in Belfast
#13
I started a new build today, still a work in progress: 32" WS, 28" tip to tail with a KFm4 airfoil (5" chord at wingtip, KF steps are 2.5" at the wingtips) - based on the hand drawn plan of the FauxJet. Built using a very large sheet of 5mm foam board (no joins, just layers). Fuse will get a few extra hollow layers of enclosure on top for electronics, and a narrow skid layer underneath. Not quite a profile, not quite built up - just enough to house everything nicely and keep the weight down.



Cheers

Leigh