Thread Rating:
  • 1 Vote(s) - 4 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Dyna-Mite Build Log
#1

Having recently got the urge to do some scratch building, with there being some unallocated balsa sheet lying about and feeling the ever increasing need for speed. It only required one more small coincidence to trigger the beginning of yet another lunch time project.
Well that coincidence came in the form of a phone call from an old aero-modelling friend in South Australia. While Doug was telling me about some drawings he'd recently acquired for what looked like a nice little speed 400 racer, a plan began to fall into place.

Speed 400 racers I'm guessing were a popular class of plane based on the old brushed type motor of the same name. By the look of it, this model is designed to go as fast as anything can, being towed around by the afore mentioned power-plant and fed by bunch of Ni-cads.

It’s a design from way back in the 90s and looks like it would really benefit from an upgraded power plant and some Lipos. It should fly pretty nicely once all that is sorted out.

As you can imagine, it wasn't long before an envelope containing a copy of the plans turned up in my mail box.

Here's a look at them.

   



“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#2

It would be interesting in seeing if you could source the original vintage power-train and NiCd batteries and see what it could do, before replacing that with a contemporary setup to compare how things have progressed.

Steve Murray
Reply
#3

I can answer that for you: Faster and Tail Heavy!
Reply
#4

(23-01-2013, 12:33 PM)smuzz Wrote:  It would be interesting in seeing if you could source the original vintage power-train and NiCd batteries and see what it could do, before replacing that with a contemporary setup to compare how things have progressed.

I think they were doing around 125-135 Klicks, so comparable to a rarebear running on a good 3S pack. Perhaps, the best ones, being just a little faster.

With a brushless motor and lipo's, not only will it have more power, it will be conciderably lighter as well.

I will make a few changes to the original air frame design. The ailerons will be a little smaller and will start right next to the fusalage instead of starting a fair way outboard. I will also use a different airfoil I'm going to use an MH-33 because it looks like it has about the best drag figures out of a number that I've looked at.

The wing will be wire cut from M Grade EPS and stratigically reinforced with Ply spars and glass capping, I wo't glass the whole wing that would make it too heavy, finally it will be covered with Iron on film.

I'm figureing on it being a quick build so I thaugh I might make two so I have a chance to saver things Smile

Here's some pics of lunch time's progress

   

   





“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#5

Gees that was quickShock... how long is your lunchtime? Biggrin

George

"Crash and Cry! Don't fly"


RadioBiggrinX9 & DX8
HK Cri Cri ugly,Super Cub 1870mm balsa, Sbach 1000mm balsa, Vampire, Katana E50 balsa, BA Hawke 90mm (on hold for large runway), Durafly BF110, Corsair,
EScale Zero
Freewing Eurofighter Typhoon & SU-34
Starmax F5e Tiger & 70mm F-18
FMS T-28 Trojan, P-38 Silver, 50mm F-86, C-17 Globmaster

Fly fly F-100
B-25 2.0m LX and A10 1.5m Langxiang (being glassed and re-built)
Seagull Super Tucano
Reply
#6

(23-01-2013, 02:32 PM)kizza42 Wrote:  I can answer that for you: Faster and Tail Heavy!

Smile Yep - although Jason could still move the wings further back if he wanted to.


(23-01-2013, 03:03 PM)secant0give Wrote:  I think they were doing around 125-135 Klicks, so comparable to a rarebear running on a good 3S pack. Perhaps, the best ones, being just a little faster.

Hmm - those estimates are pretty quick! Interesting ...


Steve Murray
Reply
#7

(23-01-2013, 04:23 PM)Raptorfly Wrote:  Gees that was quickShock... how long is your lunchtime? Biggrin

Lunch is 45minuets, But I allways eat at morning tea time which is 15 mins. That way I have the whole of lunch to get something done Smile Oh and it's not the first model I've scratch built.


(23-01-2013, 04:24 PM)smuzz Wrote:  
(23-01-2013, 02:32 PM)kizza42 Wrote:  I can answer that for you: Faster and Tail Heavy!

Smile Yep - although Jason could still move the wings further back if he wanted to.


(23-01-2013, 03:03 PM)secant0give Wrote:  I think they were doing around 125-135 Klicks, so comparable to a rarebear running on a good 3S pack. Perhaps, the best ones, being just a little faster.

Hmm - those estimates are pretty quick! Interesting ...

This model will be much more slippery than a RareBear so I expect it to take a lot less power to drive fast.
I'm not sure what motor to use yet, I might have to go for an inrunner to get the revs/prop speed up enough. Just have to see how we'll go with that.

It would probably be hard to find a decent speed 400 motor these days. Also they are very heavy things and produce little power. I'll be shuffeling the lipo pack and elevator servo to try and get the C of G right, Hopefully I can get it in the ball park with out moving too much. I'm thinking of running either a 1000 4S or 13004S high discharge lipo's

The good thing is that Doug has just about finished his one so I'll be able to find out how he went in that regard.

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#8

Yes - I bought a kit a long time back from an eBay seller which had a brand-new "Wattage Super 400 Cobalt 27 T" motor in it. I've never run it up, but I probably will one day - just to add it to my personal motor database. I've got a 30A brushed ESC somewhere too ...

However, you're right Jason - it wouldn't be a simple "unbolt the brushed combination, bolt-in the brushless" because of the weight re-distribution problems. It's a shame because I'd love to know in real percentage terms just how superior a modern brushless power-train is, given a direct comparison in a single airframe. I guess a static test will have to do ...

Steve Murray
Reply
#9


That link with all the motor specs that you posted gave data for a number of speed 400 motors, all seemed to be producing around 100 W and drawing around 10A. I think you'd be pushing them a little harder if you were racing, but I don't think they would put out a hell of a lot more and be expected to live very long.

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#10

Yes - the numbers are the bottom line ... which means that the brushed power-trains that would have propelled the original Dyna-mites at 125+ km/h would have been top-notch configurations for their time?

Steve Murray
Reply
#11

(23-01-2013, 09:36 PM)smuzz Wrote:  Yes - the numbers are the bottom line ... which means that the brushed power-trains that would have propelled the original Dyna-mites at 125+ km/h would have been top-notch configurations for their time?

Absolutly you can't do that with out having a very nice slippery airframe.

The thing to bear in mind is that in order to double the speed you need to more than square the power, so you would expect that if 100w = 125 kph then 200w would equal about 150kph and 400W would get you somewhere in the rehlm of 190kph

It's much better to reduce that drag by a little bit than add all the weight of a more powerfull drive system. Because weight also increases drag you get to a point of diminishing returns.

Fortunatly technology has given us the extra power of a brushless motors and lipos with no weight penalty. How nice is that !! Smile







“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#12

(23-01-2013, 09:57 PM)secant0give Wrote:  ... Because weight also increases drag ...

I'm with you on all the bits of your post - except this bit.

Certainly there's a non-linear relationship between the power transferred to whatever is providing the thrust (propeller, impeller, turbine, whatever ...) and the velocity of the airframe - but in level flight the drag and weight vectors are orthogonal and therefore independent?...

Steve Murray
Reply
#13

Here's a link to the airfoil polars for the MH 33
It was designed by a German proffessor, who obviously has a love for aeromodeling

http://www.mh-aerotools.de/airfoils/mh33koo.htm

Very thankfully, he's published a bunch of stuff that would have taken quite a bit of time and resources to put together!!

If you look at the calculated polars, this foil does a little better than most at Renalds numbers around 400,000. probably not suprisingly it's about the thinnest too. But is has quite a constant velocoty gradient accross the top surface and doesn't seem to suffer detached flow at the Re I want to use it for. Mind you the stall looks like it might get a bit sudden when it slows up, you can't have it all can you. the trick is to keep it as light as possible then when it slows up it won't need to opperate at a CL where it's likely to stall suddenly Smile .........................that's the plan.

All those polars are just calculated by computer models and probably don't match the real world all that well any way. At least it's a method of comparison I guess.

Matrin Hepperle also has the nicest explanation of how to read airfoil polars as well. see link below

http://www.mh-aerotools.de/airfoils/index.htm

There is also a great deal of other technical info on his web site !!



(23-01-2013, 10:12 PM)smuzz Wrote:  
(23-01-2013, 09:57 PM)secant0give Wrote:  ... Because weight also increases drag ...

I'm with you on all the bits of your post - except this bit.

Certainly there's a non-linear relationship between the power transferred to whatever is providing the thrust (propeller, impeller, turbine, whatever ...) and the velocity of the airframe - but in level flight the drag and weight vectors are orthogonal and therefore independent?...


They are at 90 degrees to one another that is true but to balance that force you need lift and that means angle of attack and that causes drag. especially in a tight turn when the model is pulling 30Gs ie weighs 30 times its static weight

......edtied to fix some of the spelling Wink

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#14

(23-01-2013, 05:23 PM)smuzz Wrote:  It's a shame because I'd love to know in real percentage terms just how superior a modern brushless power-train is, given a direct comparison in a single airframe.

I can answer that for you...

I don't know if you saw it in its first powered configuration, but that 2x6 glider of mine with a Speed 400 + bolt-on speed controller could barely get out of its own way. With a brushless in-runner + ESC on 3S, it practically goes vertical at WOT.

Better yet, the prop/brushless/ESC/Lipo/modern receiver and servo combo is less weight than the original nicad pack/receiver/servos... meaning in its current powered configuration it has a lower all-up weight than the original unpowered glider had!

Consequently, I too have a Speed 400 + ESC to donate to the cause if Jason would like to do a direct comparison.


(23-01-2013, 09:57 PM)secant0give Wrote:  The thing to bear in mind is that in order to double the speed you need to more than square the power, so you would expect that if 100w = 125 kph then 200w would equal about 150kph and 400W would get you somewhere in the rehlm of 190kph

It goes up by the cube of velocity, not the square. (although perhaps this is what you meant by "more than square the power", since your examples closely represent a cubic relationship)

The Drag FORCE goes up by the square; consequently, the POWER required to overcome it goes up by the cube.

http://en.wikipedia.org/wiki/Drag_%28physics%29#Power


(23-01-2013, 10:12 PM)smuzz Wrote:  
(23-01-2013, 09:57 PM)secant0give Wrote:  ... Because weight also increases drag ...

I'm with you on all the bits of your post - except this bit.

Certainly there's a non-linear relationship between the power transferred to whatever is providing the thrust (propeller, impeller, turbine, whatever ...) and the velocity of the airframe - but in level flight the drag and weight vectors are orthogonal and therefore independent?...

They are related, essentially by the lift to drag ratio. Every extra unit of weight requires more lift to overcome it, and every extra unit of lift induces an extra amount of drag.

If your airframe has a lift-to-drag ratio of 10, and you add 10g of weight, well, you're going to need another 1g of thrust force to overcome it at comparative speeds.

Parkzone Stinson SR-10
Extra-300S EPP
F-18 Blue Angels 64mm EDF
HK Mini Cessna EPO
Spektrum DX6i - Mode 1
Parkzone T-28 Ultra Micro
E-Flite UMX BEAST
SRL Index
CloudsFly / AXN Floater
"2x6" basla/ply kit built glider
SBach 1000mm
Skyartec Cessna 182 (small UAV)
UAV-168 (bigger UAV)
"BigBoy" Hugin (biggest UAV)
X-8 flying wing
Reply
#15

Yep - that all makes sense. Thanks gents!

Steve Murray
Reply
#16

^^^^^^^^ smart arses eh !!!! . love ya work . Smile

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
Reply
#17

Some more pics of the fuse going together.

It's only a small model about the size of a Rarebear only slipperier


Chain drilling the hole in the former
   


sheeting the fuse
   

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#18

All this mathematics is going to make my head explode .....
I use the Gazz equation.... MORE POWER RULES!!!
But not before doing the Ecalc maths of course!

Parkzone Stryker 27 Evolution
E flite Ultra Stick , T 28 Carbon Z
Skyartec Skyfun Scorpion,Skyfun 90 EDF
Hobbyking Voltigeur, Funfighter T28, Mirage 2000, Minimoa 2.4m Glider
Jet Teng L-39 HPAT Stumax 90
Pheonix Tiger 50
FliteWork Extra 300 LPX 2.6M
Spectrum DX9i , DX6

Don't ever let the fear of landing keep you from taking off!
Reply
#19

Some more Pics of the progreaas so far

Tail surfaces are cut and shaped from solid 3mm balse sheet and covered in iron on film

Horosontal tail is all blue on top and yellow with blue elevator on the bottom

   


“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#20

I've been looking at motors, lipo's, and other similar model specs to get an idea of wing loadings and all up weights. I'm thinking along the lines of retaining about the same weight as the original or a similar model and seeing what sort of performance can be obtained with relatively inexpensive parts. Mostly Stuff from HK.

Here is a bit of a list I put together in xl of

The first sheet has motors that could be made to fit the Airframe I'm sure there are many more than in this list but I think it's going to be hard to go past the NTM 2836 3000 or the 2700 version of the same motor. Frank is running the 2200 version in his RareBear and it slips along quite well.
It's lighter than the original motor, a speed 400 motor weighs about 95 grams and this one weights 87 and for $17.00 plus postage I think that clinches the deal. I'll be getting one of the 2700 KV and one of the 3000.

The second sheet in the file shows a comparison of Lipos
Because the model needs to fly for about 2 mins (I'll accept 115 seconds at a pinch) I've worked out how long each pack will last at various amounts of current draw. and also what their max continuous current rating is.

So it looks like it's a choice between the ZIPPY Compact 4S 35C 1600providing 50A for 115 seconds this would suite the 3000KV motor (with the right prop of course) and the Turnigy Nano 4S 45-90 1300 providing 40A for 117 seconds. The weights are 178g and 155g respectively. For comparison 7 2/3A nicad cells would weigh 140 grams with out wires or leads. We must be in the same ballpark weight wise so far.

As far as all up weight goes I don’t want to exceed a wing loading of 20 oz per sq ft to that gives a maximum all up weight of around 570 grams. I hope to be well under this perhaps as low as 450 grams this should give me a wing loading of around 15 oz per sq ft. which will make it a lot friendlier to fly !!

So far with out the airframe we are looking at 346grams and counting so we’ll have to see how we go.

.xls motors for S400.xls Size: 39.5 KB  Downloads: 234

Here's a Pic of the MH 33 Airfoil I'm going to use to develope the templates to hot wire cut the foam wing cores.

   

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#21

The motors and ESC's have arrived quickly from HK's Aus warehouse. Smile
I decided to go with the Turnigy trust 45 A esc for the 2700 Kv motor and the trust 55A esc for the 3000kv motor

The links for the motors are here

http://www.hobbyking.com/hobbyking/store...duct=25878

and here

http://www.hobbyking.com/hobbyking/store...duct=25042

and links to the ESCs are here

http://www.hobbyking.com/hobbyking/store...ouse_.html

and here

http://www.hobbyking.com/hobbyking/store...ouse_.html

It will be interesting to see how they go towing around this little airframe.

These seem to be about the lightest ESCs that will provide the required performance. Under the heat shrink they seem to have a very decent heat sink. I will most likely be removing the plastic to allow a bit more airflow for cooling!!

I've decided to mount the motors from the back so I've cut the extra shaft off that usually hangs out there, because it's not needed and it's in the way. Knowing my luck, in a crash the battery pack will move forward and impale it self on this shaft if I leave it there.

Here’s a pic of the fire wall being test fitted to the fuse.

   

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#22

looking forward to seeing these speed demons in the air , its even better that you have different setups in both to compare them , how exciting mate .

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
Reply
#23

Looking good Jason, I can only dream of attempting this myself.
Reply
#24

Wayne,
This is a realy easy machine to make, If you like, your more than welcom to a copy of the plan.
It's only little at 635mm span, I'm streching the wings a bit out to 720mm In an attempt to ease the extra drag when pulling tight turns. Your more than welcome to a set of cores for the wings as well.
This airfoil should be very fast in a straight line but, on paper at least, it falls back to about par, as far as drag goes, when it's asked to produce enough lift to corner hard.

I'm hoping the extra aspect ratio will help a bit there. If my wing is not great It should be easy enough to make another to try, they just unbolt.

By all accounts the original design was a hit with the S400 class fliers in the UK back in the 90s.
It is very easy to make and depending on how it's powered it shouldn't be an ogre to fly.

It could have a much lighter drive system in it too. I reckon it would fly wickedly well with a 35 Amp esc, a 1000 4S and an $8 RareBear replacement motor. Should be faster than a RareBear with that set up because it's a much, much slipperier airframe. In that configuration It would be substantually lighter than the original Dyna-mite as well.

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#25

A little more progress of late.

Here's some pics of how I'm doing the faring at the front.

I used a peice of PVC tube as the frame for it so I could blend it down to an edge around the hole where the motor fits in.

   

   

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#26

ineresting . i would've went solid balsa wood and carved to suit . there must be a reason your building the cowel this way . ???
after a 2nd look i think i get it , no side clearance , so your building up an elongated oval , that will be strong for heavy landings , looking forward to seeing it finished . LOOK AT THAT DONK Shock

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
Reply
#27

Yep that's right this is the only way make it strong enough at the thin edge up the front.

You can see what I mean from the photos

   

And here's it is with the hatch on The original design was closed up at the front of the fuse but I wanted access to get at the motor screws and the ESC.

   

There is room under the ESC to slide the batterys forward to adjust the C of G. That way I can use different packs if I want to.

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply
#28

beautiful mate . nice job .

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
Reply
#29

Clever thinking Jason, good to see you thinking outside the square ... As usual !

Parkzone Stryker 27 Evolution
E flite Ultra Stick , T 28 Carbon Z
Skyartec Skyfun Scorpion,Skyfun 90 EDF
Hobbyking Voltigeur, Funfighter T28, Mirage 2000, Minimoa 2.4m Glider
Jet Teng L-39 HPAT Stumax 90
Pheonix Tiger 50
FliteWork Extra 300 LPX 2.6M
Spectrum DX9i , DX6

Don't ever let the fear of landing keep you from taking off!
Reply
#30

Thanks Gazz Smile

Now for a start on the wings
These are going to be made from a composite of "M grade" or denser EPS foam, glass, epoxy, brown paper and ply wood. I'm going to try something a little different in the way I construct them as well. They will be spared with 3 lengths 1.5mm ply which will be capped with unidirectional glass fibre. Needless to say the fibres will go span wise and to give a nice smooth finish on the outer surface and blend off the slight bulge from the glass uni I'll put brown paper on the out side. The Paper will extend a short distance past the glass this will blend it in nicely to the airfoil profile. The leading edge will just be left, "as wire cut" EPS foam and I will use light glass cloth and brown paper over the whole trailing edge span wise to about an inch forward of the trailing edge. This should give a very thin and strong trailing edge. The ailerons will be formed by cutting them out of the finished layup and there should be enough glass ang brown paper still on the wing to provide a sound structure to hinge them off.

The Idea is to be able to do it with out Vacuum bagging. This method would lend it self well to being vac bagged but I want to avoid the extra complexity because to do so makes things quicker and easier.

After the wing is finished it will be covered in Iron on film to give the bare foam bits a nice surface for the air to flow over and for the over all colour scheme.

The advantages I hope to achieve by doing the wing this way will be. Speed and ease of construction combined with the strength of a fully composite wing, minimum expense and a reasonability accurate reproduction of the intended airfoil profile. By this method it should be easy to make deadly straight wing panels as well. Which always helps if you want a nice flying model. The leading edge being just EPS foam covered with iron on film will act as a crumple zone and do less damage to any thing it hits. Should the unthinkable happen It shouldn't act like the hard edge of a fully molded composite wing.
The templates to cut the foam cores take a little work, but it's a job that only needs to be done once and many cores can be cut using The same templates.

Here's a sketch of the wing construction
   


Here's a shot of the marking out for the templates. The Airfoil profiles have been scaled to the right size then printed out. They will be fixed onto the aluminium sheets using double sided tape. Then I'll cut them out and file them to the finished size. This will form the templates for hot wire cutting the foam wing cores. There are 4 templates to be made, top and bottom for both the root and tip…….more Pics to come 

   

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)