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HELP ! EE P1 Lightning ... EDF or Prop ?

Old 01-30-2016, 03:20 PM
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solentlife
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Default HELP ! EE P1 Lightning ... EDF or Prop ?

Ok ... I have scaled up a Jetex plan 140% to produce a P1 Lightning ... P1 is the Prototype No. 1 of the record breaking awesome EE Lightning ... After various changes to design / increased power ... fuel etc. - the final P6 variant gave new meaning to Climb Rates and Vertical performance ... even to repeated intercepts of the supposed untouchable U2.

Anyway ... I am part way through the build, chose the P1 because its basically a hollow straight tube with wings and tail !! .... and I have to decide whether to fit a 50mm EDF unit or go for a prop.

Here are the photos so you can see my dilemma ...(51mm EDF unit used to ensure 50mm unit will fit)

Overall :



51mm unit sitting in front section ahead of main wing .. shows I have enough airflow UNDER wing :



51mm unit sitting at front of tail section :



51mm unit seen from exhaust outlet :



Looking down length of that 28" fuselage :



Proposed position of battery and gear on top of wing inside fuselage :



OK some dimensions so people can help me :

Overall fuselage length : 700mm (27.6")
Span : 460mm (18.1")
Fuselage width internal : 51mm (2.0")
Fuselage depth internal : 78mm (3.07")
Wing root chord parallel to fuselage : 205mm (8.1")
Tail plane chord : 130mm (5.1")

Fixed tailplane with hinged elevens to give pitch and roll ... no decision yet on ailerons on wing due to the 60 deg sweepback !

She will have no bulkheads in the lower section to allow full air passage ... but will have bulkheads to divide up above main wing to give battery / Rx / ESC areas.
Area above and below tail will be without bulkheads to allow max air exhaust.

Now question is ............. would you fit the 50mm EDF or go for a prop and allow use of bulkheads / wider range of battery choice ? If Prop ... Tractor or Pusher ?

Help !!

Here's video so you can see the original P1 ...



Nigel
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Old 01-30-2016, 03:47 PM
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JetPlaneFlyer
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I love the Lightning. A company not far from here has one parked outside their premises. They overhaul gas turbines and buying an old Lightening was the cheapest way to get a couple of Avon's for their technicians to use for training.

A prop will always give better performance and be easier for the reasons you mention. Main reason for an EDF is aesthetics but on a box construction foamy where scale fidelity takes back seat to practicality/ease of use then i'd have thought a prop would be more in keeping. A pusher would be my choice.

I think your aileron authority might be a bit marginal if using 'tailerons' only?

Last edited by JetPlaneFlyer; 01-30-2016 at 08:00 PM.
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Old 01-30-2016, 03:55 PM
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I have a few 1900kv and more motors capable of 3S / 4S power ... and so a prop job is easily sorted.

I would like to have a tractor prop for safety .. but with that long nose and incredible sweepback ... would make balancing difficult without adding weight.

Must put it through the CoG calculator.

Nigel
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Old 01-30-2016, 04:17 PM
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Ok ... calculator gives 167mm from LE of wing ... basically brings it back to near the rear of root chord.

Now the question which I have tried to avoid ... HOW to do ailerons.

The wing is 6mm depron flat plate with a single pine spar. Will it survive 5gr servos out at span to operate trailing edge of the sweep or should I go for the inner trailing edge extending out from fuselage accepting that ailerons are then at 60 deg to airflow ? If I take the inner route - then servos can be mounted close to fuselage ...

Nigel
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Old 01-30-2016, 04:21 PM
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fhhuber
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Generally 50% more watts needed for an EDF to perform the same as a traditional 2 blade prop.

That means more battery weight (so even more power) is needed to get equal flight time. Expect to need double the battery and double the watts for the same top speed and flight time.

Often, to avoid the weight EDF models sacrifice flight time with 3 to 4 min flights being common vs the prop driven planes averaging closer to 10 min.

As long as you know what you are getting into...
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Old 01-30-2016, 04:29 PM
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I'd have thought that you could bury a couple of servos in the wings with ailerons in the scale position. You might need some wing stiffening though, ailerons or no?

Here's the Lightning i was referring to, quite a nice colour scheme too:
http://www.thunder-and-lightnings.co...vor.php?id=134
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Old 01-30-2016, 04:49 PM
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Originally Posted by fhhuber View Post
Generally 50% more watts needed for an EDF to perform the same as a traditional 2 blade prop.

That means more battery weight (so even more power) is needed to get equal flight time. Expect to need double the battery and double the watts for the same top speed and flight time.

Often, to avoid the weight EDF models sacrifice flight time with 3 to 4 min flights being common vs the prop driven planes averaging closer to 10 min.

As long as you know what you are getting into...
I know well what I'm getting into ... have EDF's ... Pushers ... tractors ... as well as all the others ... currently over 50 RTG models in the hangar.

Decision is for a Funfighter 1950 KV 4S capable motor up front ... 60A ESC + SBEC halfway down fuselage ... 1600 4S sits as far back as I can get it !! I may have to shorten the fuselage front section if I cannot get LiPo back enough.

5gr servos set into wings ... decided to go the inboard section where full size has her flaps ... that way I'm not hanging weight out on the extreme span of wings.

Nigel
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Old 01-31-2016, 02:37 PM
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Originally Posted by JetPlaneFlyer View Post
I'd have thought that you could bury a couple of servos in the wings with ailerons in the scale position. You might need some wing stiffening though, ailerons or no?

Here's the Lightning i was referring to, quite a nice colour scheme too:
http://www.thunder-and-lightnings.co...vor.php?id=134
Its nice to see someone preserve iconic machines UK has produced !

Anyway .. I took your point on ailerons and agree ... so here is a series of installation photos .... only thing is I elected for safety as it will be hand launched ... tractor prop.











I did experiment with mixing ... having the 4 servos via a Vtail mixer to give pitch and roll via all 4 in unison ... but I would have to open up servos to do a bit of reversing .. so elected in the end to use a 7 ch Rx and keep servos separated ...

The elevators I think will be enough ... the ailerons out on the wing 'ends' ... can't really call them tips !! .. will give a lot of authority.

I only had two 5gr servos left ... so they are the aileron servos ... with two 9gr servos for elevators.

The LiPo ... 4S 1600 will sit in a box just in front of the tail plane. If you look back at photos - you see the XT60 is at rear of ESC ... drops in to the box.

She is turning out to be quite heavy ... given the wing area. So she will need to fly fast ...

Ok ... onto colour scheme ... interestingly I found a reference to Czechoslovak Air Force flying the Lightning - that was a surprise ! Picture attached.



Nigel
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Old 01-31-2016, 05:51 PM
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OK ... top is done ... hatch made ... battery box sorted ... balance is spot on as calculated without additional weight.

She's in 'paint shop' so no photos at present ...

Note before final piccies .... this follows my simple routine of box fuselage ... removing the need to plank and shape skins. My Concorde may be 'cartoon style' but in the air she gives that iconic shape illusion .. so has convinced me that the box style works.

The P1 was a basic tube and wings added ... unlike the later F3 ... 6 etc. which had shape and form. Later I wish to build a better scale EE Lightning ... so this is really a test bed to see it all works ...

Nigel
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Old 01-31-2016, 07:20 PM
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Actually... you don't have to open the servos for reversing... Try swapping which servo is plugged where.

For elevon the common issue is reverse switches get you to correct aileron but reversed elevator. At that point swap what servo is in which output and its correct.

those ailerons are so far to the rear that they'll have good authority as elevons.
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Old 02-01-2016, 11:36 AM
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Here she is in my typical striking visibility scheme .... and bringing the RAF Roundel in !!









Specs :

Motor: Funfighter 1950kv, 4S 1600 LiPo, 6x6 racing prop, 60A ESC

Span : 60mm
Length : 670mm

Weight without battery : 300gr
Weight with battery to fly : 485gr

Nigel
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Old 02-01-2016, 11:41 AM
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Originally Posted by fhhuber View Post
Actually... you don't have to open the servos for reversing... Try swapping which servo is plugged where.

For elevon the common issue is reverse switches get you to correct aileron but reversed elevator. At that point swap what servo is in which output and its correct.

those ailerons are so far to the rear that they'll have good authority as elevons.
Problem was 4 servos via a VTail mixer and not by Tx mixing. Separate elevator / separate aileron servos. Tried all permutations but always one servo would end up wrong way. The only way via this unit is to reverse one elevator servo so they can be Y leaded to one side of the Vtail mixer ... ailerons are fine y lead to other side. No way round it I'm afraid..... unless >

I do it by Tx ... but I've had a couple of Vtail mixers sitting on the bench doing nothing ... thought I'd give one a try.

nigel
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Old 02-01-2016, 12:49 PM
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Solentlife
You must have had one servo that was 'built' reversed.
It is perfectly possible to run 4 identical servos from one mixer with Y leads - unless of course one of your Y leads was itself reversing - as used for flaps!
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Old 02-01-2016, 02:00 PM
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Originally Posted by quorneng View Post
Solentlife
You must have had one servo that was 'built' reversed.
It is perfectly possible to run 4 identical servos from one mixer with Y leads - unless of course one of your Y leads was itself reversing - as used for flaps!
Nope ... all 4 out of box new.

I have split elevator ... split ailerons ... 4 in all.

The Mixer is the simple Vtail / Delta mixer that used to be supplied with the HK Parkjet. It takes two leads in ... Elevator and Aileron. It has only two outlets ...

Therefore two Y leads of the mixer ... one to ailerons - this is fine and you get exactly what you want.

But the elevator servos act just same as aileron by one pulling while other pushes at same time. Rotation of arm is same direction.

So to get the elevator halves to respond same - one servo must be reversed.

I even tried swapping one elevator servo with one aileron to cheat it ... no. I just ended up with a different servo operating wrong way.



Nigel
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Old 02-01-2016, 04:18 PM
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Ah!
Does this mean you want the elevators to act only as elevators?
Then the elevator servos must not go through the mixer.
So aileron servos through the mixer as normal, no Y lead required. They will act as elevons.
A Y lead from the Rx elevator port one side to the mixer, the other to another Y lead to both elevator servos. They will act only as elevators and yes one will require reversing in some way.

If you run all four servos through the mixer then all the surfaces act as elevons in the normal way - provided the elevator and aileron servos are mounted in the same geometric orientation. Was there a reason why you did not want to do this?
As in this video with 4 servos on a mixer.

All work in unison for aileron function (because the pairs will be mounted the opposite way round!). Two pairs in opposition for elevator function.
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Old 02-01-2016, 05:11 PM
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Q ... now you see where I am coming from.

Here's my video showing it as well ...



I was trying out just a simple setup but it needs as you see quite a bit of playing with to get it to work. Simplest idea in the end was to just connect up with 2 aux ch's mimicking the ELE / AIL ch's and leave it alone.

Nigel
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Old 02-01-2016, 05:18 PM
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Originally Posted by quorneng View Post
Ah!
Does this mean you want the elevators to act only as elevators?
Then the elevator servos must not go through the mixer.
So aileron servos through the mixer as normal, no Y lead required. They will act as elevons.
A Y lead from the Rx elevator port one side to the mixer, the other to another Y lead to both elevator servos. They will act only as elevators and yes one will require reversing in some way.

If you run all four servos through the mixer then all the surfaces act as elevons in the normal way - provided the elevator and aileron servos are mounted in the same geometric orientation. Was there a reason why you did not want to do this?
As in this video with 4 servos on a mixer.

All work in unison for aileron function (because the pairs will be mounted the opposite way round!). Two pairs in opposition for elevator function.
Your Elevator servos illustrate exactly what I am saying ... because you have mounted same way both. On the model ... the arms both point DOWN but servos are 180 deg opposite ... they are in fuselage sides facing OUT. That means if you take one arm of an elevator servo in your set-up ... place it 180 deg out ... THEN try it ...

OK ?

Nigel
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Old 02-01-2016, 05:22 PM
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Anyway ... forget the mixer ... its all sorted now and ready to fly.

BUT I'm of to Dubai again for a few days so it will sit on the bench with my Stampe waiting maidens.

Even though the P1 is a box with wings ... I'm actually quite pleased with how it looks. If it flies OK - then I hope she looks ok in the air. That's the main thing.

Nigel
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Old 02-01-2016, 06:21 PM
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If I was worried about the roll and elevator response I would have simply had all four surfaces acting as elevons, which you can do with a mixer and Y leads.
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Old 02-02-2016, 06:24 AM
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Originally Posted by quorneng View Post
If I was worried about the roll and elevator response I would have simply had all four surfaces acting as elevons, which you can do with a mixer and Y leads.
Q - leave it alone please - as my video showed with servos as per model orientation - it cannot be done with the mixer unless one servo is reversed.
Your video has all servos orientated same upright - my setup has two servos 180 deg from that.
The only possibility is if I grouped pairs per side - then I get four elevons, which is I reckon unnecessary on this model.

Its all via Transmitter mixes now.

The elevators and ailerons are more than enough to give desired results, and this baby I hope will have some speed meaning surfaces will only need small movements.

Nigel

Last edited by solentlife; 02-02-2016 at 07:12 AM.
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Old 03-20-2016, 06:20 PM
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OK ... one of my fears was this would be subject to serious torque on launch ... well - my fears were well based as that is exactly what happened ...



That high pitch prop .... 4S motor on such limited span ...

So the matter now is to find a way to get her airborne and fast enough to make the wing work.

Nigel
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Old 03-20-2016, 07:23 PM
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Looked like a duff launch to me. I think with a fast launch and rolling on the power she will be fine. Check CG too because it did seem to pitch up.
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Old 03-20-2016, 08:01 PM
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Originally Posted by JetPlaneFlyer View Post
Looked like a duff launch to me. I think with a fast launch and rolling on the power she will be fine. Check CG too because it did seem to pitch up.
CoG is per plan ... if anything its a little forward.

As to launching .......... I reckon she needs real speed with the flat plate seriously swept wing .... maybe a candidate for a catapult launch !

??

Nigel
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Old 03-21-2016, 10:52 AM
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Maybe, but the launch still looked poor to me. Looking at it frame by frame it was pointing up at about 60 degrees on release and seemed to immediately yaw sideways.

The tractor prop might be causing some longitudinal/directional stability issues too which might explain why it seemed to want to point in any direction other than the one it was supposed to be heading. Larger tail surfaces might be in order to compensate for the tractor prop?
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Old 03-21-2016, 11:35 AM
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The attempt to launch it appx 45 deg up is just wrong. That's a good way to make any plane crash. General hand launch should be aim it at the ground about 50 yards out. If it doesn't have more than 1:1 thrust to weight the high climb angle launch will fail every time. It will still fail many times even with above 1.5:1 thrust:weight.

From my EDF experiences... Its often a good idea to hand launch at a reduced power. (barely more than needed to maintain altitude) then ramp up power as you build airspeed.

High power = high torque being applied and you're at low airspeed (near 0) so the wings have no authority to counter it.
Good formula for having the pilot try to use aileron, inducing adverse yaw and snap-rolling into the dirt.

I'd try a take-off dolly. This eliminates the issues of hand launch and doesn't need the strong point to mount a hook for the bungee launch.
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