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I want to fly an A-4 at Flite Fest...

I set up a rudimentary thrust test with the plane on rollers and the nose against a kitchen scale. I only got 700-800g of thrust. I know this isn't an accurate test but it's a long way short of what I expected as the thrust stated by fms is more like 1700g.
Possible reasons for the reduces thrust could be:

There is a little bit of crumpling in my thrust tube. I think this stems from the fact that I taped 3 pieces of card together so i would have a large enough piece of card to work with. When I've rolled it the tape and card may not have wanted to bend together.

I haven't used the intake ring. I didn't think it would fit but after gluing al the fuse together I think I could have made it work.

The whole where the wired come though is not a super tight seal. Maybe I'm losing some pressure or disrupting the airflow here

The more I read about edfs the more I think how sensitive they are to things like this and the little things I thought wouldn't matter DO matter.

I had another flight yesterday but it didn't last long. Before I damaged the nose again. I had a bit of damage to the aileron Hirn form the last crash that I hadn't noticed and I lost control. Luckily not at high altitude or speed. However the CG was much better and I launched by myself on flat ground quite easily.

I hope I can get some decent flights in before I smash it up too much!
 

Mid7night

Jetman
Mentor
My static tests produced a little more than yours, but not much. Curious, because I'd expect more from 6s.

On the EDF installation and thrust: Clean thrust tube is important. I DID use the inlet lip, there is room. Plugging up the wire hole would probably help. Once I get the tube wrapped and taped on, I put a bit of hot glue around the wires as they come out, to plug the hole.
 

Mid7night

Jetman
Mentor
The inlets are admittedly sub-optimal; there are corner losses due to the lack of a continuous round side leading into the fan face, to name one.

If the inner sidewalls were brought in slightly, that might help clean up the inlet flow, however that would require separate inlet sidewall pieces. Right now they are connected pieces on the fuselage sides. This simplifies cutting and number of parts.

This also would necessitate a few rounds of static testing, and ideally some sort of "wind tunnel" test where there is some free-stream flow simulated at the inlet. This could be something as simple as a shop vac blowing into the inlet. Unfortunately, I just don't have a ton of extra time to take on that level of optimization testing. I'd be thrilled to incorporate elements that improve performance, as long as it doesn't dramatically increase the build complexity.
 

SlingShot

Maneuvering With Purpose
Yeah I think it will run much more optimally when it's moving through the air. I'll get it in the air again soon. It certainly didn't feel slow on the maiden.
That's the way I was thinking about it. Better flow when it's moving through the air. Maybe a little more air density.

I thought about clean flow as well. If you could make the thrust tube without a seam, that might be worth a point or two...
 
The weather here has been horrible!! No flying all week. This is extra annoying because I've had loads of free time too.

I've been thinking about my roll rate issue. My rates are that low that I have really bad resolution.

I can't put the pushrod any closer to the pivot point of the servo because it would foul on the wing. So I was thinking one of the following.

1. Cut down the aileron and glue the outside edge in place.
Pros- easy and quick to do. No need to mess around with the servo or any of the linkages. Should provide plenty of reduction in roll rate.
Cons- it brings the ailerons more inboard. I'm not sure about the aerodynamic effect of this apart from the aileron will have less leverage to roll the plane.

2. Reposition servo with a spacer underneath. In order to free up the closer servo horns holes.
Pros- potentially create the ideal throws with correct aileron set up.
Cons- quite a lot of work. May have to replace linkages. May end up damaging the plane in the process.


I would rather do option one. Any thoughts?
 

Mid7night

Jetman
Mentor
How bad would it "foul on the wing"? Is it the servo horn, or the pushrod that would interfere? If it's the horn, I say just cut away a bit of the upper surface and don't worry about it. If it's the rod itself; if you use a thicker rod, say 0.040"-0.060" wire, it's stiff enough that you can bend it up and over so it goes around the foam on its way to the surface horn, and it will still transmit the control. I've done this on a few low-profile wing installations.

I would use a Z-bend on the servo-arm side:
servo_link.jpg

The other option I didn't see you list is increasing the height of the horn on the aileron, which it sounds like isn't a bad idea anyway. That might give you some of the rod-interference relief you need as well.
 
How bad would it "foul on the wing"? Is it the servo horn, or the pushrod that would interfere? If it's the horn, I say just cut away a bit of the upper surface and don't worry about it. If it's the rod itself; if you use a thicker rod, say 0.040"-0.060" wire, it's stiff enough that you can bend it up and over so it goes around the foam on its way to the surface horn, and it will still transmit the control. I've done this on a few low-profile wing installations.

I would use a Z-bend on the servo-arm side:
View attachment 88926

The other option I didn't see you list is increasing the height of the horn on the aileron, which it sounds like isn't a bad idea anyway. That might give you some of the rod-interference relief you need as well.
Can you "jack" the servo higher in the wing to get it more inline with the top surface? I suppose you could also put the servos and control horns on the bottom of the wing, but that may be back for landings.
 

SlingShot

Maneuvering With Purpose
The weather here has been horrible!! No flying all week. This is extra annoying because I've had loads of free time too.

I've been thinking about my roll rate issue. My rates are that low that I have really bad resolution.

I can't put the pushrod any closer to the pivot point of the servo because it would foul on the wing. So I was thinking one of the following.

1. Cut down the aileron and glue the outside edge in place.
Pros- easy and quick to do. No need to mess around with the servo or any of the linkages. Should provide plenty of reduction in roll rate.
Cons- it brings the ailerons more inboard. I'm not sure about the aerodynamic effect of this apart from the aileron will have less leverage to roll the plane.

2. Reposition servo with a spacer underneath. In order to free up the closer servo horns holes.
Pros- potentially create the ideal throws with correct aileron set up.
Cons- quite a lot of work. May have to replace linkages. May end up damaging the plane in the process.


I would rather do option one. Any thoughts?
Did you ever get a chance to weigh her?
 

SlingShot

Maneuvering With Purpose
My EDF, 80a ESC and (2) 3300 mAH 4 cell batteries is 30.1 oz.

With one battery it's 19.7 oz. I have my plans. Happy Birthday to me :) Think I'm gonna fast track this one...
 
The AUW is 1252g with the 6s battery on board and some extra glue from repairs.

I just went out for a test flight after I eventually got round to doing the repairs. I either need a big hill to launch off or someone to throw it for me. I almost got it airborne bit just didn't quite get enough airspeed.

The second attempt I tried to throw it too hard and it flipped over. No damage but the battery shot forward pulling out the bullets again. It's a simple job as I already made a hatch but didn't have my long nose pliers with me.

I need to secure the battery better. I had Velcro straps which also gripped onto Velcro on the battery, but now the battery is further back it's not very effective. I might try to rig something up with a removable BBQ skewer.

Can't wait to have a trouble free flight!
 
Sorry you're having such a rough time getting airborne, Chris! Maybe I overestimated the 6s potential? I thought the 6s fan would have a lot more kick and get it moving, but evidently that's not been the case.
 

DamoRC

Elite member
Mentor
@Chris - It tough that you are having so much trouble getting her going on 6S.

Was your initial rough estimate on thrust (I think you said 700-800 grams) on 6S or 4S?

At 1252g AUW and 800g thrust on 6S your thrust to weight is 0.64.

I just did a quick check on mine - with no thrust tube whatsoever (the fuse acting as a kinda square, kinked, inefficient thrust tube).

At 860g AUW I get 600g thrust on 4S. So my thrust to weight is 0.7 - not a huge difference to yours - and it flys well (even flew it on 3S with no thrust tube)

Because of the extra AUW, your stall speed is going to be higher so she'll need to go a little faster to fly right. But I think your main issue is how much thrust you are getting out of that EDF on 6S.

You probably already checked this, but did you look to see if the thrust tube is somehow collapsing under power (could the seams you mentioned earlier be catching the air and deforming the thrust tube)?

I am sure if you can get your thrust issue sorted this thing will fly great (and on 6S - fast!)

DamoRC
 

SlingShot

Maneuvering With Purpose
The AUW is 1252g with the 6s battery on board and some extra glue from repairs.

I just went out for a test flight after I eventually got round to doing the repairs. I either need a big hill to launch off or someone to throw it for me. I almost got it airborne bit just didn't quite get enough airspeed.
I haven't built mine yet. I have paid fairly close attention however.

Assuming that your motor is developing decent power, I am reasonably certain that the problem lies in your launch. You really need to step into it and chuck it good. But not in such as way as to let the model flip backward. I think that your hand should be a little forward of the CG so that you are pulling the plane forward like a catapult. Your hand should smoothly accelerate up to around 25-30 mph or so. Level or slightly nose up on the release.
 
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SlingShot

Maneuvering With Purpose
@Mid7night

I printed out ver. 2 by mistake. Which pieces are needed to update to ver. 4 please?

Is it just the tube, canopy and nacelles?
 
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