LD-4 Design and Build Thread

[Tom Harper]

Many of the questions posed here enter the 'how high is up' category because they are not associated with a goal or problem. The realities of construction limit design zeal. The two cannot be separated.

So, I thought it might be interesting to some to follow a model from concept to flight verification and see how it works out.

What follows is the fourth in a series of models that I call 'Look Down'. The goal is an inexpensive AP model that is rugged, easy to transport and infinitely repairable. In previous discussions on this board you have suggested SPAD or other construction materials. I have purchased and evaluated some of them. SPAD is about three times the weight and cost of foam board. Also it cannot be assembled with resin glue.

Criteria:

Power..........................OS /15 glo
Propeller.......................Zinger 8x4 pusher
Area............................4 sq ft
Weight.........................40 ounces
Camera/mount weight.....5 ounces

Design:

Foam board construction - light, cheap
5:1 aspect ratio - good strength, reasonable drag
Straight line cambered section - has worked well so far
Half inch foam profile fuselage - minimum weight and complexity
Short coupled pusher configuration - easy to transport
Single wheel, stab skids - minimum weight - remove after test
Long nose to allow balance without added weight -
Rigging - wing +3, engine -3, stab 0

I invite your critique -

[Tom Harper]

Look Down - 4

[Tom Harper]

Look Down - 4

[Tom Harper]

Look Down Design and Build Thread

[Tom Harper]

The weight is right at 40 ounces but the nose is not long enough to balance with just the battery. That's OK because I can remove the lead when I add the camera.

This Sunday should be good for a test flight.

[Tom Harper]

Got in a couple of test flights:

+ Take off with the single wheel works well. Once I had to support the left tip until it gained speed but then it raced on down the runway.

+ The straight line wing section works fine. The model is fast and floats in the glide so I do not think the flat leading edge is causing much drag.

+ The OS .15 carries the 4 sq ft wing like a pylon racer. Great little engine.

- I balanced it on the wing spar - bad deal. The CG wants to be an inch or so forward of the spar.

- The foam profile fuselage is weak. It showed damage on both landings. I will patch it with sections of 1/16" ply but think it should have ply on one side if not both.

- (not design issue) The tank is leaking - replace.

I'll work on it and test it again next week.

[Sparky Paul]

Tom, pure foam makes good wings and tails, but it's not sturdy enough for the stresses the fuselage encounters.
The front ends on my EPP 3-Ds catch **** with any less than optimum landings.
Some sort of "real" structure backbone with foam filler to smooth out the airflow probably works best.
1/64" ply on both sides...
A pair of wire tip skids would make takeoffs a bit easier.
I'd made up a potential foamie 3-D using 1/4" foam board, but with the same equipment.. motor, battery, servos, it weighed about 7 oz more than the equivalent EPP airplane. Didn't bother to fly it.

[Tom Harper]

Sparky,

I hadn't considered going as low as 1/64th but it makes sense. I'll check the ply shelf and see what's there.

I made the wire skids. just have to glue them on. Once it starts to move it is fine. Looks good on take off!

[Tom Harper]

Sparky,

I put the wire skids on - didn't notice that they raised the tail a bit. Without the + angle it just scooted around and refused to take off. Finally I picked it up and chucked it - took the hand launch great! That was where we started this discussion sometime back. Looks like with enough power the TL doesn't make any difference (or maybe it was the down thrust aft of the wing).

So now it looks fine under power. But, as soon as the engine stops it wants to drop off into a spin. Think I'll put small tip fins on the stab and cut down on the area up front. Also will box the forward fuselage to give it some strength and to make it act less like a forward rudder.

[Tom Harper]

It took more than a week but it all worked (I've done worse). I removed the single gear, boxed the front of the fuselage and added fins to the stab tips. Checked the CG and added about four ounces of lead to the nose. This is about right because I can remove the lead when I add the camera.

The model is very well behaved. It hand launches well, climbs aggressively and has a straight, controllable glide.

So:

The wing section works

The high thrust line does not prevent hand launching

The very short tail moment is not a problem but you have to have a lot of fins.

Next step is the camera.

[Sparky Paul]

Tom, good stuff!!
I'm looking around for a more expendable/expanable airframe that slaps together..
:)

[Tom Harper]

Sparky,

I still like the foam board but it may be too heavy for electrics.

If you expand the left thumbnail above you can see that the top of the fuse is covered with paper. I asked the art store if they had any paper with the same plastic coating as foam board and sure enough they do. It weighs about the same as 1/16th inch balsa and costs $2.70 a sheet. It is stronger than balsa in tension and isn't as brittle. You just cut it out with scissors and glue it on. Goes around curves real nice.

[Tom Harper]

I ran some numbers for the LD-4 with present mods:

Total fin+rudder area as a percent of wing area = 24%

Total stab+elevator area as a percent of wing area = 42%

The stab is too big. The elevator movement has to be minimal to keep from overcontroling. I think it should fall between 30% and 40% of the wing area but it works fine and I'm not going to mess with it. It trims to almost 0 degrees so there's not much drag and better too much than too little.

The all up weight with the Olympus C-50 is now 57 ounces. Well over the 40 oz goal. That's also 4 ounces over last weekends flying weight. It works out to:

Wing loading = 14.25 oz/sq ft
Power loading ~ 40W/pound

Wing loading is OK but power loading is getting marginal.

Anybody have views on this?

[Tom Harper]

Just flew at the above weight and got pictures. The plane and engine carry the weight but I breath easier when the hand launch is over. Thanks to the excellent skills of pilot CARL MOORE everything went fine. The model even makes 'power on' landings without the wheel. Not bad for a $5 paper airplane.

The photos are:

In the air and taking pics

Approach

Almost down

The little red things in the ground are plastic feathers for runway alignment.

[avf]

Looks very neat !

[Tom Harper]

avf,

Thanks!

I hope to do some serious aerial photography tomorrow. And - Look Down 5 should be ready next week:

[Tom Harper]

Got out early this AM to make a first try at an actual site. Fantastic day! The plane and gear pack nicely in the car - design requirement. The hand launch was acceptable and the photo passes were OK for a start. It is difficult to place the model exactly on target. Made four passes and then decided to bring it down while we still had power.

On site landing ability is one of the major design goals. It only has to survive and be repairable. It came in nicely aligned with the old road, Just about down and a gust caught it and dumped it over the edge of the cliff. The glue joint of the stab snapped so it could not make another flight but it survived intact. That was the design requirement:

[vintage1]

Nice to see someone flies off worse terrain than I do :D

Prickly pears eh?

[Tom Harper]

Yep, and creosote, mesquite and cholla too, but no rattlesnakes today.

[vintage1]

haha.

I spent three years in S Africa, and during that time I never saw a snake bar once, when we wer canoeing up a creek, and one was swimming across it.

I was going to bash it over the head with the paddle, but my GF said not to, so I took a photo instead.

Later on we ID'ed it as a puff adder. One of the most dangerous snakes in the country.

I've seen more snakes in the UK than in Africa :(

But I saw more Rhino and warthogs there :D

[Tom Harper]

Warthogs, yuk! I'll take rattlesnakes.

LD-4 mods:

Since this model was designed for simplicity and quick use the tank was only 2oz. Turns out that is not enough. Carl wants time to make some practice passes before I turn on the camera. So it gets a 4 oz tank. Also lengthened the needle valve for last minute adjustments. Added a stern post to the foam aft of the wing.

This is trivial stuff but I'll bet it adds 3 ounces to the take off weight. Still considering some kind of bungee powered catapult. But, the plywood and dowel launch hook will add another ounce or two. Creeping obesity!

Oh yeh, I trimmed the sub rudders. Try to keep them from dragging in the dirt.

[Tom Harper]

If LD-4 is a design, and not just an excercise in rigging, then it should 'scale' and yield a model of similar performance. To test that we need to move on to LD-5. I decided to scale up to 6 sq ft. The two wings are actually 576 sq in and 869 sq in and (869/576)=1.51. The square root of 1.51 is 1.23 so I scaled the linear measurements by a multiplier of 1.23. The result:

Area=869 sq in ~6 sq ft
Span=66"
Root chord=14.125"
Tip dihedral=6 deg
Washout=3 deg
Power Norvel .25 BB (.6 hp 448 watts)
Prop Zinger 9x4 Pusher
Weight=90 oz (12 oz of this is the camera and it's mount)
Wing Loading=15 oz per sq ft
Power loading=80 watts per pound, 74 watts per square ft

The max weight scales to 104 ounces. At 90 ounces this one is heavier than I want but still lighter loaded than LD-4.

Although designed for hand launch I bolted a tri gear on the bottom for testing. ROG is gentler than hand launch and may allow less traumatic debugging. Then I can remove the gear and bolt on some skids.

We shall see this weekend:

[Tom Harper]

Well they both fit in the car and you can get them in and out without breaking anything important. But, today it was WINDY. Too windy to think of flying.

So I ran up the engines to make sure everything is OK. LD-5 did fine. It is ready to go if we get a good day this week. LD-4 had serious problems with the new tank. It is too high. I did not want to cut into the wing because early models of this design had the bad habit of shedding wings in flight. But, there was not much choice so I sunk the tank into the wing and reinforced the surface with 1/16th ply. I think it is enough because the front part sandwiches the spar and brace. We shall see. Anyway it is a lot better tank mount. Should run fine without hydro lock during start.

[Tom Harper]

Got out early today and enjoyed 4 hours of light breeze. LD-5 flew right off the drawing board without alterations. Really nice in the air and trimmed for hands off. On the third flight we loaded the camera on board and got some reliable photo runs. Our aim is lousey. Gotta get better at that.

Also flew LD-4 with the new tank. Plane works fine but creeping obesity is taking it's toll. Could not get a hand launch without some wind. Of course the calmest part of the day was when I was standing out there with the engine running waiting for a breeze. The shadow photo of LD-4 is kinda cool.

So, once again we got flights and photos and the airplanes came home in one piece. However, yours truely left the ground camera in close up mode so the great shot of LD-5's first take off is BLURRED.

[Sparky Paul]

I've found that providing some sort of "line in the sky" helps hold a heading-ground line.
I use the edge of our sunshade canopy, both the vertical posts and the bars between the posts to give me a reference as to where the plane is in the air, not relying on what I feel my head position is telling me.
A long vertical pole can be used to provide this "line", standing on one side when flying in one direction, and on the other side to fly along on the way back.
Lateral offsets from the desired ground track are very difficult to project up, from the pilot to the plane when flying it.
A second set of eyes can be very handy here, with the pole as a reference.

[Tom Harper]

Thanks for the comments.

I copied the plan for the rig you posted a while back. It makes sense but there's too much to it. Now a single pole might make sense. You are essentially flying a collision course with the pole so the position of the plane does not appear to change - old sail boat trick. We'd have to guy it or maybe a small PVC stand with some rocks in it could work.

The other option is to stand on the target and fly past almost overhead. That and a flagman to signal where you are on the approach might be enough. Our next target will be a small mesa about thirty feet wide and a hundred feet long. That should be an ideal target. After that we want to do some Prairie Dog towns. They are about 200 feet square. Definitely tougher. We'll start at high altitude and use a flagman and move down until we determine the resolution required.

I think we have the airplane we need now we have to work on procedures.

[Tom Harper]

Hmmm....two steps forward and one back.

We were out on the mesa shortly after seven. No breeze to speak of. LD-5 has 4 flights on it without incident so we decided that it was the best camera plane to use.

Nice hand launch and a couple of camera passes then tried to gain a bit of altitude and get position for serious photography. The wind aloft was so great that the model would not make headway. It just stood in place with the engine blaring away. There was less than a breeze on the ground. Went around to the east to gain position and suddenly the left wing folded. A strong gust must have hit it broadside.

The model spun down vertically onto the side of a hill over across an arroyo. Check out the hole where it hit. Didn't break the prop though. The photos are:

1. Crash site
2. Hauling stuff down the hill
4. Scrunched rcvr
5. Wing that folded

The camera and most else survived but I think the rcvr is toast. No pictures, the camera had retracted before launch - gotta look at that.

The wing break started just at the end of the center spar doubler. It looks like that is the max stress point. The center wing brace on LD-5 is and inch or so shorter then on LD-4. That may have been a mistake. LD-4 is more heavilly loaded and has survived worse.

The model can be rebuilt. I think craft of this size require 1/2" Foam Board for the wing surface with 1/2" x 3/8" spruce center spar. A six square foot model of this weight may also require a Norvel .40.

[Sparky Paul]

I was talking to Tony Frackowiak today.. he's flying a mule for NASA/Sandia..
Weighs 76 pounds, uses 400 feet of runway for takeoff, has a DA-100 for power.
Wingloading is 97 oz/sq. ft. !!!!!
It flies a payload to 3000 feet and releases the payload.
.
On LD-6.. you're getting into the region where foam board is counterproductive weight wise. Balsa-spruce structure is much more efficient.. less work for the motor.
But more fragile.
Possibly cutting a foam wing from block, with a real airfoil and glass cloth covering..
I've wrecked three of the 2M wings I use for AP.. have replaced 2 of them, ready to cover, but lack any enthusiasm to complete them right now.
A reliable airframe is still not in hand.

[Tom Harper]

76 pounds - Yikes!

I did not expect the wing to fold. The tips are just butt glued to the root. I thought one of them might go but not the wing root. Obviously there is a large force with a sizeable moment arm acting there.

I have it pretty much back together. Now I have to make a decision on the wing. I want to stick to Foam Board for a while longer. 1/2" foam board does not weigh much more than 3/16". It's the paper that weighs not the foam. But the LE and TE get large and the spar is heavier. I'm committed. I'm going to make it work. The sound you hear is either my fingers against the keyboard or perhaps my head against the wall.

Anyway a couple of pics:

1. Wreckage
2. Tracing the tattered remains
3. Clean up the lines
4. Make two the same
5. Build a new front end

This stuff is so neat to work with!

[Tom Harper]

Since I am adding a new wing I have the luxury of testing the old one to destruction. I chucked the undamaged side in a vise and attached a spring scale at the MAC. Then I pulled until the spar cracked. It cracked at the same place the other one failed. The pull was 9 pounds. So if we assume that each wing carries 1/2 the load then the g force (for a 5 pound aircraft)was:

18/5=3.6 g

And, we know that the model is being subjected to g forces greater than 3.6. I will make the same test on an equivalent of the new spar.

[Tom Harper]

Replaced the wing with one built from 1/2" foam board. Used a 1/2 by 3/8 spar and broad balsa TE. The wing weighs 20 0z as opposed to 15 oz for the one that folded. The wing is strong enough to stand on. It won't fold but it might rip the fuselage apart.

1/2 inch foam board is tougher to work with than 3/16. I was not able to get as much camber into it. My fault - should have made the spar slot slightly larger. And you end up with a 1/2 inch blunt TE. Had to use a massive hunk of TE stock. The result was a wing of less camber and lower incidence angle.

But, hey, it should be OK. With enough power anything will fly.

The previous weight was 5 pounds 9 ounces. The weight now with repairs and 2 oz of lead the get the cg right is 6 pounds 6 ounces. The calculated scale weight, from LD-4 is 6 pounds 7 ounces.

Well the two pics show it at the field and ready to go. The engine fired up and away it went. It taxied at a great rate of speed and that's about all. Finally got it off the ground but it was sluggish. Not it's usual self. Aborted the take off and it came down hard. Did not do any damage but oddly the nose hit and broke the welds on the battery pack. That's a first.

The 1/2 inch foam produces too clunky a wing for this size model. I'll leave the 1/2" spar and leading edge in place. But, stripped off everything aft. It will be replaced with 3/16 foam with a reasonable TE. Will fair the spar with TE stock yielding a crude Jedelsky section and the camber will be restored.

[Arthur P.]

Very interesting development. I hope you don't mind. I just put a link to this thread into the Aerial Photography forum (where I would have actually expected this thread to have been located).

Any updated plans? Might get a few more people working on the design and rapidly improving it.

[Tom Harper]

Arthur,

Thanks, I put it here because the layout is unusual and the purpose of the thread is to track the compromises in design issues. I'll post a current plan.

[Tom Harper]

Replaced all four rear wing panels but left spar and everything forward.
The wing section is shown below. Not bad. Will try it on the club field Sunday. No real field work until next week.

[Tom Harper]

Arthur et al,

This is the current layout for LD-5. The area and aspect ratio of the wing is still 6 sq ft and 5:1 but I have moved the dihedral break to put more of the area at the tip.

(error on drawing - stab span is 32")

[Tom Harper]

Two flights today without incident. Takes off nicely. Requires some up trim for hands off. More than the original wing.

The original wing had much smaller washed out tip panels. So the effective incidence on this wing is about +1.5 deg instead of the original +3 deg. The up trim makes sense in that case.

[Tom Harper]

Meanwhile, back at LD-4. The OS .15 has been snitty lately so I put it on a bench mount. The problem was that the needle valve wants 1 turn open - no more! Now starts easy, runs fine.

As the summer heats up LD-4 has not been very enthusiastic about hand launches. One source of more power would be more nitro. So while I had it on the bench I tried some old (very old) 25% nitro to compare to the usual 15%. It picked up 1000RPM on the 8x4 and turned 8x5 at the same RPM. Fresh fuel would probably do a bit better.

Next time out I'll use 25% nitro and an 8x5.

[Tom Harper]

I've got two of this design flying and ready to do some serious AP.

It's time to do a design summary and use what's been learned to build another one. One thing I need to know is how much power is actually being delivered to the prop. So, I packed up the American Hobby Products dyno and went out to the field.

The results - 24 inch ounces torque at 13000 RPM on a Zinger 9x4 (.25 cu in). That calculates to .31 HP or 231 watts. The mfg claims .6 HP at 17000 RPM. On a cold dry day at sea level, with 35% nitro that's possible. I was running a mile high at 100 deg F on 15% nitro.

During break in I tached this engine at 15,500. Think I'll check everything and try it again. Although the results are not all bad. That's 1.28 HP per cubic inch. And it is actual power delivered to the prop.

[Tom Harper]

You need a firm stable mount to get reliable readings out of the dyno. The readings I took yesterday on the flimsly stuff at the field were definitely suspect. So, I moved a table into the shop bathroom and rigged an exhaust tube to run out the window. Then firmly mounted the dyno and got good lighting for the tach.

Next, and most important, checked with the wife - "it's your shop, do anything you want", says she - wonderful woman.

So I put in the ole earplugs, turned up the cooler fan and fired up the engine. Now that's neat. Comfortable chair, good light, air conditioning it doesn't get any better than that. Well at least not until my exhaust rig melted. Gotta use more silicone tubing on the leader.

Anyway - new data:

28.8 inch ounces at 15800 RPM for 336 watts delivered to the prop
.45 horse power.
1.8 HP per cubic inch

[Tom Harper]

Reworked the exhaust tubing and it is much better. There is some odor but it seems to be the engine rather than exhaust.

Ran the pusher prop again and got the same readings as I did at the field - .31 HP and 231 W at 12800. The engine gets hot fast with the pusher and no augmented air. So, I decided to just use a Zinger 9x4 tractor on the stand. Should give the same readings as the pusher in the air. I must have 2 dozen Zinger props but not a single 9x4 tractor among'em. I did find an old Top Flite 9x4 tractor. It is close so I used it. I got 13300 RPM. Did not bother with the torque reading. The engine held a steady setting without getting hot.

So what's with the Master Airscrew 9x4? twenty two hundred more RPM and more torque. It weighs 30% more than the Zinger and has a slightly narrower, molded blade. I have not been able to find a molded 9x4 pusher prop.

Anyway tomorrow I'll fire up the engine and launch it immediately. That should give me good runs.

[Tom Harper]

Beautiful day! Fired up LD-5 and launched quickly and it nosed into the dirt. Don't know why. It just didn't like the idea of flying. So we flew Carl's SS and looked for artifacts for a couple of hours then decided to try one more time. Fired up the engine and launched and it flew out of my hand like a bird. I must have screwed up the first launch.

Carl complained that it was not turning right. We test flew it the previous week and did not notice any problem picked up during repairs. When I examined the photos I see a 30 degree drift. It may have just been fighting the wind. In any case it needs more control so I will increase the rudder size. Or possible just cut down on the passive outer fins.

Got the best photo runs ever. Landing was a problem and it looked like Carl set it down nicely on a fairly barren point. But he was about 20 feet south and it wound up on the side of the point instead of the top. Interesting recovery problem.

Photos:

Flying area
Landing
Here I am falling down the hill
Recovery
Aerial shot

[Tom Harper]

In the above landing the model appears to have hit the side of the hill head on. Previously it had nosed in from an aborted take off and once from a bad hand launch. The nose was battered (first photo). That's OK since 'good looks' is not a design goal. Opened the paper to examine the structure and you can see that the 1/2" foam board crutch is crumpled. That's OK too. I will reglue any separated joints but not replace the foam yet.

The only other damage from the hillside landing was that about half the elevator hinge was torn off the stab. Hit a creosote branch. The monokote hinge remained attached to the paper. The paper separated from the foam. Reglued it.

[Sparky Paul]

The photo of Carl with the plane.. that's a BIG plane!
The size hadn't made itself obvious previously.

[Tom Harper]

That's me, Carls too old to climb around on those rocks.

Yeah, it's six square feet.

[Tom Harper]

Design Review:

LD-5

Area=6 sq ft
Weight=107 0z = 6.7 Lbs
Power=.31 HP 231 Watts
Wing Loading=18 Oz Sq Ft
Power Loading= 35W/Lb
Power Loading= 38W/Sq Ft

(power is measured at prop so multiply times 1.4 to compare to published stuff)

Cost: The Foam Board, spruce spars, balsa LE and TE add up to about $15. Everything else can be salvaged.

+ This model meets all of the design goals and has yielded some great photos.

- It is not an aggressive flyer. A more responsive model would be easier to place on target and would be more confident at low altitude.



So LD-7 (LD-6 is under construction but I'll finish this one first)

I can jump the power 50% by just turning the engine around and using a Master Airscrew molded prop. The engine can then be moved up over the wing which allows the nose to be shortened giving a much more compact model. The basic construction will follow LD-4 - a 1/2" Foam Board profile with the fuselage boxed around it. The goals are:

Area=6 Sq Ft (same wing with ailerons)
Weight=80 0z = 5 Lbs
Power=.45 HP 336 Watts
Wing Loading=14 Oz Sq Ft
Power Loading= 67W/Lb
Power Loading= 56W/Sq Ft

Same airplane - just turned the engine around, shortened the nose and raised the stab 7" above the wing.

The initial sketch:

[Tom Harper]

Decided to Tear down LD4 and use the wing on the tractor version. Which becomes LD4-2. It really is the same airplane with the engine truned around. I slimmed the fuselage quite a bit and moved the engine as far forward as necessary to get the CG right without adding weight. It looks pretty good so far:

[Tom Harper]

Should fly it this Sunday. Bolted a landing gear plate on the bottom for testing. Still using Sparky Paul's suggestion and it definitely makes first flights less damaging. Everything is new except the wing which shows some of the wear it got as LD-4.

No camera yet. Just a half pound of lead under the hatch cover.

[Tom Harper]

It balanced a bit nose heavy so I did not bother to check the CG with the tank full - dumb, Dumb, DUMB! The 4 oz tank is 8" behind the CG - that's a big deal.

Anyway it made a nice take off. The controls were wildly sensitive and it never gained altitude. Went behind the club shelter and Carl could not see it. So it plowed in to the ground. Not much damage but it does need a nose job.

The configuration looks OK. The high thrust line did not give any problems and the take off speed was good. It just did not like the idea of flying with the CG on the LE of the rudder - picky, picky, picky. I'll move the engine forward so it is over the CG and mount the tank opposite the engine cylinder. The tank is just too far back.

[Tom Harper]

Spliced a couple of inches into the profile to move the engine over the CG. Replaced the nose housing. The servos are still in the nose cone but the battery is now just forward of the engine. The fuel tank is in the cheek cowl almost over the CG.

We'll fly it again tomorrow. The monsoon has started so I hope won't be too wet.

[Tom Harper]

Problem:

In the pusher configuration the wing was up close to the thrust line. Now it is well below the thrust line in order to clear the propeller. With the high thrust line and low set draggy wing the nose down vector is just too great. The model would take off but not gain altitude.

One of the 'secrets' that made the pusher fly was setting the engine to provide up thrust. I did not do that when I converted it to tractor.

The other problem is marginal power. The OS.15 is a great little engine. But a four sq ft wing and >50 ounces is border line for it.

I installed a Norvel .25 with 5 deg of up thrust. Should fly it today:

[Tom Harper]

Lot's of flash flooding last night - the north end of the field is washed out. Today is overcast with threatening clouds. However we did get some flights.

The first flight showed no improvement. It slurred around and settled back to earth. Decided to add weight to the nose. For the next flight it was carrying just under a pound of lead. Spent some time on engine adjustment. Released with the Norvel running slightly on the rich side.

The model roared off the ground straight and level. After some trim it flew hands off and did not show any bad habits. The elevator trim is flat. There is some right trim. I will examine the model to determine the reason.

The CG is at 14% of the chord. It has to be so far forward because when the AOA increases the engine tilts back and the CG moves back. It must be far enough forward to compensate.

The model looks good and flys reliably. The tractor mod is a success. I want to put in at least two more flights before I place the camera on board.

The CG information let's me go ahead with construction of a larger version.

[Tom Harper]

The present numbers on LD4-2 are:

All up weight= 72 ounces = 4 lbs 8 oz

Wing loading = 18 oz per sq ft

Power loading:

84 watts per sq ft

75 watts per pound

(Based on my dyno readings)

LD5-2 is under way. I am using the old wing and stab to keep it as close as possible to LD5. Ii will again be LD5 with the engine turned around. Here is the vertical crutch being glued to the wing. The stab is getting some repairs in the background.

[Sparky Paul]

The wing loading is a bit porkish... :)
Makes for a fast glide.

[Tom Harper]

Yeah, when the engine quits you gotta be ready!

I can move the battery up front and get rid of some of the lead. When the gear comes off, for hand launch, it should be right at 16 oz per sq ft. It ain't no sail plane.

[Tom Harper]

Moved the battery into the nose and removed ~3 ounces of lead. Still have a couple of ounces of lead for safety (and the 9 ounces of lead to simulate the camera).

Beautiful day. Spent some time on the ground adjusting the engine low end. Put in three flights - two ROG and one hand launch. The hand launch was in still air. Rose very nicely.

With the present rigging the model performs very well for the intended application. It flys aggressively and goes where you aim it. The hand launch is smooth with no tendency to drop on release. Climb is outstanding. Most of the flight is at 1/3 to 1/2 throttle. Duration is about 18 minutes on 4 ounces of fuel.

The tractor engine works much better. It does not overheat on the ground. This allows time for adjustment and it does not sag during hand launch.

Ready to do some application AP next week.

Problems:

1. Control surface ends fray with use. I will use thin plywood inserts and small nylon hinges at the surface ends.

2. Short coupling makes the plane difficult to orient at high altitudes. In a high altitude circle it is a blob. Will add reflective covering to one side but I don't think it will help much.

[Sparky Paul]

You might paint the bottom of the wing black.
I find that having one tip transparent yellow aids in orientation as well.
Or, since like mine your skies are usually blue..
Dayglo on the tips.. red-orange on the left, green on the right.

[Tom Harper]

I'll try color. There's no light transmission so it won't be as dramatic as yours above. Bright yellow might work though. Will give it a try.

Thanks!

[Tom Harper]

Gave LD4-2 a real field test yesterday. Drive 75 miles and take the weather you get. The wind was a problem.

The throttle servo detached itself. I need more plywood under it for the screws to hang on to. Blew a glo plug. The camera servo grabbed a bunch of foam rubber and made growling noises. All stuff that worked after a quick field fix.

The wind was a problem because the engine did not throttle properly. Couldn't get the thing down without killing the engine. Initially it was due to the loose servo. After that it was just lack of adjustment. So, back to the local field for a while.

The Camera set up worked fine. Top access to the camera is a must. I downloaded the images to a lap top after each flight and put in a fresh camera battery. I'll work on an external USB rig but to do any good I'll have to use an external battery on the camera.

LD4-2 is just what I need. It flys away from a hand launch and goes where you tell it to. No problem with the rough field landings. Small and easy to transport. And, it's cheap. Still very happy with it.

Photos:

Santa Fe Tank and Prairie Dog town from close to 600 ft alt
My car is the black blob lower center

Non aerodynamic hazard - he did not want to give up his mud hole

[Sparky Paul]

I was riding around the perimeter road out in the desert, and saw a "range cow" taking its leisure.. as I passed.. HE stood up! To get back to the base, I had to come back past him... he was still waiting, but confused about exactly what kind of thing he was seeing..

[Tom Harper]

LOL -- watch out for those kind of 'cows'!

[Tom Harper]

Spent the day with the throttle control and glad I did.

The throttle servo is in the wrong place - seems there is more to design than wing loading. I need to lower the servo mount. That will be a stronger position and make the run to the throttle arm a straight line.

The weakest link on the Norvel is the spring loaded Idle Stop Screw. The spring is not strong enough to keep the screw in place. Fortunately the carb barrel drops out (on a sidewinder) before the screw blows off into the wind. The barrel hangs on the fuel line so it does not go any place. I think the combat guys glop the carb area with RTV or Goop. I'll do that or put some LokTite on it or both.

Last week's sortie in the boonies picked up a lot of dirt. The plane was covered with red dust. Some from flying and a lot that blows into the car during transit. Definitely had carb adjustment problems from dirt. Need to develop some better habits and maybe add some fuel filters.

However, When the fuel line was clean, the carb barrel stayed put and the throttle linkage moved the little arm thingie, LD4-2 flew fine. It still has a tendency to turn left which may simply be torque. At low throttle it performs nicely. Made a number of slow speed passes over the field. The carb fell apart before we could get it down low.

Will work on throttle problems and put in more time at the club field before heading back out to the wilds.

[Tom Harper]

Removed and disassembled the carb. The barrel was galling in the cylinder and noticed that the idle stop slot was nibbled on the edge. Cleaned everything. Lapped the barrel into the cylinder with a mixture of castor oil and baking soda. Cleaned again. Works smooth.

The Idle Stop Screw was too loose and the spring was not holding it in place. It was so loose it allowed considerable end play. That would make idle settings unreliable. Also the steel pin against the steel barrel created a rough bearing surface.

Rethreaded the Idle Screw hole in the carb and tapped it out to take a 4:40. The hole is tapered so it required a little tap oil and some care. Replaced the steel screw with a nylon 4:40. I tapered the end as little as possible. Now I have a thread that I can replace (for a lot less than $29.50) and a nylon Idle Stop Screw that bears smoothly against the carb barrel. The nylon screw compresses in the taper so it fits tight and won't back out. I used the spring too - just in case.

Moved the throttle servo down so the linkage is aligned with the throttle arm. Made a new link out of steel rod. Also added a tensioner (rubber band) so that there is no end play in the carb barrel. I now have a very smooth throttle set up that I can control with micrometer accuracy.

I have seen this same problem on Super Tigres. Usually ignored it because the engine is either on or off. But, this design needs to be overpowered on the hand launch and accurately controlled for low speed passes. Think I'll do the same mod to the Super Tigres.

[Tom Harper]

Checked my Norvell .40 and found a compression spring behind the carb barrel. Then found it on the parts list. Musta lost it when the carb fell apart.

Looked at another Norvel .25 and found that it too was missing the compression spring. I wrapped the thinnest piano wire in my stock around a 10:32 bolt for a six turn spring. The bolt pitch is about right for the spring. Made one for each Norvel .25. They droppped in behind the barrels and both work well.

[Tom Harper]

The mods worked, but it needs more right thrust. Still prefers left turns under full power.

Carb problems. This is a dirty operation. Dirt seemed to be the problem. Engine ran after we pulled the carb and cleaned all of the tubes and holes. From now on the engine travels covered.

Put the training wheels on for the day. It flew nicely, Made lot's of mid level (120 to 180 ft) passes at low throttle. I estimate the velocity at 30 FPS +.

Next flights will be in creosote.

[Tom Harper]

I don't like the tank on the cheek mount. Without padding there is some foaming and that position increases drag and probably vibration.

Also, I'd like a good way to filter the air to the carb. Those little plastic screen jobbies at the hobby shop don't do much.

There is a solution that has been published over the years. The carb manifold can be extended by running a 1/2" PVC tube from the engine and pushing the carb into the other end of it. I have seen this done for a couple of feet as an experiment. There are numerous benefits. The tank can be placed anywhere you want since you can mount the carb next to it. The carb can be buried in the fuselage so you can build a filter box around it. The engine sucks on a large volume manifold so there can be an rpm increase. Problems? Starting can be a problem because you have to get the manifold full of mixture before the engine can use it.

The advantage to this operation is that I could get the tank inside of the airplane and directly below the engine - on the CG. And, I could build a monster air filter around the carb.

Rummaging around the shop I found some thick walled aluminum tubing that is slightly larger than the carb mount on the Norvel. I can turn it down a few thousandths for a good fit. Half inch ID PVC was 40 cents a foot at the hardware store. So, I got the parts.

I'll try it on the bench and see what happens.

[Tom Harper]

Turned the aluminum tube down a few thousandths so it was a good fit in the carb socket. Added a foot of PVC and stuck the carb in the end. Then I tied the carb to the top of the tank.

Starting was different. You have to get the manifold walls wet. Like pumping the accelerator to start my old La Salle. The engine starts OK once you get the hang of it. The run didn't seem to be completely smooth. It looks like droplets slough off of the manifold wall and cause little surges. There was good response to the throttle and the idle was normal ~900 RPM.

The main difference was slow response to needle changes.

The guy who wrote the article on this scheme claimed a slight RPM increase. That's not what I observed. The following measurements were made sequentially. Temp 87 degrees, humidity ~35%, altitude 5000':

Stock muffler extended manifold.......12,000 RPM
Ky Mousse muffler extended manifold.15,400 RPM
Stock muffler stock manifold............15,900 RPM
Ky Mousse muffler stock manifold......17,600 RPM

An unexpected result is that the RPM increases for the first third of throttle closure. It looks like the constant flow requires a smaller carb throat. A bit of engineering is in order.

Think I'll set it aside for now. When I get time I'll try again with a longer, right angle aluminum insert and a carb from an .09. Also need a priming port. I think I'll run the manifold vertically in a rigid mount.

Anyway it was an interesting couple of hours. The tank will have to stay up in the cheek mount.

[Tom Harper]

Still working on turning the engine around on LD5. Mounted the engine on the stand and it turns a good 1000 RPM higher than the Norvel on LD-4. This one spent a year in combat competition. Must be broken in!

Plan to fly both of them this week.

[Tom Harper]

Last part - the cowling. I used to cross grain sheet with 3/32" balsa and cover it with Monokote. Expensive and time consuming. Poster board (paper) is lighter, cheaper and stronger. It's also a lot easier. Just wrap the paper around the nose, trace the outline and cut it out with scissors. Glue to the top first then turn it over and do the bottom. Finish the edge with sand paper.

All that foam up front is to protect the camera in a crash - it works!

The weight is just under 93 ounces. LD-5 pusher topped 103 ounces. So I have saved some weight.

[Tom Harper]

Beautiful day! The Kombat Kan muffler is amazing. The model lifted out of my hand. And, it idles down to 900 rpm.

It was very windy at altitude but we got 190 images. The aerial below was at 360 feet. The flight lasted about twenty minutes. Landed in the creosote with preditctable damage. The profile section snapped off of the wing. That's the idea. Take it home and glue it together for the next flight. If I strengthen the joint the landing will just rip off the wing.

Pictures are:

1. Car and pilot area - we are down and to the right of the car.

2. Creosote with LD4-2

3. LD4-2 where it hit.

[Tom Harper]

Really nose heavy. That long snout should have been a clue. Overcompensated for the problems with LD4-2. Oh well - saw off the nose and move everything back.

Flew OK in spite of problems until I ran into carb galling again. Others have had the same problem. Dirt, I assume. Lapped the carb barrel with castor oil and baking soda during the football game until I fell asleep...zzzzzzzzz

[Tom Harper]

Cut about four inches out of the nose. Moved everything back toward the LE of the wing. I over did it a bit. The camera sets the CG and I want to be able to use a larger camera. So I made a ballast box and compensate with film cans full of lead when empty or using the Olympus C-50.

This weekend was our annual club Fun Fly. Not much time to check out LD5-2. Did get in a couple of flights Sunday morning. Same old stuff. Flew fine with close to a pound of lead in the ballast box.

May not do more testing this week. Have to get a retina (or something) repaired with a laser. Must be like my paper airplanes - when stuff falls off you just glue it back on.

[Tom Harper]

Dr. says I'm just getting old. I didn't need to pay him a hundred bucks just to hear that. Anyway they didn't do anything, so that's the good part.

That last flight (post 69) yielded a ton of useful photos. I want to get out there again before it gets too cold (must be age). But, I want to move the tank into the fuselage first. The intake extension worked OK so I made an adapter about four inches long. The manifold ID is 1/4" instead of the previous 1/2". I didn't bury the carb in the fuselage yet. I left it on top of the wing for easy access.

The tank is in the left (from the rear) side of the plane and the right side is filled with foam rubber to act as an air filter for the carb. The carb intake is fitted with a couple of inches of plastic tubing that extends into the filter foam. The feed from the tank comes up through the wing directly under the needle valve.

Threaded a primer fitting (necessary) into the adapter and capped it with a nylon screw.

The pressure and filler tubes extend through the left side of the wing. The left side of the model shows the ravages of endless modification and numerous crashes. It may be time for a new profile section...........nawwww.

Forecast is for rain but I still may be able to test it this weekend. Then back out to Parida Hill for more photos and probably more damage to the long suffering airplane.

[Tom Harper]

Ran up the engine today. It ran OK but peaked out at 15,500. I was letting it breathe on fuselage leakage (there are lots of small holes). That definitely is not enough. Cut an opening in the fuselage side and it jumped to 16,600. It's obvious that the filter needs lots of ventilation. I'll open it up and add a scoop.

I'll also try just sucking the fuel 6" with the carb mounted on the engine.

[Sparky Paul]

I'd mount the tank on the other side of the fuselage next to the motor.

[Tom Harper]

sparky,

Neat airplane - is it really a plank?

That's where I moved it from. The extended manifold is something I have wanted to try and this offered the opportunity. It does allow a large air filter. I think it is going to work out. If not I'll just put the tank back where it was.

On the next model the engine will move forward to the LE of the wing. A tank behind the engine will be about on the CG. A round tank should fair in reasonably well.

[Sparky Paul]

Tom, that was a profile Somethin' Extra.. had an engine failure right after flipping inverted on takeoff, and was landed upside down.
I took advantage of the situation to cut off the tail, make the ailerons into elevons, and go fly.
It did well for its short second life. :)

[Tom Harper]

Sparky,

Maximum utilization!

[Tom Harper]

LD4 is going to cover some tough territory in the next week or so. I doubt that it will survive more than a couple of flights in that environment. So it's time to ready a replacement.

LD5 is too big. It will do the job for a while but it is not as quick and easy to position as LD4. I think the LD4 wing size is just right. It carries the weight and is very transportable. The things I'd like to change are:

1. Smaller stab - the barn door stabs work well but are not really necessary - drop down to 30% of the wing area.

2. Shorter overall - move the engine forward one more time and pull back on the snout.

3. Transverse camera mount. The camera takes pics at .7 seconds per frame. That gives me too much overlap. With the camera crosswise I get better coverage and less overlap.

4. Narrower fuselage - These models are wider than my Sr. Telemaster - don't think that's necessary.

5. Strengthen joint at wing TE.

6. Lighter AUW.

7. Forward camera view.

To get a narrow fuse with a transverse camera I decided to use a pod on the nose. The pod is a symmetrical (NACA 0045) section containing the camera mount.

The smaller stab shortens the tail.

The tank and servos are all inside to clean up the lines:

[Tom Harper]

Used a 3/8" wing spar with 3/16"x3/4" TE stock on either side for fairing. This causes a dip in the camber line but this thing doesn't have the greatest ever camber line anyway.

Tapered the spar and fairing evenly along the span.

Used a Foam Board form, with glass tape on the edges, to hot wire the camera mount. Worked well.

[Sparky Paul]

I had (had) two AIPTEK SDs mounted side-by-side looking vertically down, with the long dimension of the image to the side. Great coverage!
Just enough overlap at the image centers to allow stitching for a very wide image.

[Tom Harper]

Sparky,

That's not a bad plan. When looking for trails, coverage is important and lo res can be an advantage. I have noticed that Carl's Aiptek blends the background and exagerates changes. Two Aipteks would fit in place of one Olympus with room to spare. Did you angle the cameras?

I got the pod sheeted - 3/32" balsa. A couple of inches on top is a hatch. This thing may be too fragile. But, Randall gets away with it. Of course he has a long gear and two horns to protect the camera. Probably be at least two weeks before I find out.

[Sparky Paul]

The Aipteks were tilted 20 degrees off vertical. With the 42 degree field of view on the long side this gives a reasonable but small overlap of the images at the center.
I did have trouble with using 2 Backpack switches.. there was a slight delay between one camera shutter and the other.
With a single switch triggering both cameras this went away.
Unfortunately I lost the whole smear due to wing flutter before I could get any good images from high up.
Here's the basic geometry:
Then two images:
Merged with Ulead360:
And the difference in position due to the sync difference. Not a whole lot but it's there.

[Tom Harper]

Sparky,

That's a good result. Easier to merge when both shots are at exactly the same altitude. Thanks for the angle info. I may try it but it will have to wait in line behind some other projects.

FYI: I'm going to take our state representative out to Parida Hill next week. I am hoping the state or fed will come up with some money to authenticate and date the tracks we have found. There is interest in the area because of the El Camino Real Center that they have poured tons of bucks into.

[Tom Harper]

Here it is with the tip tacked on and the wing slid into the wing slot. Everything fits, just like on the drawing. Now I have to wrap the rocket tube around the tank and stuff.

I used a plain bearing Norvel .25 because it is a little bit smaller and lighter than the BB. This model is definitely more compact than the others.

[Tom Harper]

A while back I replaced the hinges on LD4-2 and LD5-2. Made thin plywood inserts to reinforce the area attached those little nylon hinges with the wire pivot and epoxied the whole thing into slots in the foam.

It was a really bad idea. They do no align well and normal use or a couple of shocks will pull the ply/epoxy out of the foam in one lump. I had covered the hinge line with monokote which worked as a crutch to keep the hinge operating.

Someone on this board recommended clear packing tape for hinges. Well, duh, the tape roll was sitting on the bench. I thought you were supposed to wrap packages with it.

Pulled off the control surfaces and cleaned out the epoxy. Sanded and straightened the hinge lines. Replaced some shop worn surfaces. And put everything back together with long strips of 2" clear packing tape. Wow, does that work great. Packing tape is not an expedient. It is the only way to make hinges with foam board.

[Sparky Paul]

Hee, hee.. the structural capability of foam is zilch!
No matter how well you reinforce the area, the foam WILL break just outside the reinforcement.
Dubro repackages hospital "DermaBlend" adhesive tape as "Electric Flyer Hinge Tape (5 yds), # 916.
By far the easiest hinge tape to use, although you may need a waiver to use it on a slimer... :)

[Tom Harper]

Hey - it seemed like a good idea at the time.

[Sparky Paul]

I'm building up a stack of unrepairable 3D foamies... the stuff just sucks for longevity.

[Tom Harper]

They do seem to age. The foam crushes under the paper and the rigging changes. That is happening less as the design matures, but they still have a limited life. Still OK for disposables.

I think 6 check out flights at the field and 6 operational flights on site is about the max. But, that's 600 to 1200 images. I'll settle for that!

[Tom Harper]

Here we are a mile from the car, deep in dirt and creosote. Ran the engine before the hike and it checked out fine. But, on the first launch, the engine lagged and the plane nosed in. Let it sit while we looked for artifacts. Lot's of interesting stuff.

Tried to launch again. Engine ran fine but the fin was offset by the previous crash and it rapidly rolled into a Prickley Pear.

This poor airplane has accumulated too many crashes, mods, repairs and wierd ideas. Time it goes to the great hobby shop in the sky.

The next one is still on the bench. I manage an annual birding festival and it's only two weeks away. Darned inconvenient to my AP!!!

[Tom Harper]

Back in the shop at last! - three week work break.

Got the right wing quarter section on - the training wheels mounted - all electronics installed and checked out. Decided to put a window in front of the camera. The easiest source of optically flat glass is to get a UV filter. So off to eBay where I bought a 77mm. Should have settled for a 55mm but maybe I'll do that next time. I've been wrestling with mounting it since it is an after thought. Think I'm close - RTV it in place soon.

Tomorrow is slated to be windy with rain and snow. Should be a fine building day.

[Tom Harper]

It's cold and WINDY outside. I got the fireplace warm and Pueblo Indian DJs on the radio and no interruptions. I mean it's windy - 40 to 50 mph.

So I got the rocket body on for the center pod and planked the nose section. Also mounted the glass plate in the camera window. Think I need to flat black that foam to avoid pink photos.

Weather looks good by the end of the week. Should be ready to fly by then.

[Tom Harper]

Still cold and windy so I spent more time, effort (and weight) on this model than I usually would on a plane with a service life of twelve flights.

Have to add the stem piece then some trim and touch up and it's finished.

[Tom Harper]

There was no wind today and it warmed to about 40 deg F at 3:00. So, called Carl and we zipped out to the club field. Engine roared away and all seemed ready for the launch when Carl pointed to fuel pouring off the rear of the fuselage. Not much I could do about it so I adjusted the high and low end of the engine and checked it's throttle response. Then shut it down.

Examined the raw fuel spots looking for the source. Finally had to cut open the rocket tube and remove the tank. The plastic stopper thing was stripped. It leaked as soon as exhaust pressure developed.

Brought it home and put in a bigger screw. The rocket body cut clean and fit back in place. Passes the 'easy to repair test'. But we sure missed a great flying day.

[Tom Harper]

Great day for flying.

Put in three very nice flights before the engine got snickety. Flys very nicely. I rigged it nose heavy to be safe so it required some up trim on low power. Otherwise the control response is excellent and it trims for hands off flight.

The smaller horizontal stab is an improvement. This model does not overcontrol in pitch. Visibility is still a problem. With all the short coupling it looks, at a distance, like a white ball.

Hand launch will be a snap. Given a chance this thing would VTO. Notice the take off angle even carrying 14 ounces of lead in the camera pod.

[Tom Harper]

Pulled the fuel tank (again) and found a hairline crack in the brass tube on the pressure side. It was OK when covered by the flex tubing but I must have pulled on it during refueling and exposed the crack.

In the interest of domestic tranquility we probably won't fly again until after the weekend.

[Tom Harper]

Flight checked it today with good results. Engine problem must have been the crack in the tubing. It ran strong and steady for the entire flight. I need to rig a little up trim for slow speed passes.

Will probably do some field photography tomorrow.

[Tom Harper]

Great flying day. Wind on the ground was 5-10 MPH, aloft 20 MPH +. The model performs reliably. Left the wheels on the soften the landing but hand launched. No difficulty there it just climbed into the wind. With a bit of reduced throttle it would hover almost overhead.

The 3/8" spruce spar paid off. If it was going to fold a wing it would have done it today. Flew for 10 minutes +. Got 77 images and called it a day. Carl throttled back and made agalloping approach in the wind gusts. Got the airspeed down and almost missed the last Creosote bush. The wing caught pulling the model into the bush, where it sat with the engine running. A small branch went through the fuselage. No serious damage.

Had fun. Flew the airplane. Got pictures. Went home with the airplane in one piece. Good day!

[Tom Harper]

It's 20 degrees outside. Too cold for me!

LD4-2 is doing fine. It may outlive it's projected 6 field flights - remains to be seen. Only problem so far is that it sanded the bottom off of the camera pod by scraping it's nose in the gravel.

So, it's still building time. Decided to see how much the construction of LD4-2 could be simplified. Hence LD4-3:

No dihedral or wash out in wing panels
Straight 3/8 x 3/16 spruce spar no taper
1/8 x 3/16 doubler at wing root
Inverted engine to lower CG and simplify mount
Thickend pylon for strength
6 ounce tank for a flight time safety margin
Wide body to incorporate camera pod
Hand launch only - use skids for launch handles

The model almost consumes a 40 x 60 x 3/16 sheet of foam board. It requires an additional 12 x 24 x 1/2 for the pylon. The total cost with spruce, plywood and foam board is around $15.

I am keeping track of time spent on this one. Curious as to how long it actually takes. Gotta prefab a bunch of parts to assemble while watching the games this afternoon.

[Tom Harper]

The basic structure is complete. Need to finish the camera bay and rcvr bay, round the leading edges, cover the top and bottom of the fuse and add the skids.