The AFB (Amazing FleaBike)

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pictsidhe

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Jul 15, 2014
Messages
8,812
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North Carolina
Really?
This seems to be the go to here on HBA from the deep state.
There really is a way to build an aircraft without testing and analysis.
You may not approve but it is the right of anyone who wants to build and fly.
This is AMERICA 🇺🇸
There's no reasoning with people like you.
Welcome to the list.
 

Protech Racing

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Joined
Jul 10, 2020
Messages
404
I hope that your rearwing mount has some adjustment . It is very steep . The rear wing will fly at plus 2 degrees regardless of the front wing. That puts the engine at minus 6 when it should be zero ish.
 

rtfm

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Joined
Jan 3, 2008
Messages
3,406
Location
Brisbane, Australia
I hope that your rearwing mount has some adjustment . It is very steep . The rear wing will fly at plus 2 degrees regardless of the front wing. That puts the engine at minus 6 when it should be zero ish.
Hi,
Actually, the rear wing incidence you are referring to is that of the standard HM293 (a picture from the HM293 plans overlays my drawing back on page 4).

[Duncan get's ready for some lively discussion...]
Actually, my rear wing is fully movable, being connected to the main wing incidence controls. Both front and rear wings pivot in concert. I have written extensively about this in my Flea design paper, if you care to read it, starting on page 23.
 

Protech Racing

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Jul 10, 2020
Messages
404
Right. The 293 is a bit too high also. 6*?
Gets the tail up but the thrust line is way too low. My Friends '293(modded to have some wing gap ) had it set up to about 4 and we moved the engine about 1/2 in up at the front mount. Ran out of room at that point but it was better. Mostly the rear wing angle determines the view, but why compromise the thrustline? A side relationship is that the rudder moves it's vector higher as the rear wing is higher. This reduces the rudder's effect on yaw. Lower vector tips the plane in the direction of turn. Higher does the opposite. This was the second most pronounced effect of the rear wing angle change .
The landing angle moves with rear wing angle just like the view. At 6* you will have nose wheel landings.
I suggest you build in some adjustment . And start at 4 for tail draggin , try 2-3 . for tri gear.
 

rtfm

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Joined
Jan 3, 2008
Messages
3,406
Location
Brisbane, Australia
Right. The 293 is a bit too high also. 6*?
Hi,
As I say, the incidence of the rear wing is a vexed issue, with no clear "right" answer if the rear wing incidence is fixed. In the early days, the incidence angle used to be set at 0 deg. Over the decades it has increased, till the now "standard" incidence is 6 deg. But a fixed incidence is self-limiting anyway, irrespective of where one sets it.
 

Protech Racing

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Joined
Jul 10, 2020
Messages
404
The rear wing will make right around 62% per sq ft lift of the front wing due to the wake.
The airfoils good on the Flea are most reflexed foils . The 43015/13 works very well and easy to cut. The 23015 is kinda standard but has a sharper stall and fall value. My 43015 could mush at 60% power very steady. The 23015 would not ., It bobbed a lot more but was controllable .
The 6* rear wing works OK , but not great on the 293 Tail dragger . Wont work on a tri gear . I tried many settings on both airplanes. Jack McWhorter s's and mine. The high speed rear wing crashing thing may be part of the 6* thing . Neither of us ever had issues at WOT dives at 80mph.

If you pitch both wings , you will over control it badly . They are very sensitive . You are overthinking a lot of things .
Spread the wings on both directions. That addresses your valid concern for pitch authority and down wash . 1/4 scale model the wing areas and CG. It seems to scale almost perfect .
Stress test your hinges.
 

Malcolm C

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HBA Supporter
Joined
May 18, 2020
Messages
48
What do you suggest the for the rear wing angle for a tricycle flea ?
 

rtfm

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Joined
Jan 3, 2008
Messages
3,406
Location
Brisbane, Australia
Hi,
Bad news, I'm afraid. I ran into some unexpected issues when I tried to actually construct the fuselage. First, the bloody plywood sheets are so !@#$% heavy that when I tried to get it onto the router table I hurt myself. Left shoulder hurts like a bastard, and I put my back out. I can't do this on my own again.

The second issue is more a matter of not actually knowing HOW to bond everything together before the epoxy sets. I'm using West system with slow hardener, but in 32 deg heat in the shed, I couldn't apply the stuff quickly enough. I had to really scramble in the end, made a terrible mess, and I am very unhappy with the result. The good news is that a fully finished fuselage side weighs 4.7kg. I am on target for a fully constructed fuselage of under 20kg.

Given the issue of not being able to physically handle sheets of plywood, I've decided to continue building the plane as a proof of concept/learning experience. There are still many mistakes to make, and I don't want to fly an aggregation of builder errors. For example, I'm struggling to envisage how to bond in the bulkheads - both in terms of keeping everything square, and in terms of not blocking myself off from areas where I have to install hardware etc. I just KNOW I'm going to get it wrong first time round.

To get past the weight and trying to manage unwieldly sheets of ply, I've managed to source 190mm wide Hoop Pine planks (that'll please many of you). I've placed my order for ten of them which is sufficient to construct both sides. Good news - it works out quite a lot cheaper than a full sheet of Hoop Pine ply, and weighs about 20% less - and I'm not going to hurt myself getting them on the router table. I am also about to pop down to the $2 shop to pick up some 25mm wide rollers. I figure that if I do the bonding before 9am, and roll the epoxy on rather than applying it with a tongue depressor, I can get the entire skin bonded in a single sitting by myself without the epoxy going off mid-job.

So - a setback, but the new wood arrives on Wednesday, so I won't have lost much time. The good news is that the router is working beautifully, and the parts (before I tried to bond them together and then to the outer skins) fit beautifully.

Regards,
Duncan
PS Two variants are possible: The Topless and the Enclosed:
1605299674251.png
 
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cluttonfred

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HBA Supporter
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Feb 13, 2010
Messages
8,065
Location
Fort Walton Beach, Florida, USA
There is absolutely nothing wrong with Duncan's approach and hundreds of designs have used similar arrangements, it just needs to be calculated and the members sized appropriately where the stresses are concentrated under the seat. I will say that if going with the roof supports then there is an opportunity to simplify the design by creating a rigid triangle around the door opening, something like this, greatly reducing the number of parts.

HBA concept sketches (12).jpg
 
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pictsidhe

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Jul 15, 2014
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8,812
Location
North Carolina
It can be made to work. The underseat is a critical area. About the max bending moment for the fuselage is the thinnest. Guess wrong, it is either too weak, or adding a lot of weight.
I suspect that Duncan's eyeballs are on the small side... Without a dimensioned drawing, nobody can do anything but eyeball it.
 
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Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Joined
Nov 14, 2009
Messages
7,567
Location
Rocky Mountains
As simple as this is for him to cut out and glue together he could make a second set of parts, for just the center section. Build that and then load test the area in question.
seat.jpg
We have to (should) test anyway to prove the math. Some times it is quicker/cheaper to just skip the structural math.........IF you already know the loads.
 
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