# CAR-251: The Cheap Air Racer Discussion thread.

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#### nerobro

##### Well-Known Member
Log Member
the 18 isn't feet.. it's stations. I did areas of each 6" section.

So to modify the curve... I need to, instead of multiplying the curve by each station, multiply the curve by "how different it is from the ideal".

Say my wing has an average chord of 2.5'. At the tip, where it's 1.5' it's only .6 the expected cord. So I'd multiply the lift there by .6. (well a little more since we'd be talking a point 3" in from the tip..) And at the root, where it's 3.5', I'd multiply the lift there by 1.4. (well, a little less because we'd be talking the slice of wing that's the last 6")

I can't wait to compare how the two number sets come out. Knowing the error will be ... uh.. entertaining.

#### Autodidact

##### Well-Known Member
Average chord has nothing to do with it. I'm assuming that you're not wasting time and effort on purpose, so that means that you're just not getting the fundamental idea here... :cross:

Once more. Find the area of a slice, divide that slice by the total wing area, multiply the total lift by that ratio.

I don't see how you can not get this when you've been shown a really large attachment of a dotted line half-way between a trapezoid and an ellipse. Maybe I'm assuming wrong? OK, I'm being intolerant; it took me a while to catch on, too.

#### nerobro

##### Well-Known Member
Log Member
Nope, not on purpose.

I think we're saying the same thing. Let me take another swing at this tonight.

#### nerobro

##### Well-Known Member
Log Member
Nerobro, I think the problem with your trapezoidal area is that you didn't use an area for it equal to the area of the quarter-circle. If you non-dimensionalize the circle by giving it an area of 1, then the trapezoidal area must also have an area of 1. To do this, make the length equal to the radius of the circle, and the root and tip heights such that the ratio of tip height to root height is the same as your wing's tip chord divided by root chord. Thus, the taper ratio of the trapezoid must be the same as the taper ratio of your wing, and the area of the quarter circle (or ellipse) must be the same as the area of the trapezoid.
And that's where I suggested taking the mean chord and finding the modifier for each station. What I did last night was just use the actual mean chord of each station. so the numbers varied from 1.6 to 3.6. When they really should have been more like .6 through 1.4. (That way both my straight wing, and trapezoidal wing would have the same "area")

#### Matt G.

##### Well-Known Member
To save yourself future time and aggravation, I'd recommend setting up the quarter-circle and trapezoid with an area of 1 so that later on when you have to tweak the wing dimensions, you won't have to redo all of that.

#### nerobro

##### Well-Known Member
Log Member
Geeze, I havent' touched this for three weeks. I have time this weekend.

#### Topaz

##### Super Moderator
Staff member
Log Member
Geeze, I havent' touched this for three weeks. I have time this weekend.
It's hard keeping it going. Life has a way of interfering with priorities. :ermm:

If we both stick with it, we'll get there!

#### nerobro

##### Well-Known Member
Log Member

Tri-gear, using 6" wheels. What wheels? I don't know yet. Who cares yet.

Wings still built on a flat surface.

Open cockpit. The ledge for the cockpit is 3.5 feet off the ground, which.. I don't know how that compares to other airplanes. I'm sure a toehold could be cut in the side of the fuselage for boarding.

Lots of room on the sides, and uninterrupted space across the tops of the wings for sponsors, race numbers, and whatever else might come to mind.

I think the engine could come up 6" or 12", but that will need to be re-done after an engine is converted for aero use. Sadly, if the engine moves up, it'll also make the nose look quite "normal" and I was hoping to keep the distinct profile.

Given my little "tutorial" on tapered surfaces in another thread, perhaps I should do something about the taper of the control surfaces on this thing. But I probably won't.

Autodidect gave me a bit of a tutorial on lift distribution. So.. next update will be full of numbers. If my brain won't do that, it'll be fuselage strength.

I came home and did this instead of going to the hackerspace for the holloween party.

#### BBerson

##### Well-Known Member
HBA Supporter
In the old days, they worried about small planes having the cockpit " blocking the air flow to the tail" or disturbing the effectiveness of the tail.
Looking at your side view reminded me of that. Something to consider.
Might be a big difference with open cockpit or smooth canopy like CriCri.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Kudos on keeping at the design, I need to get back to work on my own. A few thoughts...

--I'm sure you've run the numbers with a range of pilot weights, but that cockpit does look a bit far back to me.

--For simplicity and ease of building, why not run the top longeron in a straight horizontal line from nose to tail?

--How about moving the engine up so that the cowling top is in line with the wing upper surface and with the firewall projecting a little above the top longeron? That would give more prop clearance and allow a single fairing straight from firewall to wing a bit like the Volksplane.

--With the engine a bit higher you could more easily bevel the bottom of the firewall to reduce digging in during a hard and/or off-field landing.

Cheers,

Matthew

#### nerobro

##### Well-Known Member
Log Member
In the old days, they worried about small planes having the cockpit " blocking the air flow to the tail" or disturbing the effectiveness of the tail.
Looking at your side view reminded me of that. Something to consider.
Might be a big difference with open cockpit or smooth canopy like CriCri.
I wonder if model testing would prove that out.. Otherwise that fin and rudder may need to grow.

--I'm sure you've run the numbers with a range of pilot weights, but that cockpit does look a bit far back to me.
It is! There's weight left over to allow for nose weight.

--For simplicity and ease of building, why not run the top longeron in a straight horizontal line from nose to tail?
It does! the wing bolts on top of the top longeron.

--How about moving the engine up so that the cowling top is in line with the wing upper surface and with the firewall projecting a little above the top longeron? That would give more prop clearance and allow a single fairing straight from firewall to wing a bit like the Volksplane.
A big portion of the cowling is defined by the 18" height of the engine. the crank is quite low, only about 6" off the motor bed.

--With the engine a bit higher you could more easily bevel the bottom of the firewall to reduce digging in during a hard and/or off-field landing.
I think this is the best argument for raising the motor. I'll ponder it. Say, raise the motor 6", lower the plane by 3". That'll lower the frontal area too.

#### BBerson

##### Well-Known Member
HBA Supporter
I wonder if model testing would prove that out.. Otherwise that fin and rudder may need to grow.

o.
Model testing might help. But only if you load it down so much that it barely climbs to simulate the full scale.
The model pilot might not like the handling at scale weight.

#### nerobro

##### Well-Known Member
Log Member
Model testing might help. But only if you load it down so much that it barely climbs to simulate the full scale.
The model pilot might not like the handling at scale weight.
I'm completely ok with flying underpowered models. I had a lot of fun seeing just how much my planes could get off the ground. Up to, and including, planes that couldn't climb while turning.

#### BBerson

##### Well-Known Member
HBA Supporter
I'm completely ok with flying underpowered models. I had a lot of fun seeing just how much my planes could get off the ground. Up to, and including, planes that couldn't climb while turning.
I didn't really mean underpowered. It should be scale power, not overpowered or underpowered. But also scale wing loading to get the scale downwash and other affects to provide useful results.

#### BJC

##### Well-Known Member
HBA Supporter
Anyone know what happened to this project? Aerochia LT-1

BJC

#### Rienk

##### Well-Known Member
Anyone know what happened to this project? Aerochia LT-1
That's a really good question.
I wonder if they lost momentum when HKS closed down production for a while (that is the engine they were using).

I'm not sure if I think the airplane is good looking or ugly... it seems a bit cartoonish.

#### Hot Wings

##### Well-Known Member
HBA Supporter
Log Member
Make it a claiming race:
My thought as well. Might be interesting to resurrect this old thread?

But \$45K is way too much. For that we could all buy used 150s and re-license them in Experimental-racing/exhibition and still have money left over for a bunch of modifications.

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