# schrenk approximation

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#### rich_aero

##### Member
Does anyone have a schrenk approximation excel spreadsheet set up?

I created my own using the info found in the link below.

I'd like to compare my findings to another spreadsheet if possible.

#### wsimpso1

##### Super Moderator
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I am not sending my files out for a variety of reasons. Probably true of others too.

If you tell us the planform, weight, and max g, I can plot the elliptical, plan form based, and Schrenk approximation spanwise lift distribution, so you can compare yours to mine. You put the data on this thread, I will put the plot.

Billski

#### rich_aero

##### Member
I am not sending my files out for a variety of reasons. Probably true of others too.

If you tell us the planform, weight, and max g, I can plot the elliptical, plan form based, and Schrenk approximation spanwise lift distribution, so you can compare yours to mine. You put the data on this thread, I will put the plot.

Billski
That would be much appreciated! Is it possible you can also plot the moment and shear diagrams along the semi span? I have plotted the schrenk spanwise lift distribution, moment distribution and the shear distribution.

Being able to compare your findings to mine would help very much, currently I don't have a good way of validating my results.

Wingspan= 70" (5.833 ft)
Planform Wing area = 980in^2 (6.8056 ft^2)
Max G = 1.4 assuming maximum bank angle of 45 degrees
Take off weight= 25 pounds

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#### wsimpso1

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Only 1.4 g's!? A 45 degree banked level turn takes you to limit g's?

I will run it. Good thing you are validating your work. Many never bother with the "laugh check"...

#### rich_aero

##### Member
Only 1.4 g's!? A 45 degree banked level turn takes you to limit g's?

I will run it. Good thing you are validating your work. Many never bother with the "laugh check"...
Well, considering we do not plan to do any extreme maneuvers in the air; only take off, make a large circle in the air, then land, per competition requirements. What do you recommend for a conservative g force guess? My aerodynamic "common sense" knowledge is very small to say the least

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#### wsimpso1

##### Super Moderator
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Cantilever wing or strut braced? BL for attach point of wing to fuselage? If strut braced, BL for strut mount?

#### rich_aero

##### Member
One piece cantilever wing that will be mounted on top the fuselage.

#### wsimpso1

##### Super Moderator
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Well, considering we do not plan to do any extreme maneuvers in the air; only take off, make a large circle in the air, then land, per competition requirements. What do you recommend for a conservative g force guess? My aerodynamic "common sense" knowledge is very small to say the least
Min used in man-rated airplanes is usually +3.8/-1,9 g. 3.8g Normal category is just so that we can go places, deal with the weather and bumps that are out there. No aerobatics. Stalls and turns up to 60 degrees of bank, +/- 30 pitch. +4.2g/-2.1g Utility is where you can get into Lazy Eights and Chandelles, and in some birds, Spins. Aerobatic is +6g min - this is where you start to do loops, rolls, spins, etc.

I know this is not man rated, but 1.4 says is if you go 45 degree bank and then pull a tiny bit above a level turn or get any upward gust, you just exceeded limits. If the airplane is built to those limits, the wings fail right there. Then there is the typical plop type landing that RC's and drones typically make...

A while back I was a named volunteer consultant for composite structure to a team that did a design-build-fly senior project at Western Michigan University. We stated 10 g with a FOS of 2, so it was a 20 g design. Two airframes - good thing as they broke one.

Now if you want to design at 1.4g for limit load, fine with me, but I suspect you will find it flimsy in the extreme.

Billski

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#### wsimpso1

##### Super Moderator
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One piece cantilever wing that will be mounted on top the fuselage.
Do you understand the frame of reference for dimensions in airplanes. FS is how far aft of datum, WL is how far up or down from datum. BL is how far left or right from datum. I am looking for how far from this center plane the wing attaches to the fuselage - max moment and max shear in cantilever wing is reached at that point, and so the spar system does not need to carry any more moment or shear than is made there. I could skip it...

Billski

#### wsimpso1

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Oh, and straight wing or tapered? If tapered I need chord at BL00 and chord at BL35.

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#### rich_aero

##### Member
Well our fuselage is still under design as well. However I can tell you it will roughly be a square shape with about 10 inch sides and 36 inches long overall. Wing will be top mounted. Straight wing (tip chord=14 inches, root chord =14 inches). Selig 1223 airfoil.

#### wsimpso1

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I used BL4, the deal was you put up your data and then I put up my plots.

#### rich_aero

##### Member
I used BL4, the deal was you put up your data and then I put up my plots.
thanks! will you post the plots here? our would u like to email them to me?

#### wsimpso1

##### Super Moderator
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Here is OK, or send me your email on a PM.

#### ragflyer

##### Well-Known Member
if you post it here you will get more than one set of eyes... and others will benefit too

#### rich_aero

##### Member
if you post it here you will get more than one set of eyes... and others will benefit too
either is fine with me

#### rich_aero

##### Member
Attached is my excel file containing the schrenk approximation and corresponding plots

#### ragflyer

##### Well-Known Member
Straight wing (tip chord=14 inches, root chord =14 inches). Selig 1223 airfoil.
Your spreadsheet has chord varying with span but you suggest constant chord here. Clarify?