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Based on the calculations to date, I don't think the web is likely to collapse. There will likely be some wrinkling as the load is increased. This is normal in sheet metal wings. The idea of doing calculations for the buckling is that it gives us a good idea of where to expect problems and we...

I think the next step is to check the buckling of the shear web. So far we have calculated the following stresses in the web: Shear Stress = 2725 psi (limit) and 4088 psi (ultimate) Bending Stress at top and bottom edge of the web = 16094 psi (Limit) and 24141 psi (ultimate) To begin I will...
3. ### 99lb/45kg primary glider

also BRO-23 (not sure of exact weight but clearly fairly light): ** Edit: If Wikipedia can be believed the empty weight is 184 lb .... ** Oškinis BRO-23KR Garnys - Wikipedia So about twice was the OP was looking for ....
4. ### 99lb/45kg primary glider

Also the Russian ANB (no idea of weight): **** Edit: According to this website which is a Russian mob selling pirated plans of dubious quality .... ANB-M PART103 SAILPLANE – PLANS FOR HOMEBUILD – FULL METAL PRIMARY GLIDER | https://buildandfly.shop the empty weight is 70 kg (154 lb) ... Not...
5. ### 99lb/45kg primary glider

Yeah the Hippie is a good example. Also consider the Volmer VJ-24 Sunfun. Not exactly what is going asked for because of the lack of a seat and the need to reconfigure the landing gear, but it was 110 lb empty and provides a yardstick to confirm that the requirement could be met with careful...

OK .... here is the first installment of the buckling calculations for the spar root area. There will be a few steps after this to build up the complete picture of what is going on. First here are the spar dimensions that I am working with: Today's step is to check the inter-rivet buckling...
7. ### 99lb/45kg primary glider

Sounds about right. The number I quoted (68 lb) is for the wing alone. It is right out of the Mitchell B10 literature although they use both 68 and 70 lbs in their documentation. That includes the control stick and tip rudders ... but no cage.
8. ### How much to tighten bolts?

For a 1/4" bolt (AN4) I agree with your calculations: i.e. min torque is 50 in.lb for a tension nut. At 50 in.lb the preload on the bolt is: F = T/(kd) = 50/(0.16*0.25) = 1250 lb (where k = 0.16 and is the value for cadmium plated bolts). OD of a AN970-4 is 1.125" and ID 0.265" so area is (pi/4)...
9. ### 99lb/45kg primary glider

The plans for the ULF-1 (Sheet 1) state "Empty Weight 46 kg" (101.2 lb). The following weight breakdown is also provided: wing weight 46 lb fuselage + fin + rudder 46.3 lb horizontal tail as 7.7 lb However a lot of balsa is used, even in fuselage framing, not just for fairing. Also all metal...
10. ### 99lb/45kg primary glider

From one of my old sketch books but redrawn just now to adjust a few weights since the original was meant for the 155 lb Part 103 weight limit for gliders. Separate elevator and aileron control surfaces on the trailing edge like a Monarch (not separate elevons like the B10 with a mixer)
11. ### 99lb/45kg primary glider

VB, this is not a bad concept. Do you think the lower pilot position under the wing in the Monarch contributes to stability by pendulum effect of the pilots weight ? I think it does .... Also, depending on where you located the spar, you might need to use a small amount of forward sweep.
12. ### 99lb/45kg primary glider

The original wood wing Monarch weighed 250 lb empty. Span was 42 ft and wing area 185 sq ft. It would be a big ask to reduce the weight to 99 lb without reducing the span and area. I have always felt that Marske didn't encourage the popularity of his designs by the way that they were built and...
13. ### How much to tighten bolts?

The torques for bolts are in FAA AC43.13-1B. https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43.13-1b_w-chg1.pdf Use AN970 washers to spread the load. AN970 REV-6 WASHER FLAT
14. ### 99lb/45kg primary glider

The LAK-16 shown in this video is heading in the right direction but its weight is twice the 99 lb weight limit that the OP is looking for. For me the interesting thing in that video is the winch setup ..... looks like the winch lines are diverted 90 deg suggesting that they might have some...

What is the size and thickness of the web stiffener angles. What is their spacing on the web ?

Yes, in a stack like this, it is normal practice to check the crippling stress for each element separately. They do not behave as one homogeneous angle of X number of lamination's in thickness. We also need to be mindful of interrivet buckling where thin web or skin can buckle as a column...
17. ### A question for all Flying Flea aficionados

Billski is right .... the control forces will change. The best way to think about this is to use the engineering principle of "Work" and treat the control system as a black box containing some combination of bellcranks and pushrods to achieve the desired drive ratio. Work = Force x Displacement...

Yes I agree ... the figure above was just meant to understand whether an extra angle can be added considering rivet placement etc. Now that we have confirmed that the spar cap is on the front of the spar at the root and there is plenty of space, we will need to look at the design of that...

Example follows: Note: this approximate method only works for a thin web with relatively heavy caps. Use it on a rectangular spruce spar and it will under predict the shear stress by 50% !!! It is important to understand the theory ... This calculation is pretty close for your load test...
20. ### A question for all Flying Flea aficionados

Hi Duncan, I sent you a private message which I am not sure if you saw. I think what you are proposing is reasonable. That is similar to what trike pilots did in the early days ... they had a row of holes to experiment with and adjust the handling and bar forces. What I am not clear on (I...