Calculating Bend Allowance in Aerospace Maintenance

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Questions and Answers

What is the alternative method to calculate bend allowances when the Bend Allowance Chart is not available?

Using the bend allowance formula (correct)
Subtracting the flat dimension from the overall dimension
Using the setback for each bend
Dividing the bent object into flats and bend allowances

What is the purpose of calculating the bend allowance in tube bending?

To calculate the overall length of the bent object
To calculate the flat dimension
To obtain a smooth bend without flattening the tube (correct)
To determine the minimum bend radius

How is the development length calculated?

By adding the flat dimensions and bend allowances
By multiplying the flat dimensions and bend allowances
By subtracting the setback from the overall dimension
By dividing the bent object into flats and bend allowances, then adding them up (correct)

What is the minimum bend radius in tube bending?

2.5 to 3 times the OD (A) Signup and view all the answers

What is the acceptable method of bending soft, non-heat-treated aluminium tubing in an emergency?

Bending by hand to form the desired radius (A) Signup and view all the answers

What is the purpose of calculating the flat dimension?

To subtract the setback from the overall dimension (D) Signup and view all the answers

What is the formula for calculating the bend allowance?

angle of bend / 2πR (A) Signup and view all the answers

What is the result of adding up the flat dimensions and bend allowances?

The development length (D) Signup and view all the answers

What is the primary function of the handle and slide bar in the simple hand bender?

To provide mechanical advantage to bend the tubing (B) Signup and view all the answers

How is the forming die on the mechanical tube bender calibrated?

In degrees (C) Signup and view all the answers

What is the purpose of bending a replacement tubing to a specified number of degrees?

To match the original bend in the tubing (B) Signup and view all the answers

Why is a tube cutter not suitable for stainless steel tubing?

It tends to work harden the tube (D) Signup and view all the answers

What is the recommended margin of safety when cutting a new piece of tubing?

10% longer (D) Signup and view all the answers

What is the purpose of marking the tube with a felt-tip pen or scriber before cutting?

To align the cutting wheel with the cutting mark (D) Signup and view all the answers

What should be avoided when using a tube cutter to cut stainless steel tubing?

Applying too much pressure (B) Signup and view all the answers

What is the primary difference between a hand bender and a mechanically operated tube bender?

The power source used to operate the bender (A) Signup and view all the answers

What is the first step in forming a single flare?

Slip the fitting nut and sleeve onto the tube (A) Signup and view all the answers

What is the purpose of a double flare?

To form a stronger connection with small diameter soft aluminium alloys (B) Signup and view all the answers

Why is it important to check the flared end of the tube after forming a single flare?

To verify that the flared end is no larger than the largest diameter of the sleeve (A) Signup and view all the answers

What is the main advantage of using flareless fittings in high-pressure systems?

They produce leak-free attachments without flares (C) Signup and view all the answers

What is the purpose of the pre-setting tool in flareless fittings?

To create a leak-free attachment between the sleeve and the tube (B) Signup and view all the answers

What should be done to ensure a secure connection with a flareless fitting?

Select the correct size flareless fitting body (D) Signup and view all the answers

Why is it important to avoid over-tightening when forming a single flare?

It can damage the flare (D) Signup and view all the answers

What should be checked for after forming a double flare?

All of the above (D) Signup and view all the answers

What is the primary function of a mandrel in fabricating hose assemblies?

To protect sealing surfaces and support inner tubes (A) Signup and view all the answers

What is the common but dangerous method of removing skived pieces of rubber from a hose?

Taking a piece of rod or tubing and trying to poke it loose (A) Signup and view all the answers

What is the typical procedure when a failure occurs in a flexible hose equipped with swaged end fittings?

The unit is replaced without attempting a repair (D) Signup and view all the answers

What is the purpose of a protractor in fabricating hose assemblies?

To measure the angle of the fitting nipples (C) Signup and view all the answers

What is the recommended tool for cutting the hose to the required length?

Hose cut-off machine (B) Signup and view all the answers

What is the purpose of a marking pencil in fabricating hose assemblies?

To mark the hose with the correct length (A) Signup and view all the answers

What is the procedure when a failure occurs in a hose assembly equipped with reusable style end fittings?

The undamaged end fittings are removed and reused (B) Signup and view all the answers

What is the purpose of adding 5%–8% to the determined hose length?

To allow for expansion or contraction from pressure application (B) Signup and view all the answers

What is the purpose of a thickness gauge in fabricating hose assemblies?

To measure the thickness of the hose (C) Signup and view all the answers

What is the purpose of wrapping the circumference of the hose with masking or plastic electrical tape?

To prevent braid flare-out if the hose outer cover is wire braid (D) Signup and view all the answers

What should be done after cutting the hose to the required length?

The hose should be blown clean with filtered shop air (D) Signup and view all the answers

Why should a vice not be over-tightened on thin-walled lightweight fittings?

To prevent damage to the thin-walled lightweight fittings (A) Signup and view all the answers

What is the purpose of screwing the hose anti-clockwise into the socket?

To ensure a secure connection (C) Signup and view all the answers

How should the hose be turned after screwing it into the socket?

A quarter turn back to secure the connection (D) Signup and view all the answers

What is the purpose of assembling the nipple and nut?

To connect the hose to the tube or component (D) Signup and view all the answers

What is the purpose of the socket in the hose end fitting installation?

To fit over the outside diameter of the hose (C) Signup and view all the answers

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Study Notes

Calculating Bend Allowances

Use the Bend Allowance Chart if available, otherwise use the bend allowance formula: angle of bend = 2πR / 360°
Calculate flats by subtracting the setback for each bend from the overall dimension
Calculate overall length by dividing the bent object into flats and bend allowances, and numbering them progressively

Tube Bending

Objective: obtain a smooth bend without flattening the tube
Minimum bend radius: 2.5 to 3 times the OD
Tube bending methods:
- Hand-operated tube bender
- Mechanical tube bender
- Hand bending (for soft, non-heat-treated aluminium tubing smaller than 1/4 inch in diameter)

Tube Cutting

Cut new tubing 10% longer than the tube being replaced
Cutting methods:
- Fine-tooth hacksaw
- Roller type tube cutter (for soft metal tubing like copper, aluminium, or aluminium alloy)
Avoid using tube cutters on stainless steel tubing as it tends to work harden the tube

Tube Flaring

Single flare: use a tube flare tool to form the flare
Double flare: used with small diameter soft aluminium alloys to reinforce the flare
Flareless fitting: used for high-pressure systems, requires pre-setting with a specialized tool

Hose Assembly Fabrication

Basic hand tools required:
- Bench vice
- Hose cut-off machine
- Fine-tooth hacksaw
- Open-end wrench sets
- Sharp knife
- Slip-joint pliers
- Oil can
- Marking pencil
- Steel ruler
- Thickness gauge (leaf type)
- Protractor
Recommended tools:
- Mandrel kit (protects sealing surfaces, supports inner tubes, and guides fitting nipples into hoses)

Hose Assembly Procedures

Determine the necessary hose length from the table and diagram
Add 5%-8% to allow for expansion or contraction from pressure application
Wrap the circumference of the hose with masking or plastic electrical tape at the cut-off point
Cut the hose to the required length using a cut-off machine
Blow the hose clean with filtered shop air after cutting
Remove the tape and clamp socket in a vice
Install the hose end fitting, ensuring a square cut and cleanliness
Avoid over-tightening the vice on thin-walled lightweight fittings

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