# Making a V-speed calculator - assistance needed!

Folks, it’s been quite awhile since I’ve posted here. I had an idea the other day - find slow flight speeds (not necessarily full stall since it’s so hard to determine that in a sim) for every aircraft at basically no payload and virtually empty tanks except just enough fuel to keep the engines running, and at MTOW. Interpolate between the results to get practical v-speeds for flight.

I have to say this method has worked quite well and I’ve began a stand-alone load sheet generator and performance calculator in Google Sheets linked up with OpenasApp for the GUI. The calculator determines a random payload, specific down to pax gender/age, and personal item/checked bag/carry on baggage. It will then compute V1, Vr, V2, flap/slat retraction speed, Vapp, and Vref for the airplanes currently programmed in. I will attempt to make the openasapp version public here later on today in its current edition. So far, I have developed v-speed calculators for the C750, CRJ9, A220, A318, A319, A320, A321, and E175. Obviously there are dozens more aircraft to work on. Which brings me here to the IFC. Would anyone like to help me gather stall speed info on the various IF aircraft so I can complete this project faster and hand it out to the community? I would greatly appreciate the help! Real world aviation experience and understanding of aerodynamic principles is preferred, not all of this stuff is quite basic flight sim knowledge.

The criteria I have set forth for each test:

Minimum weight:

• cabin and cargo load EMPTY
• just enough fuel to keep the engines running, or fueled to the nearest 1000 number closest to empty. For example, if you put 200lb in the tanks but your TOGW is 87,800, just fill it up to 88,000lb, for sake of making the math I do easier.

MTOW:

• Simple: Fill the plane up to MTOW but not over MTOW.

Make sure to denote the weight definitions in the spreadsheet as you add your data. I will add a data format layout in boldface at the top that you can copy and paste down the list on the spreadsheet as you need to.

Criterion for tests:

• Standard day, meaning ISA +/-0 C deviation. If you’re at altitude, you’ll need to figure out what standard temp at that altitude is and set it in the sim.

• I have determined V2 to be equivalent to Vlof (lift off speed) through a little bit of research. I know they aren’t quite the same, but unless you want to do the math of figuring out what speed you can climb out on single engine over a 50’ obstacle if you lose an engine right at V1, be my guest, lol.

• Set takeoff flaps. If there are two settings, you will have to repeat the process for each.

• Apply takeoff power (but not too much) and carefully bring the nose up to +5 deg and hold it.

• IMMEDIATELY note of what speed you’re at when the FPV appears on the HUD. A margin of error of +/-2 knots is fine but anymore than that and this becomes unreliable. If it’s too difficult, proceed to takeoff but slightly pull back on the throttle and reduce angle of attack, then pitch back up to +5deg and increase power again. Try to determine the speed at which the FPV moves above the horizon line and you get a positive rate on the VSI.

• Mark this speed as V2. From that, you can get Vr from V2/1.05, and V1 from V2/1.1. Vfs is V2 x 1.3.

• Repeat the process for additional landing flap settings.

Next on the test is determining Vmca, or minimum controllable airspeed, in landing configuration.

• At a safe altitude, drop gear and flaps to landing settings (if there are two flap settings, e.g. Airbus and Boeing 737, you’ll have to do a Vmca test for each setting).
• Reduce power to idle and pitch up approximately +3 deg.
• Watch the VSI. When it drops to -600 FPM, note your IAS. We will call this Vmca. This will be equivalent to Vref. If you 10 to this, you will have Vapp.
• Repeat the process for additional landing flap settings.

THEN, repeat the ENTIRE gamut of tests above for MTOW.

I told you it’s a lot of work. But if we all can do just one plane a day, this project will be done in a week!

Let me know if you have any questions, comments, or suggestions. Thank you so much!

Public stall test info link (editable):

11 Likes

Thanks! I’ll try to help with the X-Cub, C208, and B737s if I have the time!

MATLAB is great software as well!

1 Like

I would love to help if possible

Thanks man. I appreciate it!

You’re more than welcome to! Please post what planes you work on!

1 Like

Your work is very interesting. That must have been work. Congratulations👏👏👏👏

This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.