If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. 


Thread Tools  Display Modes 
#1




Calculating vertical time and distance in a stall turn (US Hammerhead)
I've been teaching aerobatics for years but last weekend (after a session of
stall turns) a student said he was surprised at how long we were vertical. Afterwards it occurred to me that it would be fun/interesting to look at the sums, later I realised that I didn't know how to DO all the sums!! If the propellor thrust and form drag are initially ignored it's easy (forgive the elderly units): induced drag = 0 (in an ideal stall turn the CG track is vertical so the AOA needs to be zero, therefore the induced drag should be close to zero) initial velocity u = 120kts (200 fps) final velocity v = 40kts (67 fps) acceleration f =32 fps/s v**2 = u**2 + 2fs so distance s = 555ft. v=u+ft so time in the vertical t = 4secs. Now to bring in form drag and thrust..... If we assume the deceleration is linear the form drag could probably be based on the average speed. And if we assume the engine is producing 200BHP with a propellor efficiency of 75% we should be able to work out something useful. Thinks  but Thrust is proportional to torque!..... elderly brain gives up. How can I factorin the propellor thrust and estimate the form drag to give a realistic estimate of time and distance? In practise I think it would be possible to estimate the net acceleration due to thrust and form drag by flying a ballistic push (zero AOA) from some angle above the horizon to the same angle below (to eliminate the effect of gravity), starting at 60kts and then timing the acceleration to whatever speed is reached. I'll try this next weekend and then see how the final estimate matches the reality of a stall turn. ....but I'd still like to know how to calculate the approx thrust....?? Dave S 
Ads 
#2




Dave,
I have a simple Qbasic program to do just that  it can be downloaded from: http://groups.yahoo.com/group/ozaeros/files/Technical/ You'll need to register with that Yahoo group to get access. Regards, Dave Pilkington "Dave" wrote in message ... I've been teaching aerobatics for years but last weekend (after a session of stall turns) a student said he was surprised at how long we were vertical. Afterwards it occurred to me that it would be fun/interesting to look at the sums, later I realised that I didn't know how to DO all the sums!! 
#3




Thanks Dave  I've downloaded it. How do you estimate thrust and drag?
It's many years since I wrote any Basic, what do I use to run it? Dave S "Dave Pilkington" wrote in message om... Dave, I have a simple Qbasic program to do just that  it can be downloaded from: http://groups.yahoo.com/group/ozaeros/files/Technical/ You'll need to register with that Yahoo group to get access. Regards, Dave Pilkington "Dave" wrote in message ... I've been teaching aerobatics for years but last weekend (after a session of stall turns) a student said he was surprised at how long we were vertical. Afterwards it occurred to me that it would be fun/interesting to look at the sums, later I realised that I didn't know how to DO all the sums!! 
#4




There's a QBasic compiler to download there as well. One you've got
that you can see all the equations in the program. I estimated thrust from prop data I obtained from one of the manufacturers  you're close enough with prop efficiency. Approx drag deduced from a rough drag polar analysis of published info for max level speed and climb. All the data is in the program for several aircraft types. Have you got MS FlightSiM? It works pretty well and should give you what you want too. We've set it up at our flying school  if it gets much better I might give up real flying. You can contact me direct via www.ozaeros.com "Dave" wrote in message ... Thanks Dave  I've downloaded it. How do you estimate thrust and drag? It's many years since I wrote any Basic, what do I use to run it? Dave S 
Thread Tools  
Display Modes  

