What Thrust Angle Right and Down for FT Mustangs and Spitfires for dedicated pwr pod?

[ProfessorFate]

Figure thrust angles, see pg 2 vector solution, prev what thrust angle

Hi, I have a new wood design for a power pod that will only be used for Mustangs and Spitfires or Hurricanes, all low wing warbirds and will be made out of wood and use blind nuts and be bolted onto a 1/4" ply firewall with blind nuts.



View attachment 56209 View attachment 56210




I don't want to just center it zero degrees and put washers.
Straight true flight, no trim, no washers, what deg R what deg Down?




When you do this, it pushes your prop and spinner off center and it looks crooked; if you leave it zero deg it flies crooked and needs correction.




I have 2 power systems I may apply to this pod and may make a different pod for each motor:

1: The well known "Beef" Suppo 2217 70g 222watt motor using a gws 9x5 dd on an FT Mustang. holes = 23mm

2: Cobra 2820 1170kv 142g 490watt motor with an apc 10x6 e on an FT Mustang. holes = 30mm



There are so many people out there building flying and rebuilding FT Mustangs and Spitfires, some of you correct the thrust angles, I can figure out from your answer, how to make mine from your answer if only in reference to the screw hole spacing on the motor mounts and the measurement of the height of the stacks of washers you used to set it right.

Now if you actually know the angles in degrees, that would be perfect, I can measure that and put it on the wood panel sides of the dedicated power pods I'm building for FT Low Wing Warbirds that have about 40" wing spans and weigh 1 to 2 #.

I don't know, but the picture on the FT article about thrust angle was a lite plane with a small 6 inch prop and they used 6.5 degrees, I could measure that from the picture.


My initial close guess is 4 degrees Right and 4 degrees down, thinking if I don't go too far out it might make it good.

Could anyone tell me an exact answer and would it be about the same for the Beef 2217 with gws 9x5 and the Cobra 2820 with the apc 10x6e ?


Everywhere I look and search where the issue is discussed, nobody ever says anything with any typical numbers for specific cases or pwr systems and models and all I got from the video pic was our flight test guys showing the pic from one view where I could measure and get the 6.5 degrees, but this is a kind of light airplane, the FT Mustang is a little heavier and I will have one Beef motor pod with a 9x5 prop and another Cobra motor pod swinging an apc 10x6.

Be clear and know that I cannot be experimental about it if I want to permanently mount the firewall with the angle built in and the motor set toward 2 oclock to center the prop and spinner, I do know how to use washers and find out, but I am building this now and I don't have an FT Mustang with a pod to experiment with. This is the 1st pod I will make for FT airplanes. I do know how to fly, but my earlier experience with gliders from 25 years ago is not the same as problems with thrust angle that you have with powered planes.


But, I have seen the video of the guy hand launching his FT Spit as it leaves his hand, it rips extremely toward the Left!

 

[saiga556]

I used 0 and 0 putting about 550 watts in to my clipped wing ft p51 and had no problems with torque roll. If I had it to do over again I might have added a couple degrees down thrust. The plane was still very manageable without it.

 

[ProfessorFate]

OK well it's very good to know that, but I would like to make it fly straight without any trim correction at all, see?


I am building a dedicated wood pod that will only be used for this kind of airplane.


Your answer makes me think I should maybe cut it back to 3R and 3D and that would make it right and fly straight without any trim correction at all, that's my goal.


I am now building the new improved pod design

and decided to use the larger Cobra 2820 142g motor with this pod and drive with apc 10x6e props and I might make the Mustang 20% larger, my motor is 5oz and the batt is 7oz


Another fig I have heard, kind of a standard, I thought, repeated so many times was 3R 2D


Does anybody know?


I can figure degrees if you tell me the measurements as mentioned above post or IN degrees, if you know that



My guess as of now, conservative might be better than overcompensation, is 3 degrees Right, 3 degrees Down.

 

[nerdnic]

You won't be able to have one thrust angle that will produce level flight at all speeds on the FT planes. The flat bottom wing, under camber tips, and angle of attack on the wings is all conducive for ballooning when power is applied. It's not noticible so much under 500w but it becomes very drastic when you run above that. You'll either have to use trim or set up a pod with enough down thrust that it will fly level at your desired speed but will then drop altitude at slower speeds.

My Sonic Series nnP-39 suffers from the same issues. The best thing to do is find a thrust angle somewhere in the middle based on your power setup and then use flight modes with trim that engage at X throttle position. A sophisticated radio can be programmed to do this without much trouble.

 

[ProfessorFate]

Hey Nic, that is a pretty cool answer.

Tie the rudder trim to the throttle and same with the elevator!!


Very interesting!!



Well I got that about it depending on the amt of speed/throttle applied, I just wanted to ballpark a good medium thrust correction right in the middle


A lot of times I like to get it up there, kill throttle and fly it like a glider, sometimes do touch n goes, or chase birds!


I have the Futaba T14SG, their radios are great for integrity/reliability, just difficult to learn to program, but I don't know any other radio I could trust as much




I am tempering my ideas about numbers back toward a conservative small number, maybe I should make the big one 3R,2D?



What do you think would do this middle ballpark, NIC? 3R3D or 3R2D or 2R3D?????????

Hi Nic!



I have a stryker flying wing, one thing I never liked about it was they put waaaaaay too much down thrust in the back, always made it climb excessively when you gave it any throttle.




Well here is one thing tho in response to the idea that the power doesn't affect it much below 500watts, in general, there is a video of a guy hand launching his FT Spitfire, it has a 22mm motor like a Suppo Beef and 8x4 or 9x5 and it veers off quite noticeably toward the Left Like it really was needing thrust correction, I looked for that video, wish I had saved it so I could show you

 

[ZoomNBoom]

The best thing to do is find a thrust angle somewhere in the middle based on your power setup and then use flight modes with trim that engage at X throttle position. A sophisticated radio can be programmed to do this without much trouble.

On a sophisticated radio you can just mix roll/rudder/elevator with throttle, but that wont entirely solve the problem either. As you rightly pointed out, the pitch tendency depends on airspeed. Throttle position is a decent, but hardly perfect proxy for airspeed. And the other factors to counter include torque roll, which depends on acceleration of the propeller (good luck mixing that away , P-factor, which is dependent on AoA, and the prop wash helix hitting the vertical stabilizer, which is dependent on who knows what.

In short: there is no way to account for all these effects with a single setting

 

[ProfessorFate]

Hello ZoomNBoom!

one thing about angle of attack I like the thrust lines of my wings airfoils straight neutral to be lifting foils producing lift by bernouli rather than and AoA


Maybe a good ballpark thrust corr might be 3R and 3D for average, you see, with no correction at all, we DO know that most all our Spits will veer Left, meaning SOME Right thrust corr is needed

and some keep mentioning the tendency to go up with any throttle applied, tells me SOME amt of Down thrust is needed, I'm just wanting thrust corr for average 40mpg flight, not beasty 80mph nervous hi speed stuff, my stryker zoomed upward so much, it over compensated so much, it's motor mount was non adjustable fixed too low, I did not like fast flight with the stryker


Now really, I'm not sure


and was asking for help as to the best guess for this style of flying, this plane, could be 1.5 to 2.5 #


to make the Mustang fly mostly straight at about half throttle 40mph 2# plane, you know, this ballpark.



Do you think 3R and 3D would be about right?


I can apply a single setting to apply an average effect for about 40-50mph flight for the flat bottomed wing of the mustang...... I am shooting for an average answer, not for extremes,

if I just do nothing...... and use 0R,0D....... it flies crooked and too easily baloons up with any med amt of throttle, see?

142g motor 10x6 prop 45mph, sloppy med ballpark, what would make it right for this?

 

[ZoomNBoom]

Well hello

one thing about angle of attack I like the thrust lines of my wings airfoils straight neutral to be lifting foils producing lift by bernouli rather than and AoA

Hmmm, what ?

I guess you're trying to say you use airfoils than rather than planks, but any wing has an angle of attack.

Thats not even what I was referring to though, the P-factor is about the AoA of the propeller:
https://en.wikipedia.org/wiki/P-factor

Not having flown the FT spit, I can not give you any advice on that. I also dont know which of the effects I mentioned dominates.

 

[ProfessorFate]

Yes

Thought of it just now, zero wing incidence?


Some fig of R and D would give me what I want for said conditions/expectations, making it 0,0 we would see with any thrust applied, that it needs some amt of correction.







If no one really has anything to help,


I can just go with my own guesses of 3R 3D, I don't have the flight experience with these power planes that yall have





It's only an average solution for average 45mph speeds, no extremes or complicated stuff, what makes the FT Spit and Mustang fly just about straight at about 45mph, what thrust angles? Some pair of average numbers would just about do it, right?



Just looking for that nice, sloppy, horseshoes n handgrenades approximate figure that will do it just about right, see?


OK, after I build the new power pod with 3 degrees Right and 3 degrees Down thrust correction, used with the Cobra 2820 1170kv 142g motor with an apc 10x6 e prop, I will post how it flies at about 45-50mph cruise and throttle behaviors


I have a pretty good grasp of forces and math including geometry, power and electricity and I think 3 n 3 may do it,


Now,


I put some numbers to it,



that's what I asked for,



numbers that worked. I'm only guessing, hope it works about right, about right, is, what I wanted.

 

[nerdnic]

Starting with 3 down and 3 right is good. Should help a lot at 40mph.

 

[ProfessorFate]

Good Morning, Nerdnic!!!!!! Hi, Thank You!

Yes, I kind of guessed 3 n 3, OR, 4 n 4, would be "about" right, but, I wanted to run it by others here, like you who have more flight experience with powered airplanes,


just in case you thought that was not enough.



That one in the freeze frame picture on the FT Thrust Angle article, measured in a paint shop, shows 6.5 degrees Right thrust




Thank You, Nic

Leonard



** I like to share what I know that is good with people and I see members here, do too,


That Ross Foam Board from Walmart looks like a super discovery, better than Adams or DTFB.

http://forum.flitetest.com/showthread.php?21937-ROSS-Foam-Board-Review

Just stumbled on this in Mad Scratch Builders..., and sooner or later the thread may sink into oblivion, but, it's worth repeating here.

Anything good, materials, glues, techniques, etc are worth repeating and sharing


Thank you, Leonard


Do we have any more threads or posts with info about sites for 3views/pics, like this one?
Image Directory of Aircraft
http://forum.flitetest.com/showthread.php?22242-Image-Directory-of-Aircraft

 

[ProfessorFate]

Figures for 3R and 3D calculated, but, correct?

I really like to do these things by hand and hope the right logic here is to add the same amount

This is a square 44mm on a side ( 1.75 inches on a side )

44 x Tan 3deg = 2.3mm so 3R + 3D = 4.6mm at the bottom Left corner on the wood with 3 arrows, set firewall back at this point 4.6mm,

now if I have this correct, the idea of adding them like vectors, then, I am just sharing the process with you, since this is a kind of build log


Next will be how far toward 2 O'clock to put the center of the motor mount so that the prop outside is at the exact center

 

[ProfessorFate]

Figs How much to shift motor towards 2 O'clock



Now that I got these figs, mark n drill holes for the blind nuts, hammer them in, and glue the side panels, 14" floorboard, and firewall of pod

 

[quimney]

Professor Fate,

You probably already know this but the FT power pod by design does not fit in the plane. The back engages but the front does not because of the block with the skewers. This tilts the power pod down and gives about 2 deg of down thrust. Because this setup is not that strong I modify my power pods so they fit flush allowing both tabs to engage creating a much stronger setup. That eliminates the down thrust caused buy the fit so I make custom power pods to compensate. The pod I run in the FT mustang is set for 2 deg down and 2 deg right. The plane climbs just a little at full throttle and I liked it that way as I was learning. I suspect 2.5 to 3 degrees would remove the climb altogether.

I did experiment with throttle mixing to change the elevator trim based on throttle level and was able to get it to fly completely flat when the throttle was changed slowly. As stated here the lift is related to airspeed not throttle setting so abrupt changes in throttle caused some unsettling pitch changes until the airspeed caught up. Eventually I just took the mix off because it was easier to manage the throttle climb than this new behavior.

I get a little lost in the math of your last post... I'm not sure where the 6 degrees came from. It seems to me that if the prop is 59mm in front of the firewall then you would want to move the mount 3.08mm up to compensate for the 3 degrees down thrust and 3.08mm left to compensate for the 3 degrees right thrust. That should put the prop in the center again.

 

[ProfessorFate]

Hi, 6 degrees yes

I think all the pod installations will fit better if straight, leaving ( in my 48" foam Hurricane ) enough room to make curved formers for and aft of the canopy, see all the pics of thread in Pod post and my gallery, straight with the thrust line works best for sure,

I hastily modified a Hurricane 3v for fit up with wing and pod, it was sloppy so I found a much better SVG line drawing and then made fuse curves better fit wing placement and the pod was straight on in the right place

6 degrees, if I remember right, like vector addition, 3R and 3D should add up to 6, some things are NOT linear like that and actually you make me want to verify this to be sure, but at the bottom left is the deepest point on the firewall adding the amount for both R and Down thrust.

This wood pod w/ 3r3d is 16" long and looks like it's going to be perfect for most 48" WS airplanes




Leonard

 

[quimney]

I really like your plane and the tough power pod concept. Your comments on the math got me wondering so I had to do a quick sketchup model this morning to make it easier to visualize. Sometimes I get lost in the math.



3R & 3D does indeed cause a shift of 3mm in X & Y. The resultant angle off the axis is 4.3 degrees.

Back in the real world 3mm doesn't seem to amount to much.... I would likely miss-measure by that much anyway.

 

[ProfessorFate]

Did you see how the Mnemonic SOH CAH TOH works?

Hi
I had a bad time in school with algebra, so later to get proficient with these and the things of physical math like trig and using algebra for scaling and building, these things came hard for me, but, then the understanding I got when I figured them out... well now I am pretty comfortable doing these things by hand and I like to know the answer sometimes instead of having to trust a program, like to be able to check it and have a feel for it myself

In the navy we did an interesting form of vector addition on paper mho boards
In calculus and algebra we also did this, with numbers, not physically with compasses and parrallels

Here we use the Tangent ratio, knowing the angle and the adjacent side is 44mm, all that’s left is what the opposite side length is,

the form is Tan 3 = Opp/Adj

Get Opp by itself

Adj Tan3 = Opp

Now insert the #s

44 x Tan3deg = Opp Side Length

44mm x 0.0524077 = 2.3mm

We want 3 deg R and 3deg Down, so both vectors push at the maximum on the bottom starboard corner at ( around where 7:30 on the clock would be )

Looking at the nose/FW, I put 0mm upper R, 2.3mm upper L, 2.3mm Lower R, 4.6mm Lower L

All anyone would have to do is just make sure you have your ends lined up, then mark it

It sure helped me to have all 4 points and lines drawn between them for aligning the firewall after the 3 pods sides were glued.

It was all a tight fit and I could just barely get enough Right to insure the prop was in the center, big motor, couldn’t go up that far fm center but I could go Right just about all the way for center correction

I’m still struggling with designing, I got in a little of a rush making the fuse and did not make the Hurricane fuse full scale width but all else is scale proportion

You might really like this pod, it only weighs about 4oz with the hatch, and you just tape it to the top edges and it sits in the paper cradle/seat made of that tough heavy poster board, must be like 200 pound paper?

If you want to see something that makes scaling pictures easy, here:

** I made a small mistake, fortunately with small quantities, those two vectors or angles don't just add up, I don't think like 2.3 + 2.3 = 4.6, I think for confirmation of same it's 2.3^2 + 2.3^2 take square root of that to get 3.26mm for the Lower Left corner, not 4.6mm, but OK so it has a little bit more down and side correction than I intended

The motor in my pod looks right, prop looks pretty close to the center in spite of small mistakes, close enough.


You might be right on, I think I just put the motor over to the Right of center, about 1/8".

 

[quimney]

Eureka!

Professor,

Thanks for the clarification. Now that I understand your approach I see where the 6 degrees came from.

I believe the 4.6 you calculated is correct. The trouble is is the adjacent side.

You correctly calculated the length of the diagonal from the 0 to the lowest point but then used the length of the side in your calculation instead. That’s where the 6 degrees crept in. Had you used the 62.2245mm the rest looks like it would all fall in line.



If you built the pod based on 4.6 I think you got the 3R 3D that you were looking for...

We had better stop this now before the moderator kicks us both off for excessive use of math

Quimney

 

[ProfessorFate]

3R, 3D, checked with vector addition

Hi
Knowing whether I got this right or not was bothering me, I mean just leaving it there as an unknown, something I did with my own hands and that I can figure it out, this is not like calculus

For 4 yrs I was an Operations Specialist, Navy, then in college in physics and algebra and trig we saw how to add vectors both physically and numerically

What better way to check than this, the degrees are like units of force, 3 units at 090, 3 at 180

Resultant vector is 4.24 at 135 degrees, a little confusing sounding, I know, but the thrust angle is thought of as the amt of force of negative inclination....... R U negatively inclined?







****** There was an extra "Double Check I did that was not quite apparent, only because it ran on 45deg, did I know easily that the vector length was also ( a square with sides of 3 )

1.4142 x 3 = 4.2426


Since I was so unsure of how or if I got the right solution, I wanted to work this out completely, so, I got the amounts in metric to place the firewall, 0, 2.3 on both and 4.24 bottom at 7:30oclock
BUT
It's 3deg across, and 3deg down.

What angle is across the diagonal? ArcTan (4.2426/62.2245) = 3.9 degrees! That's it!

4.25mm incline to get the angle, and 3.9 degrees "IS" the angle.

So for now, truly, if anyone wants to set their firewall at a fixed thrust angle, all you have to do is just lay out the numbers on the graph paper, vectors end to end but front to tail, then you can accurately get the right amount to set the bottom corner by measuring the result that looks like the diagonal, but it sure helped me to mark each corner and draw lines to follow, that thing was squirrely even in the clamps.




OK, this has been a very satisfying puzzle.


If you draw bearing lines toward your solution, their intersection will be where your answer lies.


"Push the button, Max!"

 

[Craftydan]

Ok, OT and unproductive rabbit trail . . . Prof Fate, I knew I liked you for some reason. Anyone who defaults to RPN can't be half bad

I miss my HP-48. Droid48 just isn't the same without the clicky buttons and the tinny beep.

. . . and now back to your regular thrust angle discussion, already in progress . . .