Dihedral questions

aeromed202

aeromed202

SOH-CM-2014
I thought I'd ask a question I've had about wing dihedral in FS. I remember from my short flying days that in some turns in a low wing four seater that after initiating the bank, sometimes opposite aileron input was needed to maintain it otherwise the bank would increase. I have not found this to happen in FS and wondered if it was simply not modeled in the program or I don't have things set up right to simulate it.
 
That doesn't make sense to me. I thought the point of dihedral was to increase roll stability. Maybe in the case of low wing civil planes it's a matter of the CG being higher than in a similar high wing plane. If the CG was above the wing, that would tend to decrease roll stability. I think...
 
One often forgotten reason for the dihedral on low wing aircraft is to simply increase wing tip clearance.Long wings on a low wing would not allow for much clearance over groung obstructions close to the runway edge. Especially in a crosswind wing-low or slipped approach to landing.

Raising the tip gives a few more degrees of bank to balance out more cross wind.
Even if like me you prefer the crabbed approach in the final second or two you need to transition to a slip to get the upwind wheel on the ground first.

The over-banking tendency on modern GA aircraft is very low up to about 45° of bank.
Usually the need for the opposite aileron input has more to do with the pilots feet ;)


Cheers
Stefan
 
I actually had more questions until I popped over to Wiki like Milt showed. I then shortened the question to the one concerned with FS only. Again, my memory is fuzzy but I remembered having to put in small righting aileron input to maintain steeper banks on a low wing single engine (but I do have big feet) and have read similar descriptions in some books. If this is correct I was wondering if FS is capable of this effect.
 
Aeromed:
Yes there is a setting in the .air file that affects whether an aircraft with bank on self rights, or whether it stays banked. On the spur of the moment I cannot remember which item it is but will report back anon.
Keith


[edit] Just experimented with the 1100 block entry for Stability & Control - Roll heading then the figures for 'Cl_r Roll Moment-Yaw rate'
Using Ron Freimuths Air Edit I found -4000 increases bank, -1000 is neutral & -100 is self righting. What I do not know is if there is any other interactions with the rest of the .air file.
If you use the Aircraft Airfile Manager - it describes the setting as 'bank angle -ve tends to roll aircraft level in turns', although the coefficient numbers are different.

[Edit2] Re-reading your question - if you are talking about needing rudder to keep the nose up in a turn, which some aircraft need, then I've not tried that, but would think its in the same area of the air file.
Keith
HTH
Keith
 
In my learning to get a PPL, the dihedral of the wing is to add stability the aircraft. The planes I have actually flown, when put into a bank, will stay in the same bank, until correction is added. I asked my CFI if this was true for all fixed wing planes. He said yes. I have noticed that a number of FS planes will continue to steepen the bank or roll out of the bank. I have yet to find one that maintains bank angle.

Just my 2 cents.
 
Thanks for the real-world info. Maybe what I read concerned fighter planes where all bets are off. I do know that in FS, maintaining a bank with marginal inputs is somewhat achievable by adjusting the dihedral value, the vertical Cog and a bit of cheating with the roll MoI and roll stability values, all for a particular AC. Problem is that doing those things may enhance that particular performance aspect for some AC, but it usually messes up a score of other flight characteristics for the rest and isn't worth the bother.
 
Sunny9850 said:
Usually the need for the opposite aileron input has more to do with the pilots feet ;)
Click to expand...

Ha ha ha! This reminds me of my gliding lessons many years ago. For a long time my problem was that I was not properly applying rudder when making curves, so they became often rather sloppy. My club instructors just couldn't get me using my feet properly. Then from another club there was this young instructor called Martin. One beautiful day full of thermals he took the place of my club instructors for a change. Before the lauch by winch he told me he wouldn't touch the stick or pedals at any time. Only correct me verbally. We had the most beautiful (two hour) thermal flight in the ASK13 (see avatar), climbing 4,800 feet after release at 1,200 from the winch. After we had landed Martin said: "Maarten, you did this all by yourself. Thanks for this great flight." And to the club instructors he said: "Maarten just found out that he has feet too." ;)

Cheers,
Maarten
 
dandog said:
In my learning to get a PPL, the dihedral of the wing is to add stability the aircraft. The planes I have actually flown, when put into a bank, will stay in the same bank, until correction is added. I asked my CFI if this was true for all fixed wing planes. He said yes. I have noticed that a number of FS planes will continue to steepen the bank or roll out of the bank. I have yet to find one that maintains bank angle.

Just my 2 cents.
Click to expand...

Your CFI lied. Try a Piper Tomahawk, Piper Warrior with the Hershey Bar wing, or an early Bonanza at around 45° of bank and they will all roll into a steeper bank. And these are fairly tame airplanes. There are some that are much more interesting to fly yet still have fixed wings and a prop.

Stefan
 
I tried it in a C172 and a Cherokee 160. Both held the bank. What made me ask the question in the first place was that there are many constants in flight, examples: constant rate turns at different speeds and angle of attack on stall (to name just two). I was wondering if this was a similar constant. Just my 2 cents. And the Cherokee did have a big 'ol Hershey Bar wing.This could change when you get to 45+ degrees of roll. I'll ask to see what he says.
 
Well that's just it, I flew Tomahawks and Warriors and I remember those first turns having to apply a little opposite aileron, and those were 15deg banks.
 
Assuming that all other control inputs are correctly applied and the aircraft is rigged correctly the Hershey Bar Warriors will steepen the bank on their own once you get to 45° of bank in a level turn.
The taper wing Cherokee series were much more benign. But at 60° or so they do start to over bank as well.

I flew a friends "new to him" 172 once and the airplane felt funny to me pretty much right of the runway. It got even "worse" as I went through a few of the basic PPL maneuvers with it.
After getting back to the airport I mentioned the handling to the A&P entrusted with my Saratoga and he said that most likely at some point the wings had been removed from that airplane and not installed properly. He checked it out and sure enough the left wing had basically a different angle of attack than the right one. Luckily for my friend this is relatively easy to fix on the Cessna...though we are still somewhat puzzled how it passed the most recent annual and pre-buy inspections :)


Stefan
 
Ok, here's some new poop. Theoretically, in shallow to medium turn, the lift differential between the raised wing and the lower wing is rather insignificant. That is why the bank angle should hold (theoretically, and sometimes in real life). However, when in a steep bank, the lift factor on the raised wing becomes significantly more than the lower wing. This causes the bank angle to increase over time. So, I guess we were all correct, based on our bank angle assumptions. :mixedsmi:
 
There are other factors to consider, besides the lift generated by the high wing being different from the low wing, that influence how the real aircraft behaves in a steep turn.
Fuel carried in the wing now turns into a significant weight pulled toward the outside of the turn by centrifugal force. In a 2G level turn in a Warrior that may be 240lbs pulling outward and downward.
In my Saratoga in that same 2G turn a full fuel load in the wing would now be 600lbs.
I have never flown her with completely unbalanced wings, since at about 20 gal difference the heavier wing starts to bank the airplane, meaning it requires aileron just to fly straight and level.

Stefan
 
I would also suggest that the farther up the CoG is from the CoL, the more pronounced the effect. Dihedral tends to get the CoL closer to the CoG to lessen the effect in steeper angled turns.
 
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