I am not saying there is no risk in a SEP, there are lot of factors such as the limited view from high/low wings and windows wich make things very tricky (except few SEPs with a nice view like cub, aerobatic, open cockpits or gliders) and you still have speed/handling differences from aircraft specs and cockpit distractions, so as you said one has to keep that formation as loose as it should given aircraft limitations/pilot training…if you give PA28 and C172 to two fighter pilots, they may hit each other anytime the Cessna flies low ;)
Personally, I would invest in a nice camera with a powerful zoom while keeping good distance instead of pouring money on any “fomation flying training” course (in theory this has to be done with your other “flying mate” ;) ), I think any PPL can do that kind of relaxed flying…
Don’t take formation flying lightly. It must ALWAYS be briefed before the flight. Contrary to what most think formation flying is more difficult in aircraft with light wing loading and poor power to weight ratio. That means SEP is generally more difficult to fly in close formation than heavy military jets, even if it doesn’t look or sound as impressive to the untrained eye. That’s especially true in any significant turbulence. PPL, CPL or ATPL doesn’t matter its training from someone that knows formation flying that counts. And if you mix aircraft types in the same formation with different performance parameters, including some that has poor lookout it gets even more difficult (side by side usually has poor lookout to the right, and those with a solid roof has poor lookout upward).
THY wrote:
Don’t take formation flying lightly. It must ALWAYS be briefed before the flight. Contrary to what most think formation flying is more difficult in aircraft with light wing loading and poor power to weight ratio. That means SEP is generally more difficult to fly in close formation than heavy military jets, even if it doesn’t look or sound as impressive to the untrained eye. That’s especially true in any significant turbulence. PPL, CPL or ATPL doesn’t matter its training from someone that knows formation flying that counts. And if you mix aircraft types in the same formation with different performance parameters, including some that has poor lookout it gets even more difficult (side by side usually has poor lookout to the right, and those with a solid roof has poor lookout upward).
This.
Ibra wrote:
instead of pouring money on any “fomation flying training” course (in theory this has to be done with your other “flying mate” ;) ), I think any PPL can do that kind of relaxed flying…
Not this.
And by the way, a preflight briefing is not only a vitally important safety initiative, it’s a legal requirement for formation flight – at least in Canada.
If you’re relaxed flying formation, something is very wrong. If training for formation flying is proposed from your mate, better figure out where your mate received their training. If it wasn’t either military, or team aerobatic, the mate would do everyone a favour by not attempting to train anyone in formation flying. A little bit of knowledge is a dangerous thing – particularly in formation flying.
Thread drift 
The Q was if the engine can cope with slow flying. The answer is simple. If the oil temperature remains above 80 deg celsius or at least 70 and the CHTs over 150 deg C the engine is happy. The test is not a big deal and I expect the necessary sensors are in the 400. I normally fly at 160kts with 65% (but not a 400) and 100kts is too slow for me to keep the temps up. Whether or not its convenient to fly a 400 at 100kts over hours is another Q. Dont know the lower AP limit and how loose your formation is
There are no figure for % of power at 100kts on the C400 (POH quotes 30% power on 136kts), but I think with a rough extrapolation at 100kts it probably around 18% of power (power % =
(100/230)×(100/230)), I don’t that will give you that much oil temperature…
Karl_Acht wrote:
The Q was if the engine can cope with slow flying
I don’t see why not. Get the RPM up and the oil will keep circling around as usual, and if the temps are within normal limits it should run forever IMO. Why not just try it first, and see how the engine behave? I also think the oil could possibly be too cool, but try it and find out.
It’s kind of puzzling why people ask questions instead of trying things. There is only one way to find out if this works, and that is by trial (and error). 
There are no figure for % of power at 100kts on the C400 (POH quotes 30% power on 136kts), but I think with a rough extrapolation at 100kts it probably around 18% of power (power % =
(100/230)×(100/230)), I don’t that will give you that much oil temperature…
It doesn’t work that way, due to the engine needing a lot of power just to turn it at the required rpm. An engine is an air pump which happens to share the pistons etc with the bit which produces the power. It takes a lot of power to pump all that air. And all the mechanical friction. See this for example and extrapolate the axes backwards.
Also the pumping losses increase (relatively) at low power because the pump is sucking against a nearly closed throttle,
It’s kind of puzzling why people ask questions instead of trying things. There is only one way to find out if this works, and that is by trial (and error).
It is a perfectly good question to ask, especially as it will work (otherwise, as I wrote earlier, the plane could not land) but there could be issues with doing it for some hours, and it is better to ask than to end up with a bunged-up engine.
Here’s two more out-of-the-box ones
1. Forget 100 kts, let the whole squadron slow down to 80. This way the Col400 will be behind the power curve, needing lots of power.
2. Load the Col400 up, as far forward as possible. Guess with what.. The bags of the other ones, making these faster, and the Col slower
A combination of 1 and 2 works too of course.
If nobody is impressed by my creativity this early in the morning, well at least i am
Since we are being creative, why not flying inverted? I don’t know the 400, but most airplane flies a lot slower once upside down !!!!
