Thread Tools
Apr 03, 2018, 10:04 AM
Registered User
Thread OP
Discussion

Motor thrust angle ... up/down ... or what?


I have a 2m powered glider. It's just a simple balsa box, wearing a wing from an old Nebula glider.

The pic shows the front end of the model, with the motor removed from the nose. There's a bit of wood sticking out from the upper surface of the fuselage, and this represents the position of the motor' pylon.

I am in the process of converting it for FPV use, and I want to mount the motor as a pusher, on the wooden pylon (in the pic). So, the final configuration will be a bit like a Bixler.

Should I arrange things such that the motor's thrust tends to pitch the nose down ... or up ... or is it just 'suck-it-and-see' ?

The tail end of the model is totally conventional, with a low-set tailplane. The wing' section is a simple Clark Y-type.

Is there any compelling reason why I should not orient the thrust to be parallel with the wing?

The model will be used as a training platform, to familiarise me with FPV flight, including landing and departure. The camera will be mounted ahead of the motor pylon.

.
Sign up now
to remove ads between posts
Apr 03, 2018, 03:16 PM
Registered User
aeronaut999's Avatar
The "good" pilots all say the trainer-type planes are designed with too much decalage. too forward a CG, and too much motor down thrust. See for example Paul Naton's video on tuning the Radian --
Parkzone RADIAN Modification Clinic.mp4 (31 min 53 sec)
. But, there must be some reason they were designed that way-- and maybe the original setup would be a good configuration for FPV? Or not? Steve
Apr 03, 2018, 07:06 PM
B for Bruce
BMatthews's Avatar
The pylon is ahead of the wing so the prop is going to end up more or less where it would be with a wing mounted pylon and a tractor motor. So I'd say you want the motor axis to point down to somewhere around the base of the rudder. That'll give the motor a strong upthrust angle.

Be aware too that if the motor is one that is really strong for the weight of the model that it may still try to drive the nose down at higher power settings. Flying with pylons and other odd force arrangements is all about the thrust and the ability of the tail to compensate for it. So don't be surprised if you motor it up and full throttle still pushes it into the ground eve with full up elevator but half throttle lets it fly just fine.
Apr 04, 2018, 03:50 AM
Registered User
Thread OP
Well, I guess that the model is going to exhibit some odd coupling, whatever I do. To be fair, in its standard condition ... with a tractor prop on the nose ... it pitches up quite markedly under power.

I know that on full-size, they can't 'design out' these thrust-related problems, so I'd be daft to think that I can. I'll just take a punt at it, and live with the consequences.
Apr 04, 2018, 11:21 AM
B for Bruce
BMatthews's Avatar
Quote:
with a tractor prop on the nose ... it pitches up quite markedly under power.
When the prop is down close to being in line with the CG and the overall center of drag a strong pitching up with power added is more commonly related to the CG being well forward and the tail being trimmed to match that CG placement. With the angle this provides between the wing and tail we get a strong pitch up response to any added flying speed. Be it from a dive or from an increase on throttle.

Move your CG back so it's closer to but still in front of the overall neutral point for the design and you'll have a weaker pitch up with speed changes.
Apr 04, 2018, 12:41 PM
Registered User
Thread OP
Yes, I discovered that the CG as flown, provided a Static Margin of about 20%.
Apr 04, 2018, 01:31 PM
Suspended Account
You can always employ TX mixes to help with the pitch changes while under power. I had to use a mix to put in a fair amount of down elevator at full power on my Calypso powered sailplane.
Apr 04, 2018, 04:07 PM
Registered User
Thread OP
Quote:
Originally Posted by EXF3BMAN
You can always employ TX mixes to help with the pitch changes while under power. I had to use a mix to put in a fair amount of down elevator at full power on my Calypso powered sailplane.
Yes, I'll prolly do that. I want to fly the model FPV and it would pay me to make things as easy-peasy as possible.
Apr 05, 2018, 12:46 AM
B for Bruce
BMatthews's Avatar
THAT'S CHEATING ! ! ! ! ! !



Hey, whatever it takes to get the job done with as little trouble as you can.

I'm keen on trying out FPV this year. I'm going to dive in with a camera on a pan&tilt and get a head tracking headset. I'm going to stick it into one of my old timers so I know that the model will at least fly itself if I let it do so. Who need a fancy auto pilot when you've got a perfectly stable and self correcting free flight model with some radio just to suggest it go this way and that....
Apr 05, 2018, 01:05 AM
Registered User
Thread OP
Quote:
Originally Posted by BMatthews
THAT'S CHEATING ! ! ! ! ! !



Hey, whatever it takes to get the job done with as little trouble as you can.

I'm keen on trying out FPV this year. I'm going to dive in with a camera on a pan&tilt and get a head tracking headset. I'm going to stick it into one of my old timers so I know that the model will at least fly itself if I let it do so. Who need a fancy auto pilot when you've got a perfectly stable and self correcting free flight model with some radio just to suggest it go this way and that....

Yes, my own philosophy is much the same. My little glider wafts about like a vintage model ... well, it did. It may be a little more positive with the addition of various batteries and oddments. There's a lot to be said for baby-steps.

The plan is to build up to a level of competence such that I can conduct a whole flight FPV, then swap over to a model which is more appropriate for aero-towing. A couple of my friends are working on the glider end of the business.

I just bought some goggles, a camera and Vtx from BangGood. All seems to work quite well. Best of all, I can use the goggles without the need for spectacles.

What I'd really like to do is to tow exclusively vintage gliders, using a nice vintage tug. I think that would provide a really pleasing spectacle. But, finding people who are sufficiently interested and motivated to get involved, is a bit of a problem (Oh, and they have to be competent flyers). It's a tall order. Been trying to involve guys for years, in aero-towing vintage stuff by LOS. Plenty of people like the idea ... but, making it happen is a different story.

A few years ago, we got very involved in LOS aero-towing, and it was the best fun I've ever had with model planes. The challenge, the novelty and the collaborative nature of the task ... all combined to freshen up my experience of the hobby. The only modelling experience to compete with that, were those months (back in '85) when I was learning to fly. Do you remember how totally absorbing it was, when you were a novice?
Last edited by bogbeagle; Apr 05, 2018 at 01:44 AM.
Apr 08, 2018, 10:06 AM
Registered User
Thread OP
Flew the model quite extensively, this morning.

Got a surprise.

I arranged the pylon a bit like a Bixler ... with the motor pointing down by a couple of degrees, relative to the wing. It was just guesswork, but it worked very well. The model pitches up very mildly, under power. So, that's great.

The surprise was the amount of roll induced by power. If I trimmed the model to fly 'wings level' with the power off, then the application of power led to a very pronounced roll to the right ... and quickly into a spiral descent.

Anyway, I was able to mix rudder trim, such that increasing power is compensated by increasing Left Rudder deflection. This works well for moderate power settings, but falls apart at very high power settings. I suppose that it's a bit of a rough solution to the problem, but it's good enough for me to move on to the next phase of the job, which is flying by FPV.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question What is more important when looking at motor specs. Thrust or Watts hog2soar Power Systems 11 Oct 27, 2015 07:13 PM
Discussion Motor thrust angle question (up, down) 1101 3D Foamies 7 Sep 28, 2015 08:09 PM
Discussion Thrust angle issue (Too much down angle?) Navet97 Electric Plane Talk 13 Nov 22, 2013 11:08 PM
Help! thrust angle on flying wing combat.... up or straight warhawk crazy Combat 1 Jun 29, 2009 07:00 PM
Question Thrust angles, how many degress down and/or right? birdlives1955 Power Systems 5 Aug 03, 2006 02:02 AM