Thrust angle for a power pod?

batjac Tue Mar 28, 2023 3:09 am

I had a project I started working on a couple of years ago, but had to put on hold when we moved. A post in the coroplast vs. balsa thread reminded me that I needed to finish it up real quick so I can fly it at S.M.A.L.L. in a couple of months. I was originally going to put it in my Q-Tee, but decided that a motor glider would be better to test the system out first. I don’t have one at the moment, but the post had a foam glider with a 1/2A engine grafted to the nose. Actually looked pretty good. We’ve all seen them. But, I don’t want to do a graft on the nose. I do have a power pod that’s been sitting in a box for a few years and thought that that would be a fun afternoon project. It is one of these Cox beam mount pods:

Now, I know the rules for down and right thrust for tractor engines, but I don’t remember ever reading about thrust lines with a power pod. So, I went to OZ and did a search by putting “power” and “pod” in the search fields. I downloaded 24 sets of plans for gliders with power pods, figuring I could just look at the average thrust lines and get an idea of how to set the pod. Wow! Wide range. Most were somewhere between +3 and -3 degrees. One as low as -6 degrees and one at +16(!) degrees. One design wasn’t even going to commit to a thrust line, so the pod had a pivot bolt and slot that would swing the thrust line between -15 and +15. I guess that’s smart in that you can set your optimal thrust line for the finished plane/engine. But the plans did not give a suggested starting position. I know that with elevator control it's not critical, but I'm wanting to set this up for rudder only control, so the thrust line has to give the glider a gentle climb under power with the plane trimmed for a shallow glide engine off. Going old school here.

So, is there any good thumb rule for power pod thrust lines?

The O.G. Mark

GallopingGhostler Tue Mar 28, 2023 6:21 am

Under rudder only (only regarding side - left/right thrust), I kept my fingers "clamped" on the stick, so even if I had to give a touch of rudder one way or the other was the norm, as long as glide is correct with the stick. If off significantly, then I adjusted the thrust angle.

Since these were designed as temporary power to get the glider up to thermaling altitude, it probably was not considered that critical, since the standard tanks on the Bees don't give a long run time anyway, only enough to get there.

Most critical adjustment would be especially the up/down thrust angle. On a rudder only, that is sort of experimental from short test flights under power. Only then you know how much to shim where.

If an external tank is used for longer run, then perhaps a more accurate tweak would be less tiring to fly.

Under rudder only though, my finger was so busy on the stick, that minor side thrust misalignments didn't matter. Doh!

getback Tue Mar 28, 2023 6:33 am

That s a good question Mark , I have a tow glider that I was thinking about putting a power pod on with ?? engine and had not thought of the thrust angle , its rudder/elevator though , I see George has chimed in he is a rudder only man so maybe he has a good'er answer but you may want to take a look at this only 3 min.s

rdw777 Tue Mar 28, 2023 7:40 am

I built a Thermic Trooper some years ago and installed rudder only control in it … I made an electric power pod for it that would just run until power ran out… The pod was just rubber banded onto the wing so it could be shimmed as necessary….. It needed about five degrees of “up” to climb out on a calm evening….

Here’s a photo of the Trooper I pulled from RCG that was at an indoor fun fly…. I had to take most of the up out of it to keep from climbing too much…

I would start by trimming for glide then try with power and few degrees of “up” with short runs til you find the sweet spot for climb….Shimming as necessary….

The Ace RC Guppy I built last year is two channel and I also gave it above five degrees up thrust …..It seems to be about right on the nickel without having to mess with elevator too much during climb …

sosam117 Tue Mar 28, 2023 9:39 am

I have flown my Graupner Amigo II with a Cox Tee Dee .049 with 8% nitro (back in 2001)
The pylon had 4 degrees "up" thrust and it pulled my Amigo II at about a 30 ~35 degree angle.

I unfortunately sold the Graupner Amigo II in 2008 (needed the money --- rolling lay-offs).

Purchased a Graupner Amigo IV in 2014 with "plastic" power pod kit (accessory) from Graupner as well that goes with the Amigo kit.
The power on this Amigo IV is a Axi outrunner with a 9x4 electric prop running on a 3 cell 1300 Lipo pack.

The setup is "close" to what Graupner suggested but I have a little more powerful electric motor than what Graupner suggested.

Now, the "up" thrust for the Amigo IV power pod is 5 degrees, and at full throttle it climbs at almost between 40~45 degrees.
What is nice is I can throttle back and it will reduce the steep climb to a slow gradual climb.

Now I was fortunate enough to acquire "" Graupner Amigo V kits before Graupner closed down.
Got as many Amigo kits as possible that I could straight from Graupner's website when I found out they were no longer making the kits.
Purchased them from Graupner in 2018.
I was able to purchase "ONE" Amigo IV with the plastic pylon and "THREE" Amigo V kits with the laser cut pylon kits ( in the small square brown box in the photo on one of the Amigo V kits.

The Amigo V has the electric motor in the nose of the plane as an option.
But I was able to purchase the laser cut plywood pylon kit if I want to make the Amigo get pulled up by a pylon mounter motor?

So, I would suggest having the "up" thrust starting at 4~5 degrees?
The side thrust on my old Amigo II aand my newer Amigo IV have a 4-degree right side thrust.

As for your power pod.
The placement on the wing will be important as yours could be either on the C/G or back behind the C/G?
The best placement is on the C/G and what also needs to be known is the top "slop" of the airfoil that you are going to place the power pod on?
If you place you power pod on a flat and level surface, you might see that it has some "up" thrust on it?

batjac Tue Mar 28, 2023 11:54 am

GallopingGhostler wrote:Under rudder only (only regarding side - left/right thrust), I kept my fingers "clamped" on the stick,

George, the main purpose of my experiment, other than being a nifty idea, is to maintain constant control.

Eric, good video, but doesn't quite apply in this instance. Thank you, though.

sosam117 wrote:If you place you power pod on a flat and level surface, you might see that it has some "up" thrust on it?

Wow! I never noticed that. It does have built in up thrust. I was planning on just gluing in a balsa plate on top and then shimming as necessary. With this knowledge, I'll just make the plate 0 degrees and shim from there as necessary.

The Unobservant Mark

HalfaDave Tue Mar 28, 2023 12:29 pm

Hi Mark,
I've done ~dozen pods over the decades. Gliders and mostly float planes.
This is how I understand them...
A pod at 0deg actually acts like downthrust, because of it's high location.
Not done neg deg on one.
Have varied the positive to best effect. Depends on the plane.
The height difference of the pod varies the 'downthust effect' allot.
Faster float planes have had up to +15deg pod upthrust to negate the downthrust effect.
Hauling GentleLady type gliders with the pod you have is fun.
A rudder only foamy?
This will be fun!

Can do R/O manouvers with elevator backup,
Dave

Ken Cook Tue Mar 28, 2023 3:04 pm

I think that it may need experimentation vs a hard number. Lifting stabs certainly negate more down thrust. In the bit of free flight I've been playing around with, I've found some vs none is seemingly better. As the engine leans out due to fuel level running low, the nose can pitch up and cause looping if extreme. I've also had the nose pitch high and then stall once the fuel runs out. Downthrust does help with this.

NEW222 Tue Mar 28, 2023 4:01 pm

Quite an interesting topic. One I had never thought of. I have a Sig power pod for a glider. Now after reading this makes one wonder. Set the power pod too far forward, downthrust. Too far back, upthrust. pointed slightly to whatever side gives you that thrust also. So much for my simple thinking of just rubber band the thing on and go fly.....

GallopingGhostler Tue Mar 28, 2023 6:37 pm

¡Estoy muy loco! I am very crazy! lol!

I just bagged this for a nominal sum, engine and pod. Tired w/ Coffee Read

El montaje elevado con motor

@Kim, Bob @rsv1cox, please tell me I won't need to be fed 3 squares underneath the locked door! lol!

Kim Wed Mar 29, 2023 5:11 am

GallopingGhostler wrote:

@Kim, Bob @rsv1cox, please tell me I won't need to be fed 3 squares underneath the locked door!

Dude! Looks like a great score to me! I've done a lot of power pods (mostly home made) and several single channel models, but not together.

I also have a rudder-only Jetco "Trooper" slated for a pod and an .010. It's actually got a lot of flying time, but with launches delivered by a piece of Sig contest rubber and 100ft of thread. An unfortunate wing failure put it on the way-back burner...no control of the pitch/pull of a baby high-start without an elevator.

I have a tough time dealing with "degrees" of any kind, and would just head out to the proverbial "Tall Grass" to get the plane's glide right, then use some short runs and the "TLAR" method to arrive at the sweet spot.

GallopingGhostler Wed Mar 29, 2023 6:47 am

Kim wrote:
GallopingGhostler wrote:@Kim, Bob @rsv1cox, please tell me I won't need to be fed 3 squares underneath the locked door!
Dude! Looks like a great score to me! I've done a lot of power pods (mostly home made) and several single channel models, but not together.

I was being facetious! lol!

The irony was the very power pod that Mark was showing was by happenstance the same one I stumbled across! Shocked

Plus, this one has at least a .049 Tee Dee and possibly a .051! Very Happy

The only reason why it is missing the Venturi is the plastic carb body has a split down one side. That is an easy fix for the short time. I have some 22 gauge steel wire, about 2 or 3 wraps then twist with a needle nose pliers about 8 to 14 times to make a spiraled twist. Cut excess leaving a 3/8 inch pigtail. Bend end into a loop, done. Then put a new aluminum venturi, Part# 1717. If any other parts needed, they are available.

El precio con impuestos y envío incluido es $54 US. The price includes taxes and shipping. lol!

Kim wrote:I also have a rudder-only Jetco "Trooper" slated for a pod and an .010. It's actually got a lot of flying time, but with launches delivered by a piece of Sig contest rubber and 100ft of thread. An unfortunate wing failure put it on the way-back burner...no control of the pitch/pull of a baby high-start without an elevator.

I think that is why some modify the nose block and put the engine there, a lot easier to tweak.

Kim wrote:I have a tough time dealing with "degrees" of any kind, and would just head out to the proverbial "Tall Grass" to get the plane's glide right, then use some short runs and the "TLAR" method to arrive at the sweet spot.

A lot of the ancient authors, Ken Willard, William "Bill" Winter, Jack Hadley, Randy Randolph, Hoh Fang Chui and etc. used TLAR, described in their building articles to sell magazine plans. I remember the design engineers at Douglas using TLAR. One odd looking chisel like DC-9 boat tail was on a wind tunnel test that I operated the data acquisition system on. That was at the N.A. Rockwell Rockdyne wind tunnel facility in El Segundo, CA. During down time, whilst techs were changing the boat tails on the 4 foot wind tunnel model, I got to see all the different ones they tried.

Design engineer was there at the test, too. He told me about using TLAR on a few of the plugs. There is no holy grail, those equations were developed modelled from real life observations to explain the test curves done by others. They aren't perfect, used to help give a starting point. The rest is through testing and experimentation.

The infallability of math and computer simulations is a myth. Testing and finally prototyping are necessary to validate. There is no free lunch. That DC-9 chisel boat tail was used on the later MD-80 series as being the most aerodynamic. Very Happy

rdw777 Wed Mar 29, 2023 8:00 am

I also have a rudder-only Jetco "Trooper" slated for a pod and an .010. It's actually got a lot of flying time, but with launches delivered by a piece of Sig contest rubber and 100ft of thread. An unfortunate wing failure put it on the way-back burner...no control of the pitch/pull of a baby high-start without an elevator.

The Trooper with an .010 on the pod would be a neat combo Kim….And still have the versatility to remove the pod and launch with hi start…. I flew mine with hi start as well at a large practice field near where I was living at the time…. About the same kind of made up hi start you mentioned….With today’s small RC equipment it would be easy to have two channels to add elevator control as well…. Makes me think about building another one of these days Very Happy

Nice score on the engine and pod George!!…. I think gliders with gas powered pods are just classy…. I had an Ace High MK II glider with a Black Window that taught me a lot about climb and glide… Fun stuff Very Happy

batjac Wed Mar 29, 2023 2:58 pm

GallopingGhostler wrote:¡Estoy muy loco! I am very crazy!

I just bagged this for a nominal sum, engine and pod.

El montaje elevado con motor

@Kim, Bob @rsv1cox, please tell me I won't need to be fed 3 squares underneath the locked door!

Kim, that's how I got the above power pod I'm going to use. I won it in an eBay auction a few years ago for the power pod with a TD .049 for $25. Wanted the TD, got the pod as a bonus. But, I'm not sure if I'm going to use a TD or a Medallion on this. Probably a Medallion.

Hey! I just realized that with the power pod, I can finally use one of those TD/Medallion starter springs that I have!

The Milder Mark

Levent Suberk Wed Mar 29, 2023 3:28 pm

5 degrees upthrust angle for tractor propeller. You can see the angle:

sosam117 Wed Mar 29, 2023 7:29 pm

Levent Suberk wrote:5 degrees upthrust angle for tractor propeller. You can see the angle:

Hey!
That Graupner Dandy looks to be similar to the Graupner Amigo II / III/ or IV?

Nice plane!
I have had one Amigo II but now have an Amigo IV and in the process of building the Amigo V with the motor in the nose.
See my earlier posting of my Amigos.

Levent Suberk Wed Mar 29, 2023 9:09 pm

sosam117 wrote:
Levent Suberk wrote:5 degrees upthrust angle for tractor propeller. You can see the angle

Hey!
That Graupner Dandy looks to be similar to the Graupner Amigo II / III/ or IV?

Nice plane!
I have had one Amigo II but now have an Amigo IV and in the process of building the Amigo V with the motor in the nose.
See my earlier posting of my Amigos.

Amigo II released in 1966 and Dandy released in 1968 by Graupner. Here are the pylon of Dandy from instructions. Plan is available in Outerzone.

batjac Wed Mar 29, 2023 9:39 pm

Just saw this over on RCG. Good price shipped:

https://www.rcgroups.com/forums/showthread.php?4320969-Cox-Tee-Dee-power-pod-for-sailplanes

The Middleman Mark

roddie Wed Mar 29, 2023 10:28 pm

This is "cool stuff" for me... Cool

considering I have absolutely NO experience with sailplanes outside of the paper-type. My take after reading thus far; is that a "power-pod" be positioned near the models' CG for conventional sailplanes.. and that the pod itself possess a means for adjusting the thrust-angle +/- XX degrees.. but starting in the "plus' field, given that the pod; with engine mounted, is at zero degrees to the model's datum-line.

I'm sure that you'll figure it out in time for S.M.A.L.L. Mark. Thumbs Up

sosam117 Thu Mar 30, 2023 7:56 am

batjac wrote:Just saw this over on RCG. Good price shipped:

https://www.rcgroups.com/forums/showthread.php?4320969-Cox-Tee-Dee-power-pod-for-sailplanes

The Middleman Mark

I originally saw this about a week ago for $25.00.

He has since dropped the price to $15.00 and still no takers?

sosam117 Thu Mar 30, 2023 8:03 am

Levent Suberk wrote:
sosam117 wrote:
Levent Suberk wrote:5 degrees upthrust angle for tractor propeller. You can see the angle

Hey!
That Graupner Dandy looks to be similar to the Graupner Amigo II / III/ or IV?

Nice plane!
I have had one Amigo II but now have an Amigo IV and in the process of building the Amigo V with the motor in the nose.
See my earlier posting of my Amigos.

Amigo II released in 1966 and Dandy released in 1968 by Graupner. Here are the pylon of Dandy from instructions. Plan is available in Outerzone.

I should do the same for the power pod for the Graupner Amigo II that I have for others?
Problem posting it here is, it is PDF format and it is not accepted for up loading?

Levent Suberk Thu Mar 30, 2023 2:27 pm

Power pod for Amigo:

Images from rcnetwork.de

HalfaDave Thu Mar 30, 2023 5:26 pm

Hi All,
All of my 'wood pods' have all failed at the 'wing joint', despite the best of fuel proofing.
Your results may vary....
The cool part,
I have a Herr AquaStar and Norvell .061 , and Lake Ontario.
The .25/.40 pod wing joints have all failed.
And I still keep trying,

Take care,
Have fun,
Dave

cmulder Thu Mar 30, 2023 5:50 pm

Was is from oil soaked wood or cracks as a result of vibrations?

HalfaDave Thu Mar 30, 2023 8:34 pm

Hi cmulder,
Both, vibrations and fuel soaked.
It was the reason, the noseses of the gliders got Cox.049s grafted on.
(easier than stringing out the 'high start'... on small fields)
The Pod .25/.40 seaplanes have flown great. Untill...
The joint between the engine pod/wing fails, and trying to repair gets impossible.
Gliding in to landing, deadstick is allways my goal.
I live near Lake Ontario,
Cox .049s are less quiet than any Jet Skiis around here...
Not many people are up, on a calm early morning...
I know all the Cops, they know, it is fun flying with me.
All the 'Karens' around here,
Yell louder than any Cox.049 I have.
I find this very funny.
Keep flying,
My friends,
Dave

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how did they fail?

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